Crates crack, and the instinct is to repair them. In almost every case the repair costs more than the crate, and the repaired crate is still weaker than an uncracked one. The useful decision is not how to fix it but whether it can stay in service as it is.
Why repair works badly
PP does not glue well without surface treatment, and a crack is a stress concentrator that adhesive does not remove. Mechanical repairs – a plate, a rivet, a strap – add a hard point to a part designed to flex, and they tend to start a new crack next to the old one.
Welding works, and it is what a moulder would do. It needs equipment and a skilled operator, which means the repair costs more than the crate unless the crate is expensive and custom.
The decision that actually matters
Sort cracked crates into three piles rather than two.
Fine as they are. A crack in a non-structural area – a vent, a corner of the rim, a scuff on the base – that does not affect stacking or load carrying. Keep using it, mark it if you want, and move on.
Downgrade it. Not safe in a stack or on a conveyor, but fine for static storage, yard use or as a liner. This is the biggest pile and the one most operations throw away.
Retire it. A crack through the base, a cracked handle root on a crate that gets carried loaded, or any crack that has opened enough to flex when you press it. These fail, and they fail with contents on the floor.
The two cracks that always mean retirement
A crack across the base, because that is the load path and base failures drop their contents. And a crack at a handle root on a crate that is carried by hand when full.
Handle failures in particular are worth taking seriously; the pattern is described in why picking box handles tear, and the same geometry applies to crate handles.
What to do with retired crates
Recycle them. PP is widely recycled and a cracked crate is good feedstock, which is the one genuinely satisfying answer in this whole area. Grinding on site is usually not worth it; baling or collecting for a recycler is.
How to reduce the rate
Most cracking is dropping and dragging rather than load. Two-handed carrying, not dragging loaded crates across rough floors, and not over-stacking are the three that matter. None of them cost anything.
Write the retirement rule down
One sentence, on a wall: a crate goes out if it has a crack across the base or at a handle root. Anything less severe gets downgraded. Without a written rule, the decision is made differently by every person who picks up a cracked crate, and the inconsistent ones are the ones that fail with contents in them.
Two categories is the right number. Three is workable. More than that and nobody applies it.
What we can do
We make PP crates for fruit and vegetables and will tell you what grade reduces cracking in your conditions – which is usually a resin question rather than a thickness one. Tell us how the crates fail and we will say whether a different specification would help, including when it would not.