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How to Repair Stucco

Pro Referral > Home Guides > Siding > How to Repair Stucco
How to Repair Stucco

Stucco is one of the oldest building materials, perhaps used as early as 4,000 years ago. While it is similar to plaster, stucco is most commonly thought of as an exterior cladding. It is applied in one to three coats and is often finished with a distinct texture.


Considered a more exotic option than say wood or vinyl siding, brick or stone, it is a staple and is fairly prominent in some sections of the country. Stucco remains fashionable because it is durable and it is generally seen both as a decent insulator and is fire-resistant.


Ancient or antique stucco consisted of lime, sand, and water. Traditional stucco, that is stucco applied in the US for most of the 20th century, was commonly made up of the same three things, with one new ingredient: lime, sand, water, and Portland cement. There have been several modern day variations of it. EIFS, for one--an exterior finishing system--is often categorized as fiber-reinforced synthetic stucco.


Stucco is applied wet and hardens to a very dense solid. Mixed and installed incorrectly, it can very easily fail. Because it ultimately hardens and is so rigid, it is prone, like plaster, to settlement cracks. This article will focus on repairing issues that arise from this type of normal and expected wear and tear.

Tools Materials Skill Level Estimated Time
• Trowel(s) (rectangular, pointed) • Stucco caulk/sealant Advanced 1 to 4 hours
• Hawk (aka a mortar board) • Pre-Mixed stucco patch
• Whisk broom • Pre-Mixed stucco (base and finish mixes)
• Masonry brush • Builder's sand (or white sand)
• Grout sponge • Wire mesh (self-furring or cement-backer board)
• Spray bottle • Roofing felt
• 5-Gallon bucket • Roofing nails
• Cold chisel • Plastic sheeting
• Hammer and mallet • Painter's tape
• Angle grinder with a diamond masonry blade (or two) • Paint (matched to the color of the finish)
• Wire brush
• Caulk gun
• Utility knife
• Aviator snips
• Eye protection
• Rubber gloves (or better)
• Dust mask
• Shop Vac
• Mixing trough

    1. Investigate and Plan

    Traditional vs Synthetic Stucco

    In traditional installations, the stucco is applied in three coats. A “scratch coat” dubbed for the fact that when completed it is left with grooves or scratches designed to accept the second coat--“the brown coat.” The brown coat gets its name from a traditionally heavy use of sand. The brown coat gives the entire installation its soundness and make-up. These two coats together make up what could be considered the “base coat.” The third or “finish coat” gives stucco its final appearance. The finish coat may or may itself be colored, but applied naturally and unaltered it would commonly be whiter in color than the base coat.


    Traditional stucco is often installed over “self-furring” wire mesh, nailed with roofing nails to a substrate--the home's sheathing wrapped typically with a layer of roofing felt. The wire mesh, by design, is self-spacing to allow for the "weeping" of moisture that inevitably penetrates its finish.


    Note: You'll also find stucco applied directly to brick, stone, or concrete block. In these cases, there is obviously no moisture control consideration.


    In the installation of synthetic (polymer-modified) stucco, you’ll find the stucco applied directly to either cement or foam insulating board. These backing materials are often glued to the home’s sheathing and also fastened.


    In general, it may or may not be difficult to know what type of installation you are dealing with. An approximation of when the stucco was applied, or at least when the home was built, as well as the location on the exterior (i.e. at a foundation or up under an eave) might help. Synthetic stucco didn’t gain wide use until the late 80s and 90s.


    Determining the Type of Installation

    Regardless of the repair needed, a small hole or crack, or larger damage involving buckling and bowing of the installation, your first challenge will be identifying exactly the type of stucco you are dealing with--traditional “hard-coat” or synthetic stucco.


    The quickest test for this is commonly known as the “knock test.” Tap on the surface, if it sounds hollow and feels even a little soft you are dealing with synthetic stucco. A solid sound and a surface that feels like a soft concrete means you are dealing with traditional stucco.


    The “penetration test” is perhaps more reliable: remove a light fixture, a dryer vent cover, or some other fixture from the home’s exterior and inspect the edges of this “penetration.” Do you see synthetic stucco’s telltale foam or cement board backing? Do you see distinct, independent layers of material or wire mesh? What you find here will dictate how you proceed.


    Important! As a short-term, important, though perhaps temporary fix for smaller issues, quickly seal cracks and holes using a stucco sealant. This will prevent water from getting behind the stucco surface leading to more extensive deterioration. Most caulk-type sealants allow for repairs in cracks up to a half-an-inch in width. Sanded versions are made in several common colors and are applied with a standard caulk gun. They can be textured to match the surrounding area if aesthetics are a concern.


    2. Prepare the Surface

    Some other questions you might want to ask yourself are: What is the root cause of the issue? Is the substrate stable, i.e. will this issue only happen again after it is fixed? Does this issue relate to improper drainage or water penetration?


    If you determine that your issue relates only to commonly expected settlement, proceed as follows.


    Tip: If reasonable, retain a large enough chunk of intact stucco (at least 2” by 2”) to aid with both color and texture matching. Cover this area temporarily with plastic or tape while you work to match your stucco.


    For Small Cracks (1/2” or narrower)

    Begin by widening (yes, widening) the crack. This removes loose debris and provides a sound surface for bonding. This can be achieved by chiseling out the crack into a “V” and later following with both a wire brush and a Shop Vac.


