Your Place: Before painting stucco, be sure surface is sound

The stain on the chimney seems to be from an improperly sealed liner that allows moisture into the flue.
The stain on the chimney seems to be from an improperly sealed liner that allows moisture into the flue. (THOMAS ALESSI)
Posted: July 08, 2011

Here are more painting tips, this time about stucco, for which I get many, many questions, especially from Philadelphians living in a row that is a house or two short, with party walls that need repainting.

I turn, as usual, to Debbie Zimmer at the Dow Chemical Paint Quality Institute in Spring House. She says stucco can be successfully painted by following certain procedures.

As with most painting projects, surface preparation is key.

"Start by making sure that the surface of your stucco is sound," Zimmer said. "It should be free of dirt and powdery dust, and rough enough so that your primer and paint will adhere well."

You can accomplish both objectives by cleaning and roughening the surface with a stiff bristle brush, wire brush, or - if your stucco has been long neglected - a sandblaster.

Follow up with a thorough rinsing.

The next step depends upon the age and condition of your stucco. Unpainted stucco that is very new or less than a year old presents special challenges.

For one thing, it may still contain moisture from the original mixing; for another, it may have a high degree of alkalinity.

These possibilities have implications for the coatings you use, Zimmer said. If you plan to apply an oil-based or vinyl water-based paint, you must first apply an alkaline-resistant sealer or risk having the paint fail prematurely.

But you might be able to skip this step, she said. "If you are going to use top-quality 100 percent acrylic latex paint, you can often apply it directly to the stucco, since these paints resist the alkaline nature of fresh masonry."

The exception: When painting stucco that is less than a month old, you should still apply an alkaline-resistant primer or sealer.

Weathered stucco that is unpainted or previously painted involves other considerations.

If you see efflorescence - white, crusty salt deposits - on your stucco, you must remove it during surface preparation by scraping, wire-brushing, or sandblasting.

Even if your stucco shows a slight tendency to produce efflorescence - or if it is very porous or "chalky" - you should apply a sealer or latex block filler before painting.

When applying any type of latex coating to your stucco - sealer, block filler, or paint - you should dampen the surface immediately beforehand. This will allow the coating to dry more slowly, which in turn, will enable it to form a more durable protective film.

What if the stucco is badly cracked? In that case, the best option is to call in a painting contractor with experience applying "elastomeric wall coatings" - very thick, highly flexible paints that are designed to bridge and seal cracks to keep moisture out of the home.

Like other paints, elastomeric coatings come in a wide range of colors, but it takes special training to apply them properly.

Question: About four years ago, we had a stainless steel liner installed in our chimney.

Mortar continued to fall out, so the upper half of the chimney was rebuilt and the lower half removed to a one-inch depth and then repointed. About three months later, we had the brick work sealed to keep out moisture.

Ever since, we have noticed a stain forming down from the area of the liner. There is no rust on the liner cap, and we do not use the fireplace so it can't be coming from there. Any ideas?

Answer: From what I've been able to find out, there is moisture in the flue and, because the liner isn't properly sealed, the stain is appearing.

I'd suggest a call back to have the liner installer seal it properly.


Questions? E-mail Alan J. Heavens at aheavens@phillynews.com or write him at The Inquirer, Box 8263, Philadelphia 19101. Volume prohibits individual replies. He is the author of "Remodeling on the Money" (Kaplan Publishing).

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