Quick question on MDF movement trays

[Charlie_]

I've got lots of MDF movement trays which are going to be painted up soon, and was wondering if anyone had any thoughts on whether I'm going to get the dreaded warping.

My plan is to use filler to smooth out the joins between the two layers. Then spray them black. Then apply sand to the tops of the edges with PVA, and then seal the sand with watered down PVA. Then add small clumps of static grass with PVA.

Is warping going to be an issue? Anyone have lots of experience with MDF movement trays, particularly large ones?

Is it worth sealing it with something as the very first step? Spray varnish? Watered down PVA?

[SBRPearce]

You want to avoid any product that saturates the surface of the MDF - that face will swell, causing the whole piece to bend in the opposite direction.

Solvent-based products - that evaporate quickly - will help minimize this. A couple of coats of spray varnish as a base-coat will protect the material from swelling. If you can, apply whatever product to both sides at the same time.

A trick I learned while painting (full-sized) cabinet doors is drying things on a nail-board - pound a dozen or so thin  brads or nails through a piece of plywood or MDF so it looks like the proverbial bed-of-nails, then use it as a drying rack for pieces painted/sprayed on both sides. Don't forget to get the edges at the same time, too.

Once your pieces are sealed, you should be able to landscape them without much risk. Beware of thick coats of air-dry clay or PVA - those shrink slightly as they dry and can pull the piece into a warp.

[Calimero]

@SBRPearce, I have a similar question... would you also recommend to spray all the movement tray pieces before glueing them together?

Cheers!

[Charlie_]

Thanks for the info. I'll give them all a couple of sprays of varnish before the first stage (filler).

[Jabba]

Not had any problems with MDF figure bases, up to 90mm by 60mm, which i undercoat with acrylic paint then glue down sand with pva before more paint/pva and flocking. Maybe this is due to the smaller surface area vs thickness, 3mm.

On another topic where in Norfolk do you game Charlie?