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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Deck
Waterproofing:
What Works Where

Sealers, joist tape, under-deck drainage and walkable membranes each solve a different problem. Here’s which one your deck needs, what code asks for over living space, and what it costs, from the people who make ArmorDeck.
Deck Coating Quotes

Want it waterproofed properly? Get a quote from a certified applicator.

Tell us what the deck is made of, what's underneath it and roughly how big it is. We'll connect you with an ArmorThane-certified applicator who will quote the system, film thickness, slope work and flashing details in writing.

  • Balconies, roof decks and decks over living space
  • Concrete patios, walkways and pool decks
  • System, mils and flashing spelled out on the quote
  • Contractors: ask about ArmorDeck and spray rigs
Rather talk now? Call (417) 831-5090
Step 1 of 3
¼ in./ft
Minimum slope under a deck membrane
IBC 1507.14.1; ICC-ES ESR-2151
1–3 yr
Life of a tinted finish on deck boards
USDA Forest Products Lab, Table 16-2
6 ft
Height that triggers California balcony inspections
HSC §17973; Civil Code §5551
60 mils
Minimum sprayed film in our deck spec
ArmorThane deck coating steps

"Deck waterproofing" gets used for four different jobs: sealing wood boards, protecting the framing, keeping the patio under a deck dry, and turning a balcony or roof deck into a walkable waterproof surface. The products for one job fail at the others. Most of the bad advice online comes from mixing them up.

Quick answer

Match the method to the deck. A wood deck with gaps between the boards can't be made waterproof: seal the boards with a penetrating finish, tape the joist tops, and add an under-deck drainage system if the space below has to stay dry. A solid plywood or concrete deck, a balcony, or any deck over living space needs a continuous walking-deck membrane, sloped at least ¼ in. per foot (2%) and flashed at every wall, door and edge. Over a room, that membrane is legally a roof covering. Run the method finder or check your slope.

Most pages ranking for this topic are either a sealer how-to or a product pitch. None of them tells you which of the four jobs your deck needs, what slope the membrane requires, what the code says when there's a bedroom underneath, or what any of it costs. This page does, with the code text and the math shown.

We make polyurea and polyurethane deck coatings, including the ArmorDeck system, in Springfield, Missouri, and we've been supplying applicators for 35+ years. That's also why we'll tell you plainly when a $40 gallon of sealer is the right answer and our coatings aren't.

What's in this guide
  1. 1The four jobs called "deck waterproofing"
  2. 2Which method fits your deck? (finder)
  3. 3Wood decks with gapped boards
  4. 4Waterproofing under a deck
  5. 5Walkable coatings and membranes
  6. 6Slope, drainage and door thresholds (checker)
  7. 7Balcony waterproofing
  8. 8Concrete decks, patios and pool decks
  9. 9Is your wood ready to coat? (check)
  10. 10What it costs (estimator)
  11. 11Common mistakes
  12. 12Where ArmorDeck and polyurea fit
  13. 13Deck waterproofing FAQ
Start here

What does deck waterproofing mean? Four different jobs

Deck waterproofing is any method that keeps water from damaging a deck or the space beneath it. In practice that's four separate jobs: making the boards water-repellent, keeping water off the framing, catching water before it reaches a patio below, and building a membrane you can walk on. Which one you need depends on the deck surface and what's underneath.

JobWhat it protectsTypical productsWorks onPublished costRefresh
1. Seal the boardsBoard surfaces from checking, splitting and grayingPenetrating water-repellent sealers, semitransparent stainsGapped wood decks$0.75–$4/sq ft pro sealing (HomeAdvisor, 2026); $1.57–$4.04 staining (HomeGuide, 2024)About every 1–3 years (FPL; HomeAdvisor)
2. Protect the framingJoist and beam tops, the ledgerJoist tape, ledger and wall flashingAny deck, while the boards are offMaterial cost; no reliable published installed priceInstalled once, at build or re-board
3. Keep the space below dryA patio, storage or hot tub under a raised deckOver-joist drainage membranes; under-joist troughs and ceiling panelsGapped decks one story upVaries by system; no reliable published rangeClean gutters and outlets
4. Make the surface waterproofEverything below: plywood, framing, roomsLiquid-applied membranes, sprayed polyurea, vinyl sheet, under-tile membranesSolid plywood or concrete decks, balconies, roof decks$3–$12/sq ft concrete resurfacing (HomeGuide, 2025); $6–$12 polyurea (ArmorThane, 2026)Per the system's maintenance terms
Costs and refresh intervals are from the dated sources in the cost section below. FPL = USDA Forest Products Laboratory, Wood Handbook chapter 16.

Two mistakes cause most of the failures. The first is putting a job-4 product (a film or membrane) on a job-1 deck (gapped boards): it can't bridge the gaps, and films on horizontal boards peel. The second is expecting a job-1 product to keep a room dry. Sealer makes wood shed water for a while. It doesn't stop water.

Interactive tool 1 of 4

Which deck waterproofing method fits your deck?

Tell the finder what the deck is made of, what's below it and how you use it. It returns the system that fits, what to add, what to skip, the code items that apply, and whether our products belong on the job at all. The rules come from USDA's Forest Products Laboratory, the IBC and IRC, ICC-ES evaluation reports and our own application specs.

Method finder

What should go on this deck?

Pick the closest match. "Living space" includes a garage, storage room or anything enclosed below.

