responds: Several things make this type of job
very challenging: It can be difficult to finish the
wall on the same plane as the existing stucco.
You’ll undoubtedly wind up with shrinkage
cracking around the perimeter of the old opening.
And most challenging of all, it’s
extremely difficult to match the color and texture
of existing weathered stucco with a new mix.
It’s likely the existing coating on the
foundation is a multi-layer cement parge coat, and
not true stucco. True stucco contains white
waterproof cement, lime, and silica sand, and is
applied over metal lathe. Each coat is mixed to
different strengths, starting with the scratch
coat, which has the highest cement content for the
highest strength. Each layer outwards gets
increasingly weaker, with the finish coat being the
weakest and least brittle to minimize cracking.
Instead of using a bagged mortar mix, repair the
parge coat with a product such as Monocouche
(Parex, P.O. Box 189, Redan, GA 30074;
800/537-2739). This can be applied in one coat
(just add water). It’s incredibly strong;
you can build it up to about 21/4 inches thick
without it checking or cracking. Also, like true
stucco, Monocouche has a white base, so it can be
tinted with iron-oxide pigments to closely match
the existing finish.
Steve Thomas is a former stucco contractor
in Columbus, Ohio.