| Type | Penetrating water repellent |
| Chemistry | Water-based silicone (Behr No. 980) |
| Coverage | About 250 sq. ft. per gallon |
| Cure | 24–48 hours |
| Not for | Surfaces under hydrostatic pressure, such as basement walls or floors |
| New concrete | Let it cure at least 30 days first |
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The Siloxa-Tek 8500 manufactured by Kretetek Industries is an excellent example of a concrete sealer. The Siloxa-Tek solution is a special one that promises waterproofing protection. While many sealers offer this level of protection, which is such a huge benefit for people looking to protect their concrete, the Siloxa-Tek is of a different chemical make-up; it is, therefore, much better suited to locking out water. The Siloxa-Tek is a silane/siloxane solution, which both penetrates within the concrete as well as giving it a level of surface protection. Because of this, water is locked out in two steps: from within and from without. The water will actually bead on the surface of concrete treated properly with the Siloxa-Tek 8500, so you can see the sealer in action. The sealer is water-based and VOC free, offering such benefits as preventing efflorescence and resisting stains, as would be expected of any high-quality sealer. The Siloxa-Tek 8500, a DOT approved, water repellent impregnating sealer changes the surface tension of mineral substrates to produce a water repellent surface to keep water and aggressive water-soluble salts, such as chlorides and sulfates, out. Also the 8500 provides excellent resistance to freeze-thaw cycles, spalling, cracking and pitting. While the Siloxa-Tek 8500 is not suitable for every single concrete sealing project (such as for decorative concrete on a pool deck, for instance), it is one of the best choices for many of them especially driveways, sidewalks, roads and bridges. Readily available at HomeDepot.com this sealer is an excellent choice for most projects.
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| Type | Clear film-forming masonry waterproofer |
| Chemistry | Water-based latex |
| Finish | High gloss, non-yellowing |
| Coverage | About 90–100 sq. ft. per gallon |
| Rating | Tested to resist 4 psi hydrostatic pressure (ASTM D7088) |
| Warranty | 7-year transferable limited warranty |
| Not for | Vehicle traffic |
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Moisture is the most common reason concrete sealers and floor coatings fail. Too much moisture moving up through a slab can make epoxy blister, acrylics turn white, and flooring adhesives let go. Testing before you seal, coat or install flooring tells you whether the slab is ready.
Why Concrete Holds Moisture
Water is part of every concrete mix, and new slabs can take weeks or months to dry out. Slabs on grade, especially basements without a vapor barrier, can also wick moisture up from the ground indefinitely. A certain amount of moisture is normal. The goal of testing is to find out whether there is more than your sealer, coating or flooring can tolerate.
Method 1: Plastic Sheet Test (Quick Check)
This simple test (based on ASTM D4263) gives a yes/no indication of moisture.
- Tape an 18″ x 18″ sheet of clear plastic tightly to the floor on all four edges.
- Leave it for at least 16 hours (24 is better).
- Lift it and check. Condensation under the plastic or a darkened slab means moisture is coming through.
It’s quick and free, but it isn’t quantitative. Use it to decide whether more precise testing is needed.
Method 2: Calcium Chloride Test
The calcium chloride test (ASTM F1869) measures the moisture vapor emission rate (MVER), the pounds of moisture released per 1,000 sq. ft. over 24 hours. You seal a dish of calcium chloride under a plastic dome on the slab for about three days, then weigh it to see how much moisture it absorbed. Kits are inexpensive and widely available.
Method 3: Relative Humidity (RH) Probes
The most accurate method (ASTM F2170) measures relative humidity inside the slab. You drill a small hole to a set depth, insert a probe sleeve, let it equalize, and take a reading. Most flooring and coating manufacturers now specify a maximum RH reading, so this is the test to use before installing an epoxy coating or flooring.
What to Do If the Concrete Is Too Wet
- Give new concrete more time to dry, with heat and air movement if indoors.
- Fix drainage, grading and gutters that send water toward the slab.
- Use a coating system rated for higher moisture, such as a moisture-mitigating epoxy primer.
- For basements, a penetrating water repellent or densifier can reduce dampness. See best sealer for basement waterproofing.
Always compare your results with the limits on the product’s technical data sheet; acceptable moisture levels vary by product.
Frequently Asked Questions
Do I need to test moisture before sealing outdoor concrete?
Usually not with breathable penetrating sealers, as long as the surface is dry. Testing matters most before film-forming coatings and indoor flooring.
Can a sealer stop moisture from coming through a slab?
Penetrating sealers reduce water absorption, but they don’t stop vapor pressure from below. High-moisture slabs need moisture mitigation, not just a sealer.
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| Type | Silicate densifier/hardener |
| Finish | Natural, no sheen |
| Best for | Porous or older concrete and cinder block |
| Not for | Decorative, stamped or exposed-aggregate concrete |
| Where to buy | Mainly online |