Also true
Seal it; don’t coat itPenetrating sealer
Do this

The system that fits

  • A penetrating water-repellent sealer or semitransparent stain, brushed on and limited to what the wood absorbs. USDA’s Forest Products Laboratory recommends penetrating finishes for decks.
  • Reseal when water stops beading and soaks in: roughly every 1–3 years for tinted deck finishes (FPL Table 16-2).
Also

Details that matter

  • Check the ledger flashing where the deck meets the house. The IBC requires flashing where decks and balconies meet the wall (1404.4).
Skip

What won’t work here

  • Paint, solid stain and thick “deck restore” films on the boards. FPL rates paint and solid stain low for decking because horizontal films peel.
  • Spray polyurea or membranes over the boards. They can’t bridge the gaps; our application spec calls for a solid surface, not slats.
ArmorThane fit

Where our products fit

  • Honestly, this isn’t a job for our coatings. Buy a good penetrating sealer.

Good DIY job. Sealers are brush-and-weekend work; drainage kits are sold for DIY installation on new builds.

A screening tool, not a design. Your building official, and the installation instructions and evaluation report of the system you choose, govern.

Gapped wood decks

How to waterproof a wood deck with gaps between the boards

You can't make a gapped deck waterproof, and you shouldn't try: the gaps are there to let water through. What you can do is keep the boards water-repellent so they don't check and split, and keep water off the tops of the joists. A penetrating sealer handles the boards. Joist tape and flashing handle the framing.

Penetrating sealer vs. film-forming coating

USDA's Forest Products Laboratory (FPL) is blunt about this. Horizontal surfaces exposed to sun and rain "are prone to peeling," so penetrating finishes are recommended for decks, and solid-color stains "form films and so will be prone to peeling just like paint." A penetrating finish soaks in and wears away gradually. It can't crack or flake, so recoating is a wash and another coat, not a stripping job.

FPL also explains why sealing matters even on treated lumber: "Wooden decks are most commonly replaced because of checking and splitting, not decay." Its advice is to keep water beading on the surface instead of soaking in, which is how you get "40 or more years of service life" from the wood.

Finish on deckingSuitabilityService life, new smooth boardsService life, weathered or rough-sawn
Tinted deck finishes (lightly pigmented water repellents)High1–2 years2–3 years
Semitransparent stainModerate (new) / High (weathered)2–3 years3–6 years
Paint and solid-color stainLow––
USDA Forest Products Laboratory, Wood Handbook (2021), Table 16-2. Estimates for an average U.S. location; sunny, horizontal boards wear faster.

One catch: plenty of products labeled "penetrating" leave a film anyway, especially high-solids waterborne stains. FPL's test is simple. If the dried surface has a sheen, it's a film, and it can peel. Put on only what the wood absorbs, brush rather than roll or spray, and wipe off excess before it dries.

How often should you reseal a deck?

When water stops beading and starts soaking in. That's FPL's test, and it's better than a calendar. As a guide, HomeAdvisor and TimberTech both say every one to three years, and HomeGuide says to stain every two to three. Sunny, south-facing decks land at the short end.

Sealing a wood deck, step by step

  1. Pick the weather

    TimberTech's window for sealers is 50–90°F with dry weather. Check the label; some products want a dry forecast for a day or more.

  2. Inspect and repair

    Replace soft or split boards, reset popped fasteners and look at the ledger flashing. Sealer doesn't fix rot.

  3. Clean

    Remove dirt and mildew with a deck cleaner. FPL notes mildew is an appearance problem, not finish failure, but it has to go before recoating.

  4. Sand only if you need to

    TimberTech sands rough spots with 60–80 grit, then 100 grit or finer. Don't polish the wood; penetrating finishes need open grain.

  5. Brush it in

    Work with the grain and apply only what the wood absorbs. On weathered or rough wood, FPL applies a second coat while the first is still wet.

  6. Let it cure

    TimberTech waits at least 24 hours between coats and 48 hours before putting furniture back.

Protect the framing: joist tape and ledger flashing

Treated joists still get wet on top, where water sits under each board and around every screw. Joist tape is a self-adhered strip that covers the top of each joist and beam. TimberTech and Polyguard both sell it; we found no independent performance data, but it's inexpensive and only practical to install while the boards are off. On a new deck or a re-board, it's cheap insurance.

The joint that matters most is where the deck meets the house. The building code requires flashing where decks and balconies meet an exterior wall (IBC 1404.4). If the ledger area shows rust streaks, soft sheathing or stains inside, that's a repair job before it's a sealing job.

Composite and PVC decks

Composite and PVC boards don't need a sealer. The framing under them is still wood, though, and it gets just as wet. TimberTech's own guidance is that the lumber underneath still needs protection. Joist tape during the build and good ledger flashing are the upgrades that matter; add under-deck drainage if you want the space below dry.

Dry space below

How to waterproof under a deck

To keep the patio under a second-story deck dry, catch the water between the boards and the joists and carry it to a gutter. On a new deck, or when you're replacing the boards anyway, that's an over-joist drainage membrane. On an existing deck you'd rather not tear up, it's a system hung below the joists.

Over-joist drainage (new decks and re-boards)

Over-joist systems drape a membrane over the joists to form troughs in each bay, then the boards go on top. Water runs down the troughs to a gutter at the low end. The bonus is that the joist tops stay dry too. Trex's installation guidance adds gutter outlets "every 12′–14′" and says its RainEscape system "is not recommended for an existing deck unless you remove the deck boards." TimberTech sells a comparable system (DrySpace).

