- Q. When making a patch in stucco, is it possible to use hydraulic cement or a fast-setting cement for the first couple of layers so that the patch can be completed in one day?
A.Steve Thomas, a construction estimator in Columbus, Ohio, with many years’ experience in the stucco trade, responds: I would advise against either hydraulic cement or any "hurry-up" product for the base coats. The reason is simple: You can almost bet the surface you’re attempting to patch (and match) was not created using these products, but a less expensive, standard cement/lime/sand mixture.
The capillary suction of the undercoats — their tendency to absorb moisture from the finish coat — will directly affect the drying time and therefore the color of the top coat. The hard, fast-drying products you refer to are much less absorptive than a standard cement mix. Even if you use the exact same finish-coat recipe as the original, it will end up looking different over a fast-setting undercoat. Typically, the faster the stucco dries, the lighter the color will be.
If possible, seek out the original stucco contractor and try to get the recipe for his finish mix, to get you as close as you can to a perfect match. Even so, you’ll have some difficult hurdles to overcome. Age and weathering tend to darken stucco colors. You may have to add more pigment to the recipe to account for this. Your best bet, depending on the size of the patch, may be to repaint that entire side of the house.
In general, it’s not a good idea to rush stucco work. Put on the scratch coat one day, let it cure overnight, then put on the brown coat. The brown coat should be flat and held consistently about 1/8 inch below the surrounding finish coat. Irregularites in the brown coat will cause the finish coat to dry unevenly, and produce a mottled color as well as excessive cracking. For best results, leave the brown coat for a week before putting on the finish coat. This will minimize cracks in the top coat.