Dry mounted posters curving

[WannabeFramer]

Just curious what I'm doing wrong.

I dry mounted some posters in the hot press, onto display board. Cooled them under weight, all good and perfectly flat so I put them in the plan chest for a few days until I was ready. When I took them out, all the boards have curved.

These are only for me so aren't a huge issue, but I wonder what made them curve after a few days, when they were completely flat and cold before I stored them? I have a few more to do so would like to perfect the technique going forward.

(Just to pre-empt, humidity and temperature in the workshop are all fine).

Thanks as always.

[Tudor Rose]

You are bonding something to the surface on one side of the board - and then leaving it loose, ie flat in a drawer. So that side will naturally want to curve inwards towards the thing you have bonded to it. The reason we don't tend to notice it, is because we pop them into frames where they are held differently.

If you want to leave them loose long term, then bond something to the other side of the board to counteract the effect.

[WannabeFramer]

Thanks Jo,

Ahh, that makes sense.

So if I were to have put them in frames shortly after mounting, they wouldn't have curved? Or they still would, but the pressure of the frame package just counteracts it?

Can I bond anything to the back if I need to? Thin board or does it need to be more technical?

[Tudor Rose]

The pressure from being in the package of the frame would have curtailed the curve, keeping them visually flatter.

Effectively if you bonded something the same thickness/weight to the other side it should counteract it. Don't get too technical, common sense approach.

Worst we ever experienced was some hand painted silk de gournay wallpaper which needed to be bonded to panels. We got a specialist company to wet mount it for us and they were stunned because the board curved like a banana. Their only experience had been putting it onto walls so they had no idea it would do that. They bonded plain wallpaper to the other side and it resolved it.

[WannabeFramer]

Thanks,

These are only for the kids rooms, so I am going to experiment bonding something on the back of the next batch and see if I can get them to stay flat. Just for curiosity really.