How to Apply Elastomeric Roof Coating
Surface prep, application methods, coverage rates, and curing times for elastomeric roof coatings on commercial flat roofs
Last updated: February 17, 2026
Introduction
Elastomeric roof coatings form a seamless, waterproof membrane over your existing roof. A properly applied coating can add 10-20 years of life to a roof at a fraction of what a full replacement costs. But if the application is wrong, the coating fails early. Most failures come down to bad prep or bad timing.
This guide walks through the full process for acrylic, silicone, polyurethane, and SEBS rubber coatings: surface prep, application, coverage rates, and curing. For background on coating types and properties, see our elastomeric roof coating guide.
Who this is for: Building owners, facility managers, and roofing contractors coating commercial flat or low-slope roofs. Always follow the manufacturer's instructions for your specific product.
Roof Preparation
Prep is 80% of the job. A coating applied to a dirty or damaged surface will fail no matter how well you put it on.
Cleaning
Pressure wash the entire roof at 2,500-3,500 PSI to remove dirt, debris, mildew, and loose coatings. For roofs with biological growth, pre-treat with a TSP (trisodium phosphate) solution and scrub before pressure washing. Let the roof dry completely, usually 24-48 hours depending on weather.
Repair
Inspect for and repair all damage before coating. This includes:
- Seal cracks and splits with roof-grade sealant or fabric reinforcement
- Replace rusted or damaged flashing
- Re-secure loose seams and fasteners on metal roofs
- Fill ponding areas (standing water after 48 hours) with roof filler compound
- Repair blistered or delaminated areas by cutting, drying, and patching
Browse roofing sealants for repair products compatible with elastomeric coating systems.
Moisture Testing
Moisture trapped under a coating causes blistering and delamination. Scan the roof deck with a non-destructive moisture meter. Anything reading above 25% moisture needs to be dried or replaced before you coat. On built-up roofs, an infrared scan can help find wet insulation.
Primer
Not every substrate needs primer, but it helps adhesion on porous or chalky surfaces. Use an acrylic primer for acrylic coatings, silicone primer for silicone coatings. Apply at the manufacturer's recommended rate and let it fully cure before you topcoat.
Tools & Materials
Get everything together before you start. Nothing slows a coating job down like stopping mid-roll to run to the supply house.
| Tool | Purpose | Notes |
|---|---|---|
| Pressure washer (2,500+ PSI) | Surface cleaning | Use fan tip, not zero-degree nozzle |
| 3/4" nap roller (18") | Coating application on flat areas | Use 1" nap for rough surfaces like SPF |
| 4" brush | Edges, penetrations, detail work | Polyester brush for acrylic; chip brush for silicone |
| Airless sprayer (3,000+ PSI) | Large-area spray application | 0.021-0.031" tip size; not needed for small roofs |
| Wet film thickness gauge | Verify mil thickness during application | Check every 100 sq ft |
| Caulk gun + roof sealant | Seal cracks and penetrations pre-coat | Use sealant compatible with your coating type |
| Polyester fabric (4-6" wide) | Reinforce seams, cracks, and transitions | Embed in wet base coat |
| Moisture meter | Pre-application moisture testing | Non-destructive pin-type or impedance meter |
Application Methods
You can roll it, brush it, or spray it. Which method you pick depends on the roof size, your budget, and how much control you need over thickness.
Roller Application
Most common method for roofs under 10,000 sq ft. Rollers give you good thickness control without spending much on equipment.
- Use 18" roller frame with 3/4" nap cover for smooth substrates
- Use 1" nap for textured or rough surfaces (SPF, granulated cap sheet)
- Apply in one direction per coat; alternate direction on second coat (crosshatch)
- Maintain a wet edge to avoid lap marks
- Typical coverage: 800-1,200 sq ft per hour for one person
Brush Application
You'll use a brush for detail work around penetrations, edges, and transitions. Brush the perimeter and all penetrations first, then roll the field. This "cut-in" approach makes sure you get full coverage where it matters most.
Spray Application
Fastest method for large roofs (10,000+ sq ft). You need an airless sprayer rated for heavy coatings. Spraying gives you the most uniform thickness, but it takes more skill to avoid runs and thin spots.
