There is a version of uv stabiliser in the quotation and a different one in the goods. The gap between them is a tolerance, and it is where the money is.
What uv stabiliser actually controls in PVC slats
Without it, white goes yellow and colours fade within a season outdoors.
This is why two suppliers can quote the same headline price and deliver products that behave differently in the second year.
For PVC blinds and slats, the working range is required, stated in phr. Inside that band the choice is commercial; outside it, the product changes category and so does the price.
What required, stated in phr does not tell you
| Position | Value | Effect on PVC slats | Where it shows up |
|---|---|---|---|
| Floor | required, stated in phr | Lowest cost, least margin for process variation | Cold brittleness within a season |
| Working middle | required, stated in phr | Predictable performance at a normal price | Nothing to negotiate, nothing to explain |
| Ceiling | required, stated in phr | Best performance, highest cost | Cost the end product may not recover |
Buyers default to the floor because it is the cheapest compliant answer. That is rational until the first claim, and then the saving is measured against a replacement shipment.
The figure that decides the outcome is not uv stabiliser itself but the tolerance around it. A supplier who quotes required, stated in phr without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.
How to measure uv stabiliser
The reference method here is Impact at low temperature, run to -10 C drop test, with an acceptance of no crack. The method is the easy part; sampling and conditioning are where reports diverge.
Condition the sample before measuring. Results in this family move by 10-20 % between a dry laboratory and a humid one, and two labs can disagree on the same material without either being wrong.
Record the measured value rather than pass or fail. A marginal pass on uv stabiliser tells you the process is running at the edge, which is the information you need before the next lot rather than after it.
UV stabiliser does not stand alone
UV stabiliser moves with yellowing resistance (QUV 300-500 h, dE <= 3) and with heat deflection (>= 65 C). Tightening one usually costs money in another, and a supplier who accepts every tolerance without comment has either not understood the interaction or is planning to substitute.
This is why a specification written as a list of independent tolerances is weaker than one written as a construction. The list lets a supplier satisfy each line while missing the product.
The clause to write for uv stabiliser
The line below is the version we can quote against without inventing anything. UV stabiliser appears with a tolerance and a test, not as a standalone number.
PVC venetian blind, 50 mm slat, 2.0 mm wall, UV stabilised, QUV 300 h dE <= 3, HDT >= 65 C, co-extruded woodgrain, cordless to EN 13120
The clause that protects you is not the value, it is the sentence that says what happens when the value is missed. Put it in the purchase order, not only in the enquiry.
When uv stabiliser goes wrong
Cold brittleness. Slats crack when handled in an unheated warehouse in winter.
The cause is usually high filler content (calcium carbonate) to cut cost.
The test that catches it: Impact test at -10 C.
What to specify instead: Limit filler content and specify impact-modified compound for cold markets.
None of this is visible in a quotation. It becomes visible in a retained sample and a lot record, which is why the paperwork matters more than the price on this parameter.
Four questions about uv stabiliser, before you order
- What tolerance do you hold on uv stabiliser, and what did your last three lots measure against it?
- Which method do you use for impact at low temperature, and which laboratory signs the report?
- When uv stabiliser falls outside required, stated in phr, do you rework, downgrade, or ship and hope?
- Which of yellowing resistance or heat deflection would you move first to hit a lower price?
The answers are more useful than a certificate, because they show whether the process is controlled or merely inspected. Full ranges for PVC slats are on the product page, and the measurement regime is described on the quality control page.
Questions buyers ask before ordering
How does PVC compare with basswood on price?
Typically 20-30 % cheaper per set at the same size, and lighter to ship than wood but heavier than paulownia.
Can you supply fire-rated PVC?
Yes to EN 13501 B-s1,d0 with certification, at a price premium and a longer lead time.
From quotation to specification in seven lines
Leave the tolerance and the method out and every dispute is settled by whoever needs the goods more.
- Slat width (25 / 35 / 50 mm): fix the value per shipment, and state who pays for the re-test if a lot lands outside it.
- Thickness: 1.8-2.5 mm is not an answer on its own. Ask for the last three lots’ actual readings and the spread behind them.
- UV stabiliser: agree the test method with the number. Two labs, two methods, two answers, one argument.
- Yellowing resistance (QUV 300-500 h, dE <= 3): state where in the band this order sits. The middle of the band is not what a tolerance is for.
- Sample retention: one production sample per lot stays with the mill for twelve months. Claims are settled against it, not against memory.
- Test reports: name the standard as well as the test. A pass on a development sample is not a pass on a production lot.
- Deviation rule: anything outside the agreed bands is reported before shipment, not after arrival.
Questions worth asking before the price is agreed
The questions below are the ones that cannot be answered from a catalogue, which is exactly why they are worth asking.
| Question | Answer that should worry you | Answer that holds up |
|---|---|---|
| Who signs the test report, and against which standard? | “Our QC department signs it.” | A named standard, a named method and a signature that belongs to somebody who can be asked again next year. |
| How do you hold thickness inside 1.8-2.5 mm? | “That is standard for us, no problem.” | The last three lots’ readings, the instrument used and who signs the report. Heat warping starts here. |
| What happens if yellowing resistance misses the QUV 300-500 h, dE <= 3 requirement? | “It will not happen.” | A re-test clause, the tolerance on the re-test, and the point at which the lot is remade rather than discounted. |
Need uv stabiliser specified and tested against your end use?
Send a window schedule or a single set size and we will return a quotation with the loading plan, the safety standard that applies to your market and the lead time for the colour you need. Catalogue and current price list on request.
Related reading
- Pvc Slats for Commercial kitchens and labs
- Thickness in PVC blinds and slats
- What Pvc Slats Really Costs
Catalogue and current price list · Neutral packing and private label · Consolidation, documents and lead times
