Moisture resistant MDF

[RogerS]

As part of the flat refurb I hid all the pipework behind MR MDF..mounted onto 3x2 inch battens fixed to the walls. I've now noticed that where the joins are, fine cracks keep appearing in the paintwork. Has to be minor movement although the flat is in a stable (?) old concrete building...so maybe minor changes in the battens, I guess. Can't be moisture as it's not been used in anger yet.

I used 18mm MR MDF but wondered whether 12mm MR MDF might be better crackwise, as I have another identical flat to do? Certainly lighter 8)

 

[judder]

Is the MDF just painted Roger ?

if so then it will crack the paint at the joints no matter what you try. I recon you would still (even though its MDF) need to use joint tape and velvet to smooth the joints and should prevent cracking.
HTH.
Stephen

 

[RogerS]

Is the MDF just painted Roger ?

if so then it will crack the paint at the joints no matter what you try. I recon you would still (even though its MDF) need to use joint tape and velvet to smooth the joints and should prevent cracking.
HTH.
Stephen

Hi Stephen...yes it is just painted. Velvet?? Can you please explain a little more? Thanks

Roger

 

[judder]

Think it might be a slang term. It's the mix plasterers use afterusing fastset to fill in the finer defects and it sands easier than fastset.
I bought a bag from my local builders merchant - about 15GBP - expensive compaired to 5GBP for fastset, but worth it when it comes to sanding. I would also use the self adhesive mesh joint tape instead of the regular stuff.

Stephen

 

[RogerS]

Ah..I see..but wouldn't the plaster also crack at the same point?

 

[judder]

Sorry Roger, I can't guarantee it won't crack through time, but it will certainly be better than not being there at all. The mesh tape is supposed to bind the two surfaces together, then feather over the tape with the velvet.

Stephen

 

[RogerS]

OK - thanks, Stephen. I'll give it a try.

 

[jasonB]

Roger, did you glue the joints or just screw the boards to the battens?

All my built in painted furniture is done in HR MDF and I have not had this problem on exposed joints.

Just out of interest, I left a small wedge cut from 18mm MR buy my pond a few months ago, the 18mm dimmension is now in excess of 25mm :!:

Jason

 

[RogerS]

Jason

I just screwed the MDF to the battens ..which are substantial in size ..3 x 2 inch.

Roger

 

[judder]

I left a small wedge cut from 18mm MR buy my pond a few months ago, the 18mm dimmension is now in excess of 25mm

Resistant, not proof !

 

[JFC]

I agree with Jason , glue the joint , i do this on all my wardrobes etc and dont have a problem with cracking . Another way would be to mitre the joint . Maybe the problem is the pipes are heating the void in the box and making the timber move ? I normally box in using mdf batterns on the wall and let the mdf do the work for the rest of the boxing structure (if possible) it saves on timber and works just as well .

 

[trevtheturner]

If they are just 'hairline' cracks, Roger, I suspect that temperature variations are the cause. When you have covered the joints, I suggest you use a flexible paint (Polycel Evenceil or similar) designed to cover hairline cracks when re-decorating before applying final paint finish. I have found this successful with plasterboard ceilings and minor cracks in walls.

Cheers,

Trev.