Under-joist systems for existing decks

These mount panels or troughs to the underside of the joists and slope them to a gutter, so the boards never come up. They're the practical retrofit. The trade-off, which Trex argues in its own guide, is that a closed ceiling can hold moisture against the framing and hide it from view. If you go this route, keep it ventilated, keep the gutters clear and pull a panel to look at the joists now and then.

ApproachWhen it fitsProtects the joists?Walking surfaceWatch for
Over-joist drainage membraneNew build or re-boardYes, tops coveredNormal gapped boardsNeeds a gutter and outlets at the low end
Under-joist trough or ceilingExisting deck, boards stayNo, water still hits the joistsNormal gapped boardsMoisture held against framing; clogged gutters
Solid deck with walking membraneRebuild, balcony, or deck over living spaceYes, fully coveredThe membrane itselfNeeds ¼ in./ft slope and full flashing
Our summary of Trex and TimberTech installation guidance and the membrane requirements covered below.

Gutters, outlets and where the water goes

Every drainage system ends in a gutter, so size and route it for real volume. One inch of rain on a 12 × 16 ft deck is about 120 gallons (192 sq ft × 0.623 gallons per sq ft-inch, our arithmetic). Send it well away from the foundation, not onto the patio you just made dry.

Balconies, roof decks, decks over rooms

Walkable deck coatings and membranes: what goes on a solid deck

A walkable deck coating is a waterproof membrane you walk directly on. It needs a solid substrate (plywood or concrete), slope to drain, and flashing at every edge. The main families are liquid-applied membranes, sprayed polyurea, heat-welded vinyl sheet, and membranes that go under tile.

SystemHow it goes onSeamsExample buildBack in useDIY?Best for
Liquid-applied (e.g., ArmorDeck)Squeegee or notched trowel, aggregate broadcast, topcoatNoneBasecoat + aggregate + topcoat (mils per data sheet)Recoat 16–48 h after basecoat (ArmorDeck)Some systemsPlywood and concrete decks, walkways
Sprayed polyureaHeated plural-component spray rigNone60 mils minimum (our deck spec); 60–80 on pool decksWalkable in 45–60 min; heavy use at 24 h (our deck spec)NoPlywood, concrete, odd shapes, fast turnaround
Vinyl (PVC) sheetGlued down, seams heat-weldedWelded lapsNominal 60 mils (Duradek, ESR-2151)Per makerInstaller networkPlywood balconies and roof decks
Under-tile membranePeel-and-stick or liquid, tile on topLapped sheetsNominal 70 mils (Protecto Deck)Tile the same day (Protecto Deck)Tile settersTiled decks and balconies
Sources: ArmorThane ArmorDeck BaseCoat page and deck coating steps; ArmorThane pool deck resurfacing guide; ICC-ES ESR-2151; Protecto Wrap. Film thickness and cure times vary by product; the data sheet governs.

Liquid-applied membranes

These are rolled, squeegeed or troweled on and cure in place. Our ArmorDeck system is a typical two-step example. The ArmorDeck BaseCoat is a single-component, moisture-cured, aromatic urethane polyurea membrane, sold in grey in 5-gallon pails and applied with a notched trowel or squeegee above 60°F. Sand, garnet or rubber crumb (about 16–20 mesh) is broadcast into it for grip. After 16 to 48 hours, the aliphatic ArmorDeck Topcoat goes on to take the UV and abrasion. Miss the 48-hour window and you're into surface prep again.

Sprayed polyurea

Polyurea is sprayed from a heated, plural-component rig and sets in seconds, so it builds a seamless membrane in one visit and follows every curb, post and drain. On a deck, our application spec calls for at least 60 mils (1/16 in.) total, with the final coats textured; the surface is walkable in 45 minutes to an hour, with 24 hours before heavy traffic and furniture. The deck coating steps page shows how our applicators do it.

Chemistry matters in the sun. Most spray elastomers are aromatic and chalk and change color outdoors, so they need a UV-stable topcoat. ArmorFlex UV is aliphatic and color-stable, so it can go on by itself. Either way, this is an applicator's job, not a weekend project: the rig is specialized and uncured isocyanates are a respiratory hazard (OSHA).

Vinyl sheet membranes

PVC sheet is glued to plywood and the seams are heat-welded. It's a mature category with good documentation. One example, Duradek Ultra, has an ICC-ES report (ESR-2151, reissued May 2026) as "a walking deck and classified (rated) roof covering system." Its conditions are a useful checklist for any system: at least 5/8-in. exterior plywood with tongue-and-groove or blocked edges, substrate sloped at least ¼ in. per foot, installation in dry weather at 45°F or warmer, and metal flashing at every penetration and termination.

Membranes under tile

Tile and grout aren't waterproof, so a tiled deck has its membrane underneath. Peel-and-stick sheets like Protecto Deck (a nominal 70-mil membrane with a fabric top) take thin-set and tile the same day. If a tiled deck leaks, the fix is almost always under the tile.

Applicator in a protective suit rolling a liquid-applied waterproof coating across a flat rooftop deck
A liquid-applied membrane going down on a flat roof deck. Walkable decks get the same continuous film, plus texture.

