How to Verify Your Coating Was Applied Correctly
10 minute read
After reading this page, you will know how to verify that a roof coating project was completed to specification — what to measure, what to look for, what documentation to require, and what recourse you have if the work does not meet the standard.
Quick answer: Verification requires three things: dry film thickness readings at multiple points (minimum one per 2,500 square feet, targeting 20-25 mils for silicone), a visual walk checking for holidays/thin spots/blisters, and documentation including thickness records, material usage logs, and before/after photos. If any readings are below 80% of the specification, the area should be recoated before you accept the project.
Why verification is non-negotiable
You cannot visually determine whether a coating was applied at the correct thickness. A 15-mil coating looks identical to a 25-mil coating from standing height. Both are white (or whatever color was specified), both are smooth, and both cover the substrate. But the 15-mil coating has 40% less material and will last 40% fewer years. Without thickness testing, you have no way to know whether you received the coating system you paid for.
Verification also establishes the baseline documentation for any future warranty claim. If the coating fails at year 5 on a 12-year system, the first question will be whether the coating was applied at the specified thickness. Thickness readings taken at project completion provide the answer. Without those readings, the manufacturer may argue that the failure was caused by under-application (contractor liability) or the contractor may argue it was a material defect (manufacturer liability). Your documentation resolves the dispute.
The contractor who follows best practices already includes verification in their process. Requesting thickness readings and documentation is not adversarial — it is standard practice for quality-focused contractors. If your contractor pushes back on providing thickness verification, that resistance itself is a red flag about the quality of the installation.
Thickness testing: the primary quality metric
Dry film thickness (DFT) is the single most important quality metric for a coating installation. The DFT specification determines the coating's performance — its UV resistance, waterproofing capability, physical durability, and expected lifespan all scale with thickness. A coating at 80% of the specified DFT delivers roughly 80% of the expected lifespan. A coating at 60% of specification may fail in half the expected time.
DFT readings should be taken at a minimum of one point per 2,500 square feet of roof area. On a 20,000-square-foot roof, that is at least 8 readings spread across the roof in a grid pattern. Additional readings should be taken at areas of concern — near spray lines (where overlap may be insufficient), at the roof perimeter (where spray pattern may have been disrupted by wind), and at complex geometry (where application may have been difficult).
The acceptable DFT range is typically 90% to 120% of the specification. For a 25-mil specification, readings between 22.5 and 30 mils are acceptable. Readings below 22.5 mils indicate under-application — the area should be recoated. Readings above 30 mils indicate over-application — not a performance problem, but a sign of uneven application technique and wasted material.
| Chemistry | Target DFT | Minimum Acceptable | Action if Below Minimum |
|---|---|---|---|
| Silicone | 20-25 mils | 18 mils | Recoat area to meet spec |
| Acrylic | 15-20 mils | 13 mils | Recoat area to meet spec |
| Polyurethane | 20-30 mils | 18 mils | Recoat area to meet spec |
Visual inspection checklist
A visual walk of the completed coating should check for the following deficiencies. Walk the roof in a systematic grid pattern, examining each section from standing height and then looking more closely at any areas that appear inconsistent. Bring a camera to document any deficiencies for the punch list.
- Holidays (missed spots): Areas where the substrate is visible through the coating. Any holiday should be coated.
- Thin spots: Areas where the coating appears lighter in color or where the substrate texture shows through. May require DFT measurement to confirm.
- Blisters: Raised bumps in the coating surface. Isolated small blisters (under 1 inch) in small numbers are cosmetic. Widespread blistering indicates preparation or application failure.
- Fisheyes: Small circular defects where the coating pulled away from the surface. Indicates contamination beneath the coating.
- Runs and sags: Areas where coating flowed downhill before curing, creating thick lower edges and thin upper edges. Common on vertical surfaces and curb flashings.
- Debris embedment: Leaves, insects, or other debris trapped in the coating surface. Minor debris is cosmetic. Large debris (branches, tools) should be removed and the area recoated.
- Lap marks: Visible lines where spray passes overlapped, creating ridges. Minor lap marks are cosmetic. Severe ridges indicate improper spray technique.
Adhesion testing methods
Adhesion testing verifies that the coating is bonded to the substrate — not just sitting on top of it. The most common field test is the cross-hatch adhesion test (ASTM D3359): a grid pattern is scored through the coating with a utility knife, adhesive tape is pressed over the scored area and pulled off, and the amount of coating that lifts with the tape is evaluated. Minimal or no coating lift indicates good adhesion. Significant lift indicates adhesion failure.
Pull-off adhesion testing (ASTM D4541) provides a quantitative measurement of adhesion strength. A metal dolly is adhered to the coating surface with epoxy. After the epoxy cures, the dolly is pulled perpendicular to the surface using a calibrated gauge that measures the force required to pull the coating from the substrate. The result is expressed in PSI — typically 150 to 300+ PSI for a well-bonded coating system. Values below 100 PSI may indicate adhesion problems.
