Always paint both sides of MDF?

[Alko]

I'm planning to build a wall-mounted shelf in 16mm MDF and I'm wondering if it's okay not to paint the sides that aren't visible. I've heard that sheet material can warp if it's painted on only one side. Not sure if this also applies to slightly thicker dimensions. And surely it should be enough with just primer in that case?

 

[Avemo]

MDF is usually dimensionally stable as long as it is not exposed to moisture. And in that case, it is more likely to swell and lose its shape rather than warp. Painting only one side should not be a problem.

 

[jonmo]

I'm going to build a wall-mounted shelf in 16mm MDF and I'm wondering if it's okay not to paint the sides that are not visible. You sometimes hear that sheet material can warp if it's only painted on one side. I'm unsure if this also applies to slightly thicker dimensions. And surely it should be enough with just a primer if that's the case?

My custom-made trims in 19 mm MDF are not painted on both sides. There is no tendency for them to warp. However, I regret not painting both sides of my 27mm thick laminated desk, as I see a clear warping there.

 

[Plupp 284245]

Mdf warps significantly, just look at the outer/uppermost board in the stack at the carpentry. But things that are assembled with short distances between braces, shelves, etc., usually hold up well.