How to Fix Hairline Cracks in Stucco: A Florida Homeowner's Guide

What Counts as a Hairline Crack

Parex, one of the larger stucco makers, defines hairline cracks as 1/32 inch wide or smaller. That's about the thickness of a credit card. A hairline crack:

• is thin enough that a fingernail barely catches, or doesn't catch at all,
• runs in a fine line or a web of lines (sometimes called crazing or map cracking),
• has both sides level with each other.

A crack wider than that, one with an edge where one side sits higher, or one that runs in steps is a different job. Our guide to stucco crack repair products sorts cracks by size.

Are Hairline Cracks in Stucco Normal?

Yes. Stucco is a cement plaster, and cement is rigid. It shrinks a little as it cures and dries, and the wall under it moves a little with heat and cold. Fine cracks are how the plaster relieves that stress.

The Stucco Manufacturers Association puts it plainly: the occasional hairline crack in cement plaster "is not detrimental, nor should it be considered a defect." Control joints reduce cracking, but the SMA notes that even a wall built to the standard comes with "no guarantee of a crack-free cement plaster."

Do Hairline Cracks Need to Be Repaired?

Not for the wall's sake. Parex calls cracks this size "more of an aesthetic nuisance." Good reasons to fix them anyway:

• Looks. A web of fine lines shows on a smooth or freshly painted wall.
• Painting. If the house is due for paint, it's the right time to fill or bridge them.
• Growth. Parex notes that cracks wider than 1/32 inch can let moisture in and lead to blistering or peeling paint, so a crack that's widening is worth sealing.

Two Ways to Fix Hairline Cracks

A few cracks: fill them one at a time

For one or two cracks, a textured elastomeric sealant pressed into the crack is the simplest fix. It stays flexible as the wall moves, and the texture blends in. Sashco Mor-Flexx and DAP Elastopatch Textured are two common examples. Sashco says Mor-Flexx repairs can be made "with a caulk gun and one's finger."

Many cracks: bridge them with elastomeric paint

For a wall covered in fine cracks, filling each one takes forever and shows. Parex's repair bulletin calls instead for two coats of elastomeric coating, about 16 mils wet film each, over the area. That's several times thicker than ordinary house paint. The film stretches across the cracks instead of splitting over them.

Sherwin-Williams' ConFlex XL is one example made for stucco: its maker says it "bridges hairline cracks and helps keep water out, even in wind-driven rain." Parex's advice is to carry the coating to a corner, edge or other natural break, or over the whole wall, so the repair doesn't show as a patch.

Step by Step: Filling a Few Hairline Cracks

1. Work on a cool, dry morning. Stucco contracts as it cools, so cracks are at their widest in the morning and close up a little as the sun heats the wall. In a Florida summer, finish before the afternoon storms.
2. Clean the wall. A garden hose and a soft brush are usually enough. Parex's procedures start every repair with a clean surface that's been allowed to dry. If you use a pressure washer, keep the pressure low and the tip moving, since a narrow, hard stream can etch stucco.
3. Press the sealant into the crack. Run a small bead along the crack and work it in with a damp finger or sponge. On a hairline crack, the goal is to fill it, not to build a ridge over it.
4. Match the texture. Dab the wet sealant with a damp sponge or stiff brush, and wipe any extra off the wall.
5. Let it cure, then paint. Follow the label: Mor-Flexx takes exterior latex paint after 4 hours, and Elastopatch wants at least 24 hours and a primer. Painting the whole section of wall, corner to corner, hides the repair better than a spot.

Step by Step: Elastomeric Paint Over a Wall

1. Clean the wall and let it dry. Same as above: clean, then dry.
2. Fill anything wider than a hairline first. Parex fills cracks from 1/16 to 1/4 inch with a patching compound before coating.
3. Prime if the label calls for it. Each coating's instructions say which primer, if any, goes on stucco.
4. Apply two coats. Parex's spec is about 16 mils wet film per coat. Elastomeric paint goes on thick, by roller or sprayer, and covers less wall per gallon than regular paint.
5. Cover the whole wall to a natural break. Stopping at a corner, a control joint or the trim keeps the new film from showing as a patch.

Cracks That Aren't Hairline

Cracks from 1/32 inch up to about 1/4 inch get sealed with a textured elastomeric sealant: see stucco crack repair products. Beyond that, have it seen in person:

• a crack wider than 1/4 inch, or with one side higher than the other,
• a crack that reopens after a flexible filler,
• stucco that sounds hollow, feels soft, or has blistered paint around a crack.

None of these mean the wall is failing. They mean the fix goes deeper than the surface. Your local Stucco HQ contractor sees the wall in person and gives you a free written estimate. See how a stucco crack repair works.

Can New Stucco Be Built to Crack Less?

Yes, within limits. Control joints give the plaster planned places to move. The Stucco Manufacturers Association also describes a "base and mesh" upgrade, a skim coat with fiberglass mesh embedded in it over the brown coat, that it says is "proven to greatly reduce cracking." It's an upgrade, not part of a standard job, so ask for it by name when you collect bids. Our stucco installation guide covers control joint spacing.

Frequently asked questions