    For Small Non-Structural Repairs (Holes)

    Stucco Patch can be used in non-critical areas where the repair may or may not be 1/2" or larger. Prep for these cases is similar to that above. For these repairs, you will need to build up the stucco in multiple layers, and match the texture in the final coat. The great thing about latex-modified patching products is that they will remain relatively flexible in locations that may remain prone to stress and movement.


    For Larger “Structural” Repairs

    If you determine that at minimum an inspection of the substrate (what’s behind the stucco) is required, cut out a square that is perhaps 25 percent larger than the area to be repaired. Work to determine the depth of the cut before you begin cutting. Mark the surface using a pencil and a level; otherwise drive masonry nails in partially at appropriate locations and snap chalk lines. Cut using an angle grinder (or better) fitted with a new diamond masonry blade. Chisel back stucco or use the butt end of a clawed hammer to reveal the substrate.


    Ensure that wire mesh has not buckled or that board-type underlayments have not popped out from the substrate. Re-attach these to the structure using appropriate fasteners--1 ¼” or longer roofing nails will work well in most cases.


    3. Selecting or Mixing Stucco

    Regardless of the species of your repair, material may require a special order from your building warehouse or a masonry supplier. Synthetic stucco manufacturers today offer hundreds of colors in several stock textures. If you suspect that you are working with a synthetic stucco installation, start by calling local suppliers as they might not only have an exact product match (with repair specifications), but they may even have a record of your specific installation.


    Stucco today may be purchased fully pre-mixed or as a pre-mixed powder. If you are a purest, sure--the individual components can certainly be purchased and you can mix up your own. These recipes are readily available online.


    Note: Recipes will vary based on what layer of the installation you are applying.


    When mixing, try thinking of this process as mixing the stucco into your water. A perfect mix should be much like the consistency of peanut butter, not runny but pasty. You should be able to pick it up and almost roll it into a ball. It should leave a residue in your gloved hands, but it should not stick to them.


    Color, in part, will be dictated by the exact proportions of your mix's components. If it is heavy on Portland cement it will produce a white-gray color, if it is heavy on sand it will appear to be more brown in color. A mixture of Portland cement and white (not builder’s) sand will produce a white color. Traditionally colors are achieved by mixing in coloring agents like oxide powders, which are widely available.


    Stucco like concrete accepts latex paint finishes. In the context of a repair, it may make sense to strive for a match in your components and texture, while planning to use paint instead later for a match in color. Follow manufacturer recommendations for details on when it is safe to paint new stucco. When in doubt, wait at least a week before painting.


    4. Applying Stucco

    Getting both the mix of your materials as well as your finishing pattern just right will be key.


    Tip: In all cases, sacrifice a scrap piece of plywood (2’x4’) and play around with your mixture as well as your application and finishing technique(s).


    A trowel is used to blend your repair product into the surrounding stucco surface.


    A rectangular finishing trowel will work well for moving a batch of material to the wall. Use your pointed trowel for fine tuning at edges.


    Important! Use either a grout sponge or a spray bottle to spritz the vicinity of the repair with water. Skipping this step will allow existing stucco to pull moisture from your new repair material. This may cause the repair to shrink hyperactively, potentially causing it to crack or to even fall away.


    When applying stucco to larger areas, have a rhythm in mind: trough, hawk, trowel, wall. If you have a large repair in front of you, try to get in this groove. Be warned, working with a hawk and any cementitious product is an art form. Tilt your trowel upwards, almost cradling your stucco, and transfer it to the wall. Apply your stucco in an upward stroke, feather off edges, and move either side to side or up and down, whichever makes sense. Between each layer, cover with plastic and spritz again with water before moving to the next stage.


    Patching-type latex-fortified products can be applied with a smaller pointed trowel or even a putty knife. Regardless of the type of product, again, you'll look at building up in multiple layers. The first layer (and potentially the second, depending on the thickness of your stucco) should finish just below your stucco's finished level.


    5. Finishing Your Repair

    Be mindful of the various options in decorative finish. Remember the success of your repair will likely be judged by how well you match the wall's existing texture.


    Common Finish Textures

    A few common finish textures are a floated (or smooth) finish, a splatter dash or pebble-embedded finish (prominent in the US in the 30s and 40s), a finish called "English cottage" (the non-uniform repeating of ridges), travertine (created by jabbing and later flattened), stippled, knockdown, swirled, wavy, and scratched, a technique achieved with a wood block that oddly resembles finger painting.


    The point here--no two stucco textures are exactly alike. In fact, the type of texture you might find is literally limitless. It is your job to make a reasonable match.


    While it may seem somewhat non-sensical, styles in finish are typically informed by and support an architectural style (another cue regarding what you might be working with). Finish-coat stucco is applied with a trowel but is often later addressed with an additional implement--a brush, broom, sponge, or wood block. All that can be said is ... Practice!


    With traditional stucco, lightly mist the repair a few times over the next 24 hours. Cover with plastic for about two days. Paint when appropriate.


Level of Difficulty

All things being equal, a repair to stucco may be easier than some other siding or cladding repairs. But a repair to stucco might require patience and practice, plus a surprisingly wide arsenal of tools. Simple, small repairs can be accomplished by you, the homeowner, larger repairs may require a stucco artisan.


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