Adhesion testing is not always required for standard coating projects, but it is warranted when adhesion concerns exist. If the substrate was difficult to prepare (heavily contaminated, unusual membrane type), if primer compatibility is uncertain, or if the project is high-value and warrants extra verification, adhesion testing provides objective data about the bond quality. Ask your contractor whether adhesion testing is part of their quality protocol.
Detail inspection at penetrations and edges
Every penetration, flashing, drain, and perimeter edge should be individually inspected because these are the most common failure points. Check that reinforcing fabric is fully embedded — no visible fabric weave pattern showing through the coating. Verify that the coating covers the fabric completely and extends beyond it by at least 2 inches on all sides. Confirm that the coating transitions smoothly from horizontal to vertical surfaces without pools, sags, or thin areas.
At pipe penetrations, check that the coating wraps the pipe boot completely and seals to the pipe surface. The coating should extend at least 3 inches up the pipe above the roof surface. There should be no gaps between the coating and the pipe. Pull gently on the coating at the pipe interface — it should feel firmly bonded, not loose or easily lifted.
At drains, verify that the coating does not restrict water flow into the drain opening. Check that the coating edge is cut cleanly at the drain collar and that no coating has pooled inside the drain. Poor drain detail work can create a dam that causes ponding around the drain — exactly where you need the best drainage performance.
Documentation you should receive
A complete project documentation package includes the following items, all provided before final payment. Before-and-after photographs of the roof surface, details, and all repaired areas. Wet film thickness readings taken during application. Dry film thickness readings taken after cure. Material usage records showing total gallons of each product used. The manufacturer's batch numbers for the coating material. Weather logs showing temperature and conditions during application. The manufacturer warranty certificate. The contractor workmanship warranty.
The documentation package is not an extra — it is a deliverable of the project, like the coating itself. Include documentation requirements in the contract so there is no ambiguity about what the contractor must provide. A contractor who resists providing documentation may not have taken the measurements or may not want to share results that reveal deficiencies.
Store the documentation in a permanent building file. You will need it for warranty claims (if the coating fails prematurely), insurance documentation (if a storm damages the coating), property sale due diligence (the buyer's inspector will want to see it), and future re-coating decisions (the original thickness readings become the baseline for evaluating coating condition over time).
When to hire a third-party inspector
Third-party inspection is appropriate for high-value projects, complex installations, or situations where you want independent verification of the contractor's work. A qualified roof consultant or inspector not affiliated with the coating contractor performs the same verification — thickness testing, visual inspection, adhesion testing — and provides an independent report. This report provides unbiased quality documentation and identifies any deficiencies before you release final payment.
The cost of third-party inspection ranges from $500 to $2,000 depending on roof size and scope of testing. On a $70,000 coating project, that is 0.7% to 2.9% of the project cost — a small price for independent verification that the $70,000 was well spent. For projects above $100,000, third-party inspection is strongly recommended. For projects involving unusual substrates, complex geometry, or contractors without a long track record, it provides an additional layer of quality assurance.
The manufacturer may also offer or require their own inspection for warranty certification. Some coating manufacturers dispatch their own representatives to inspect the completed installation before activating the full warranty. This manufacturer inspection is not a substitute for your own verification — it focuses on the manufacturer's warranty requirements, which may not cover every quality concern you have.
Warranty activation and what it requires
The manufacturer warranty is typically not automatic — it must be activated through a registration process after project completion. Registration requirements vary by manufacturer but commonly include: completed project registration form, contractor's application report showing product batch numbers and quantities used, photographs of the completed installation, and in some cases, a manufacturer representative inspection of the completed work.
The contractor is responsible for initiating the warranty registration process. This should happen within 30 days of project completion. Ask for confirmation that the warranty has been registered and request a copy of the warranty certificate once issued. If the contractor does not register the warranty, you may have a coating with no manufacturer backing — leaving only the contractor's workmanship warranty as protection.
Read the warranty terms before the project starts — not after. Key terms to understand: the coverage period, what is covered (material defects only, or also application quality), what is excluded (storm damage, foot traffic, improper maintenance), whether the warranty is transferable (important if you sell the building), and the claim process (written notice, inspection, timeline for resolution). Any terms you disagree with should be discussed before signing the contract, not after the coating is on the roof.
What to do if verification reveals problems
If thickness testing reveals areas below specification, the contractor should recoat those areas at no additional cost. Under-application is the contractor's error, not a change in scope. The contract specifies a certain DFT, and the contractor is obligated to meet it. Request the contractor to recoat all areas below the minimum acceptable threshold and take new readings after the additional coating has cured.
If visual inspection reveals widespread deficiencies (extensive holidays, blistering, or adhesion failure), the remedy may be more complex. Widespread blistering may require removing the blistered coating, re-preparing the surface, and recoating from scratch. Adhesion failure may indicate a preparation problem that cannot be resolved by adding more coating on top. In severe cases, the contractor may need to strip and redo the entire project.
Withhold final payment until all verified deficiencies are corrected and re-verified. The contract should include a retention clause — typically 10% of the project cost — held back until the final verification confirms the work meets specification. This retention provides financial leverage to ensure deficiencies are corrected. Releasing full payment before verification removes your most effective tool for ensuring quality. Call (251) 250-2255 to discuss verification requirements for your coating project.