Orange stain on MDF that comes through paint

[bigtones]

We had some 18mm mdf boxed shelves made for our kitchen. i noticed a stain on the bare material, but even after a coat of primer and two coats of gloss, the stain remains. it's bright orange :(

There is no warping to indicate dampness in the mdf, and there are no screws through that particular bit that may have rusted. it seems to start in the corner and has spread out.

does anyone know what it might be, and have any ideas of how to fix it please?

thanks!

[rosebery]

Its leeching through the primer fairly obviously. What primer did you use? No undercoat for your gloss?

Technically MDF isn't wood at all - its chewed up sawdust held together with glue so it sucks moisture out of the paint like billyo.

Just priming isn't sufficient you have to seal as well. Personally I'd use Zinsser BIN to prime/seal the MDF but there are others on the market. Google MDF primer / sealer and you'll find quite a few.

Cheers

[bigtones]

Thanks for your help - i'll give it a go. do i have to remove the gloss layers now?

Anthony