Drum testers tell you how a carpet looks after simulated traffic. The Lisson Tretrad tells you how much of it is gone. Instead of tumbling a ball inside a drum, it walks loaded, rotating feet along a tensioned strip of carpet, scuffing the pile the way shoes do, while travelling nozzles remove the fibre that comes loose.
The method is ISO 12951:2020, Textile floor coverings — Determination of mass loss, fibre bind and stair nosing appearance change using the Lisson Tretrad machine. It is the third edition and replaced ISO 12951:2015.
Four methods, four different questions
ISO 12951 is not a single test. The 2020 edition describes four methods for textile floor coverings, tested with or without underlay:
| Method | What it determines | Typical product |
|---|---|---|
| A | Mass loss; also used for fibre bind on synthetic pile carpets | Cut and loop pile carpets |
| B | Change in appearance at stair nosings | Carpets intended for stairs |
| C | Fibre bind | Synthetic loop pile carpets |
| D | Fibre bind (hairiness) | Needled and non-pile floor coverings |
Specifications that say only "ISO 12951" are incomplete. Ask which method — and whether the specimen is to be tested on an underlay — before quoting a result. The methods answer different questions, and their results cannot be converted into each other.
How the machine works
The principle is easy to describe and hard to reproduce. Using our two-station machine as a worked example of what the standard asks for:
- the specimen is clamped under longitudinal tension (on our machine, by a 20 kg tension weight);
- four-footed rotating heads, each loaded (15 kg per head without soles on our machine), travel along the specimen over a defined track — 800 mm nominal, defined by the standard's reference rather than by the full carriage stroke;
- the soles rotate slightly faster than the heads travel, so they slip as well as press — that slip is what scuffs the pile;
- travelling extraction nozzles follow the heads and remove loose fibre.
For Method A, the result is calculated from the specimen mass before and after testing.
Error 1: re-using the sole coverings
The soles are the abradant. ISO 12951:2020 requires new sole coverings to be fitted before each test — on a two-head, four-foot machine that is eight soles per test. They are made of a specified rubber compound with a defined thickness, hardness and surface profile.
Running a second test on yesterday's soles saves money and costs the result: glazed soles grip less, slip differently and remove less fibre. If your mass loss figures have been drifting down over a few weeks, check the sole log before you check the carpet.
Keep sole coverings from one approved lot, stored flat, away from heat and ozone sources. Rubber ages on the shelf.
Error 2: weighing a specimen that is not in equilibrium
Mass loss is a difference between two weighings of a specimen that may weigh hundreds of grams, and the loss you are measuring may be a small fraction of that. A carpet that gains or loses moisture between the two weighings produces a "mass loss" that has nothing to do with wear.
- Condition specimens to the standard atmosphere (ISO 139) before both weighings, for the same time.
- Use a balance with adequate resolution — our supply scope assumes an external 0.01 g laboratory balance.
- Weigh in the same room and the same way each time. A draught across the pan or static on synthetic pile is enough to move the last digit.
Error 3: loose fibre that was never part of the carpet
Freshly cut specimens shed loose fibre from the edges and pile tips before any wear has happened. If that fibre is on the specimen at the first weighing and gone at the second, it is counted as wear.
Prepare and clean specimens the way the method describes before the initial weighing — this is why a rotary brush cleaner belongs in a Tretrad laboratory — and treat the cut edges consistently.
Error 4: extraction that does not keep up
Fibre that is loosened but not removed is pressed back into the pile by the next pass. It stays on the specimen, the mass loss falls, and the carpet looks better than it is. Check nozzle height and suction on every station before a series, and clean the extraction path; a partly blocked filter is the usual culprit when two stations disagree.
Error 5: tension and underlay
A specimen that is under-tensioned ripples ahead of the heads and wears unevenly; one that is over-tensioned changes the way the pile stands. Use the specified tension weight and check that it hangs freely. If the method is to be run on underlay, the underlay is part of the specimen and must be recorded — type, thickness and condition.
Two stations, one laboratory
On a multi-station machine, the stations should agree with each other. Run the same carpet on both stations periodically and keep the results as a control chart. A station that drifts away from its partner tells you about its soles, tension or extraction before a customer does.
Report checklist
- ISO 12951 method (A, B, C or D) and edition.
- With or without underlay; underlay details.
- Sole covering lot, confirmation that new soles were fitted.
- Conditioning before each weighing, and balance used.
- Station number for each specimen.
Our two-station Lisson Tretrad carpet wear tester for ISO 12951:2020 Method A is built in our own workshop in Istanbul; see the ISO 12951 page.