How Block Walls and Garden Walls Get Coated

Row of painted houses with red and white doors

Most people roll a standard wall paint straight onto raw block and watch it vanish into the pores, and exterior painting carlsbad low carbon grid 2030 sets the order of work deliberately so that never happens. Around Carlsbad, CA the exterior block walls that edge yards and garden beds need a masonry system, not a quick coat of house paint.

Why block drinks paint

Blue painted house wall with ornate windows

Concrete block is porous and uneven, with a rough face and open voids between the cells. A single coat of ordinary latex soaks in and leaves pinholes, so the wall looks patchy and the coverage runs far below what the can promises. The pinholes also let moisture in from the coastal fog, and the damp gets behind the film and blisters it.

Cleaning and efflorescence

Red painted wall with a window and plants

Block walls grow white crusty salts called efflorescence, where moisture carries minerals through the block and leaves them on the face. Painting over it fails every time, because the salt pushes the film off. The salts are brushed off dry with a stiff brush, then the wall is washed and left to dry for days. If they return, the cause is moisture, often a sprinkler hitting the wall or soil piled against the base, and that has to be fixed first.

Filling and patching

Cracks in mortar joints and chipped corners are patched with a masonry patching compound or a cement based filler, not spackle, which will not hold outdoors. Small hairline cracks get an elastomeric caulk. Loose old paint is scraped back, and sanding is rarely enough on a rough face, so a wire brush does most of that work.

The block filler coat

The step that separates a lasting job from a short one is a block filler, a thick acrylic primer sealer that fills the pores. It is rolled on with a heavy nap roller, and worked in with a brush at the mortar joints, and it needs to dry fully before anything else. On very porous block, two coats of filler may be needed before the surface looks sealed.

The finish coats

Over the filler goes a masonry coating, usually a thick acrylic, in two coats with the second applied at right angles to the first. A flat or low sheen finish hides the rough texture and keeps glare down. An airless sprayer speeds up a long garden wall, though it is followed by a back roll so the coating gets pushed into the face.

Wall caps and tops need attention, because water sits on them. A sloped cap sheds water, while a flat top should be sealed carefully or it will be the first spot to fail.

Walls near the lagoons

Walls close to Buena Vista Lagoon or Agua Hedionda Lagoon stay damp longer and grow algae on their shaded faces. Those faces get washed with a cleaner and allowed to dry before coating, or the green returns under the new paint.