What is plaster? It is a sticky, putty-like mix of minerals which, when dry, are used as wall coatings. The most commonly used materials are Portland cement, lime, gypsum, mud, sand, and acrylic synthetic composition (EIFS). I have nearly four decades of experience in the plastering trades and I occasionally run across little tidbits of information about plasters that amaze me, such as that fully a third of the world’s domiciles are coated with earthen materials such as clay, mud, and straw. Also, a popular common stucco found in the coastal regions of the American South is called “Tabby” and it is distinguished by the addition of roughly crushed seashells that are sometimes pressed whole into the wet stucco for a nice decorative touch. And finally, get this: In Tibet, homeowners cover their exterior walls with large yak dung patties!
Enough trivia! Regarding the basics, I am asked, “What is the difference between stucco and plaster? Answer: Plaster generally refers to interior work and stucco refers to exterior work, There is a major exception to this rule: Mud plaster, while technically a stucco, is never referred to as such but is always called mud plaster.
STUCCOS. Here in New Mexico there are two predominant stuccos, traditional cement stucco and the newer synthetic stucco.
Cement stucco. After the decline of mud plasters due to the introduction of the decidedly improved durability of water-resistant cement plaster (which consists of Portland cement, Type S lime, sand, and chopped fiberglass strand), most homes were plastered with these materials involving a four-step process: metal lath and stucco netting ground over a vapor barrier nailed to to the concrete block, lumber frame, or the adobe brick home walls followed by two coats of cement plaster mix and finally a color coat, which is also cement and most often usually applied to a sand finish.
Synthetic stucco or EIFS was developed in Germany in the 1960s as a commercial stucco but has become an attractive and popular alternative in the residential sector due to its waterproof qualities. I estimate that about half of the new homes built in the Santa Fe are stuccoed with Sto or Drivet, two of the more popular brands of synthetic stucco.
If you are fortunate enough to have a pitched roof you can expect your stucco to have a relatively long life, but if you have a flat roof you will find that you should regularly inspect your parapets and canales. These are the Achilles tendon of the traditional New Mexico flat-roofed home.
STUCCO REPAIRS. As a contractor with 40 years of experience in New Mexico, the majority as a stucco and plastering contractor, I am often called upon to evaluate potential problems on homes with both types of stucco. Patching stucco is an imprecise business and I always recommend that you solicit no less than three bids/estimates for repairs from licensed contractors.
Minor checking, smaller than you can fit a dime into, is usually not uncommon even with relatively new stucco, but this checking is cosmetic and not a structural problem. However, larger cracks and delamination issues require a professional appraisal and, in all probability, a fresh coat of stucco. A properly applied stucco will usually last 20 years or more, but most stucco jobs tend to look a little shabby after 30 years of exposure to our elements.
Elastomeric paint. If you have been advised that your home needs a re-stucco application, you might consider a less expensive alternative: elastomeric paint. This product has been engineered as an elastic, thick paint-like substance and perfect for covering ailing cement or synthetic stucco and it has the added advantage of being tintable, even to closely match the color of your existing stucco. Like synthetic stucco, it is completely waterproof, long-lasting, and most painting contractors will do this at a much lower price than a re-stucco. I have used this product with great success.
I cannot in good conscience write about stuccos without mentioning that the aforementioned stuccos used locally, Portland cement and synthetic, are not popular in many other locales. Lime, gypsum, and clay plasters are much more popular in Europe and many other places for both aesthetic and environmental reasons.
INTERIOR PLASTERS. When I first got into the plastering trade, the two most common interior finishes were Structolite, a ready-to-go gypsum plaster that was often floated out with a sponge float to a sand finish, then painted some shade of white. Also, for a finer finish, there was gauging plaster, a hand-mixed plaster of gypsum and lime putty that could be troweled smooth with a high-gloss finish. A gauged plaster finish over base coats that were applied to wooden lath strips was the traditional interior plaster finish coat for a couple of centuries, up until the 1940s when drywall began to serve many of our housing demands. Walls were often just painted or covered with wallpaper.
Today, we have a myriad of interesting plaster materials available, but the most popular interior finish used today here in New Mexico is what is commonly referred to locally as “diamond finish,” or “Venetian plaster” if pigments have been added to the mix.
The two most common brands used today are USG Red Top Finish plaster and Diamond Finish brand, both of which are ready-to-use formulas of gypsum and lime plasters similar to the formerly popular gauging plaster mix but without the time-consuming mixing process. This can be applied to a drywall substrate that has been prepped with PVC glue and one or two coats of fibered gypsum plaster. Applied by competent professional plasterers, this can be smoothed to a perfectly flat, somewhat glossy finish that can be enhanced with waxing or an Okon sealant.
There are several other interior plaster finishes that are available, some of which could successfully be applied by the industrious homeowner with the help of the many online tutorials that are available.
Clay plasters. Calcimine (lime washes) and local clays were traditionally used in home interior walls here in New Mexico for many generations, usually applied over mud plasters using local clays like the red and ochre types that you see when you travel La Bajada Hill.
American clay. For those of you who admire the look of clay plasters but are not interested in hiking the hills, dragging a heavy bag of clay home and then sifting it, you can buy our local American Clay products. The company offers several varieties in a broad range of colors. Their color packs are mixed with their white kaolin clays to produce easy-to-apply, soft-textured walls. They also offer clay finish products, which can be hard-troweled for a slick finish.
Marmorino plasters. These traditional Italian plaster finishes, also called Vencinza or Ventian plasters, are sold not only at many plaster supply firms but are also available online and at most paint and decorative-materials outlets. The products are mixes of tinted cements, acrylics, and marble dust that are applied over base coats to provide a glamorous, polished marble look and are available in white and a range of colors, including Chinese red and even jet black. Marmorino plasters are the acme of plaster elegance, and so vibrant that they are often used only as accent walls.
Finally, I have spent several decades plastering not only in Northern New Mexico but also in Ireland, New York City, and California and I can say with some authority that, although I have encountered some very knowledgeable people in the plastering trades, one could spend a lifetime and never learn all there is to know about plastering.
Here are a few interesting books on plasters: Japan’s Clay Walls: A Glimpse into their Plaster Craft, by Emily Reynolds; The Natural Plaster Book: Earth, Lime, and Gypsum Plasters for Natural Homes, by Cedar Rose Guelberth and Dan Chiras; Clay Culture: Plasters, Paints and Preservation, by Carole Crews; and Building with Lime: A Practical Introduction, by Stafford Holmes and Michael Wingate.
Local purveyors of plasters and stuccoes include American Clay, 866-404-5300; Chapparal Materials, 505-471-3491; and New Mexico Plaster Supply, 505-345-6881.
Richard Connerty (firstname.lastname@example.org) is the owner of R.P.Connerty & Son Construction Company.