Will New Stucco on My Addition Match the Old Stucco on a 1990s House?
New stucco on an addition will not match a 1990s finish on day one. How to match the texture, blend the color with a fog coat or paint, and how long to wait.
New stucco on your addition will not match the old stucco on a 1990s house on day one, and nobody can promise that it will. The national stucco standard, ASTM C926, says color uniformity “cannot be guaranteed” by the maker or by the person putting it on. The texture, the sand and the color all come out a little different on your new wall. You can still get close. First, match the texture by name and with a sample panel on your wall. Then blend the color across each whole wall of your house, out to a corner or other clear break. If your old stucco has never been painted, a cement fog coat can do the blend. If your house is painted, the blend is paint.
If your house was built in the 1990s, its walls have had decades of Florida sun, rain and salt air. That weathering is a likely reason your old wall looks different from fresh stucco. No stucco standard lists it as a cause, though, so treat it as a good guess, not a rule. The causes the standard does list are enough to explain why a patch shows on your wall.
Why doesn’t new stucco match old stucco?
Your new stucco does not match your old stucco because color and texture depend on many things that change from one day, one crew and one wall to the next. ASTM C926 says color is affected by how the mix is measured and mixed, how clean the tools are, how the coat is applied and how it is cured. It says your color is affected even more by changes in thickness and in how much water the base coat pulls in from place to place. The standard adds that these factors “are rarely under the control of the applicator.”
Your texture works the same way. ASTM C926 says texture comes from the method and the tools. It also comes from the size and shape of the sand, how wet the mix is, the base under it and any later treatment. Rain on your new wall can also change things. The standard says colored stucco can stain or shift in shade if rain, or moisture from a base coat that has not cured, reaches it too soon. On your addition, all of these are brand new, while your old wall has settled into its look over many years.
What are the common stucco texture names?
The common stucco texture names include smooth, sand (also called float), Spanish fan, dash, knockdown, lace and skip, Santa Barbara and English. ASTM C926 groups finish coats by how they are made. Sto Corp, a stucco maker, groups them by how they look. The two lists use different names, so you may hear one texture called two things.
| Texture name | What it looks like | Where the name comes from |
|---|---|---|
| Smooth trowel | A flat, smooth face | ASTM C926 and Sto Corp |
| Sand or float | A thin, fine coat with a fine, sandy feel | ASTM C926 and Sto Corp |
| Spanish fan, trowel sweep, English cottage | Trowel marks left on purpose | ASTM C926 |
| Rough cast, wet dash | Coarse sand thrown or pressed on | ASTM C926 |
| Dash, with knockdown | Sprayed bumps, or bumps with the peaks pressed flat with a metal trowel | Sto Corp |
| Santa Barbara | A semi-smooth face with fine sand specks, done with a pool float | Sto Corp |
| Lace and skip | A Spanish lace look, by hand or by spray | Sto Corp |
| Cat (California), worm, English | Other named looks | Sto Corp |
Neither list says which texture is most common on St. Augustine houses from the 1990s. You find out which one your house has by looking at the wall itself.
Why should you see a sample panel before you pick a texture by name?
You should see a sample panel before you pick a stucco texture by name because the same name can mean different things to different people. ASTM C926 says a texture term may not mean the same thing to the designer, the builder and the person applying the finish. It also says hand-troweled looks, such as Spanish fan, “may be difficult to duplicate by different applicators.” The standard advises an approved sample panel kept on site, so you have something to compare against.
For your addition, that means asking for a sample of the new texture on or right beside your old wall. Look at it from where you usually see that side of the house. Keep it on site until the new stucco is done, so everyone can check the work against the same piece.
What is a fog coat, and can it go on your house?
A fog coat is a thin cement coat sprayed over portland cement stucco to even out color differences. It can go on your house only if your stucco is a cement finish that has never been painted or sealed. The Stucco Manufacturers Association guide specification lists a “fog coat (cement finish only)” as a way to blend color. Sika, a stucco maker, says its fog coat lets the texture stay the same, needs no primer and lets the wall breathe. Sika recommends two coats on your wall.
Sika’s fog coat data sheet also says what a fog coat is not for. It is not for painted, sealed or smooth dense surfaces. It is not for a smooth Santa Barbara finish. It is not meant for spot touch-ups, so you should not use it on one small spot. If you are not sure whether your walls were ever painted, find out before anyone picks a blend method.
When does a painted house need paint instead of a fog coat?
A painted stucco house needs paint to blend a new addition, because a cement fog coat is not recommended over painted walls. Once your walls carry paint, paint is the blend. Sika says most acrylic and elastomeric paints are already made to handle the alkali in stucco. It also says not to thin the paint with water, and that painting too early can stop the stucco from curing and leave a soft finish. Sto Corp says a sand finish is usually painted with a sprayer or a roller so the stucco can still breathe.
You may choose to paint the whole house after a stucco addition so every side matches. That is your choice. The guidance asks that each wall with new stucco be painted end to end, or out to a clear break. That way you see no line in the middle.
Where should the blend stop on your wall?
Your blend should stop at a clear break in the wall, such as a corner, and never in the middle of a flat wall. Sika’s fog coat sheet says to apply it “end to end and top to bottom or to a prominent architectural break.” ASTM C926 gives the same idea for new stucco. New work should meet old work at natural breaks, such as corners, openings and joints, so your wall does not show a seam.
Many trades use a simple rule of thumb: stop at an inside or outside corner. That is a habit of the trade, not wording from either source, but it follows the same reason. Your eye reads a corner as a natural edge, and it reads a stop in the middle of a wall as a patch.
How long should you wait after new stucco before paint or a fog coat?
For paint, the usual wait on new stucco is at least 28 days, and the real test is the stucco’s pH. Sika says stucco must reach a pH of 9.5 or lower before painting, and that when fully cured this “normally occurs 28 days after application.” Dunn-Edwards, a paint maker, says most makers call for at least 28 days. It also says there is no fixed number of days, and a pH of 10 or lower is safest. Check the label on the paint you will use.
For a fog coat over new stucco, no source sets a day count. ASTM C926 says a fog coat follows the maker’s directions, so read the data sheet for the product on your job. While your new stucco cures, it has to stay damp. ASTM C926 calls for moist curing, often a fine spray of water morning and evening, and more often when it is hot, dry and windy. The 2023 Florida Building Code, Residential, calls for each coat to be kept moist for at least 48 hours before the next coat goes on.
What does this mean when you plan your addition?
Matching the stucco is part of planning your addition from the start. On a Wilson & Co home addition, the exterior match is the last step, after insulation, drywall and interior finishes. That puts your color blend near the end of the job, where the curing wait falls anyway. Settle these things early:
- Find out whether your old stucco was ever painted. That decides fog coat or paint.
- Find out which texture your house has, and ask for a sample panel of it.
- Find the corners and breaks where the blend can stop on each side of your house.
- Decide whether you want only the walls with new stucco blended, or the whole house painted.
If your addition is a new bedroom suite, the bigger choices come first: where it joins the house, what the cooling can carry and where the drain runs. Those are in what to decide before you add a master suite. If you are weighing stucco against other wall finishes, see siding and cladding choices on the coast.
When is this not a Wilson & Co job?
If you are not adding on and you only want your old stucco repaired or re-coated, call Stucco Home Repair, which has the same owner. Wilson & Co works on stucco when it is part of an addition or a remodel.
If you are planning an addition on a 1990s stucco house in St. Augustine, call (904) 792-6175 to talk through how the new walls will meet the old ones.