DRYLOK Extreme vs RadonSeal Plus: Basement Waterproofer Showdown
By Nate Sawyer, Editor · 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.
Frequently Asked Questions
- Should you use a film waterproofer or a penetrating sealer in a basement?
- It depends on whether water is actively getting in. DRYLOK Extreme forms a film on the wall and is rated to stop water up to 15 psi of hydrostatic pressure, so it is the choice against active seepage. RadonSeal Plus soaks in and reacts inside the concrete, cutting moisture vapor, radon and efflorescence on a damp-but-not-leaking wall or slab, with no film to peel.
- Which one can be used over previously sealed or painted walls?
- Neither, and this rules out a lot of basements. DRYLOK needs bare, unpainted, unsealed masonry or it blisters. RadonSeal needs to penetrate, so it will not work on already-sealed surfaces either - and it only works on concrete and block, not brick or stone.
- Which covers more area per dollar?
- RadonSeal Plus, by a wide margin. It covers roughly 1000 sq ft per 5 gallons at $65 for the container, while DRYLOK needs two thick coats at 75-100 sq ft per gallon at about $40 a gallon. For a large basement that difference is substantial.
- Does either one fix cracks?
- No. RadonSeal explicitly does not bridge cracks or resist standing hydrostatic pressure the way a film waterproofer does, and DRYLOK is a coating rather than a crack repair. Cracks need proper repair first, whichever product goes on afterwards.