Foundation Armor AR350 Acrylic Sealer -- Best Exterior Block Sealer
Foundation Armor's AR350 is a solvent-based acrylic sealer that enhances the appearance of block while forming a protective film on the surface. It produces a wet look that deepens the natural color of the block and leaves a low-sheen finish. On exterior applications, it performs well against rain, UV exposure, and surface efflorescence. The film-forming nature means it will require reapplication every 3 to 5 years as the surface layer weathers, but reapplication is straightforward. Coverage is approximately 200 to 400 square feet per gallon depending on block porosity. A strong choice when aesthetics matter alongside protection.
Check price on Amazon →Seal concrete block walls against water, efflorescence, and surface wear with a product matched to your application. These five picks cover penetrating sealers, topcoat sealers, and water repellents.
Concrete block is inherently porous and will absorb water unless it is sealed. Left unsealed, block walls develop efflorescence, allow moisture to enter living spaces, and deteriorate faster in freeze-thaw climates. The five sealers below cover the most effective categories for residential and light commercial block applications.
| Product | Best For | Rating |
| — | — | — |
| Foundation Armor AR350 Acrylic Sealer | Exterior block, wet-look finish | 4.7/5 |
| Ghostshield Siloxa-Tek 8500 | Deep penetrating water repellent | 4.8/5 |
| RadonSeal Plus Concrete Sealer | Interior block, radon reduction | 4.7/5 |
| Endura Seal 100% Acrylic Sealer | Natural-look matte finish | 4.5/5 |
| Thompson’s WaterSeal Masonry Protector | Budget exterior block sealer | 4.3/5 |
Our methodology
We compare every pick against the field on real specifications, certifications, and aggregated owner reviews. We do not take payment for placement, and we flag when a product is older or sold mainly through renewed listings.
Side by side
| Pick | Best for | Score | |
|---|---|---|---|
| Foundation Armor AR350 Acrylic Sealer -- Best Exterior Block Sealer | Check price | ||
| Ghostshield Siloxa-Tek 8500 -- Best Penetrating Water Repellent | Check price | ||
| RadonSeal Plus Concrete Sealer -- Best for Interior Block Walls | Check price | ||
| Endura Seal 100% Acrylic Sealer -- Best Natural-Look Option | Check price | ||
| Thompson's WaterSeal Masonry Protector -- Best Budget Option | Check price |
The full reviews
Foundation Armor AR350 Acrylic Sealer -- Best Exterior Block Sealer
Foundation Armor's AR350 is a solvent-based acrylic sealer that enhances the appearance of block while forming a protective film on the surface. It produces a wet look that deepens the natural color of the block and leaves a low-sheen finish. On exterior applications, it performs well against rain, UV exposure, and surface efflorescence. The film-forming nature means it will require reapplication every 3 to 5 years as the surface layer weathers, but reapplication is straightforward. Coverage is approximately 200 to 400 square feet per gallon depending on block porosity. A strong choice when aesthetics matter alongside protection.
Ghostshield Siloxa-Tek 8500 -- Best Penetrating Water Repellent
Ghostshield's Siloxa-Tek 8500 is a silane-siloxane blend that penetrates into the concrete block matrix and chemically bonds to block pore walls to create a hydrophobic barrier that cannot peel or delaminate. It leaves no visible film on the surface and does not change the block's appearance beyond making water bead and run off. The formula is breathable, allowing vapor to escape while blocking liquid water from entering. This is the preferred sealer type for applications where you want long-term protection without altering the block's look -- retaining walls, foundation walls, and decorative block installations. A single application is expected to last 7 to 10 years.
RadonSeal Plus Concrete Sealer -- Best for Interior Block Walls
RadonSeal Plus is a penetrating reactive sealer specifically developed for interior concrete and block walls. The active siliconate compound reacts with free lime and silica inside the concrete to form a permanent gel that plugs capillary pores from the inside out. This makes it effective on below-grade block walls where hydrostatic pressure pushes moisture inward. As a secondary benefit, it reduces radon gas transmission through block and concrete, which is relevant in geographic regions with elevated soil radon levels. The formula is water-based, low-odor, and safe for interior use. Coverage is 100 to 200 square feet per gallon.
Endura Seal 100% Acrylic Sealer -- Best Natural-Look Option
Endura Seal is a water-based acrylic sealer that dries to a matte, natural-look finish rather than the glossy or wet-look result of solvent-based acrylics. It is suitable for both interior and exterior block and provides good resistance to surface water and UV degradation. The water-based formulation makes application easier with lower VOC emissions and faster cleanup. Coverage ranges from 200 to 300 square feet per gallon. The matte finish makes it appropriate for decorative block, garden walls, and any application where a shiny surface would look out of place. Reapplication is needed every 2 to 4 years on exposed exterior surfaces.
Thompson's WaterSeal Masonry Protector -- Best Budget Option
Thompson's WaterSeal is one of the most widely available and recognizable masonry sealer brands in hardware stores. The masonry protector formula provides water repellency through a silicone-based compound that penetrates the block surface and reduces water absorption. It is not as deep-penetrating or long-lasting as premium silane-siloxane products, but it offers a practical level of protection at a significantly lower price point. Coverage per gallon is good, and it is easy to apply with a brush, roller, or garden sprayer. For a garden wall or above-grade block structure with light moisture exposure, it is a cost-effective starting point.
What matters most
What to consider
Decide between penetrating and film-forming before selecting a product. Penetrating sealers are better for long-term performance and below-grade applications; film-forming sealers are better when you also want to enhance appearance. For any sealer to work correctly, the block must be clean, dry, and free of efflorescence. Check the manufacturer's drying time requirements -- most penetrating sealers need 28-day-cured concrete for best results, and all sealers need the surface temperature to be within the application range listed on the label. Buy slightly more product than your square footage estimate; the first coat on raw block absorbs heavily and coverage rates will be lower than the label indicates.
What to consider
For related reading, see [best concrete block paints](/articles/best-concrete-block-paint) and [best concrete basement wall sealers](/articles/best-concrete-basement-wall-sealer). See how we evaluate masonry products at [/methodology](/methodology).
Frequently asked
Penetrating silane-siloxane sealers typically last 7 to 10 years on vertical masonry surfaces protected from direct water impingement. Film-forming topcoat sealers last 3 to 5 years before they begin to peel or chalk, especially on exterior surfaces. Reapplication timelines depend heavily on UV exposure, precipitation, and surface traffic. Inspect sealed surfaces annually and reapply when water stops beading on the surface.
No. Efflorescence -- the white salt deposits that leach out through concrete block -- must be removed before sealing. Sealing over efflorescence traps the salts beneath the surface and causes the sealer to fail and delaminate from behind. Use a masonry cleaner or diluted muriatic acid wash to remove efflorescence, rinse thoroughly, allow the block to dry completely, and then apply sealer.