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?