When a deck is a roof

If there's a room, garage or storage space under the deck, the deck surface is that space's roof, and the membrane is a roof covering. That changes the paperwork:

  • Evaluation reports. ICC-ES evaluates walking decks under acceptance criteria AC39 and roof membranes under AC75. Ask for the report that lists the system as both a walking deck and a roof covering, and install it exactly as the report says.
  • Fire classification. Under IRC R902.1, a Class A, B or C roof covering (tested to ASTM E108 or UL 790) is required where your jurisdiction mandates it, or where the roof edge is less than 3 ft from a lot line.
  • Slope and flashing. The IBC wants liquid-applied roofing at ¼ unit in 12 or steeper (1507.14.1) and flashing at wall intersections, edges and openings (1503.2.1).
Ask before you signWhatever system you choose, ours included, ask the installer which evaluation report and fire classification cover it over living space, and confirm with your building department that it will accept them. For concrete over occupied space, see plaza deck waterproofing; the principles are the same at a larger scale.
Interactive tool 2 of 4

Deck slope, drainage and door thresholds: the details that decide leaks

A waterproof deck needs at least ¼ in. of fall per foot (2%) away from the house. That's the IBC minimum for liquid-applied roofing and the minimum in at least one walking-deck evaluation report. A 12-ft-deep deck needs 3 in. of fall from the wall to the edge. The door is the other trouble spot: the membrane has to finish below the threshold without breaking the code's step limits.

Slope & threshold checker

Will water run off, and does the door still work?

Measure fall with a level and tape from the wall to the outer edge. Enter a negative number if the deck tips toward the house.

60 mils ≈ 1/16 in.; measure tile systems
⅛ in./ft
Slope today
1.0%
As a percentage
1½ in.
Extra fall needed at the edge
1⅞ in.
Finished step at the door
Slope

Needs more fall

  • You need at least 3 in. of fall over 12.0 ft (¼ in. per foot). You have 1½ in., so add about 1½ in. more at the outer edge, or build tapered sleepers under the substrate.
  • Flat or near-flat decks pond. Ponding water sits on every pinhole and seam until it finds one.
  • Aim the fall at a gutter or drip edge, never at a wall.
Door

Threshold step is within the IRC limit

  • A finished step of 1⅞ in. is within the 7¾ in. limit for exterior doors other than the required egress door (IRC R311.3.2).
  • Build-up you entered: ⅛ in. A 60-mil coating adds about 1/16 in.; tile, mortar and membrane add much more, so measure your system.
Water

Where it goes

  • One inch of rain puts about 120 gallons on this 192 sq ft deck (192 × 0.623 gal).
  • Flashing belongs at the wall and roof intersection, the outer edge and around openings (IBC 1503.2.1), and where the deck meets the wall (IBC 1404.4). Every post or bracket through the membrane is a penetration to flash.

How we calculated this: slope = fall ÷ depth (in. per ft) and fall ÷ (depth × 12) × 100 (%); fall needed = 0.25 × depth; finished step = today's step − added thickness; rain = area × 0.623 gallons per inch. Step limits are IRC R311.3.1 (required egress door: 1½ in., or 7¾ in. if the door doesn't swing over the deck) and R311.3.2 (other exterior doors: 7¾ in.).

The code sections that apply to a waterproof deck

SectionWhat it saysWhy it matters on a deck
IBC 1507.14.1Liquid-applied roofing: design slope not less than ¼ unit in 12 (2%)Sets the minimum fall for coated decks over occupied space
IBC 1503.2.1Flashing at wall and roof intersections, gutters, slope changes and roof openings; metal at least 0.019 in. (No. 26 galvanized)The wall line, outer edge, drains and posts
IBC 1404.4Flashing at exterior wall intersections with "porches, decks, balconies and similar projections"The ledger and the wall behind the deck
IRC R902.1Class A, B or C roofing where required by law or within 3 ft of a lot line (ASTM E108 / UL 790)Decks over living space near property lines
IRC R311.3.1 / R311.3.2Maximum step from threshold to landing: 1½ in. at the required egress door (7¾ in. if it doesn't swing over); 7¾ in. at other exterior doorsHow thick a system you can add at a door
ICC-ES AC39 / AC75Acceptance criteria for walking decks and membrane roof coveringsWhat an evaluation report should cite
Section text from the 2021 IBC and IRC (UpCodes); R311.3.2 wording shown from the 2012 IRC. Your jurisdiction's adopted edition and amendments govern.

Flashing: where decks actually leak

A membrane rarely fails in the middle of the field. It fails where it stops: the wall, the door sill, the outer edge, a drain, a rail post. Every one of those needs a detail from the system's installation instructions. The ESR-2151 conditions put it plainly: "All penetrations through and terminations of the sheathing must be protected with metal flashing." Rail posts bolted through the deck are penetrations; surface-mounted or fascia-mounted rails mean fewer holes to flash.

Door thresholds

The membrane has to turn up the wall and run under the door sill into a pan, and the finished deck has to stay below the threshold. That's hard on a door that was set close to the old deck surface. If your checker result shows a tiny or negative step, sort out the door (or lower the deck at the wall) before anyone waterproofs anything.

Balconies

Balcony waterproofing: what's different

Waterproof a balcony like a small roof deck: a solid substrate sloped away from the door, a walking-deck membrane, and flashing that runs up the walls, under the door sill and over the outer edge. What makes balconies harder is space. There's little room for slope, the door opens right onto the membrane, and on a cantilevered balcony the joists run back into the building, so a leak can wet framing you can't see.

