Lath and Plaster in Port St. Lucie, FL

Where Lath Work Comes Up Here

Most of Port St. Lucie is concrete block, and block takes stucco directly. Lath work shows up wherever the wall is not block. Second story wood framing, room additions, garage bump outs, gable ends, soffits and eave returns, chimney chases, and any framed wall on an older Treasure Coast house.

It also comes up on repair jobs. When we open a wall and find the wire rusted through or the paper missing behind it, the stucco above it is finished regardless of how it looks from the street. That section gets stripped back to framing and rebuilt.

What Goes on Before the Wire

Three coat stucco over framing is a drainage assembly. It is not meant to be watertight on its face. Water that gets past the stucco is supposed to hit a barrier, run down it, and leave the wall. That barrier has to be continuous and it has to be lapped correctly, shingle style, so every upper layer sheds onto the one below.

Two layers of building paper is the traditional build over sheathing, and there is a reason for it. Fresh plaster sticks to the first layer and pulls it tight against the wall. The second layer stays free to drain. Skip it and you can lose the drainage plane that the whole system rests on.

• Continuous water resistive barrier over sheathing, lapped from the bottom up
• Second separation layer so the plaster does not bond to the drainage plane
• Flashing tied into the barrier at every window head, sill and penetration
• Weep screed at the base of the wall, set at the correct height above grade
• Casing bead where stucco stops at a different material
• Control joints laid out before any wire goes up

Hanging the Lath

Wire lath has to be furred off the wall so plaster pushes through and wraps the wire from behind. Wire pinned flat against the paper is the single most common lathing mistake we find. The plaster sits on top of it instead of encasing it, and the panel has no real reinforcement.

Fasteners go into framing members on a set spacing, not into sheathing alone. Sheets lap along the sides and ends and the laps get tied. At inside and outside corners, we run the wire continuous around the corner rather than butting two sheets at the exact point where the wall wants to crack.

Every fastener and every accessory in coastal air needs to be corrosion resistant. Salt air on the Treasure Coast will find an unprotected staple, and rust stains bleeding through a finished wall means the wire behind it is going the same way.

Scratch Coat

The scratch coat is the first plaster application. It is pressed hard into the lath so the material squeezes through the mesh and locks behind it. That mechanical key is the entire reason the stucco stays on a framed wall.

Once it firms up, the surface gets raked horizontally with a scarifier. Those grooves give the brown coat something to grab. A scratch coat that was troweled smooth instead of scratched is a delamination waiting to happen, and it usually shows up years later as a hollow section that sounds like a drum when you tap it.

Brown Coat and Float

The brown coat brings the wall to thickness and to plane. This is the layer that makes a wall look straight, and it is where a good plasterer earns the money. We rod it off the accessories, fill the hollows, cut the high spots, and float it to an even, open surface.

Float finish matters for what comes next. The brown coat should be uniform in suction and slightly open, not burnished tight. A hard, closed surface will not pull the finish coat in evenly, and the finish will dry blotchy or fail to bond.

Total thickness over metal lath is nominally three quarters of an inch on vertical walls, built up across scratch and brown. Thin spots crack. Thick spots sag and shrink more than their neighbors.

Curing in Florida Heat

Portland cement plaster does not dry, it hydrates. It needs water in the mix long enough to gain strength. In Port St. Lucie in July, a south facing wall with sun and wind on it can pull the water out of a fresh coat in an afternoon. What you get is a coat that looks set but never developed strength, and it crazes and dusts.

We moist cure. That means fogging the wall on a schedule, working the shaded elevations during the hottest part of the day, and giving each coat time before the next one goes on. Rushing the interval between scratch and brown is how you get shrinkage cracking that telegraphs all the way through the finish.

Humidity here helps and hurts. High humidity slows drying, which is good for cure, but it also stretches the schedule and makes afternoon storms a real scheduling factor from June through October.

Where Lath Jobs Go Wrong

Almost every lath failure we get called to inspect traces back to one of a short list of shortcuts. None of them are visible once the finish coat is on, which is exactly why they happen.

If you are getting bids, ask what goes behind the wire, what the fasteners are, and where the control joints are going. A contractor who has a straight answer for all three is building the wall correctly.

• Wire nailed flat to the wall with no furring, so plaster never keys behind it
• Single layer barrier, or laps run the wrong direction
• No kick-out flashing where a roof edge meets a wall
• Weep screed buried in soil, mulch or a new driveway pour
• Scratch coat troweled smooth instead of scratched
• Control joints left out on long runs and at floor lines
• Fasteners and accessories that are not rated for coastal exposure