18mm MDF cupboard doors bowed

[Deansplit]

I'm making a fitted cupboard from 18mm MDF. The board has been kept in my garage since the start of the heat wave in this summer, so not exactly damp conditions. When I fitted the doors (2.4m tall) it appears they've bowed slightly, like MDF does when wet, but surely, even if slightly moist, will they not straighten out with the heat of the house/once acclimatised? They've been inside for 2 weeks and no sign of any change. Any ideas?... take off the doors and bend them under strain for a while (how?)

 

[Burnerman]

These boards need to be stored flat - any sagging in storage will be exaggerated if stored in damp conditions.
Ideally, once you've bought the MDF, make the door and hang it immediately.
It may be possible to turn the sheet over to help it flatten again but it doesn't often work.
Any coatings should be applied to both sides to keep the surfaces balanced.
John

 

[Deansplit]

Mmm, yeah, thinking about it, they were cut to size but then stored upright leaning against the wall... damage done! What way will painting one surface make it bow, ie. does the wet/paint make it curl into the painted surface or away from it? Just thinking because some doors are bowing different ways and wondering if i can therefore control the bowing to a certain extent by painting either one or both sides,depending on the direction of the bow to bring them back in line if that makes sense...?

 

[Burnerman]

Its the same sort of theory that has worktops having a laminate on both sides.....to balance any tendency to warp. Any surface treatments hold the moisture out, so absorption (no matter how slight) takes place on the other side.
Seriously, I doubt if you'll be able to correct things, but you've got nowt to lose!
John

 

[Deansplit]

wet the side which bows towards you at the ends? ie expand it a little to correct the bow?? :/

 

[big-all]

do not wet mdf
take them off lay them against the wall bow up against 2 strait batons and wait till the bow falls out-----










--------------------if your lucky

 

[Deansplit]

take them off lay them against the wall bow up against 2 strait batons and wait till the bow falls out-----

Seriously? Does it work, will the bow come out?

 

[big-all]

its a 50/50 chance just depends on your luck really
if you think off it mdf is an engineered board no internal stresses
the only forces are gravity and humidity so worth a try
the reason i don't say stack flat is to more replicate the pressures involved origionally
if it was solid timber i would suggest over bending around 20%
for example i had some 4x5/8" [88x12mm]t&g cladding that would have made a brilliant propeller all i had to do was to clamp one end off a plank by 12mm with a baton on top to protect the surface the other end was around 40mm off the plank one side and flush the other
so all i had to do was to sandwich it between 2x 20mm batons then a 20mm baton at the low edge raising the high edge to 60mm
then when i tighten the clamp it went the other way the 20mm
wet the surface then let dry over 2 or 3 sunny days
3 successive board treated this way and all went flat

if you use this method use the boards within a few days to stop them moving but remembering they may still shrink dependant on moisture content