California's balcony inspection laws

California now requires periodic inspection of wood-supported balconies and decks on multifamily buildings, and both laws name waterproofing explicitly:

  • Apartments (HSC §17973, SB 721): buildings with three or more multifamily units. "Exterior elevated elements" (balconies, decks, porches, stairways, walkways and entry structures) with a walking surface more than 6 ft above ground that rely on wood for support. "Associated waterproofing elements include flashings, membranes, coatings, and sealants." At least 15% of each type is inspected, by January 1, 2026 and every six years after.
  • Condos and HOAs (Civil Code §5551, SB 326): the same 6-ft, wood-supported definition, inspected by a licensed structural or civil engineer or architect at least once every nine years. The first round was due January 1, 2025.

Other states and cities have their own rules, so check locally. Even where nothing is required, the statute's scope is a good owner's checklist.

What to look for on your own balcony

  • Stains or bubbling on the ceiling or soffit below. Water is getting past the membrane.
  • Soft or bouncy spots in the walking surface.
  • Rust at rail posts and cracked sealant where they enter the deck.
  • Cracks or lifting at the wall and door sill. These are the first details to fail.
  • Ponding that sits more than a few hours after rain.

California's condo law describes the inspection tools: visual observation plus "moisture meters, borescopes, or infrared technology." Any of those is worth paying for before you recoat a balcony that might be hiding wet framing.

Concrete

Waterproofing a concrete deck, patio or pool deck

Concrete decks, balconies and pool decks get a liquid-applied system bonded to the slab. Most of the work is prep: the slab has to be clean, dry and profiled, cracks treated, and moving joints left free to move. Then comes a polyurea or polyurethane base, aggregate for grip, and a UV-stable topcoat.

Our pool deck resurfacing guide lays out the sequence we specify: shot blast or diamond grind to a concrete surface profile (CSP) of 3–4, dry the deck to under 4% moisture, route and fill cracks, honor expansion joints with backer rod and flexible sealant, prime, spray the base coat (typically 60–80 mils on pool decks), broadcast aggregate to rejection, and finish with an aliphatic topcoat.

Textured, slip-resistant polyurea coating on a residential pool deck beside the coping
Aggregate broadcast into the coating gives a pool deck its grip.
  • Slab on grade, foot traffic only? If it just needs to stop soaking up water, a penetrating concrete sealer is cheaper. It won't bridge cracks.
  • Patios and walkways where appearance matters: see polyaspartic coatings, which are UV-stable and roll on.
  • Concrete over rooms or parking is a plaza deck, designed as a roof assembly.
  • Vehicle traffic needs a traffic-rated system; see parking deck coatings.

Skip epoxy outside. It isn't UV-stable and chalks and yellows in the sun. For the chemistry behind these choices, our polyurea waterproofing page covers the basics.

Interactive tool 3 of 4

Can you coat a wood deck? Prep, weathering and the tape test

Yes, if it's a solid surface and the wood is dry and sound at the surface. New pressure-treated lumber is often wet on delivery, and wood left in the sun for even a few weeks grows a weak, weathered surface layer that film coatings peel off with. Meter it, tape-test it, and sand to sound wood before a membrane goes on.

Wood readiness check

Is this wood ready for a sealer or a coating?

Tape test: press a strip of strong tape onto the wood, rub it down, snap it off fast. Fibers on the tape mean the surface is sunburned.

0 = not measured
Surface color
Prep firstRoll-on membrane
Check

Before you start

  • Do the tape test. After about 3–4 weeks of sun, film-coating adhesion drops (FPL). Press strong tape onto the wood, snap it off; fibers on the tape mean sand first.
Good

Already in your favor

  • Moisture reading of 14% is under the ~20% line FPL uses for decay risk. If your coating’s data sheet sets a lower limit, that governs.
  • Temperature is above ArmorDeck BaseCoat’s 60°F minimum. Plan the topcoat within its 16–48 hour window.
Notes

How to do it

  • Seal plywood edges first. Panel edges absorb water faster than faces and are where finishes fail first (FPL).
  • Caulk or fill seams and screw holes and sand them smooth before coating (our deck coating steps).

Rules used: USDA Forest Products Laboratory, Wood Handbook ch. 16 (decay above ~20% moisture, "nothing will coat wet wood well," sunburn, tape test, sanding 100 µm, penetrating finishes for decks, KDAT); ArmorThane deck coating steps (6–8 months before spraying new treated lumber; solid surfaces; seams filled); ArmorDeck BaseCoat (apply above 60°F; topcoat within 16–48 hours); TimberTech (sealers at 50–90°F).

"Let the deck weather first": half right

Our own deck coating steps say new treated lumber shouldn't be sprayed until it has been outdoors 6 to 8 months, so moisture and treatment can work out of the wood. That's still sound for wet lumber. FPL adds the other half. Ultraviolet light breaks down the wood surface within weeks: in its tests, paint on boards pre-weathered 16 weeks peeled within 3 years, on boards exposed one week after 13 years, while unexposed boards were fine at 20. Denser species such as Douglas-fir and southern pine held up until about 3 to 4 weeks. FPL calls "let your deck weather before painting it" advice that "is now the source of much pain."

Put together: let wet wood dry, then remove the weathered layer before coating. FPL's number is about 0.004 in. (100 µm) of sanding for lightly sunburned wood, and "much more" for gray, silver wood. Run the tape test again and coat before the fresh surface weathers. Buying KDAT lumber for a deck you plan to coat skips most of the wait.

Plywood and seams

Plywood edges soak up water far faster than faces, so seal them. Caulk or fill seams and screw holes and sand them smooth before a membrane goes on; any ridge you leave will show through, and every gap is a place for the film to thin out.

