A coating specification is a contract in four parts. Most disputes come from reading the system table and skipping what decides whether it can be delivered.
Most coating disputes are not technical disagreements. They are disagreements about what a document said, discovered after the material has been bought. Learning to read the specification properly takes an hour and saves more than any negotiation over price per litre.
Four parts, and the table is only one
A usable coating specification has four parts. The scope defines what is being coated and to what standard of cleanliness. The surface preparation clause defines the abrasive, the grade, the profile and the salt limit. The system table lists coats, generic product types and film thicknesses. The inspection clause defines who tests what, when, and what constitutes acceptance.
The table is the part everyone reads, and it is the least likely to cause a dispute, because it is the most explicit. Disputes come from the other three, usually from a preparation standard that cannot be achieved in the available access, or an inspection clause that requires a measurement method the applicator has never used.
Film thickness: per coat or total
A system table giving 240 micrometres total is not the same instruction as three coats at 80 micrometres each. The first allows a heavy single coat, which can trap solvent and crack; the second produces a different film. If the table gives only the total, ask whether per-coat figures are mandatory, and get the answer in writing before mobilising.
Check also how the thickness is to be measured. On abrasive-blasted steel, the dry film thickness gauge reads the profile as paint, and the standard method for rough surfaces subtracts it. A system specified at 240 micrometres and measured without that correction can fail acceptance while the film is correct, or pass while it is thin. The specification should name the method, and if it does not, that omission belongs in the tender query.
Generic type or brand name
Specifications written around a generic type leave room to propose an equivalent, and that is where a supplier earns its margin or loses the job. A specification that names a product leaves no room at all, and any substitution needs written approval before delivery, not after.
Where equivalents are permitted, the substitution case has to be made on the properties the specification actually relies on: volume solids, zinc content in the dry film, temperature limits, recoat windows, and the ability to deliver the specified thickness in the specified number of coats. A cheaper product that needs an extra coat is not cheaper.
The clauses that decide the schedule
Recoat windows are the most common cause of a rescheduled programme. A product with a twenty-four hour minimum overcoating interval and a seven day maximum cannot be applied to a tight sequence without planning the sequence around it. Read the window before promising a completion date.
Salt limits, where stated, are usually expressed as conductivity or as mass per unit area after extraction. If the clause exists, it needs a test method, a frequency and a hold point, or it will be discovered at handover. Hold points matter for the same reason: a hold point is a work stoppage by definition, and a programme that does not include it will slip the first time it is enforced.
What to do with the document
- Read the preparation and inspection clauses first, then the table
- List every quantity that is stated without a method or a frequency, and query it
- Confirm per-coat thicknesses and the measurement standard in writing
- Check the recoat window against the actual programme, coat by coat
- Confirm who supplies the salt test, the gauge calibration and the inspection records
- Keep the tender queries and the answers with the contract documents
The pattern behind most failures is consistent: the technical content was correct, the commercial reading was optimistic, and the gap was closed by assuming. A specification rewards the reader who treats every unqualified number as a question.