Elastomeric Wall Coatings

Cementitious substrates are one of the fastest growing exterior substrates in North America. These finishes range from composites such as fiber cement to stucco and block walls. Although roughly 15% of new residential construction is cementitious, this newsletter will focus on stucco only. Stucco is attractive and durable. It adds texture. It is paintable. It serves as a robust barrier to the elements (including water). However, stucco is not completely worry-free – it has two potential issues – efflorescence and possibility of cracking. What are EWCs? Elastomeric wall coatings (EWCs) are thick, flexible coatings used to help protect and maintain the appearance of exterior masonry walls.

EWCs are designed to bridge existing and future cracks in masonry by stretching and shrinking as exterior walls expand and contract with changes in temperature.

Use of an EWC is an excellent way to help prevent wind-driven rain, acid rain and freeze-thaw conditions from damaging a building’s appearance and structural integrity.

EWCs are typically applied at dry film thickness that is at least five to six times that of conventional exterior paint.

For premium performance, the Paint Quality Institute recommends elastomeric coatings be applied at a minimum dry film thickness of at least 16 mils. Use of greater film thickness will improve performance. A thick dry film is needed to give the coating its crackbridging and other functional properties and will contribute to maintaining the overall appearance.

Additionally, care must be taken to keep moisture from getting into the masonry from above or behind (cracked wall caps, leaking roofs, sweating pipes, etc.). Moisture from behind the coating can cause blistering and, in the case of very alkaline masonry, deterioration of applied coatings.

Q & A:

Q: Why thick film?
A: Unlike wood failures (e.g. swelling and shrinkage) cementitious walls do not recover but tend to crack as sub walls and foundations move. If a thin coat is applied, these cracks will be readily apparent. A thick coating, on the other hand, coupled with the ability to expand, will bridge the gaps and hence hide cracks in exterior walls. At a minimum, a good EWC has the right elongation properties to help bridge these cracks!

Q: What other properties should a good quality EWC deliver?
A: While bridging the gaps is important, the coating must have good barrier properties and good durability. After all, why would you compromise an otherwise durable, low maintenance substrate with an inferior coating! Specifically a good quality EWC must have excellent dirt pick-up resistance and excellent efflorescence resistance. To ensure this, we recommend you buy a top quality 100% acrylic EWC and follow the manufacturer’s recommendations for applications.

Q: Should I use a primer prior to applying my EWC coating?
A: To ensure maximum protection against efflorescence, we strongly recommend using a primer/sealer. This is particularly true when coating any masonry that is green or ‘hot’ (less than 30 days old), or masonry (stucco) that is porous or chalky.

Q: When repairing stucco, how do I determine if a thick film EWC is a must vs. a thin film application? A: • Microcracks (Hair-Line Cracks) up to 8 mils    - On surface only; conventional coatings, if thick enough, many suffice • Cracks from 8 to 16 mils    - Recommend Elastomeric Wall Coatings • Cracks > 16 mils Should be repaired with quality acrylic Caulk/Sealant then coat with EWC
Q: A top quality EWC, applied at recommended film thickness will help ensure: • crackbridging • excellent dirt resistance • maximum hiding • uniform appearance

Paint Quality Institute offers several recommendations for selecting and getting the best results when using an EWC:

• Chose a top quality EWC formulated with a 100% acrylic elastomeric binder.

• Surface preparation is essential; remove efflorescence salts, dust, unbound sand, dirt and mildew from weathered masonry; apply a primer or sealer to chalky or porous masonry.

• Seal crack of 1/16” or larger (before applying sealer or primer) with a top quality 100% acrylic latex caulk recommended by the EWC manufacturer.

• Don’t apply an EWC directly to fresh, highly alkaline surfaces. Ideally allow 28 days for the masonry to cure. Apply an alkali-resistant sealer or primer over fresh masonry to help prevent alkali burn and efflorescence.

• Apply a minimum dry EWC film thickness of 16 mils to achieve desired flexibility and crackbridging capability. Increased film thickness improves both dirt pick-up resistance and performance.

• Apply two coats of EWC rather than one thick coat to help ensure a uniform film thickness, as well as cover any pinholes or holidays that may appear in the first coat.