Following the thread on mdf window boards vulnerability to water, I wonder if there is an explanation for the *bumps* in mine.
The securing screw head recesses were filled with polycell polyfilla and sanded to level. Prime, undercoat, topcoat in low VOC solvent based paint (Dulux trade brilliant white).
Now, two years later, the filler is noticeably proud of the mdf!
It is likely that a decorator attempted to wash off emulsion splash using water.
Mdf shrinkage? Corrosion of screw heads? Expansion of polyfilla?
I have fitted mdf pre-painted skirting and am about to cover up the screw holes. Any thoughts?