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OKON S-40 is Rust-Oleum’s heavy-duty silane/siloxane water repellent for porous concrete and masonry, and the stronger sibling of OKON S-20. It’s sold in 5-gallon pails at Home Depot and through distributors, and it’s a common budget alternative to premium penetrating sealers.
| Type | Penetrating water repellent |
| Chemistry | Water-based oligomeric siloxane/silane, ready to use |
| Finish | Colorless, non-yellowing, non-film-forming |
| Best for | Horizontal and vertical porous concrete and masonry: driveways, patios, old brick |
| Application | Roller, garden sprayer or low-pressure airless sprayer |
| Other | Breathable, nonflammable, VOC compliant and paintable |
What It Is
S-40 penetrates deep into porous concrete and masonry to block water, efflorescence and freeze-thaw damage without changing the surface’s look or texture. Rust-Oleum recommends a simple test before you apply: sprinkle water on the surface, and if it darkens, the surface is open enough for S-40 to penetrate.
Pros
- Invisible protection with no change in traction
- Water-based with very low odor
- Works on both horizontal and vertical surfaces
- Paintable after treatment
Cons
- Mainly sold in 5-gallon pails, which is a lot for a small patio
- No oil or stain repellency
- Won’t penetrate dense or previously sealed surfaces
Who Should Buy It
It’s a good fit for homeowners and contractors protecting driveways, patios and brick from water and salt on a budget. It’s our runner-up in best concrete sealers. Also see OKON S-20 for dense vertical surfaces.
How we reviewed this product: this is a research-based review built from the manufacturer’s technical data sheet, current retail listings and owner feedback. We have not run our own hands-on tests of this product. Details were checked in October 2026; always follow the current label.