- Q. The owner of a house with existing exterior cement stucco is unhappy with the finish. How difficult is it to install a new coat of stucco over the existing stucco?
A.Ron Webber, owner of Prime Plastering in Irvine, Calif., responds: Applying new stucco over old stucco (often called re-stuccoing) is a fairly simple-process. If the existing wall is in good condition, this job can be straightforward. But if the existing surface has imperfections, the problems that caused the flaws must be repaired, or else the problems will recur. Before re-stuccoing, thoroughly examine the existing surface and ask the following questions:
Is there any loose, spalling stucco? Rub and tap the wall, listening for hollow sounds. Any loose stucco will need to be removed by scraping or sandblasting. To patch the stucco, combine sand and cement with calcium aluminate, an accelerator, or use a good nonshrinking stucco patching material or a rapid-set mortar mix.
If the house has been painted, is the paint in good condition? Loose or chipping paint can reduce the bonding power of a new coat of stucco, so it should be removed by sandblasting. If the painted surface is in very good condition, you can apply stucco directly over it, as long as you use a bonder.
Is there efflorescence? Efflorescence is a white powder or film on a surface, composed of salt crystals left behind when salt-laden water evaporates. Efflorescence reduces the bonding power of the new coat of stucco. To neutralize efflorescence, spray on a mild acid such as vinegar. Let the vinegar sit for half an hour, and then flush the wall with water. This will bring the pH level down to an acceptable level.
Is the wall dirty? Dirt, like loose paint or efflorescence, will interfere with the bond of the new stucco. Any dirt should be washed off.
Does the wall have any cracks or leaks? Leaks near doors and windows, as well as cracks, should be repaired before re-stuccoing (see "Patching Stucco," 9/97).
Is the flashing in good condition? Inspect the metal flashing and weep screed for rust or separation at the joints, and repair or replace it as necessary.
Is the existing stucco surface rough and uneven? If so, scrape down the high points and fill in the low areas before proceeding.
Once all problems in the existing stucco have been corrected (including, if necessary, adding a leveling coat to even out the low areas), apply a new finish coat with the texture and integral color of your choice. To ensure a good bond, use a bonder between the existing stucco and the new material.