Interactive tool 4 of 4

How much does deck waterproofing cost?

Professional sealing of a wood deck runs about $0.75–$4 per sq ft (HomeAdvisor, 2026), or $0.50–$1 DIY. A coating system on a concrete deck runs roughly $3–$12 per sq ft, and a sprayed polyurea system $6–$12. For a liquid or vinyl membrane over plywood we couldn't find a reliable published per-square-foot range, so the estimator helps you compare quotes instead.

Coverage & cost estimator

How much material, and what should it cost?

Membrane math uses the data-sheet film thickness and volume solids. Installed ranges are dated published figures for the deck area only.

Walls the membrane runs up
From your system's detail
100 for most spray polyureas
200–300 is typical (HomeGuide)
197 sq ft
Area to cover
8.5 gal
Material, with waste
2
5-gal pails
$1,152–$2,304
Published installed range

Gallons = 197 sq ft × 60 dry mils ÷ (1,604 × 100% solids) × 1.15 waste. That’s 60 wet mils in total. Area includes 5 sq ft of wall turn-up. Use the dry-film thickness and volume solids from your system’s data sheet; 60 mils is the minimum in our deck spec for sprayed coatings.

DIY stain or sealer
$96–$192
Pro deck sealing
$144–$768
Pro staining
$301–$776
Concrete coating system
$576–$2,304
Sprayed polyurea system
$1,152–$2,304
Published range

$1,152–$2,304 installed

192 sq ft of deck × $6.00–$12.00 per sq ft (ArmorThane pool deck guide, polyurea systems, Apr. 2026). Railings, stairs, repairs and slope correction are extra.

Ask for

What a good quote states

  • The exact system and its data sheet, with dry-film thickness in mils
  • Prep method (grinding, repairs, primer)
  • Slope correction, flashing, door pan and edge details
  • Warranty terms, and the evaluation report if the deck is over living space

How we calculated this: area = length × width, plus turn-up length × height ÷ 12 for membranes. Membrane gallons = area × dry mils ÷ (1,604 × volume solids) × (1 + waste), because one U.S. gallon (231 cu in.) spread 1 mil thick covers 1,604 sq ft. Sealer gallons = area × coats ÷ label coverage × (1 + waste). Installed ranges multiply deck area by the published per-sq-ft figures in the table below. Estimates only.

ItemPublished figureDateSource
Professional deck sealing$0.75–$4 per sq ft; average project $974Jun 2026HomeAdvisor
Professional deck staining$1.57–$4.04 per sq ft; 12 × 16 ft deck $301–$775Jul 2024HomeGuide
DIY staining$0.50–$1 per sq ft; stain $20–$50/gal covering 200–300 sq ftJul 2024HomeGuide
Deck refinishing$3–$7 per sq ftJun 2026HomeAdvisor
Deck board replacement$25–$125 per sq ftOct 2025HomeGuide
Concrete pool deck resurfacing$3–$12 per sq ftDec 2025HomeGuide
Polyurea pool deck system$6–$12 per sq ft installedApr 2026ArmorThane pool deck guide
Rooftop deck waterproof membrane$6,000–$18,000 on averageFeb 2026HomeGuide
Consumer cost guides survey different projects and years, so treat these as bands, not bids. We couldn't find a dated, published per-square-foot price for liquid or vinyl walking-deck membranes over plywood.

What moves the price

  • Repairs underneath. Rotted boards, sheathing or joists come first, and board replacement alone runs $25–$125 per sq ft (HomeGuide).
  • Slope correction. Tapered sleepers or a re-sloped substrate on a flat deck is carpentry, not coating.
  • Flashing and doors. Wall turn-ups, door pans, edge metal and every post add labor.
  • Stairs and railings. Priced separately almost everywhere.
  • System and film thickness. Two quotes for "a deck coating" can differ by the thickness of the membrane. Ask for mils in writing.
Avoid these

Common deck waterproofing mistakes

  • Coating gapped boards. Films can't bridge gaps and peel on horizontal wood.
  • Expecting sealer to keep a room dry. Sealer repels water from wood; it isn't a membrane.
  • A flat deck. Less than ¼ in. per foot means ponding on every seam and pinhole.
  • Stopping the membrane at the wall. It has to turn up the wall and run under the door sill.
  • Coating wet or sunburned wood. Meter it, tape-test it, sand to sound wood.
  • Burying moving joints in a concrete deck instead of treating them with backer rod and sealant.
  • Aromatic coatings in full sun with no topcoat. They chalk and change color.
  • Missing a recoat window, such as ArmorDeck's 48-hour limit between basecoat and topcoat.
  • Epoxy outdoors. It isn't UV-stable.
  • No paperwork over living space. Ask for the evaluation report and fire classification before the work starts.
ArmorThane deck systems

Where ArmorDeck and sprayed polyurea fit, and where they don't

Our deck systems belong on solid decks: plywood and concrete decks, balconies, walkways, patios and pool decks. ArmorDeck is the two-step, squeegee-applied system: an aromatic urethane polyurea basecoat with broadcast aggregate, then an aliphatic topcoat within 48 hours. Where speed or complex shapes matter, our applicators spray polyurea at 60 mils or more, using SureGrip (our highest-friction polyurea, used on walkways and balconies) under a UV topcoat, or ArmorFlex UV by itself.

