MDF Painting - help problem solving

[lukecarson]

I need to finish MDF with a high gloss finish (ie car paint).

I have been told that about 6 months after it is painted it has a tendency to move slightly due to pre-existing internal moisture content (even if moisture sealed) which will mean the high gloss finish will look mottled.

Does anyone know any way to minimise this effect apart from respraying 6 months later???

Cheers

Luke

 

[Scrit]

MDF doesn't move due to internal moisture content - it swells because it is inadequately sealed, so seal the MDF properly to start with. MR-MDF (moisture-resistant, i.e the green stuff) is less likely to absorb atmospheric moisture and swell and so is a better choice of material if you can get it.

Sealing the surfaces requires MDF sealant, which most paint manufacturers such as Johnstone, ICI Dulux, etc make. The process is to "paint" with sealer then to flat back with fine sandpaper and to repeat the process several times. Flat surfaces require 2 to 2 coats of sealant, edges can require up to 6 or 7 coats as they absorb more. After sealing if the MDF is undercoated (in the same way you would undercoat a steel body panel on a car, and preferably with a high-solids undercoat) and flatted back, the top coat should produce an excellent and relatively impervious substrate for your paintwork

Scrit