DRYLOK Extreme vs RadonSeal Plus: Basement Waterproofer Showdown
By The DIYPicks Team · Updated July 2026
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DRYLOK Extreme Masonry Waterproofer
The go-to interior film-forming waterproofer for basement and foundation walls, rated to hold back water at up to 15 psi with a 15-year warranty. Best for bare masonry block or poured walls where you need a true waterproof barrier, not just a repellent.
| type | Film-forming masonry waterproofer (latex) |
|---|---|
| finish | White paint-like film (tintable) |
| coverage | 75-100 sq ft per gallon per coat |
| coats | 2 coats required for warranty |
| hydrostaticRating | Stops water up to 15 psi |
| warranty | 15 years when applied per directions |
| cleanup | Soap and water |
RadonSeal Plus Deep-Penetrating Concrete Sealer
A reactive penetrating sealer that hardens and permanently densifies porous basement slabs and foundation walls while cutting moisture vapor and radon. Choose it over a film waterproofer when you want an invisible, permanent internal seal rather than a paint-on barrier.
| type | Reactive deep-penetrating sealer (water-based) |
|---|---|
| finish | Invisible, no film |
| coverage | Approx 1000 sq ft per 5 gallons (varies by porosity) |
| penetration | Penetrates up to several inches and reacts inside the concrete |
| voc | Zero VOC, solvent-free, non-toxic |
| bestSubstrate | Older/porous concrete and concrete block (Plus formula) |
| coats | 2-3 wet coats |
Our verdict
DRYLOK Extreme is a film-forming waterproofer that coats the wall and is rated to stop water up to 15 psi with a 15-year warranty, making it the choice when you need a visible barrier against active seepage on bare masonry. RadonSeal Plus is a reactive penetrating sealer that soaks in, hardens the concrete, and cuts moisture vapor and radon without any film, ideal for damp-but-not-leaking slabs and walls. Use DRYLOK to hold back pressure and RadonSeal to permanently densify and reduce vapor; for a tough problem some pros use RadonSeal first, then topcoat with DRYLOK.