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Basement waterproofing paint calculator

Masonry waterproofing paint (DRYLOK and similar) covers as little as 75 sq ft/gal on rough block — much less than wall paint. Two coats are required to form the waterproof seal. Important: waterproofing paint is for damp / humid surfaces, not for active leaks. Standing water needs structural fixes first.

Perimeter × wall height. A 24×20 ft basement with 8 ft walls ≈ 700 sq ft.
HOW IT WORKS

Waterproofing paint vs. real waterproofing

Masonry waterproofing paint handles dampness and minor humidity, the kind of basement that smells musty but doesn't actually have water on the floor. For active water intrusion (puddles after rain, weeping seams, hydrostatic pressure forcing water through), you need exterior drainage or interior dimple-mat systems. No paint will hold back hydrostatic pressure.

Why coverage is so low

Waterproofing paints are heavily filled with portland cement and resins to plug the pores in masonry. The thick film is what does the work, so you're buying weight, not coverage area, and you should plan for two to three times the gallons of regular wall paint. The calculator sets the rate from your surface:

  • Smooth poured concrete: about 100 sq ft per gallon; the least porous basement surface.
  • Concrete block (CMU): around 75 sq ft per gallon; rough, open-pored block drinks the most.
  • Interior brick: roughly 85 sq ft per gallon, between the two.

Stiff brush, force the paint in

Use a stiff masonry brush on the first coat. Work the paint into the porosity, especially in mortar joints, then build the second coat to complete the seal. Roller-only application skips the joints, and that's exactly where water finds a way through.

What it costs to waterproof a basement

The paint itself is the whole DIY cost. DRYLOK and similar masonry waterproofers run about $32 to $50 a gallon, with 5-gallon pails around $160 to $220 — buying pails is the cheaper way to go. Because the film is heavy and covers only 75 to 100 sq ft a gallon, a typical 800 sq ft basement needs about 16 to 22 gallons for the two coats the seal requires.

  • Masonry waterproofer: about $32 to $50 a gallon; $160 to $220 per 5-gallon pail.
  • DIY 800 sq ft basement (two coats): roughly $500 to $900 in paint.
  • Real waterproofing (drainage, dimple-mat, sump): several thousand dollars and up.

Waterproofing paint only fixes dampness, so its cost is cheap insurance against humidity — not a substitute for a drainage system if water is actually coming in. For a paint-plus-labor estimate on any surface, use thepaint cost calculator.

Frequently asked questions

How much does it cost to waterproof a basement with paint?+
DRYLOK-type masonry waterproofer runs about $32 to $50 a gallon (a 5-gallon pail is roughly $160 to $220), and it covers only 75 to 100 sq ft per gallon. A typical basement with 800 sq ft of wall needs about 16 to 22 gallons for two coats, so a DIY job is roughly $500 to $900 in paint — buying 5-gallon pails keeps you at the low end. That is still far cheaper than fixing real water intrusion, where exterior drainage or an interior dimple-mat system runs several thousand dollars.
How much DRYLOK or waterproofing paint do I need?+
Masonry waterproofers cover about 75 to 100 sq ft per gallon, far less than wall paint. Smooth poured concrete is near 100, rough concrete block closer to 75. Multiply your wall area by two coats and divide by the coverage rate for your surface.
How does waterproofing paint actually work?+
These paints are loaded with portland cement and resins that plug the pores in masonry, forming a thick film that blocks moisture and resists a few pounds of water pressure. The film thickness is what does the work, which is why the coverage is so low.
Will waterproofing paint stop a leaking basement?+
No. It handles dampness, humidity, and minor seepage, not active leaks or standing water. Water under hydrostatic pressure will push right past any paint; that needs exterior drainage or an interior dimple-mat system.
Why is two coats required?+
A single coat leaves pinholes and thin spots that let water through. The waterproof seal only forms when two full coats build the film to its rated thickness. Heavily damp walls may need a third.
Can I roll waterproofing paint or should I brush it?+
Brush the first coat with a stiff masonry brush to force paint into the pores and mortar joints, then you can roll the second. Roller-only application skips the joints, and that is exactly where water finds its way through.
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