Concrete
Waterproofing
Methods & Costs

No. Concrete is porous. Microscopic capillary pores in the cement paste draw water in by surface tension, and water under pressure, such as groundwater against a basement wall, moves through it too. Crystalline admixtures, penetrating repellents, coatings and membranes make it far more water-resistant. How far you need to go depends on whether water only wets the surface or stands against it.

First work out how the water gets in. For surfaces that only see rain, a penetrating silane or siloxane sealer is the usual choice. Where water stands against concrete below grade, use a membrane, a crystalline treatment or a cementitious coating rated for water pressure, preferably on the side the water comes from, plus drainage. Repair cracks and test for moisture first.

For a slab above grade, apply a penetrating silane or siloxane sealer at the data sheet's coverage rate once new concrete has cured (7 to 28 days, depending on the product). For a basement floor, test first by taping down 4-mil plastic for at least 16 hours (ASTM D4263). Moisture coming up through a slab can undermine many coatings.

Per InterNACHI's summary of the IRC, masonry foundation walls get at least 3/8 inch of portland cement parging before damp-proofing. Where a high water table or severe soil-water conditions exist, the code calls for waterproofing instead, such as 40-mil polymer-modified asphalt or 60-mil liquid-applied synthetic rubber. From inside, a polymer-modified cement coating plus drainage is a common repair.

It depends on the water. For driveways and patios, a penetrating silane or siloxane sealer is the usual choice; one 100% silane cut water absorption by 93% in testing. For foundations under water pressure, IIBEC calls positive-side waterproofing the more effective system, typically a membrane of 40 mils or more plus drainage. For interior and tank repairs, crystalline products are marketed for either face.

Damp-proofing slows moisture where there is no hydrostatic pressure. It is normally about 10 mils thick and cannot seal cracks and holes. Waterproofing resists water under pressure and typically uses 40 mils or more of material. Per InterNACHI's summary of the IRC, basement walls need damp-proofing by default and waterproofing where a high water table or severe soil-water conditions exist.

Crystalline products react with water and cement to form crystals that block capillary pores and hairline cracks. They come as admixtures added to the mix or as slurries brushed on. Xypex and Penetron say their products seal static hairline cracks up to 0.5 mm, and Xypex's admixture showed no leakage at 150 psi in the CRD C48 test. Moving cracks still need repair.

A penetrating sealer makes concrete water-repellent, not waterproof. Euclid's silane cut water absorption by about 93% in testing, but silane makers say their products won't stop water through structural cracks or open joints and aren't for below-grade or hydrostatic conditions. Film-forming sealers can trap moisture. PROSOCO puts penetrating repellents at 5 to 20+ years of service.

Professional sealing runs about $1 to $3 per sq ft according to HomeGuide, or $1.35 to $2.50 according to Angi. Basement waterproofing is a bigger job: Angi's typical range is $2,461 to $8,202, and HomeGuide lists $6,000 to $18,000, with exterior work costing more than interior. HomeGuide puts an installed membrane at $4 to $7 per sq ft.

Yes, with limits. Interior treatments such as crystalline slurries and two-coat cementitious coatings are common basement repairs, and crystalline products are marketed for either face. But IIBEC notes that negative-side systems are susceptible to failure under hydrostatic pressure. Pair an interior coating with drainage, and consider exterior waterproofing where water pressure is high or persistent.