Elastomeric Wall & Roof Coatings
Elastomeric coatings are thick, rubbery films that stretch and recover as buildings move, bridging hairline cracks in walls and protecting roofs from water and sunlight.
Key takeaways
- Elastomeric coatings are high-build films that can stretch substantially and return to shape, letting them bridge small moving cracks.
- Acrylic latex dominates wall coatings and many roof coatings; silicone, polyurethane and other chemistries serve more demanding roof service.
- Performance depends on applying enough dry film thickness, which is far higher than for ordinary paint.
- They shed liquid water but differ in vapor permeability, so moisture behind the film must be considered.
Ordinary architectural paint is a thin, relatively rigid film. When a stucco or block wall cracks, or a roof deck flexes with temperature, that film cracks with it and lets water in. Elastomeric coatings are designed for movement: their polymers stay rubbery across the service temperature range, and they are applied thickly enough that a crack opening beneath them is spread over a length of stretchy film.
The term covers two main markets: elastomeric wall coatings for masonry, stucco and concrete, and elastomeric roof coatings for low-slope roofs. The chemistry overlaps, but roof products face standing water, intense sunlight and foot traffic, so formulations and test requirements differ. For roof system design and restoration strategy, see Roof Coatings.
What makes a coating elastomeric
Elastomeric binders have a low glass transition temperature, so they remain flexible even in cold weather. Products are characterized by elongation at break, tensile strength and the ability to recover after stretching, with good elastomeric coatings often elongating well over 100% at room temperature. Elongation at low temperature is especially important because buildings move most when cold and brittle failures happen then.
Film thickness is just as important. A thin film can only stretch a short distance before tearing; a thick film can bridge a wider crack. That is why elastomeric products are high in solids and applied at low spread rates, often building 10–20 mils (250–500 µm) dry on walls and commonly 20–30 mils (500–750 µm) or more on roofs, per the product data sheet.
Types of elastomeric coatings
| Type | Strengths | Watch-outs | Typical use |
|---|---|---|---|
| Acrylic latex | Economical, waterborne, good UV resistance, bright white for reflectivity | Sensitive to ponding water; needs warm, dry weather to cure | Masonry walls; roofs with good drainage |
| Silicone | Excellent UV and ponding-water resistance, stays flexible | Picks up dirt; difficult to recoat with anything but silicone | Low-slope roofs, spray foam roofs |
| Polyurethane | Tough, abrasion- and impact-resistant | Aromatic types need UV-stable topcoats; often solvent-borne | Roofs with foot traffic, base coats |
| Styrene-butadiene and other rubbers | Flexibility, water resistance | Varying UV stability | Roof and waterproofing systems |
| Polyurea and hybrids | Very fast cure, high build, tough | Plural-component equipment needed | Roofs and waterproofing |
Standards help define minimum performance. For example, ASTM D6083 is a specification for liquid-applied acrylic coatings used in roofing, and ASTM D6694 covers liquid-applied silicone coatings used in spray polyurethane foam roofing.
Elastomeric wall coatings
On stucco, block, tilt-up and poured concrete, elastomeric coatings resist wind-driven rain and bridge hairline shrinkage and settlement cracks. They are commonly used where a smooth or textured decorative finish is also wanted.
- Crack preparation: hairline cracks may be bridged directly; larger or moving cracks should be routed and filled with a compatible sealant or patch first.
- Primers: chalky or porous surfaces often need a masonry primer or conditioner; new masonry may need an alkali-resistant primer.
- Moisture: because many elastomeric films have lower vapor permeance than ordinary paint, moisture trapped in walls can cause blistering. Check the product’s permeance, often reported using ASTM E96, and correct leaks first.
For broader guidance on these substrates, see Coating Masonry & Concrete Block.
An elastomeric coating will not stop water entering from above through parapets, copings, windows or roof leaks. Water trapped behind a low-permeance film can blister the coating and worsen efflorescence. Fix the water source first.
Elastomeric roof coatings
On metal, modified bitumen, single-ply, built-up and spray foam roofs, elastomeric coatings add a seamless, UV-protective layer and can extend the life of an aged but sound roof. White and light-colored coatings also reflect sunlight, lowering roof surface temperatures and potentially reducing cooling loads; reflectance and emittance ratings are published by organizations such as the Cool Roof Rating Council.
Ponding water is the major chemistry decision on roofs. Many acrylics soften or lose adhesion under prolonged standing water, while silicones and some urethanes are formulated to tolerate it. Seams, fasteners and penetrations on metal roofs are usually reinforced with fabric or detail-grade mastic before the field coat.
Application best practices
- Inspect and repair. Fix leaks, wet insulation, failed flashings and structural problems.
- Clean. Pressure wash to remove dirt, chalk, biological growth and loose coating; let surfaces dry.
- Test adhesion. Apply small test patches over existing surfaces and check bond before full application.
- Prime and detail. Prime where required and reinforce cracks, seams and penetrations.
- Apply at the specified rate. Use spray, roller or brush in one or more coats, checking wet film thickness to reach the target dry film. The coverage calculator helps convert spread rates.
- Respect weather limits. Waterborne products need temperatures above the stated minimum and no rain or dew until they set.
Underapplication is the most common elastomeric failure. Mark out areas, count the pails used and take regular wet-film readings so the full mil thickness actually goes on.
Advantages and limitations
Advantages
- Bridges hairline cracks and accommodates movement
- Seamless water-shedding layer
- Reflective white roof coatings can reduce heat gain
- Can extend the life of sound existing roofs and walls
Limitations
- Cannot fix structural cracks or active leaks
- Requires high film build and more material than paint
- Lower vapor permeance can trap moisture
- Some types are dirt-retentive or hard to recoat
Frequently asked questions
Is elastomeric paint waterproof?
It resists liquid water and wind-driven rain well, but it is not a below-grade waterproofing membrane and will not stop water under hydrostatic pressure or from leaks behind the film.
Can I put acrylic over silicone roof coating?
Generally no. Most coatings do not adhere well to cured silicone, so silicone roofs are typically recoated with silicone. Follow the manufacturer’s recoat instructions.
How long do elastomeric roof coatings last?
Life depends on chemistry, thickness, drainage and climate. Thicker applications generally last longer, and many manufacturers tie warranty length to applied dry film thickness.
Educational reference. Coating performance varies by formulation. Always follow the manufacturer’s product data sheet, safety data sheet and your project specification.
