MDF shrinkage and painted furniture

[flanajb]

I recently built a tv cabinet which I sprayed white with a water based finish. The unit was in the garage loft for the summer and the mdf carcass and poplar frame on the front shrunk as the invisible joint which I spent a long time getting became visible. I then resanded it back down and resprayed the unit. It looked really good.

I brought the unit into the house. The same has happened again and I am trying to work out why this is happening. If I was to use an oil based finish would this make the unit less susceptible to the unit being able to take on / lose moisture?

Thanks

 

[Jacob]

Probably different amount of movement between the mdf and the poplar. Which makes it a design problem; how to allow movement to take place and hide the gaps.

 

[flanajb]

Probably different amount of movement between the mdf and the poplar. Which makes it a design problem; how to allow movement to take place and hide the gaps.

That makes sense. So basically a planted face using poplar is not the way to do it. Maybe I should use birch ply for the carcass and the same for the face of the unit.

 

[Paul Chapman]

I am trying to work out why this is happening.

It's happening because the wood is expanding and contracting with changes in humidity but the MDF and paint isn't, so cracks will appear. I've made some MDF doors which have been lipped with solid wood and painted and after several years no cracks have appeared. I've put this down to luck and concluded that there is not much change in humidity in the place where the doors are. I don't think using a different type of paint would help much.

Cheers :wink:

Paul

PS probably better to make it all from MDF.

 

[Jacob]

Probably different amount of movement between the mdf and the poplar. Which makes it a design problem; how to allow movement to take place and hide the gaps.

That makes sense. So basically a planted face using poplar is not the way to do it. .....

Dunno depends on the design. Photo? There are plenty of ways of making different materials work together - that's what I meant by design problem, as distinct from a material problem.

 

[Steve Maskery]

If you do this kind of project again, it's well worth paying a bit more for MRMDF. Got to be a help.
S

 

[No skills]

Bit of a worry, I had planed to make some cabinets/doors and shelves from mdf and lip them with solid timber (of what ever kind I have laying around) - are they doomed from the start?