Red Devil 0646 Masonry and Concrete Acrylic Sealant, 10.1 oz., Made in USA

A good masonry sealant should disappear once it’s cured. That’s the bar I set for the Red Devil masonry sealant, and it came surprisingly close across a handful of real-world repairs around my home: hairline cracks in a poured concrete slab, a few failing mortar joints on a brick stair, and a stubborn gap where a cinder block wall meets a sill plate.

What it is and what it’s for

This is an acrylic-based, 10.1 oz cartridge sealant formulated for concrete, masonry, brick, stone, and cinder block. It has a gritty, textured body meant to mimic the look of mortar or cured concrete. It’s water-cleanup, low-odor, paintable once cured, and it’s designed to stay slightly flexible so it can ride out the expansion and contraction that brittle cement-based fillers can’t.

If you’ve ever used a typical painter’s caulk, the workflow will feel familiar: standard caulk gun, cut the tip, puncture the seal, and go. The difference is in the texture and body. This isn’t a smooth, glossy bead; it’s dense and lightly sandy, which is exactly why it blends well in masonry repairs.

Setup and application

• Tools: Standard caulk gun, a 5-in-1 or narrow putty knife, a damp sponge, and a gloved finger for tooling. For wider joints, a foam backer rod helps control depth.
• Surface prep: Dry, clean, and dust-free. I chased each crack with a wire brush, vacuumed out dust, and wiped with a damp cloth. Any loose mortar needs to go.
• Bead control: The sealant holds a shape but isn’t runny. I had the best results with a small tip opening and lighter trigger pressure, building up as needed rather than trying to fill deep voids in one pass.

The texture is the standout feature. After laying a bead, I could press and feather it with a damp gloved finger or a putty knife to match the surrounding finish. On broom-finished concrete, a light pass with a dry brush softened the sheen and matched the grain nicely. In brick mortar joints, it looked convincing once tooled slightly recessed.

Color and blending

It’s a light-to-medium gray out of the tube—close to new concrete and many standard mortars. On my fairly new slab and newer mortar joints, the color blended well. On older, darker, or brown-leaning mortar, it can look a touch bright. A quick mist of masonry-compatible paint or a siloxane sealer after full cure evened things out where the color mismatch stood out. If you’re patching highly visible, aged mortar, plan on tinting or overcoating for a perfect match.

Working time, cure, and cleanup

Open time is forgiving, and the sealant remains workable for a few minutes before skinning, which is helpful when you’re feathering into textured substrates. It skins in under an hour in mild conditions. Full cure takes longer—count on 24 hours for light contact and up to 48 hours or more for deep fills, cool temperatures, or high humidity.

Being acrylic, cleanup is a breeze with soap and water as long as you do it before it skins. That alone makes it an easier choice for tight spots and indoor work compared to solvent-based options.

Performance under stress

• Adhesion: Very good on properly prepped concrete, brick, and block. It grabs clean mineral surfaces confidently. I also tested on a painted foundation block; adhesion was decent, though I don’t consider painted surfaces ideal for any masonry sealant.
• Flexibility: It stays elastomeric after cure. On a control joint that moves a bit with temperature swings, the bead flexed rather than fracturing.
• Water resistance: After a week of cure, I pressure-rinsed the patched slab and soaked the stair with a hose. No softening, whitening, or washout. In a light basement application along a sill plate gap, it helped tame a minor seep, but note that this isn’t a substitute for proper drainage or negative-side waterproofing.
• Shrinkage: Expect some. On wider gaps, the bead receded slightly as it dried, which is typical for acrylics. A quick second pass the next day brought the patch flush.
• Durability: On low-traffic and vertical applications—mortar joints and wall cracks—it has been rock solid. On a high-traffic stair tread, it held up to foot traffic, but I wouldn’t use it as a topping for spalled areas that take repeated abuse. For that, use a repair mortar or a polyurethane/epoxy joint product.

After a few months of sun, rain, and a couple of hot-cold cycles, my patches remain tight with no noticeable cracking or edge lift. Time will tell across multiple winters, but the early signs are good.

Where it shines

• Blending with masonry: The gritty texture and gray tone do most of the visual heavy lifting. With a little tooling, patches don’t scream “caulk.”
• Ease of use: If you can run a bead of latex caulk, you can handle this. It doesn’t slump much, so vertical joints are manageable.
• Versatility: Concrete cracks, mortar joints, cinder block seams, and small voids all responded well. It’s a smart all-rounder for small to medium masonry defects.
• Low-odor, water cleanup: Indoors and in enclosed spaces, this is a friendlier material to work with than solvent-based products.

Where it falls short

• Not for structural or heavy-duty repairs: Large spalls, deep voids, or areas subject to constant wheel traffic need a different approach. Use a cementitious repair mortar or a high-performance polyurethane/epoxy joint sealant for those scenarios.
• Some shrinkage: Plan for a two-pass fill on wider or deeper cracks to avoid a recessed finish.
• Color limitations: The stock gray won’t match weathered, brownish mortars or colored concrete. Be ready to paint or seal-coat visible patches if you’re chasing a perfect blend.
• Cure time: It isn’t instant. Give it the time it needs before exposure to standing water or load.

Practical tips for best results

• Control the depth: Use backer rod for cracks deeper than about 1/4 inch. It saves material and reduces shrinkage.
• Tool to texture: For broom-finished slabs, tamp lightly with a stiff brush before skinning. For smooth concrete, use a damp finger. For mortar joints, run a jointing tool or the rounded edge of a 5-in-1.
• Mind the weather: Apply above 40°F on a dry substrate. Avoid application before rain. Humidity slows cure.
• Don’t overfill: Build up in thin layers for large voids. It cures more evenly and looks better.
• Finish smart: If color match isn’t right, plan on painting with a compatible masonry paint or applying a penetrating sealer after full cure.

Comparisons and use cases

Compared to traditional hydraulic cement or premixed patching compounds, this sealant is faster, cleaner, and much easier to blend invisibly on small defects. Against polyurethane joint sealants, it’s less rubbery and more concrete-like in appearance, with simpler cleanup but a bit more shrinkage. If your priority is aesthetics on low-to-moderate movement joints and hairline cracks, this acrylic formula is a strong option. If your priority is long-term movement in wide joints, aggressive freeze-thaw cycling, or heavy traffic, step up to a polyurethane or epoxy-grade product.

Bottom line

The Red Devil masonry sealant lands in a sweet spot for DIYers and pros who need a convincing, textured, paintable repair for small to mid-size masonry cracks and joints. It adheres well, tools nicely to match surrounding textures, and cleans up with water—traits that encourage careful, tidy work. It’s not a cure-all for structural failures or high-traffic spalls, and you should anticipate a second pass on wider gaps and consider a coating for perfect color matching. Within its intended scope, though, it delivers a dependable, unobtrusive repair.

Recommendation: I recommend this sealant for routine maintenance of concrete and masonry—filling hairline to moderate cracks, re-pointing small mortar joints, sealing block seams, and stopping minor seepage where appropriate. It earns that recommendation because it blends better than most, bonds reliably, remains flexible, and is straightforward to apply and clean up. For heavy-duty or structural repairs, choose a more robust system, but keep this on the shelf for everything else.