Moisture resistant MDF - advice please????

[Captain Slow]

I've got to do a bathroom next week and have just found out that the builder has used moisture resistant MDF (the green stuff) for a false wall for the shower enclosure and all pipe boxing. I have, previously, done the en-suite for the couple and had to fix ceramic tiles to a small section of the same MDF (I used Mapei D2 and it worked brilliant), but they want large format porcelain in the bathroom.

They have bought the tiles from Topps and, also, purchased BAL white single part flexi with porcelbond plus adhesive.

Can anyone advise whether I can use the BAL adhesive on the MDF or should I be looking for an alternative, please?

I normally use Ardex or Mapei and don't really know much about the BAL adhesives.

Many thanks in advance,

Daz

in my experience you can not tile onto mdf (moisture resisitant) or otherwise with any adhesive!!!!!!!!!!
m.d.f is basicly layers of paper!... we all tile on ply which is layers of wood.....and that is not a great tiling substrate (tile some ply with offcuts and flex the ply,you will see!), use wedi,hardi,no more ply or other cement board.

as a bare minimum overlay the m.d.f with ply and screw @ 6" centres (countersunk!)

[Captain Slow]

Thanks Protilers,
That was my thought pattern, too. When I turned up to do their en-suite and found the MDF I contacted the Mapei tech support who were more confident of the adhesive working with the MDF than they were of it drying quickly for tile on tile - Confused the hell out of me, but I decided to give it a go and it seems to be okay, hence my questions for the main bathroom. There's a lot of the effin MDF in their main bathroom so it could get very expensive having to replace it with Wedi? I don't think overboarding is an option as they are trying to maintain certain lines and heights (if you understand what I mean).

[GazTech]

[quote=protilers;59788][B]in my experience you can not tile onto mdf (moisture resisitant) or otherwise with any adhesive!!!!!!!!!![/B]
m.d.f is basicly layers of paper!... we all tile on ply which is layers of wood.....and that is not a great tiling substrate (tile some ply with offcuts and flex the ply,you will see!), use wedi,hardi,no more ply or other cement board.[/quote]Bal Mosaic-fix..[B]MDF ( internal dry areas only )/ plywood/ chipboard:
[/B]Ensure that sheets are capable of carrying expected laod without deflection,dry, securely fixed and rigid and that all fixings do not protrude.Where necessary insert noggins to support all board edges and to allow screw fixing at 3oomm centres. Seal the reverse side and edges with BAL BOND SBR. Do not seal or prime surfaces
that are to be tiled......MDF no good in wet areas...Gaz

well....i am surprised,as a retailer (of mapei) and a full time contractor (personally)
i can not belive that they would advise you to use a bucket adhesive (D2) to tile on mdf...odd!.........i will check myself!
anyway medium desity fibreboard and moisture [U]resistant[/U] (note resistant) fibreboard are not waterproof in any way!!!!!!!!!!!
mdf is an excellent product for cabnets,wardrobes etc...........but not in bathrooms...................but im gonna double check the adhesive situation!!!!!!!!!
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okay gaz.....there may be a product for tiling on mdf in [U]dry areas only[/U] with a lot of prep and expense, but what would you do.......really....

[Dave]

Any area's where the MDF have been used are going to be subjected to wetting needs to be tanked......I would use schluters kerdi mat and stick this to the mdf with rapidsetting flexi adhesive....this will make very little difference to the substrates thickness as it is only about 1mm thick.....but will make sure it is water tight.....



Schlüter-KERDI is a crack bridging waterproof membrane made of soft polyethylene, which has been covered on both sides with a special fleece webbing to anchor the membrane in suitable tile adhesive. Schlüter-KERDI has been developed for bonded waterproofing assemblies with coverings of tiles and pavers.

