Most paulownia specifications treat grain as a single number. It is a distribution, and the width of that distribution is what your customer experiences after a year.
What grain actually controls in paulownia
Coarse pores drink lacquer, so sealing coats are heavier.
That makes it a design decision rather than a purchasing one, which is why changing it after the product is fixed costs more than changing the material.
For Paulownia blinds and slats, the working range is straight, coarse pores. Inside that band the choice is commercial; outside it, the product changes category and so does the price.
What straight, coarse pores does not tell you
| Position | Value | Effect on paulownia | Where it shows up |
|---|---|---|---|
| Floor | straight, coarse pores | Lowest cost, least margin for process variation | Denting within a season |
| Working middle | straight, coarse pores | Predictable performance at a normal price | Nothing to negotiate, nothing to explain |
| Ceiling | straight, coarse pores | 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 grain itself but the tolerance around it. A supplier who quotes straight, coarse pores without a tolerance has not quoted a specification, and the first lot will define the tolerance for you.
How to measure grain
The reference method here is Janka hardness, run to ASTM D143, with an acceptance of report value. The method is the easy part; sampling and conditioning are where reports diverge.
Ask which instrument was used. For grain, two instruments that both claim the same standard can differ by enough to move a marginal lot from pass to fail.
Record the measured value rather than pass or fail. A marginal pass on grain tells you the process is running at the edge, which is the information you need before the next lot rather than after it.
Grain does not stand alone
Grain moves with coating (3-4 coats, sanding sealer first) and with hardness (low (about 1.5-2.0 kN Janka)). 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.
When you change grain, re-check the two neighbours before you approve the sample. Most of the samples we re-make are caused by a change in one figure that was not followed through.
The clause to write for grain
The line below is the version we can quote against without inventing anything. Grain appears with a tolerance and a test, not as a standalone number.
Paulownia venetian blind, 50 mm slat, 2.8 mm, density 0.25-0.32 g/cm3, moisture 9-11 %, sanding sealer + 3 coats, warp <= 2.0 mm/m, cordless to EN 13120
Write it once and reuse it. The buyers who avoid claims are not stricter than everyone else; they send the same well-written clause every time.
When grain goes wrong
Denting. Slats show dents and marks after a season of cleaning and use.
The cause is usually low density and a soft early-wood layer.
The test that catches it: Janka hardness and a drop test with a 50 g ball from 30 cm.
What to specify instead: Use paulownia for residential and low-traffic use; specify basswood or PVC for contract.
The pattern is consistent: the failure appears months after delivery, is hard to attribute, and the cost lands on the buyer. That is the argument for measuring grain on every lot rather than on the development sample.
Four questions about grain, before you order
- What tolerance do you hold on grain, and what did your last three lots measure against it?
- Which method do you use for janka hardness, and which laboratory signs the report?
- When grain falls outside straight, coarse pores, do you rework, downgrade, or ship and hope?
- Which of coating or hardness 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 paulownia are on the product page, and the measurement regime is described on the quality control page.
Questions buyers ask before ordering
Why is paulownia cheaper than basswood?
Faster growth, higher availability and lower density, which also lowers freight. It is not a cheaper process; it is a cheaper raw material with different mechanical limits.
Can paulownia be used in hotels?
Only in low-traffic areas. It dents under cleaning and trolley impact. For guest rooms we quote basswood or PVC.
Seven lines that turn a quotation into a specification
Most post-delivery arguments are not about quality. They are about a document that never said which figure would be measured, on which instrument, at whose cost.
- Coating: the figure you will accept inside the 3-4 coats, sanding sealer first band, the tolerance on it, and the method used to measure it.
- Hardness (low (about 1.5-2.0 kN Janka)): name the number, not the word. If the answer only repeats the band, ask which point inside it is being offered for this order.
- Warp tolerance: <= 2.0 mm per 1 m is the market band. Fix the figure you will test at goods-in, and the instrument you will test it with.
- Density (0.25-0.32 g/cm3): fix the value per shipment, and state who pays for the re-test if a lot lands outside it.
- Deviation rule: anything outside the agreed bands is reported before shipment, not after arrival.
- Packing and marking: shipping mark, roll or carton count and the tolerance on quantity, since a short shipment is a claim too.
- Who inspects: third-party, in-house or none, decided in advance, with the AQL level written down.
Three questions, and the answers that separate mills
If the paulownia figures on this page is going to be decided on a call, take these three questions into it.
| Question | Answer that should worry you | Answer that holds up |
|---|---|---|
| Which test catches patchy finish? | “We have never had a complaint.” | Warp — on the production lot, with the acceptance figure written into the report and not into the email. |
| May I see a report for a lot you shipped last month? | “That is confidential customer information.” | A redacted report, which carries every number that matters and none of the customer’s identity. |
| Where in the low (about 1.5-2.0 kN Janka) band will this order sit? | “In the middle, normally.” | A stated target and the readings behind it. Hardness drifting inside the band is how a conforming lot still fails. |
Need grain 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
- What Paulownia Really Costs
- Paulownia for Non-contract hospitality overflow
- Density in Paulownia blinds and slats
Catalogue and current price list · Neutral packing and private label · Consolidation, documents and lead times
