Moisture resistant MDF - advice please????

[Daz]

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

 

[protilers]

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!)

 

[Daz]

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]

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.

Bal Mosaic-fix..MDF ( internal dry areas only )/ plywood/ chipboard:
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

 

[protilers]

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 resistant (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!!!!!!!!!
----
okay gaz.....there may be a product for tiling on mdf in dry areas only with a lot of prep and expense, but what would you do.......really....

 

[DHTiling]

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.....

 

[Daz]

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?

 

[protilers]

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........

 

[Daz]

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]

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?

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

 

[DHTiling]

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...
----
Soz gazza mate. ..Don,t use whitestar etc on top of kerdi..takes to long to dry....use cement based adhesives only......

 

[protilers]

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!!!!!!!!!!!!!!!!!!!!!!!!

 

[Daz]

I'm supposed to be starting the job on Monday so getting the builder back in could be an issue. I'm gonna take a look at what he has done tomorrow and see how much work is involved in ripping out the MDF.

On the tanking front, the Tilesafe tanking that I have used has a very aggresive universal adhesive and sticks like the preverbial to a blanket. I may suggest this to my customer but will make a, now, informed decision tomorrow.

 

[DHTiling]

We know the MDF is not the best substrate for bathrooms but tanking will do the job ..as for kerdi...you use a rapidsetting flexi cement based adhesive..it will set before moisture from adhesive soaks into MDF...

Ripping the whole lot out will cost the customer a packet...we are trying to offer an easy option here not full re-fit......

god luck captain slow and let us know how it goes..........

 

[protilers]

We know the MDF is not the best substrate for bathrooms but tanking will do the job ..as for kerdi...you use a rapidsetting flexi cement based adhesive..it will set before moisture from adhesive soaks into MDF...

Ripping the whole lot out will cost the customer a packet...we are trying to offer an easy option here not full re-fit......

god luck captain slow and let us know how it goes..........

dave with all due respect......i do not know of an adhesive (even s2) that a manafacturer will reccomend to stick to mdf in wet areas, even if its (just) sticking kerdi....the important fact here is the expense.....even if you have to pay a carpenter to come and remove the mdf ad replace with 18mm ply ...£150 (example) per day @ 1 day.......
captain to tank at (example) £150 per day @ 1 day

total prep = £300


plus 18mm ply 8" x 4" ft @ £40 and tanking @ most expensive bal wp1 = £70


all in £410..........and no leaks and no problems.....do the time and motion calculation, any other way costs more and has more chance of failure due to multiple substrates flexing against each other! IMO.

p.s you will not have to rip it all out......just the mdf.......fein multimaster.....mmmmm

 

[DHTiling]

Lee..as you say adhesive manufactures will not guarantee there adhesives on MDF in wet area's...but that is if tiling onto MDF...If kerdi was used onto MDf then no moisture can penetrate it..thus no problem with delamination or swelling.....that's what tanking membranes are for....I know what you are saying about tiling onto MDf and yes you are right....but using a tanking membrane or similar will do the job no probs......and so will ripping the whole lot off and using backerboards....

 

[Ric]

brill post, very interesting lads, i have bath panel to tile (mdf) with mosaics and was going to use mosaic fix as it says you can as long as not primed , but, it also says dry internal areas. Didn't really want to board over the top as i think it would bring the tile out too far, the kerdi option looks good can u buy as little as a square metres worth?

 

[DHTiling]

brill post, very interesting lads, i have bath panel to tile (mdf) with mosaics and was going to use mosaic fix as it says you can as long as not primed , but, it also says dry internal areas. Didn't really want to board over the top as i think it would bring the tile out too far, the kerdi option looks good can u buy as little as a square metres worth?

You certainly can rik mate......You will get it at CTD.....

 

[tiler burden]

this is why tilers should prepare and advise on substrates when it affects the areas they tile.

general builders are a pain in the r's. i totally agree that there is no way that green mdf should be used in a continual hot/wet area. ok the tanking will prevent water penetration, but moisture can build up behind the tanking area due to condensation and eventually break down the mdf. maybe not in a years time but it can and does happen. australian and american tilers will vouch for that..

any area that has extreme variations to temperature changes can be affected by condensation..if you have ever worked on loft conversions you will realise that the plasterboards in the loft need to have a foil backs to there underside and there has to be a vapour barrier behing them also,,,,this is the same principle really.

the building world is a fast moving enviroment and wedi boards and backer boards have been introduced because they are the best solutions available today.

just make sure that if the tiling fails, then the customer is aware that you cannot give a 100perc gtee because of the mdf that the builder installed, cover you backside and hold him responsible...good on top of bad doesnt necessarily = good??

