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Old-House Online » Old-House Tips, Restoration Stories, & More » Repairs & How To » How To Repair Stucco Cracks

How To Repair Stucco Cracks

Patching damaged stucco can be difficult and time-consuming, but not if you use this straightforward repair technique.
By Steve Jordan | Photos by Andy Olenick

    Repaired stucco houseHairline or map cracks—the scourge of many a stucco wall—can occur due to settlement, poor construction, or as self-healing control joints. They may be long and barely visible, or widen gradually to 1/8″ or more. Whether static or moving with weather changes, hairline cracks can allow water between stucco and sheathing, attracting insects or promoting rot and mold. They are unsightly, but repairs often make them look worse. Marty Naber of Naberhood Restorations in Rochester, New York, has perfected a special technique for repairing hairline cracks.

    Step 1

    You’ll need a small trowel, duster brush, caulking gun and tube of tri-polymer sealant, hammer, and a 12″ x 12″ piece of sheet metal or thin cardboard. Purchase the sealant at a good builder’s supply store. Don’t substitute another caulk or sealant—tri-polymer is highly flexible, UV-resistant, and has outstanding adhesion, so it will move with the crack without failing. Your only patching material is a piece of finish stucco taken from the same structure—ideally from a larger failing area or a sacrificial area.

    Materials for repairing a stucco crack

    Step 2

    Start by cleaning the crack with a trowel or putty knife, then brush away any loose material or debris from it and the adjacent surface. Note if any large areas (cracks approaching ¼” wide or large areas on either side of the crack) are loose; if so, this indicates the need for more comprehensive repairs. Using a damp paintbrush, gently sweep dust or powdery residue from the crack and let it dry.

    Cleaning the crack

    Step 3

    Take a piece of the finish (top coat) stucco that has failed; place it on the sidewalk or driveway on a heavy piece of plastic, cloth, or cardboard; and pulverize it with a hammer until it resembles the original powdery mortar mix first used to create the wall (a few chunks are OK). Set it aside.

    Pulverizing the old stucco

    Step 4

    Next, fill the crack with tri-polymer sealant. Cut a fine orifice on the sealant tube, approximately ¼” below the tip (more if the crack is wider) and fill the crack, taking care to keep the sealant in the crack only and to not get any onto the stucco surface. Since some caulk guns work better than others, this can be difficult. If you apply too much or smear it on the surface, clean it immediately with a soft rag dipped in mineral spirits. Depending on the weather, fill about one linear foot at a time—the sealant will skin over quickly when it’s warm, and you don’t want it to set up before the next step in the procedure.

    Filling the crack with sealant

    Step 5

    The final step requires some practice so you don’t waste the precious pulverized repair material. Make a cradle with the metal or cardboard, and put a small handful of the pulverized stucco in it. Holding the mix adjacent to the freshly filled crack, gently blow the material so it sticks and covers the sealant, then carefully tamp it in with a soft brush.

    Note: The image shown at right depicts the finished repair. The version of this image that originally appeared in the printed issue of the magazine showed an example of a bad repair.

    Blowing the repair material onto the sealantFinished repair
    Published in: Old-House Journal August/September 2013

    { 1 comment }

    Scott S July 11, 2013 at 10:55 pm

    Great idea! I’ll have to try this soon.

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