Exterior Wall Covering: Patching Stucco – On the House

Exterior Wall Covering: Patching Stucco

By on August 21, 2016

Yes, it actually has been us, the Carey Bros., who have written each and every On The House column since its inception. But lately, it has been our artist Stan Kohler who has been selecting our topics. To give you a general idea of how experienced he is, Stan was an long-time illustrator at Associated Press before Teddy Roosevelt was elected. Finally, about a year ago, Stan retired from AP Newsfeatures to illustrate our columns full time. In any event, a recent visit to our e-mail box revealed Stan’s next topic — Patching Stucco. Well, that gave us a real giggle. Stan is an accomplished do-it-yourselfer and takes his work very seriously. Unfortunately, he didn’t realize that Stucco is a brand name for a mixture of cement and sand generically known as plaster. Essentially, Stucco is to exterior plaster what Coke and Pepsi are to caffeine free diet cola. Well, brand name or generic title, Stan picked a great topic to discuss — for two reasons. First of all plasterers charge a small fortune to do patch work, and second, a stucco patch is one of the easiest home repairs that you can tackle.

Plaster is made by mixing sand and Portland cement in various ratios to create base, middle and finish coats. And although you can easily mix your own we suggest that you purchase ready-mix patch – it’s easier. Modern plaster is applied in five layers. And although you will not have as many steps with patchwork, it is a good idea to know that there is a difference between a patch and a new installation.

With wood framing, plaster is always applied over a thickness of building paper such as asphalt impregnated felt. Next, a layer of chicken wire known as wire lath (or lath) is attached with spacer nails to hold the it about one-quarter inch away from the paper. The paper acts as a waterproof barrier and the lath grasps the plaster. Three individual coats of plaster are then applied. By adding the plaster in layers the chance of cracking is greatly reduced. Deep scratches are etched into the surface of the first coat – that’s right – the scratch coat. The long narrow indentations and other surface irregularities help to insure a bond between the first and second coats. Both coats are gray in color, and when dry, resemble plain old fashioned mortar or grout. The final coat contains a dye giving it color and is therefore referred to as – you got it again – the color coat!

Patching plaster is not nearly as difficult as a first time installation. This is mainly because small areas do not expand and contract in the same way that larger areas do. 3 coats for large areas – 1 or 2 coats for small areas. Aren’t you lucky.

So what is so difficult about mixing sand and cement and troweling it into an opening the size of a baseball? Nothing really. You need only insure that there is a ragged base to bond the patch mix to what exists. If the wire and paper are showing it is important to be sure that there are no holes in the paper. Fear not, there are several good sealants available that can be applied with a caulking gun. All loose chunks of old mortar (and powder too) should be removed from the repair area. Also, the wire lath should be pulled away from the paper far enough so that the patch material can ooze in between.

You can make your patch in three coats if you wish but we suggest no more than two applications. Also, we don’t suggest trying to match color coats. It is almost impossible to get two new coats of plaster to match let alone an old coat and new one.

It is much easier to apply the first two coats as one layer and a second coat with no color. Once cured it can be painted to match exactly. So who said we were purists – anyway? When applying the first coat make sure to leave about a quarter inch recess. The final coat doesn’t have to be as thick. Although normal practice is to wait 7 days between coats for proper curing time, with patchwork the second coat can be applied as soon as the first layer dries. By the way, the consistency of the patch material should be somewhere between pancake batter and bread dough. That is, it should be thick enough to stick to the wall and thin enough to manipulate with a trowel.

Exterior plaster is usually textured. Textured finishes are less expensive than smooth surfaces because the texture hides flaws. Isn’t it interesting how certain construction techniques have derived their origin? Any way, you may have to finish your patch with a texture to match the surrounding. There are two common textures: dashed and skip troweled. Another word for dashed could be splattered. That is because the finish can be splattered on with a paint brush. Thin down a batch of the finish material and holding a board or a broomstick as a barrier between yourself and the wall strike the paint brush against the barrier. For skip a troweled finish add a cup of sand to the finish mixture instead of thinning it. The added sand will cause the material to stick randomly and miss or “skip” areas as it is being applied with a trowel – hence, the name skip troweled.

Stan was right about one thing though. If you do have a Stucco brand finish on your home the matching finish coat will have to be purchased by brand. In all other instances – shop for plaster. And, good luck!

For more home improvement tips and information search our website or call our listener line any time at 1-800-737-2474! All you need to do is leave your name, telephone number and your question.


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