INSL-X AMW100009A-01 WaterBlock Acrylic Masonry Waterproofer Paint, 128 Fl Oz (Pack of 1), White

Basement walls have a way of telling you what’s going on outside. After a stretch of heavy rain left a couple of persistent damp spots on my cinder block foundation, I reached for INSL-X’s WaterBlock to see if a water-based acrylic could tighten things up without turning the project into a multi-week ordeal. Short version: it did what I needed, applied easily, and left the space looking cleaner and brighter—so long as I respected its limits and did the prep right.

What WaterBlock is (and isn’t)

WaterBlock is a water-based acrylic waterproofing paint designed specifically for vertical concrete and masonry surfaces—think basement walls, foundations, retaining walls, stucco, brick, and cinder block. It’s formulated to tolerate high-alkaline substrates (up to pH 13) and is rated to withstand up to 12 psi of hydrostatic pressure. That last spec matters: it’s aimed at stopping seepage through porous masonry, not solving major drainage failures or active water streaming in through joints.

It’s also fast-drying and low-odor, which makes it practical to use in lived-in spaces. The white finish is crisp and immediately brightens a basement, which is a welcome bonus if you’re trying to turn a dingy utility area into workable storage or shop space.

Where it shines

• Masonry that’s sound but porous: cinder block, parged walls, stucco, and brick that darken with damp but don’t have active running water.
• High-alkaline surfaces: newer concrete and lime-rich mortar beds that can challenge conventional coatings.
• Interior spaces where low odor and water cleanup matter.
• Exterior vertical walls where you want a breathable but water-resistant coating.

If you’re battling capillary seepage, efflorescence, or “sweating” block walls after storms, this is in its wheelhouse.

Prep is 80% of the job

Waterproofing coatings magnify whatever you skip in prep. I started by scraping and wire-brushing all loose paint and efflorescence (those white, chalky deposits). Any powdery or flaking material has to go or it becomes a release layer. I washed the walls with a masonry cleaner/degreaser, rinsed thoroughly, and let things dry. Hairline cracks and minor mortar gaps were filled with a compatible masonry patch. On especially tight pores, I lightly etched a small test area to confirm porosity, then neutralized and rinsed per product directions.

Two small but important points:
- Surface must be sound. If your mortar is crumbling or you can dislodge sand with your fingernail, repair that first.
- Temperature matters. I worked between 60–70°F with low humidity, and that made application predictable. The label’s 50–90°F range is there for a reason.

Application experience

This is a dense coating—not syrupy, but definitely heavier than standard wall paint. That’s a positive for waterproofing, but it means technique matters. I got the best results using a 3/4-inch nap roller to load the pores, then back-brushing with a stiff nylon brush to push the coating into every pinhole. On smoother poured concrete the roller alone did fine; on rough block the back-brush made a visible difference.

Coverage depends entirely on how thirsty the wall is. On bare cinder block, the first coat soaked in quickly. The second coat evened out the color and built the film thickness you need for waterproofing. On an exterior stucco test panel, the first pass covered more generously and the second coat dialed in the uniform white.

I avoided overly thin passes. A light dusting won’t waterproof; you need a continuous film with the coating worked into the surface. Two coats were the sweet spot in my case. If you have noticeably active seepage, don’t expect the first coat to stop it mid-application; let it dry and build with the second.

Dry time, odor, and cleanup

“Fast-drying” proved accurate. By the time I wrapped the first wall, the starting area was ready for another pass before the day was out. Odor was minimal—acrylic “painty” but not solvent-sharp—so I didn’t need to vacate the basement beyond normal ventilation with a fan. Brushes and rollers cleaned up with warm soapy water without drama, which is one of the biggest differentiators versus solvent-based waterproofers.

Performance and results

After the second coat, the damp ghosting spots on my foundation wall stopped appearing after rain events. The wall surface stayed dry to the touch, and there was no new efflorescence bleeding through. The bright white finish is matte and hides small imperfections well, which makes an old basement feel more finished. On my exterior retaining wall test, the coating bonded well and shed wind-driven rain, with no softening or chalking early on.

That said, WaterBlock isn’t a miracle cure for every moisture problem:
- It won’t fix bulk water intrusion from failed drainage, clogged gutters, negative grading, or water pushing through the wall-floor joint. If you have water welling at the cove or through a cold joint, you’re into drainage corrections or interior drain/tile systems.
- It isn’t intended for floors. It’s a vertical-wall product; foot traffic and hydrostatic pressure from below grade are different challenges.
- It doesn’t dehumidify your basement. It reduces water seepage through the wall, which can lower ambient moisture, but you may still need a dehumidifier and air movement.

As for the 12 psi hydrostatic pressure claim: that’s a lab rating I didn’t attempt to reproduce. In practical terms, it handled the kind of intermittent seepage common to older basements and exterior block without issue in my use.

Durability and touch-ups

A nice perk of an acrylic film is how easy touch-ups are. I had a few small scuffs from moving shelving; spot-rolling blended them without flashing. On porous masonry, the coating keys in mechanically, so adhesion has been solid. I’d still avoid pressure-washing at close range on exterior walls and would keep garden beds and sprinklers from constantly wetting the surface if you can.

Tips for best results

• Do a moisture test. Tape a square of plastic to the wall for 24 hours. If you see beads of water or heavy condensation, check for drainage issues before painting.
• Address cracks and joints first. Use a hydraulic cement or compatible masonry patch for active weepers; then coat.
• Use a long-nap roller and back-brush. The goal is to fill pores, not just tint the surface.
• Plan for two coats. The first primes and seals; the second builds the continuous barrier.
• Respect the temperature window. Cold walls slow drying and can affect film formation; hot, sunlit walls can skin over too fast.
• Ventilate. Low odor doesn’t mean no ventilation—airflow helps cure and keeps the workspace comfortable.

How it compares to other options

Solvent-based or epoxy waterproofers can offer higher ultimate resistance and chemical hardness, but at the cost of stronger odor, stricter prep, and trickier cleanup. For most residential vertical masonry, a water-based acrylic like WaterBlock hits a practical sweet spot: enough hydrostatic resistance for typical seepage, compatibility with high-alkaline substrates, fast recoat, and easy maintenance. If you’re waterproofing a space you still need to live near, those trade-offs matter.

Bottom line

WaterBlock earns its keep by solving the common, aggravating moisture issues that plague masonry walls without turning your basement into a hazmat zone. It goes on like a heavy paint, bites into rough substrates when you work it properly, dries fast, and leaves a clean, bright finish. It won’t cure structural or drainage failures—and it’s not for floors—but within its design intent it performs reliably.

Recommendation: I recommend WaterBlock for homeowners and pros looking to stop minor to moderate seepage through vertical masonry, especially in basements and on exterior block or stucco. It’s user-friendly, forgiving to apply with the right technique, and the water-based formula keeps odor and cleanup in check. If you suspect major hydrostatic pressure or have water intruding at joints or floors, address drainage and structural issues first; then use this as the finishing layer that keeps walls dry and presentable.