Why the record is the entire job
On a firestopping job, a bad seal can be found and opened up. On a coated steel frame, the dry film thickness is the performance, and it is invisible the moment the coating cures. If the record of thickness per member is missing, incomplete, or written up from memory on a Friday, there is no way back to it short of re-measuring a whole frame, and often no access to do it.
That is why third-party inspection of intumescent coating exists as a trade of its own, and why a coating handover file with gaps is expensive in a way that other trades' paperwork is not.
The loading schedule is the specification
Required thickness is not a single number for a building. It varies member by member, driven by the fire resistance period and the section factor - the heated perimeter over the cross-sectional area, the ratio that decides how fast a section heats up. A stocky column and a slender beam in the same building, to the same rating, need different thicknesses. The manufacturer's loading tables turn that ratio and that rating into a required dry film thickness.
Assaya holds the loading schedule as part of the job rather than as a PDF somebody has on their phone. Each line carries the fire rating, the section factor range it applies to, and the required thickness. When a member is recorded, its readings sit against the line that governs it, so the comparison between required and achieved is in the record itself rather than in somebody's head.
What gets captured at the member
Intumescent coating is one of the trades with its own capture fields rather than a general purpose form. On a coating record the app asks for the substrate and its preparation, the element being protected, each coat applied, the film thickness readings, and the topcoat - alongside the fields every Assaya record carries: the pin on the current drawing revision, the element and its fire rating, photographs, the operative and the date.
- Wet film readings as applied, which is the only chance to catch a shortfall while it can still be fixed cheaply.
- Dry film readings per member, recorded against the loading line that applies to it.
- Primer and topcoat, because compatibility is part of the tested system and a wrong topcoat can void it.
- Photographs before, during and after, with the reference and capture time burned into the image so they stay meaningful after export.
- Who applied it and when, captured at the steel.
It all works with no signal. Steel frames are usually coated before the building has power, let alone coverage, so the whole record including photographs captures on the device and syncs later.
The reading that comes back under spec
Nobody writes about this and everybody deals with it. A dry film reading comes back below the required thickness. What happens to that number?
The honest answer is that it stays. A record that only contains passing readings is not an inspection record, it is a marketing document, and the first competent person to notice will treat the whole file as unreliable. The useful thing is to record the reading, record what was done about it - an additional coat, a re-measure, a technical query to the manufacturer - and keep both on the same record so the sequence is visible.
In Assaya that happens by default, because every change to a record is kept and hash-chained rather than overwritten. A re-measure after a further coat shows as a re-measure. That is a stronger position in front of an inspector than a clean file nobody believes, and it is the same argument as the rest of the product: the value is in the record being hard to quietly change.
What belongs in an intumescent handover file
There is no single UK page that sets this out, so here is the working list, and Assaya produces most of it from the register rather than by assembly.
- The loading schedule used, with the manufacturer's tables it came from.
- Product data sheets for primer, basecoat and topcoat, and confirmation they are a compatible system.
- Batch numbers and dates of application.
- Wet and dry film thickness readings, member by member, against required thickness.
- The conditions recorded at application - manufacturers set limits on humidity and on substrate temperature relative to dew point, and work outside them is a defect even if the thickness is right.
- Photographs before, during and after, tied to specific members.
- Who applied it, who inspected it, and when.
- Any readings that failed, and what was done about them.
Where the requirement comes from
The legal requirement is B3 of Schedule 1 to the Building Regulations 2010 - the structure has to maintain its stability for a period - with Approved Document B as statutory guidance on satisfying it. Approved Document B is guidance, not law, which is worth stating precisely.
Reactive coatings are assessed by test to the BS EN 13381 series, which is what stands behind the manufacturer's loading tables; structural fire design sits under BS EN 1993-1-2 for steel. The industry guidance used across the trade for measuring and reporting thickness is the ASFP Yellow Book, Fire protection for structural steel in buildings. Environmental limits during application - humidity, and substrate temperature above dew point - come from the manufacturer's data sheet for the product you are using, not from a general rule, so record what the data sheet says and what the conditions were.
At completion the information reaches the responsible person through regulation 38, and for higher-risk buildings it has to stay current as part of the golden thread.
What it costs
The whole price list is published, with no demo call first and no per-member, per-pin or per-drawing charge. A steel frame is a lot of records, and a per-record price quietly taxes the biggest jobs. Client observers are free, so the third-party inspector reviewing your work does not cost you a seat.
See fire-stopping records captured on site, pinned to the drawing and locked to a tamper-evident history - with the whole price list published and no demo to sit through first.
How is intumescent coating thickness recorded?
As wet film thickness while applying, which is the only chance to catch a shortfall cheaply, and as dry film thickness once cured, member by member, against the required thickness for that member. Required thickness comes from the manufacturer's loading tables, driven by the fire resistance period and the section factor of the member.
What is a section factor and why does it change the thickness?
The section factor is the heated perimeter of a steel section divided by its cross-sectional area. A high value means a lot of surface relative to mass, so the section heats faster and needs more protection. Two members in the same building to the same fire rating can need different thicknesses because their section factors differ, which is why a single blanket thickness for a frame is a warning sign.
What happens if a dry film thickness reading is below specification?
Record it, then record what was done about it - a further coat, a re-measure, or a technical query to the manufacturer - and keep both on the same record. A file containing only passing readings invites the assumption that failures were deleted. In Assaya every change is kept and hash-chained, so a re-measure after a further coat reads as exactly that.
What should be in an intumescent coating handover file?
The loading schedule and the manufacturer tables behind it, product data sheets for primer, basecoat and topcoat with confirmation they are a compatible system, batch numbers and dates, wet and dry film readings per member against required thickness, the conditions recorded at application, photographs tied to members, who applied and inspected it, and any failed readings with the action taken.
Which standards apply to intumescent coating?
The legal requirement is B3 of Schedule 1 to the Building Regulations 2010, with Approved Document B as statutory guidance. Reactive coatings are assessed by test to the BS EN 13381 series, which stands behind the manufacturer's loading tables, and structural fire design for steel sits under BS EN 1993-1-2. The ASFP Yellow Book is the industry guidance for measuring and reporting thickness.
Does it work without a signal on site?
Yes. Steel frames are usually coated before a building has power or coverage, so the whole record including photographs captures on the device and syncs when a connection returns.
This page is general information about record-keeping for intumescent coating, not fire engineering advice. Required thicknesses, product compatibility and application conditions must be taken from the manufacturer's certified data for the product in use.