Commercial
Writing an acrylic specification that survives a tender
A specification that names a product gets substituted. One that states a performance and a test method gets what was intended.
Commercial
A specification that names a product gets substituted. One that states a performance and a test method gets what was intended.
A tender specification has one job: to describe the outcome precisely enough that any compliant supplier produces the same thing, and loosely enough that more than one supplier can bid. Most acrylic specifications fail at one end or the other.
| Approach | Example | Strength | Weakness |
|---|---|---|---|
| Product named | Panel to be [brand] clear cast acrylic 8 mm | Unambiguous | Restricts competition; brand may be discontinued |
| Performance stated | Clear cast PMMA, light transmission ≥90%, thickness 8 mm ±10%, flatness ≤2 mm/m | Allows equivalents, survives product changes | Requires the specifier to know what matters |
| Hybrid | Performance criteria plus an approved-equal clause | Competition with a benchmark | Needs a fair evaluation process |
For most projects the hybrid is right: state the performance that matters, name a benchmark product as an example, and include an approved-equal clause with a clear evaluation basis.
Substitution is the most common failure in plastic glazing procurement: a bidder supplies a thinner sheet, an extruded sheet where cast was specified, or a non-UV grade, and everything looks fine until the panels bow or yellow two years later.
The defences are documentary rather than physical:
An acrylic warranty should separate two things that fail differently.
A fabricator who will bid can review a draft specification and flag clauses that are unbuildable, ambiguous or unnecessarily expensive. That review costs nothing and usually saves a revision after tender, which is the most expensive place to make a change.
Only as a benchmark with an approved-equal clause. A named brand alone restricts competition and may be discontinued mid-project, which leaves the specification unbuildable.
State the thickness with a tolerance, require the mill certificate with each delivery, and measure on delivery. A specification without a tolerance and without a certificate requirement cannot be enforced.
UV-stabilised cast acrylic can support a 10-year appearance warranty under stated exposure. Structural warranty should be shorter and must exclude impact and incorrect fixing.
If the panel is a lining or a large internal surface, the local reaction-to-fire class may apply. State the class and the thickness, and require the report at that thickness.
Yes, at no cost. We flag clauses that cannot be built, that are ambiguous, or that add cost without adding performance.
A well-written clause can still be lost between tender and delivery, and it usually happens in one of three places: it is translated into a purchase order that drops a requirement, it is met by a substitution that is technically compliant, or it is tested by a method nobody agreed on.
| Stage | Where the clause is lost | What prevents it |
|---|---|---|
| Tender to PO | The PO references the schedule but not the specification annex | Name the annex in the PO and attach it, not just reference it |
| PO to drawing | A performance requirement is translated into a product name | Keep performance clauses in the drawing notes; never let a brand name stand in for a property |
| Drawing to part | A tolerance is applied "typically" rather than to a named feature | A tolerance table with feature references |
| Part to acceptance | Test method unspecified, so both sides measure differently | Name the instrument, the temperature and the sample size |
| Acceptance to file | Records not retained past the project | State a retention period in the contract |
The single most effective sentence in an acrylic specification is a test method rather than a property. "Flat to 0.2 mm" invites an argument; "flat to 0.2 mm, measured on a granite surface at 20 °C with a dial indicator at five points" does not. The second version costs nothing to write and removes the entire dispute.
Where a framework agreement runs for years, add a clause about change notification: if the sheet grade, the supplier of the sheet or the process sequence changes, the fabricator notifies before supplying. That clause is what stops a compliant part in year one becoming a non-compliant part in year three without anybody deciding to change anything.
A review now is cheaper than a revision after award. We will tell you which clauses cannot be built as written.