UV stabilisers work by being used up. Absorbers take the energy and dissipate it, moving a little each cycle; hindered amine stabilisers are regenerated in the reaction they interrupt, but not indefinitely. So the right way to think about a stabilised crate is not “UV resistant” but “rated for a certain amount of sunlight”, and the number is only meaningful next to an exposure figure.
Why supplier claims are hard to compare
Two suppliers can both say UV stabilised and mean very different things, because the loading level, the additive type and the test method all vary. Accelerated weathering tests use a defined light dose, and a result quoted without the dose is not a result. Ask for the test standard and the hours or kilojoules, and be suspicious of any claim that has no number attached to it at all.
What a realistic outdoor life looks like
For a crate with a proper stabiliser package living outdoors year-round in a high-sun region, several seasons before crazing appears is a reasonable expectation, and longer than that if the fleet is nested and shaded. For a crate stored indoors for most of the year, the stabiliser is effectively never consumed and the crate will likely be retired for other reasons. The gap between those two cases is large, which is why a single “lifespan” figure is misleading.
The stabiliser migrates
Additives move slowly toward the surface, where they are washed or rubbed away, and the reservoir in the middle of the wall replenishes what is lost until it is gone. Frequent pressure washing accelerates that loss. It is one of the reasons a wash regime matters to outdoor crate life, and it is worth considering alongside the chemical question discussed in washing and sanitising reusable produce boxes.
How to tell when it is spent
Chalking is the signal. Once a surface blooms after washing, the protection at that surface is gone and the rate of damage increases sharply. At that point the crate will usually give one more season of light use and then start cracking. Grading the fleet on that signal – move chalking crates to indoor or short-cycle work – gets the most life out of the purchase.
Buying the right grade
Paying for a high stabiliser loading on a fleet that lives in a cold store is wasted money. Paying too little on a fleet that sits in an orchard all summer means replacing crates a season early. The question to answer before buying is how many months a year the crates spend in direct sun, and the honest answer is often “less than I assumed” once someone actually counts.
What stabiliser does not fix
It does not protect against impact at low temperature, it does not stop stress cracking from aggressive cleaning chemicals, and it does not make a crate immune to being driven over. A stabilized crate with a crack in the base corner is still scrap. Where a fleet is failing, look at the failure mode before assuming the answer is more stabiliser.
What to ask for on the datasheet
Ask for the stabiliser type, the loading level if they will give it, and the weathering test with the dose. A supplier who can provide all three is selling a specified product; one who says “UV stabilised” is selling a claim. Neither is necessarily a bad crate, but only one of them can be compared.
Then match it to the exposure. Count the months the crates spend outdoors and in sun, and be honest about it – a fleet that is nominally stored indoors often spends half the year in the yard, and that is the gap between the specified life and the observed one.
What we can do
We supply produce crates with the stabiliser loading matched to the exposure, and we will quote both an indoor grade and an outdoor grade rather than one price for both. Tell us the region and how much of the year the fleet is outside.