Block and Foundation Stucco in Port St. Lucie, FL

Block Takes Plaster Directly

Concrete masonry units are absorbent and rough. Cement plaster bonds to them chemically and mechanically without any wire in between, as long as the block face is clean, sound and unsealed. That is why a standard Florida block house gets a two coat application rather than the three coat build a framed wall needs.

It also changes what can go wrong. On a framed wall the failure is usually behind the wire. On block, the failures are bond failures at the block face and moisture problems coming up from the bottom of the wall. Those are the two things we look at first on any block job.

Parge Coat, Skim Coat and Two Coat Work

The words get used loosely, so here is how we use them. A parge coat is a thin cement coat troweled directly onto masonry to close the surface, even out the block joints and give a uniform face. It is what goes on stem walls, retaining walls, block fences and the exposed foundation below a finished wall.

A skim coat is thinner still, used to smooth an existing surface that is already sound rather than to build any real thickness.

Two coat stucco on block is the residential standard. A base coat brings the wall to plane and covers the mortar joints, then a finish coat carries the texture and the color. Nominal thickness on block is thinner than on lath, typically around half an inch total, because the block itself is doing the structural work.

Getting Bond on CMU

Bond is the whole job on block. Plaster will not stick to dust, to form release oil on precast or poured elements, to old paint, to a sealer, or to a glazed slick face.

Dry block also steals water from the mix. A hot block wall in the Port St. Lucie sun pulls water out of fresh plaster so fast that the cement never hydrates at the interface, and the coat lets go months later in sheets. Pre dampening the wall to a saturated surface dry condition, damp but with no standing water, solves it.

Where bond cannot be trusted, we do not gamble. Painted or sealed block gets either mechanical removal, a bonding agent, or lath fastened over it depending on the condition.

• Remove dirt, dust, laitance and efflorescence from the block face
• Strip or lath over paint, sealers and any coating that blocks suction
• Cut back form oil residue on poured or precast elements
• Dampen the wall ahead of the base coat, especially on hot afternoons
• Run lath across any block to frame transition rather than stopping at it
• Check that mortar joints are full and repoint any that are not

Stem Walls and the Line at Grade

The stem wall is the exposed block between the finished wall and the ground. It takes splash back from every rain, irrigation spray, string trimmer damage, and any moisture wicking up from the footing. It is the hardest working few feet of stucco on the house.

How the finish terminates at the bottom matters. On block construction the plaster is often carried down onto the stem wall and stopped a set distance above grade, sometimes with a change of texture or a foundation band. Running the finish all the way into the soil is asking for the bottom of the wall to stay permanently wet.

Where a framed wall sits above, the weep screed sets that termination and it needs its clearance, roughly four inches above earth and two inches above a driveway or patio. Adding a raised planting bed or pouring a new patio tight to the wall undoes it, and that is one of the most common things we are called to correct.

Below Grade Is a Different Detail

Standard stucco is not a below grade waterproofing product. Buried against soil it stays saturated, and constant saturation drives salts out of the masonry and pushes coatings off the surface.

Below the grade line the correct approach is a dampproofing or waterproofing membrane applied to the masonry, with any parge coat serving as the smooth carrier for that membrane rather than as the barrier itself. Above the grade line the stucco does its normal job.

The transition between the two is where the detailing counts. A clean termination, a slight kick or drip so water leaves the face instead of running down into the soil contact zone, and grade sloped away from the house. Most stem wall failures we see are drainage problems, not material problems.

Efflorescence, Rising Damp and Breathability

The white crusty deposits on a stem wall are efflorescence. Water moves through the masonry, dissolves salts on the way, reaches the surface and evaporates, and the salt stays behind. It is a symptom. Scrubbing it off without dealing with the water means it comes back.

When those salts crystallize just under a coating instead of on top of it, the pressure lifts the coating off. That is the mechanism behind most peeling paint at the base of a block wall in this area, and it is why the fix is almost never a better paint.

The rule on block is to let the wall dry outward. Cement based parge coats, mineral and silicate coatings, and breathable acrylics all allow that. Sealing a damp stem wall with a low permeability elastomeric traps the moisture and moves the damage inward. Find the water source, cut it off, and keep the wall open enough to dry.

Repairing Hollow, Cracked and Spalled Block Stucco

Tap along an older wall and the sound tells you a lot. A solid ring means the plaster is bonded. A drummy hollow sound means it has released from the block, and no coating or patch on the surface changes that.

Repair means cutting back the loose material to sound plaster, squaring the edges rather than feathering them out to nothing, dampening the exposed block, and rebuilding the coat to the original thickness. Feathered patch edges are thin, they crack first, and the repair peels back from the perimeter within a season or two.

Texture matching on block repairs is generally easier than on a smooth wall, because most Port St. Lucie homes carry sand, lace or knockdown texture that patches in well. We match on sample boards before touching the wall. On a stem wall or foundation band, the practical move is often to run the repair the full length of the band so the change stops at a natural edge.