They don't belong on gapped boards (buy a good penetrating sealer), under tile, or on a deck where nobody has checked the slope and flashing. And if the deck is over living space, ask your applicator what evaluation report and fire classification cover the system before you sign. We'd rather you ask than find out at inspection. Flat roofs are a related job; see flat roof waterproofing.

Get a deck coating quote →ArmorDeck system
Applicator in a protective suit spraying green polyurea waterproofing across an exterior concrete deck
Spray-applied polyurea on an exterior concrete deck.
Basecoat

ArmorDeck BaseCoat

Single-component, moisture-cured, aromatic. Grey, 5-gal pails, applied above 60°F. Recoat in 16–48 hours.

Topcoat

ArmorDeck Topcoat

Aliphatic, single-component, moisture-cured. UV and abrasion resistance; takes color quartz or chips.

60 mils+

Sprayed polyurea

Seamless, textured, walkable in 45–60 minutes. Applied by certified applicators with plural-component rigs.

For contractors

Decks are a service line, not a one-off.

Balconies, pool decks, walkways and patios all take the same prep, the same rig and the same training. A sprayed deck is walkable in about an hour, so most jobs finish in a day. We supply the coatings, build the spray equipment and train you on-site. Not a franchise: no franchise fee, no royalties, and startup packages start at $25,000.

Become an applicatorDeck coating business

Questions first? Call (417) 831-5090.

Straight answers

Deck waterproofing FAQ

What is the best way to waterproof a deck?

It depends on the deck. A wood deck with gaps between the boards can't be made waterproof, so seal the boards with a penetrating finish, tape the joist tops and add under-deck drainage if the space below must stay dry. A solid plywood or concrete deck, a balcony or any deck over living space needs a continuous walking-deck membrane sloped at least ¼ in. per foot and flashed at every wall, door and edge. The method finder sorts out which applies.

Can you waterproof a wood deck with gaps between the boards?

Not the surface. Water is meant to fall through the gaps, and film coatings on horizontal boards tend to peel (USDA Forest Products Laboratory). Use a penetrating sealer to keep the boards water-repellent, joist tape to keep water off the joists, and an over- or under-joist drainage system if the space below has to stay dry.

How do you waterproof a deck over a living space?

Build it like a roof: a solid plywood or concrete substrate sloped at least ¼ in. per foot, a walking-deck membrane on top, and metal flashing at walls, doors, edges and every penetration. Ask for the system's ICC-ES evaluation report as a walking deck and roof covering (acceptance criteria AC39 and AC75). If the roof edge is within 3 ft of a lot line, IRC R902.1 also requires a Class A, B or C fire-rated roof covering.

What slope does a waterproof deck need?

At least ¼ in. per foot (2%), away from the house. That's the IBC minimum for liquid-applied roofing (1507.14.1) and the minimum in ICC-ES ESR-2151 for one evaluated walking-deck membrane. A 10-ft-deep deck needs 2½ in. of fall; the slope checker does the math.

How often should you reseal a wood deck?

When water stops beading and starts soaking in. USDA's Forest Products Laboratory puts tinted deck finishes at 1–3 years on decking and semitransparent stains at 2–6, and HomeAdvisor says every one to three years. Sunny, horizontal boards wear fastest.

What's the difference between a deck sealer and a deck coating?

A sealer soaks into wood or concrete and makes it water-repellent. It doesn't form a film, so it can't peel, but it wears away and needs refreshing. A coating or membrane forms a continuous film that stops water outright, which only works on a solid, sloped, flashed surface.

How much does deck waterproofing cost?

Professional deck sealing runs about $0.75–$4 per sq ft (HomeAdvisor, June 2026) and staining $1.57–$4.04 (HomeGuide, 2024). Concrete deck resurfacing runs $3–$12 per sq ft (HomeGuide, Dec. 2025), and our pool deck guide puts sprayed polyurea systems at $6–$12. The cost estimator sizes your deck.

How do you waterproof under a deck?

Catch the water that falls between the boards and send it to a gutter. On a new deck, or when you're replacing the boards anyway, an over-joist drainage membrane goes on before the boards; Trex adds gutter outlets every 12–14 ft and doesn't recommend its system on existing decks unless the boards come off. On an existing deck, a trough or ceiling system hung under the joists is the retrofit.

Can you put a waterproof coating on a plywood deck?

Yes. That's what walking-deck systems are made for, as long as the plywood is exterior grade with tongue-and-groove or blocked edges, the deck slopes at least ¼ in. per foot and every edge is flashed. One evaluated system (ESR-2151) sets 5/8-in. plywood as its minimum; use the numbers in your system's own report.

How do you waterproof a balcony?

Treat it as a small roof deck: solid substrate, slope away from the door, a walking-deck membrane, and flashing that runs up the walls, under the door sill and over the outer edge. On a cantilevered balcony, a leak can wet framing inside the building. In California, balconies more than 6 ft up on buildings with three or more units must be inspected, waterproofing included (HSC §17973; Civil Code §5551).

Is polyurea good for decks?

On solid plywood and concrete decks, yes. It sprays on seamless, sets fast (walkable in 45 minutes to an hour under our deck spec) and takes aggregate for grip. Aromatic polyureas need a UV-stable topcoat in the sun, while aliphatic ones like ArmorFlex UV are color-stable. It's the wrong product for gapped boards, and it's an applicator job, not DIY.

Do composite decks need waterproofing?

The boards don't need sealing, but the wood framing underneath still gets wet. Joist tape during the build and good ledger flashing are the upgrades that matter, plus under-deck drainage if you want the space below dry (TimberTech; Trex).