- Use airless sprayer rated at 3,000+ PSI with 0.021-0.031" tip
- Maintain 12-18" distance from surface
- Overlap each pass by 50%
- Back-roll edges and penetrations after spraying
- Typical coverage: 3,000-5,000 sq ft per hour
| Method | Speed | Thickness Control | Equipment Cost | Best For |
|---|---|---|---|---|
| Roller | Moderate | Good | Low ($50-100) | Small to mid-size roofs |
| Brush | Slow | Excellent | Very low ($10-20) | Detail work and cut-in |
| Airless Spray | Fast | Moderate | High ($2,000+ or rental) | Large commercial roofs |
Temperature & Weather Requirements
Weather matters. Coating applied in the wrong conditions will fail, and it's the second most common cause of failure after bad surface prep.
| Condition | Minimum | Ideal | Maximum |
|---|---|---|---|
| Air temperature | 50°F (10°C) | 70-85°F (21-29°C) | 100°F (38°C) |
| Surface temperature | 50°F (10°C) | 70-90°F (21-32°C) | 120°F (49°C) |
| Relative humidity | — | 40-70% | 85% |
| Rain-free window | 24 hours after application (48 hours for silicone) | ||
| Dew point spread | Surface temp must be at least 5°F above dew point | ||
Seasonal Recommendations
- Spring (March-May): Good window in most regions; watch for rain and morning dew
- Summer (June-August): Best season overall; apply early morning before surface exceeds 120°F
- Fall (September-November): Good in southern states; ensure coating cures before first freeze
- Winter (December-February): Not recommended in northern climates; possible in southern regions above 50°F
For energy code compliance and cool roof requirements, see our Title 24 Cool Roofs resource page.
Coverage Rates by Coating Type
Coverage rate tells you how much material to buy. These rates are per coat, and most systems need two coats for warranty coverage.
| Coating Type | Coverage (sq ft/gal) | Wet Mils per Coat | Dry Mils per Coat | Total System (2 coats) |
|---|---|---|---|---|
| Acrylic | 75-100 | 16-21 | 8-10 | 16-20 dry mils |
| Silicone | 60-80 | 20-27 | 18-24 | 36-48 dry mils |
| Polyurethane | 50-75 | 21-32 | 16-24 | 32-48 dry mils |
| SEBS Rubber | 50-75 | 21-32 | 16-24 | 32-48 dry mils |
Important: Always check coverage rates on the product's data sheet. Rough or porous surfaces eat up more material. Add 10-20% for textured surfaces and up to 30% for SPF roofs.
Drying & Curing Times
Drying and curing are different stages. "Dry to touch" means the surface is no longer tacky. "Recoat ready" means you can apply the next coat. "Full cure" means the coating has reached its final physical properties.
| Stage | Acrylic | Silicone | Polyurethane | SEBS Rubber |
|---|---|---|---|---|
| Dry to touch | 1-2 hours | 2-4 hours | 4-8 hours | 2-4 hours |
| Recoat ready | 4-8 hours | 8-24 hours | 12-24 hours | 8-24 hours |
| Light foot traffic | 24 hours | 24-48 hours | 24-48 hours | 24-48 hours |
| Full cure | 3-5 days | 5-7 days | 5-7 days | 5-7 days |
Note: All times assume 75°F and 50% RH. Cold temperatures and high humidity significantly increase drying and cure times. Do not apply a second coat until the first coat passes the "thumbnail test": press your thumbnail into the coating. If it leaves a mark, it's not ready.
Common Mistakes to Avoid
These come up again and again in warranty claims and field inspections.
- Skipping surface prep. Pressure washing alone is not enough if there is chalking, oil, or loose material.
- Coating a wet or damp surface. Moisture trapped under the coating causes blisters within weeks.
- Going too thin. Using less coating to "save money" voids the warranty and cuts lifespan by 50% or more.
- Not checking the weather. Rain within 24 hours washes uncured acrylic coatings right off the roof.
- Coating in direct afternoon sun. Surface temps above 120°F cause flash drying and poor film formation.
- Skipping reinforcing fabric at seams. Seams and transitions crack first without fabric reinforcement.
- Mixing coating types. Silicone over acrylic (or vice versa) causes delamination. They are not interchangeable.
- Ignoring ponding areas. Standing water degrades acrylic coatings. Use silicone in ponding areas or fix the drainage.
- One thick coat instead of two thinner coats. A single thick coat traps solvents and cures unevenly.
- Not using a wet film thickness gauge. It is the only way to verify you are putting down the right amount of material.
Maintenance & Re-Coating Schedule
Annual Inspection Checklist
Walk the roof at least once a year (twice in harsh climates) and after any major storm.
- Check all penetrations (pipes, vents, HVAC curbs) for cracking or separation
- Inspect seams and transitions for lifting or peeling
- Look for ponding water. Mark areas where water stands after 48 hours.
- Check for mechanical damage from foot traffic or fallen debris
- Clean debris from drains and scuppers to prevent ponding
- Measure coating thickness at several points to check for wear
Re-Coating Schedule
Most elastomeric systems need a maintenance re-coat every 8-12 years. Re-coating is simpler than the first application since the existing coating is your substrate.
- Clean the surface: pressure wash to remove dirt and chalk
- Repair any localized damage with patch material
- Apply one coat at the manufacturer's recommended rate
- This extends the warranty another 8-12 years at roughly 40% of the original cost
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