Efflorescence tells the story of a foundation wall before any paint is applied. Those white, crystalline deposits on the concrete surface are soluble salts that have migrated from inside the concrete to the surface through water movement. Their presence confirms that water is traveling through the wall. Painting over efflorescence without removing it and addressing the moisture source behind it produces a paint job that fails within one season. The salts continue to migrate, push through any coating, and the paint lifts in sheets.

Foundation walls require a specific preparation and coating approach that is different from every other exterior surface on a house. The combination of ground-level moisture exposure, alkaline concrete chemistry, and the hydrostatic pressure that wet soil creates against the foundation wall demands products and preparation techniques not needed on siding or trim.

Cleaning and Etching Concrete Foundation Surfaces

The first preparation step on any concrete foundation is removing all contamination from the surface: efflorescence, dirt, oil staining, paint overhang from previous siding work, and mildew growth. None of these contamination layers accept paint bonding without removal.

Efflorescence removal requires mechanical scrubbing with a wire brush followed by acid treatment. Wire brushing alone removes the loose crystalline deposits at the surface, but residual salts in the concrete pores remain and will re-migrate to the surface after painting. A diluted acid treatment dissolves these residual salts and prepares the concrete chemistry for bonding.

Muriatic acid achieves an etching effect roughly equivalent to a 150-grit sandpaper surface profile on concrete. This texture provides the mechanical key that primers and paint need to bond to the dense concrete surface. A smooth poured concrete foundation without etching has minimal surface profile and will not hold most paint films through thermal cycling and moisture exposure.

DryLok Etch, available as either a liquid or powder form, is a safer alternative to muriatic acid for foundation etching. It produces similar surface preparation results with significantly lower chemical hazard compared to concentrated muriatic acid. For homeowners without experience handling corrosive acids, DryLok Etch is the appropriate choice.

When using muriatic acid, critical safety requirements apply: always add acid to water, never water to acid. Wear safety glasses with side shields, chemical-resistant gloves, and protective clothing that covers all exposed skin. Work in ventilated conditions and have a garden hose with running water available for immediate rinsing of any skin contact.

Test the concrete for moisture readiness before etching or priming by conducting a water bead test. Pour a small amount of water on the foundation surface. If it absorbs within 30 seconds and the concrete darkens readily, the surface is ready to accept a coating. If water beads on the surface or rolls off without absorbing, there is a sealer or contamination layer present that must be removed before any coating will adhere.

For new concrete, the standard cure time before painting is 30 days. The high alkalinity of fresh concrete (pH 12 to 13) deteriorates most paint and primer films. Sherwin-Williams Loxon products have a shorter specified window of seven days for new masonry, but 30 days is the safer baseline for most products.

Best Masonry Primer for Exterior Foundation Walls

Foundation primer selection must address two requirements that siding primers do not face: high alkalinity resistance and moisture tolerance.

BEHR Premium Concrete and Masonry Bonding Primer (number 880) uses a water-thin viscosity that penetrates into the concrete pore structure rather than bridging across the surface. It applies milky and dries clear. Apply topcoat no sooner than four hours after the primer dries, and complete topcoating within 30 days of priming. Use a 1/4 to 3/8-inch nap roller. The thin viscosity of this primer means it soaks into the concrete efficiently, but also means that highly porous concrete or concrete block may absorb the first coat completely. A second primer coat may be needed on very porous surfaces.

For foundations in areas with ground moisture pressure or in climates with significant rainfall, DryLok Extreme Concrete and Masonry Waterproofer can serve as both primer and topcoat in a single product. The oil-based version using a portland cement formula is recommended for exterior below-grade applications. DryLok Extreme can be applied to slightly damp surfaces, which is important for foundations in consistently moist climates where achieving a fully dry surface is difficult.

The Sherwin-Williams Loxon Concrete and Masonry Primer/Sealer is the professional primer in the Loxon system, matched to the Loxon XP topcoat. It handles high pH masonry without saponification and provides alkali resistance that standard primers do not.

Roller and Brush Techniques for Rough Concrete Textures

Concrete foundation walls range from smooth trowel-finished poured concrete to rough parged block surfaces to unparged concrete masonry unit block with its deeply porous texture. Each requires different application technique to achieve adequate film thickness in a single coat.

For smooth poured concrete foundations, a 3/8-inch nap roller covers the surface efficiently and provides enough surface contact to work the primer into the etched texture. Apply the primer in full, wet coats without excessive back-rolling that would thin the applied film.

For rough parged or textured concrete, move up to a 3/4-inch nap roller. The deeper nap reaches into the textured surface and deposits paint in the recesses that a short-nap roller would skip. If significant voids or rough areas remain even with a 3/4-inch roller, follow with a brush to work paint into the deepest recesses.

On concrete block foundations where the block face is unparged and the voids in the block surface are significant, apply a block filler before the primer and topcoat system. Sherwin-Williams PrepRite Block Filler fills the voids in CMU block surface to create a uniform, smoother base that subsequent coatings can cover at normal application rates. Without a block filler, coating consumption on rough block is extremely high and coverage remains incomplete in the voids even with multiple coats.

When using an airless sprayer on foundation walls, keep the tip in the 0.017 to 0.021-inch range for standard masonry paints. Back-roll immediately after spraying to press the paint into the surface texture. Spraying without back-rolling leaves paint sitting on the high points of rough concrete rather than filling the recesses, which means inadequate film thickness in the areas most vulnerable to moisture entry.

Choosing Exterior Foundation Paint That Resists Ground Moisture

Ground-level moisture is the defining stress on foundation paint. The bottom 12 to 18 inches of the foundation is routinely wet from rain splash, ground moisture, irrigation, and in some soils, capillary wicking. A paint product that performs well on walls above grade but lacks moisture resistance will delaminate at the base of the foundation within one to two seasons.

DryLok Extreme Concrete and Masonry Waterproofer claims 200 PSI of waterproofing capability. This hydrostatic pressure resistance matters for foundations in areas with seasonally high water tables or significant ground saturation. The oil-based formula with portland cement is the exterior-appropriate version; water-based DryLok is better suited to interior applications.

For foundations that have active water entry from hairline cracks, use UGL DryLok Fast Plug to stop active water flow before any waterproofing paint is applied. DryLok Fast Plug is a hydraulic cement product mixed to a thick consistency and pressed into the crack or void. It sets rapidly, typically within three to five minutes, and stops water flow. After the Fast Plug cures, the repaired area can be coated with a waterproofing paint.

Elastomeric foundation coatings bridge hairline cracks and remain flexible through the thermal and moisture-driven movement that concrete experiences seasonally. An elastomeric foundation coating that stretches across a developing hairline crack maintains the waterproof membrane. A rigid paint film that cannot stretch cracks with the concrete and allows immediate water entry.

RadonSeal deep-penetrating sealer addresses foundations in homes where radon and moisture migration below grade are both concerns. It penetrates into the concrete pore structure and reacts chemically to form a crystalline compound that blocks water vapor and gas transmission. It serves a different function than film-forming waterproofers and can be used in combination with topcoats on foundations where vapor transmission is a specific concern.

For above-grade foundation walls that are visible as part of the exterior appearance of the home, choose a masonry paint that matches the aesthetic of the siding while providing the moisture resistance the foundation surface requires. Elastomeric masonry coatings are available in a range of colors and provide the crack-bridging performance appropriate for foundation surfaces that experience movement.