 

[protilers]

Lee..as you say adhesive manufactures will not guarantee there adhesives on MDF in wet area's...but that is if tiling onto MDF...If kerdi was used onto MDf then no moisture can penetrate it..thus no problem with delamination or swelling.....that's what tanking membranes are for....I know what you are saying about tiling onto MDf and yes you are right....but using a tanking membrane or similar will do the job no probs......and so will ripping the whole lot off and using backerboards....

what about the moisture in the adhesive dave (in the two hours, if rapid,12 hours if normal set adhesive ),as mdf is (kinda) laminated........what if the first 1mm/2mm of mdf blow (expand) from the moisture in the adhesive......the tiles are gonna hold up for a while.......but i would not want to do a tap test (knock,knock!).......
----

 

[grumpygrouter]

what about the moisture in the adhesive dave (in the two hours, if rapid,12 hours if normal set adhesive ),as mdf is (kinda) laminated........what if the first 1mm/2mm of mdf blow (expand) from the moisture in the adhesive......the tiles are gonna hold up for a while.......but i would not want to do a tap test (knock,knock!).......
----

Not having been in the trade for very long, I am a little confused by your strong argument about tiling onto MDF. Not so much about tiling onto a wood based product, just that you seem to be implying that BAL, the leading British adhesive manufacturer for tiling are wrong. They quite clearly state in their literature that Mosaic-fix (for instance) can be safely used to tile onto MDF as long as it is done correctly. If you comply with BAL procedures, they will even guarantee the installation for ten years where their products are concerned.

Ardex have a similar assertion with some of their products and I have no doubts other adhesive manufacturers do too.

Weber incidently stipulate that moisture resistant MDF is not a suitable surface to tile onto. Normal stuff apparantly is OK.

Are you saying they are wrong?

Grumpy

 

[protilers]

grumpy......

i just think there is a more economical and stable way to do things,
i typed a bigger post and my internet crashed....sooooooo............
i am not saying anybody is wrong.....anybody...just if you can get from a to b securely (tried and tested) why go to c,d,e and f.....?

p.s mosaic fix is for mosaics? (does as it says on the tin....?)IMO
p.p.s MDF sould not be used in showers or other "wet" areas IMO

what i am saying is if you are a tiler,and your reputation and livlyhood depends on it............m.d.f......is it any good to tile over?

IMO...regardless of the (possible) soloutions.....is it not better to go back to the tried and tested.....i.e ply (which is still risky....will create a post) ,wedi etc..........
if not for the customer, then for your reputation as a professional tiler.....you can offer value for money and a professional job....... and a guarentee......

p.p.s adhesive manafacturers are never wrong....ever...........it will always be your fault......even if you followed the instructions to a tee.........amount of water,lack of water,too thick of a bed,too thin of a bed, not 70% coverage,wrong adhesive,underfloor heating problem.......not to sat this has happend to me.....being a retailer i have heard the storys........cover all bases...

 

[JOHNNYCLARKE]

Have To Agree With Protilers And Tiler Burden Covered Every Angle.

So Nothing More To Add.

Just Make Sure If You Do Anything That Your Adhesive Manufacturer Does Not Guarantee That You Do Not Guarantee It Yourself Even If You Think You Are Saving Client Money.

You Did Not Put The Mdf Up But You Have A Duty Of Care To Advise Your Client The Correct Way Forward.

Johnny

 

[IvegotsTILE]

Let me lighten the mood.
The pictures you put up Dave of the kerdi installment,is that one of the chuckle brothers doing the work

 

[Monsoon]

Stick the Kerdi on the MR MDF with contact adhesive

 

[DHTiling]

Let me lighten the mood.
The pictures you put up Dave of the kerdi installment,is that one of the chuckle brothers doing the work

He does look like a chuckle bro doesn't he....:lol:

 

[Dan]

Some of the threads in the tiling forum that have had a lot of views are being bumped up into current discussion. Just walk on by if it's not your flavour right now. Perhaps it'll help somebody out one day, and they become members, and then they post a thread, and professional tilers respond, and then you learn something from them...? Maybe?

 

[Gabriel]

Do i need to prine water restaurant mdf before putting lining paper on it