Tiling on chip board previously exposed to water

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dylanswall

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I have removed the old tiles from my bathroom and have now seen the hash that the previous owners made of the bathroom (and the whole house).

The old tiles were stuck onto onto chip board, with no waterproof sealant laid down. Water has got beneath the tiles and there are areas that are a bit black with mold, which I have scrapped down and throughly dried.

In removing some tiles, some chunks of mdf were pulled off off leaving a couple of holes the size of a small plate, about 5mm deep.

So my questions are (having never tiled before):

Do I need to fill the holes with some sort of filler (if so what) or can I just tile over.

I am going to waterproof the MDF first, is there any particular product that stands out or is any old stuff from B&Q all that is needed.

There is an ever so slight bow to the MDF wall, so which tiles are best to use: mosaic, small or large (I am favouring large for saving time and because of the holes plus have heard mosaic tiles show up uneveness in the wall).

Is there anything else I should know about tiling on MDF, or tiling in general (baring in mind I am a virgin at this)
 
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Cheers for the reply but I made a mistake, it is actually chip board.

How does that alter the equation?
 
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The chipboard wall

The chipboard wall


Thought I would post a picture so you could have a laugh at the state it is in.

I assume I am right in thinking my only real option is to rip out the chipboard and replace it? I am a bit of a novice so thanks for all the help but have a few more questions as a result:

1) if my only option is to rip it out and replace it, what is the best and/ or cheapest and/or easiest to fit material to replace it with (people have mentioned waterproof plasterboard or is there an alternative).

2) Obviously the chipboard stretches from floor to ceiling (I reckon I know the answer to this, but just in case there is another option) does that mean I now have to remove the bath and do the whole wall, then stick the bath back, or is there a way of just using waterproof plasterboard (or whatever is suggested) from the bath up, and sealing it at the bath level with sealant, saving me a lot of work.

If that is an option, would I need to put it on top of the chipboard, or maybe cut out the chipboard from the top of the bath to the ceiling, and then fix the plasterboard straight to the wall?
 
Last question.

I have had a look at the chipboard the whole wall is made of two sections, one which has the majority of the rotted stuff on (as per picture). The second piece finishes about 6 inches from the end of the bath (non shower end) and forms the wall that the basin is on.

My question is, if I replace the rotted chipboard with tanked, waterproof plasterboard, do I have to do the whole wall or just the rotted section that has direct contact with water from the shower? As the section at the end of the bath will have virtually no exposure to water, can I waterproof that chipboard and tile on to it or is tiling onto chipboard a no no, even if it will never get wet?

Thanks in advance for all the help.
 
You don't need to buy water resistant plasterboard - the ordinary stuff will be fine if you waterproof it with a tanking product.
You can tile onto chipboard (walls only) so long as it's not in a wet area. There's no need to waterproof it - just use a decent premixed adhesive like Bal White Star. This is good stuf and is flexible too.
For tiles, the larger the better around a shower area. I'd recommend not going for a tile larger than 300mm x 300mm because you can get problems with premixed adhesive not going off (setting) properly.
Have a read of the sticky at the top of the tiling forum.
 
your problem if you really wanted to keep chipboard near water is that you'd have to waterseal behind the chipboard... around all its edges etc, which means taking it it all out to do so.... and waterseal aint that cheap.

did you check if the board under the bath rim got rot as well?

you may as well rip the bath out, joists/studs could have rotten underneath, better to be safe if it your own house.

b/
 
I have looked underneath the rim of the bath and it isn't to bad. Water had got down there but wasn't trapped between the chipboard and tile so it hasn't gone rotten but just left a watermark.

I am thinking ripping out the bath etc is maybe a job to far for me, plus I have limited time on top of work and need it done (ideally) before the end of the year
 
I cant answer you on that cos i'm not in the trades, but if i did (from what i remember) their floors would all be on the same level and they'd be able to change bathtubs without breaking tanking/tiling.

dylan, i'm gonna do something to a bit of chipboard that i havent had cause to try before, but for curiousities sake... will take about 2 days to cure but if it seems to work i'll let you know

b/
 
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