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The following information is taken from “The Consumer’s Stucco Handbook” by John J. Bucholtz. Used by permission
An Alternate – Elastomeric Coating

One of the blessings of modern technology has been development of reliable elastomeric coatings. These coatings have properties of elongation and recovery, and when applied over stucco they retain the stucco appearance. They are applied in two coats by roller or spray to a dry film thickness of 20 mils (20/1000th of an inch). They are available in virtually any color that can be imagined.

When excessive cracking takes place in stucco, the reliable elastomeric coating may be the only practicable technique to use. All that’s required is to thoroughly clean all stucco surfaces, then apply the elastomer.

This procedure is recommended only when stucco cannot be repaired to preserve the stucco finish itself. The most difficult aspect of applying an elastomeric coating is selection of the right product. There must be a thousand elastomers on the market, 932 of which evoke some skepticism!

The elastomeric coating should be “breathable” – that is, it should not be a vapor barrier. This means a perm rating of more than 6. If the perm rating is l or less, it is a perfect vapor barrier and can create what has been described as the “aquarium effect.”

The coating must be acrylic. Acrylic is resistant to water, ultra-violet rays of the sun, and does not turn yellow, nor is it affected by water. Some polymers are adversely affected by sun and water.

Guide to elastomeric coatings

An elastomer is any of a number of various substances with properties that resemble rubber. Deciding which product to use for an application requires a little research and an exercise of ability to separate the wheat from the chaff. The advertising for these coatings is very alluring, but may not present all the facts.

Elastomers have become particularly desirable because they look just like stucco (the right ones without the ticky-tacky gloss), and are commonly used on masonry, concrete, and stucco to resolve the aesthetic problem created by cracks, and to address water intrusion through cracks. Cracks make good construction appear flawed to the disadvantage of the building owner.

The main function of the elastomeric coating is to bridge cracks and to prevent their appearance to the viewer. Properties of elongation and recovery enable coatings to expand and contract with the substrate and to keep moisture from wind-driven rain out of the building. Elastomeric coatings have been available for a relatively long time. One building in Los Angeles received a reliable coating in 1969 and has performed well ever since with little or no maintenance. This attests to the longevity of the right product. At the same time, observations have been made of coatings that have failed in as little as six months.

Suggested minimum properties of elastomers

The roster of minimum properties below was compiled from properties of elastomeric coatings that have performed well for many years. While no single item should be a determining criterion, the selected elastomer should possess, as closely as possible, the properties shown:

SUGGESTED CRITERIA FOR COATINGS

Tensile strength ……………. 150 psi

Elongation ………………… 250%

Recovery ………………….. 60%

Freeze/thaw testing ……….. 12 cycles

Weatherometer testing …… 3,000 hours

Coverage (at 20 mils DFT per gal.) . . . .48 sf

Solids content (by weight) ………. 50%
Weight per gal. (minimum) …….. 9 lbs.

Color after application ………. Uniform

Vapor permeability (min.) ……. 7 perms

Tg (optimum) ……………… -15° F.

- Other requirements -

· Capable of l80° bend over a l/8″ mandrel at – l5° F. without cracking or becoming embrittled.
· Reliable technical assistance at the job site by the elastomeric manufacturer.

· Availability of supporting documentation (test reports, history of performance, example structures. etc.)
· Service on equivalent structures for a period sufficient to indicate expected performance without maintenance.

· Meaningful warranty on labor and materials for a minimum of five years.

It is recommended that consideration be given by builders to the idea of applying an elastomeric coating over the brown coat of stucco in lieu of any other finish. This procedure eliminates the finish coat and painting. It will avoid a multitude of complaints about cracks and color problems.

Color – stucco, paint, or elastomeric coating?

The final step is choosing the decorative finish you want to use. The lowest life-cycle cost comes from integrally-colored stucco or a reliable elastomeric coating. Paint always looks like paint and it has to be re-done every few years. But no matter what finish you choose, it will only be as good as the brown coat. Whatever blemishes are in the brown coat will be apparent in the finish coat.

A colored stucco finish is preferable, but a reliable good quality elastomeric coating that looks identical to stucco, and is available in any color desired, will assure that cracking does not appear, and will prevent the wall from getting the “wet look” during rainfall.

If the integrally-colored stucco finish is applied, it can be redecorated later with a stucco fog coat. The fog coat is the same as the original stucco finish without the aggregate. Fog coats can be applied by a roller, brush, or spray, and they maintain the character and distinction of stucco. When stucco shows dirt, it can be rinsed with a garden hose. A sealer at the base of the wall around flower beds will make cleaning easier. Stucco does not need a sealer to “waterproof” it, but there are some occasions when a sealer serves other purposes.

Sealers

Sealers for stucco are unnecessary. In most cases, someone says a sealer is necessary to make the stucco “waterproof.” This is sheer nonsense and a waste of money. Stucco is already “waterproof.” Using a sealer on stucco affects bond of a stucco fog coat which you may want to use to redecorate surfaces at some later time.

Don’t be misled by well-meaning people who suffer from a belief that stucco is porous and unless it is “sealed” water goes through it. A sealer of the right type, however, may offer water repellency to avoid the “wet” look, so a sealer should be chosen very carefully. Sealers also help at the bottom of walls around flower beds to prevent mud splatters from staining the stucco and to permit easy washing off with water.

In tests to determine the best of 50 sealers, a leading agency found that they follow this order:
1. Methyl methacrylate

2. Ethyl acrylate copolymer

3. Polyester epoxy resin

4. Styrene acrylic copolymer

5. Styrene acrylic silicone copolymer

Sealers generally will not prevent or cure leaks because most water entry problems originate with many unrelated aspects of construction.

Painting conventional or one-coat stucco

Portland cement plaster, lime, and other cementitious materials, are highly alkaline when first mixed and applied to lath or other substrates, If the stucco is to be painted, it is absolutely essential that the paint be alkali-resistant, or that painting be delayed for a week to ten days to allow stucco to reach a point where the pH changes from its high of 12.4 to about 8.

Painters or do-it-yourselfers before applying any paint should ascertain the alkalinity of the wall or soffit surfaces. This can be very simply accomplished by using a pH tester in the form of litmus paper. One that is popular is a coil of litmus paper that dispenses at the front. It is named “pHydrion Insta-Check 0-13″. It is manufactured by Micro Essential Laboratory, Brooklyn, NY It, or one similar is readily available at lab supply stores.

pH 7 is neutral. Below 7 is acidic – above 7 is alkaline. All that’s necessary is to moisten a small section, then apply the litmus paper. If it turns blue, the surface is alkaline. If it is in the green or light green area, it is alkaline but not sufficiently alkaline to create a problem.

When painting, do not dilute paint with water as this affects adherence to stucco, and can result in spotty delamination.

Alkali resistant paints (usually acrylic) are available. Be sure to check the paint manufacturer’s literature and follow their directions. Most acrylic elastomeric coatings are already alkali-resistant so need no waiting time, but most paints are not resistant to a highly alkaline condition. An alkali-resistant primer can be used over alkaline surfaces to prevent paint degradation.

To get your copy of The Consumer’s Stucco Handbook by John J. Bucholtz, please contact:

The Plaster Information Center
1745 Saratoga Avenue
Suite A
San Jose, CA 95129
408-257-2444


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