Tiling on mdf....

[Tricky Dicky]

Seal the MDF first, PVA will do.

Richard

[www.GymRatZ.co.uk]

Not MDF but I've had a problem with the floor tiles I laid onto green chipboard.

Originally we were simply going to extend the wood flooring into the new extension then, like they do, the good lady changed her mind and wanted tiles. To cut a long story short I'm still waiting for any remaining tiles to loosen. The ones that parted company so far have all been over the end joins of the chip board.

Needless to say my favourite anything-to-anything building adhesive has been used to re-attach the tiles to the floor. Gun Grade expanding foam!

Where possible I left securely fixed tile adhesive on parts of the tile to give correct height alignment with adjacent tiles. Sanded top surface of chipboard to remove any waxes etc., mist chipboard and tile underside with water, apply foam to back of tile and position. Add a few weighty weights that overlap to surrounding tiles to ensure the foam doesn't have chance to expand and lift tile and leave long enough for foam to fully cure.

Still haven't grouted the tiled floor yet but the tiles that have been re-fixed with foam are very solid and the one I did try and re-lift wasn't coming up without breaking so I left it alone.

You might want to hold the tiles in position with a bit of flat timber braced from opposite reveal or allow foam to fizz out a little before applying tile to MDF as this seems to break the external skin of the curing foam leaving a very tacky residue that seems to have very little ability to expand any further and can be held in position by hand for 5 minutes or so until foam has stabilised

Damping both surfaces before applying foam ensures a quick and full cure of foam.

Sounds like a bodge but I can't immagine anything else working as well or being as easy/quick/economical to apply. Gun and gun foam are invaluable. The foam doesn't go off in the gun either unlike stuff like Gorilla Glue that you use once and what's left inevitably cures in the pot.

Pete

[Kevin H]

With respect, PVA should never be used as a sealant before tiling. If it gets wet it will fail. Use something like Mapei Primer G which isn't expensive.

[Kevin H]

Would it be possible to overboard with something like 6mm cement board (hardibacker or similar)? If the MDF is mechanically well fixed into the window reveal then the cement board will give a much better surface for tiles to adhere onto.

If there is any risk that this area will get wet then getting rid of the MDF and replacing with WBP or 15/18mm cement board would be what I'd be doing. Also, use a cement based powdered adhesive - stay away from the stuff you get in tubs.

[Brian Gaff]

Oh please don't remind me... A wall, not mdf but block and plastered but not any kind of fixing at the top. Electricians rewire hose used power tools to cut out room for socket back box in next room, tiles fell of in bathroom due to wall motion. Bah humbug. We just cleaned off loose stuff checked for more loose ones and glued them back and regrouted. Been OK so far! Brian Brian

[The Natural Philosopher]

Dont f****ng bother. It merely makes the tiles more liable to fall off when half set.

[www.GymRatZ.co.uk]

They do have a solid support. As much as any "over joist" construction can give. They're not floating on foam, they're spaced on the original adhesive "ridges" with foam run between the gaps as created with the notched adhesive trowel when initially laid. The so called "flexible" tile adhesive I originally used has zero "flex" and the same amount on non-adhesion not just to the floor but to the tile surface too.

I put the tiles down quite a few months ago now but have been holding off grouting to make sure no more tiles are going to detatch themselves. Once the the grout is squeezed into any gaps they'll be as solid as they ever could be.

I don't envisage any problems the the re-attached tiles. Perhaps hairline cracks /might/ appear in some of the grout lines but that doesn't really worry me, they're all underfloor heated and the underlying chipboard is waterproof/resistant anyway so all will be fine.

Using foam to re-adhere them was an act of desperation in preference to scrapping the floor tiles which surpassed any expectations by a massive amount. They're pretty much on a micro-thin layer of polyurethane adhesive (foam without bubbles)which is proving to be an almost molecular bond between surfaces not some ishy-squishy "foam" that moves about. :)

[Jim K..]

Apparently something of a no no, but has anyone tiled onto MDF successfully?

It's a window reveal in a kitchen. Old tiles detached, hardly any old adhesive stuck to the MDF underneath.

Wondering what to use to stick them back?

TIA

[Jim K..]

Primer G instructions refer to use on gypsum & similar surfaces, this is MDF?

I think I'm going to use MS polymer adhesive.

[Jim K..]

Not without it turning into a major retile...

Mmmm

I was surprised how dry & intact it all was when I peeled the tiles off (with 99.9% of the adhesive stuck to their backs). I've ground all that off the tiles ready for refitting.

Seems MDF & traditional "tile adhesives" are incompatible, so I think I'll put my money on MS polymer adhesive a la "sticks like s*1t", then grout traditionally, & put a decent silicone fillet around any edges (e.g. pvc window frame) to try to keep potential damp (steam, condensation etc) creeping in.

[Jim K..]

Glued with what?