Every coatings manufacturer publishes technical data sheets, and every one of them is technically true. That is the problem. A TDS is a marketing document constrained by honesty, and there is a great deal of room inside that constraint.
Here is how to read one.
A number without a test method is not a number
This is the first filter and it eliminates a surprising amount of material. “Tensile strength: 2,500 psi” tells you nothing on its own. Tensile per ASTM D412 — the standard for elastomers, using a dumbbell specimen pulled at a specified rate — is a defined measurement you can compare against another product tested the same way. Tensile with no method cited is a claim.
The ones worth knowing by sight:
- ASTM D412 — tensile strength and elongation for elastomers
- ASTM D2240 — durometer hardness, Shore A for softer materials and Shore D for harder ones
- ASTM D624 — tear resistance
- ASTM D4541 — pull-off adhesion using a portable adhesion tester, the number that matters most in the field
- ASTM D4060 — Taber abrasion
- ASTM D570 — water absorption
If two data sheets cite different methods for what looks like the same property, you do not have a comparison. You have two unrelated facts.
Shore A and Shore D are not the same scale
Durometer trips people constantly. Shore A and Shore D are separate scales with different indenters, and they overlap awkwardly in the middle. A material listed at 90 Shore A is not harder than one listed at 50 Shore D — it is considerably softer. Conversion charts between them exist and they are approximations at best. When a sheet gives you Shore A and the competing sheet gives you Shore D, somebody has chosen the scale that flatters their product, and you should ask for the other one.
Elongation and tensile trade against each other
A very high tensile number alongside a very high elongation number should make you curious rather than impressed. Broadly, within a chemistry family, stiffer and stronger comes at the cost of stretch, and vice versa. What you actually want depends entirely on the job: a truck bed liner taking impact wants elongation and tear resistance, while a trafficked industrial floor wants hardness and abrasion resistance. There is no product that is best at all of it, and a sheet that appears to claim otherwise is usually reporting the numbers at different conditions.
Check the conditions the numbers were taken at
Buried in the fine print you will find the film thickness, cure time, and temperature the samples were tested at. A tensile figure from a free film cured seven days at 77°F is a laboratory result. Your material is going onto cold concrete in November at whatever thickness the applicator managed. The lab number is still useful — it is a valid basis for comparing products — but it is a ceiling, not a prediction.
Adhesion is the number that is usually missing
Notice how often the mechanical properties are lavishly documented and adhesion gets one line, or none. Adhesion is the property that decides whether the coating is still on the substrate in five years, and it is the one most dependent on preparation, which means the manufacturer cannot promise it without qualifying it into uselessness. Where a pull-off value per D4541 is given, look for the substrate and the surface preparation it was achieved on. “3.5 MPa on abrasive-blasted steel to SSPC-SP 10” is meaningful. A bare number is not.
Chemical resistance charts need a duration and a concentration
A chemical resistance table with checkmarks and no exposure duration, concentration, or temperature is decorative. Resistance to 10% sulfuric acid for 24 hours at ambient and resistance to 70% sulfuric acid for a year at 140°F are wildly different claims. If you are lining anything that will hold a specific chemical, ask the manufacturer for the immersion test data, and if they will not produce it, that is your answer.
Watch for the word “typical”
Most sheets label their property tables “typical values.” That is not weasel wording, it is accurate — batch variation is real. But it does mean the numbers are not guaranteed minimums. If you are writing a specification, you need the manufacturer to commit to a minimum in writing, and that is a different document than the TDS.
The practical version
When you are comparing two products, build a small table yourself: property, value, test method, test conditions, source document and revision date. The comparisons that survive that table are the real ones. Most of the time you will find that two of the six properties you cared about are genuinely comparable and the rest were never comparing anything.
And read the safety data sheet, not just the technical one. It is the document with the information that can actually hurt somebody.
General trade information, not a specification. Always work from the current TDS and SDS revision for the specific product you are using.