mirror on mdf warping

[darylm]

Hi all

i recently hung a 1000mm dia mirror for a client. the mirror was fixed to 12mm mdf using mirror adhesive. on the reverse of the mirror i routed 3 keyholes to accept 3 coach bolts for invisible fixings.

I used mastic to to fill all around the mdf at the wall. then painted the visible mdf face.

all was fine and dandy for a couple of months. As time went on though the mdf (and mirror) started to cup untill the mirror exploded.

There are (apparently no visible signs of damp on the wall so I am not sure why this has happened???

12 mm mdf was used as this was the thinnest i could use with the key hole cutter. I have never had this problem with 18mm.

Any ideas???

Thanks in advance

Daryl

 

[gcol]

I think I'd be more inclined to use WBP plywood - it's more stable than MDF.

 

[Jasonb]

By sealing the back of the MDF all round you created an imbalance between the two surfaces. Even though the wall was not damp, overtime the relative humidity will change so only one side was exposed to these changes.

Would help if you didn't seal the back and used Moisture resistant MDF

Also when using mirror adhesive it should be applied in parallel lines or blobs so you do't trap any air, if you put it on in circles that will cause problems.

Jason