Can I apply a deck waterproofing membrane myself?

Penetrating sealers, yes, and some roll-on membranes are DIY-able on a simple deck over open ground. Over living space we'd hire it out, because flashing, door pans and drains decide whether it leaks, and sprayed polyurea needs a heated plural-component rig and respiratory protection from isocyanates (OSHA). Find a certified ArmorThane applicator.

AT
ArmorThane Technical Team · Springfield, Missouri
Written from code text, ICC-ES evaluation reports, USDA Forest Products Laboratory research and 35+ years of making deck and waterproofing coatings. Last updated September 26, 2026.

Methodology and sources

Code text is quoted or summarized from the 2021 IBC and IRC via UpCodes (R311.3.2 from the 2012 IRC); walking-deck conditions are from ICC-ES ESR-2151 as one documented example, not a spec for every system. Wood-finish guidance is from the USDA Forest Products Laboratory Wood Handbook (2021). Costs are dated consumer cost-guide figures and our own pool deck guide. ArmorThane product facts come only from our product and application pages. Coverage and slope math is ours.

  1. UpCodes, IBC 1507.14 liquid-applied roofing (slope): up.codes/s/liquid-applied-roofing
  2. UpCodes, IBC 1503.2.1 flashing locations: up.codes/s/locations
  3. UpCodes, IBC 1404.4 flashing at decks and balconies: up.codes/s/flashing
  4. UpCodes, IRC R902.1 roof covering materials and fire classification: up.codes/s/roof-covering-materials
  5. UpCodes, IRC R311.3.1 floor elevations at the required egress door: up.codes/s/floor-elevations-at-the-required-egress-doors
  6. UpCodes, IRC R311.3.2 floor elevations for other exterior doors (2012 text): up.codes/s/floor-elevations-for-other-exterior-doors
  7. ICC-ES, AC39 Walking Decks acceptance criteria: icc-es.org/acceptance-criteria/ac39/
  8. ICC-ES ESR-2151, Duradek Ultra roof covering and walking deck membrane (May 2026, PDF): icc-es.org/wp-content/uploads/report-directory/ESR-2151.pdf
  9. Duradek, testing and approvals: duradek.com/architectural-resources/vinyl-decking-resources/testing-ap
  10. USDA Forest Products Laboratory, Wood Handbook ch. 16, Finishing Wood (2021, PDF): fpl.fs.usda.gov/documnts/fplgtr/fplgtr282/chapter_16_fpl_gtr282.pdf
  11. California Health and Safety Code §17973 (SB 721): leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=HS
  12. California Civil Code §5551 (SB 326, as amended by SB 410): leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=CI
  13. OSHA, Isocyanates: osha.gov/isocyanates
  14. HomeAdvisor, cost to seal a deck (Jun. 2026): homeadvisor.com/cost/outdoor-living/seal-a-deck/
  15. HomeAdvisor, cost to refinish a deck (Jun. 2026): homeadvisor.com/cost/outdoor-living/refinish-a-deck/
  16. HomeGuide, cost to stain a deck (Jul. 2024): homeguide.com/costs/cost-to-stain-a-deck
  17. HomeGuide, deck repair cost (Oct. 2025): homeguide.com/costs/deck-repair-cost
  18. HomeGuide, pool deck cost (Dec. 2025): homeguide.com/costs/pool-deck-cost
  19. HomeGuide, rooftop deck cost (Feb. 2026): homeguide.com/costs/rooftop-deck-cost
  20. TimberTech, how to waterproof a deck: timbertech.com/ideas/how-to-waterproof-a-deck/
  21. Trex RainEscape, how to waterproof the deck you are building: trexrainescape.com/how-to-waterproof-the-deck-you-are-building
  22. Polyguard, deck waterproofing membranes: polyguard.com/blog/deck-waterproofing-membranes
  23. Protecto Wrap, Protecto Deck: protectowrap.com/product/new-protecto-deck/
  24. Life Specialty Coatings, pros and cons of deck waterproofing options: lifespecialtycoatings.com/the-pros-and-cons-of-deck-waterproofing-opti
  25. Dex-O-Tex, waterproof decking: dex-o-tex.com/product-family/waterproof-decking
  26. Ladiesburg Lumber, best methods for deck waterproofing: ladiesburglumber.com/the-best-methods-for-deck-waterproofing/
  27. ArmorThane, ArmorDeck system: armorthane.com/products/armorflooring-product-page/armordeck/
  28. ArmorThane, ArmorDeck BaseCoat: armorthane.com/products/armorflooring-product-page/armordeck-basecoat/
  29. ArmorThane, ArmorDeck Topcoat: armorthane.com/products/armorcoat/armordeck-topcoat-2/
  30. ArmorThane, deck coating steps: armorthane.com/deck-coating-steps/
  31. ArmorThane, pool deck resurfacing guide (Apr. 2026): armorthane.com/knowledge-center/pool-deck-resurfacing-guide/
  32. ArmorThane, ArmorFlex UV: armorthane.com/products/armorline-products/high-pressure/armorflex-uv/
  33. ArmorThane, SureGrip soft polyurea: armorthane.com/products/armorline-products/high-pressure/suregrip-soft

latest news & bLOGS

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Waterproof the deck once, and get the details right.

ArmorThane-certified applicators install ArmorDeck and sprayed polyurea deck systems with the slope, film thickness and flashing written into the quote. Contractors: we make the coatings, build the rigs and train your crew, with no franchise fee.

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