The waterproofing membrane should be bonded to an even, load bearing substrate with an appropriate tile adhesive. The tiles are laid directly on Schlüter-KERDI using the thinbed method. Other trowel applied covering materials or plaster may also be applied. Schlüter-KERDI-DS is a waterproofing membrane and vapour barrier bonded to a tile covering, e.g. for use in swimming pools and spa areas, as well as for commercial applications with high humidity levels. Vapour barriers also make sense for moisturesensitive substrates such as wood, plasterboard and gypsum plaster.

here is a series of photo's showing how easy it is to install..











all schluter products can be bought at CTD.....

[Captain Slow]

Thank you Gaz,

I think I follow your response, so just to be clear....
The MDF has to be secure and non-flexing, smooth and dry. I can use BAL mosaic-fix but must seal the reverse and side edges of the porcelain with BAL bond SBR?

For the wet area, i.e. shower enclosure, could I tank the MDF and then tile onto the tanked surface using the BAL flexi?

Originally Posted by Captain Slow

Thank you Gaz,

I think I follow your response, so just to be clear....
The MDF has to be secure and non-flexing, smooth and dry. I can use BAL mosaic-fix but must seal the reverse and side edges of the porcelain with BAL bond SBR?

For the wet area, i.e. shower enclosure, could I tank the MDF and then tile onto the tanked surface using the BAL flexi?

HOLD ON!!!!!! YOU CANT USE IT IN WET AREAS!!!!!!! i.e Shower........
and i agree with dave there is a tanking solution (not necc. kerdi) that will sort it.....but the cost is going up in labour and materials..........take the mdf out and replace with 18mm ply (glued and screwed!!!!!).............then all you need is paint on tanking.......much cheaper.....IMO........

[Captain Slow]

My sincere thanks go to Protilers, Gaz & Dave,

I'm gonna tank the MDF and then fix as normal, sounds like that is the way forward.


Wooah - Just seen Protilers last post. Can I not use a paint on tanking for MDF? does it have to be a sheeted solution, I've used Tilesafe in the past for a wetroom?

[GazTech]

[quote=Captain Slow;59804]Thank you Gaz,

I think I follow your response, so just to be clear....
The MDF has to be secure and non-flexing, smooth and dry. I can use BAL mosaic-fix but must seal the reverse and side edges of the porcelain with BAL bond SBR?

For the wet area, i.e. shower enclosure, could I tank the MDF and then tile onto the tanked surface using the BAL flexi?[/quote]If you use Daves suggestion yes,you can use white star...personally I would just take MDF boards off and replace with backerboards...then standard tank the joints...much cheaper, re- use MDF on a coffe table or rabbit hutch or summat

[Dave]

Kerdi is a faster tanking method......you can tile onto it as soon as you have applied it ( as long as you use rapisetting adhesive to apply the kerdi)..
And kerdi is not expensive..only about £7 a sqr mtr.....where as tanking kits ( soloutions ) are about £40 for a kit to tank about 3 to 4 mytrs and need to dry before tiling......just a thought mate.....lets us know how you get on...
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Soz gazza mate. ..Don,t use whitestar etc on top of kerdi..takes to long to dry....use cement based adhesives only......

Originally Posted by Gaz

If you use Daves suggestion yes,you can use white star...personally I would just take MDF boards off and replace with backerboards...then standard tank the joints...much cheaper, re- use MDF on a coffe table or rabbit hutch or summat

i am still wondering how you are going to fix the kerdi to the mdf...........mosaic fix?..... is that not for mosaics? extra white etc.......

this situataion is wrong because of the mdf......fixing the problem has gone off the radar..........and out of your bank balance, MDF = no good......ever..... to save everyone money and for you to get the job tell builder/customer remove unsuitable substrate and replace with a suitable one..... lets face it......no one ever blames the builder for his prep, all they say is our tiler is a...........(put own favorite profanity here!)......good luck!

p.s bucket adhesives are only good to a professional tiler for one reason.........4" ceramics in a kitchen splashback.....and even then the customer had to have supplied it!!!!!!!!!!!!!!!!!!!!!!!!