Hello all,
Not sure if this should be here or in the painting and decorating section but here goes,
I am in the process of converting a small study into a utility room and want to tile above the worktops and sink.  The walls are plasterboard and have been painted many times with emulsion, is this ok to tile straight over or do I need to prepare the surface in any way?  The new paint I am going to use is moisture resistant so I will not paint the area to be tiled as I could imagine this may interfere withe the adhesion, correct? ???
All help appreciated.
Big-e

The following may or may not work - I haven't tried it, but it is an enhancement to ColG's suggestion.

You can buy a wallpaper scorer from the DIY sheds (I bought one in Focus DIY). You run that over the surface and it cuts into the wallpaper, or in this case paint.

That might give you a quick and easy solution to preparing the paintwork. I think tiling directly onto the paint may cause problems because the paint is presumably water resistant, if so the tile adhesive may not bond to it properly.

You could always try a couple of tiles first and let the adhesive dry overnight. If you can peel the tiles off the wall the next day without much effort then you are going to have to key the paintwork.

Andrew

Thanks for the advice,
Scoring the wall sounds like the way to go, the moisture from the adhesive wont make the plasterboard turn to mush will it?
Cheers,
Big-e

If you were working with bare plasterboard then you might begin the tiling operation by painting with PVA adhesive and allowing that to dry overnight. That prevents the plasterboard from sucking the moisture out of the adhesive too quickly.

Andrew

run a skil saw over it in loads of lines about ¼ way deep. lots of dust later and it might bend, will probably just snap off though! yeah on more thought don't bother with that idea.

big-e
Couldnt you use bendable plywood?
This is fairly thin and has the grain of each layer in the same direction allowing it to bend to quite small radii.
I'd make a frame to fix the ply to that will prevent movement when the tiles are stuck on.
If it's a small curve you may get away with just supporting it in the middle of the curve.

I dont know if bendable ply comes as marine ply.
It's not something I've used.
I've seen it used on curved furniture but not for anything else.
It was just a thought.
I've seen plasterboard dampened then bent in a curve but it was a very shallow curve over the full 8' of the sheet and great care was taken doing it in the hope it didnt break.

cut your plasterboard to required size lean it up against a wall and wet it. it will bend overnight do not try to manually bend it or you will snap it.

alternatively you could score the back of the board, where you want the curve to be score the board vertically  about 1/2inch apart for 5inch make sure all scores are perfectly in line with each other. then snap along all the scores. so one side of the board wil have lots of cuts and your facing side will be intact bit will make a curve.

found the comment mudster made, he seems to know his stuff...............

Re: Tiling On Concrete
Posted: Aug 22, 2004 5:09 PM      Reply  


Hi Squeaky,

I took a look at the webstie you linked, this sadly is the misinformation I'm faced with on a daily basis.

I should expand on who I am and why I appear to hate PVA so much!

I'm a professional tiling contractor, I now mainly specialise in natural products but over the years I've stuck up (or down) every type of tile there is.

I have to give guarantees for my work (many of these projects are commercial such as sports centre showers and changing rooms). For me to be able to give guarantees I need to follow strictly the specification of the adhesive manufacturers.

Ardex, BAL and Nicobond are the three suppliers I use most. Their products are similar in many respects, sometimes one will make products the other don't, and I also find some of there products more useful in different applications. All three of them have one thing in common, they all specifiy that under no circumstances may PVA be used before using any of their adhesives. If you do all guarantees are void.

OK why then? Well I asked this question to Ardex when I once had problem, I'd tiled a bathroom that had been constructed in 25mm Marine ply. Thinking he was doing the right thing, the builder got his guys to seal the ply with unibond PVA...I wasn't aware of this.

I tiled it and 6 months later every single tile fell off the ply, the adhesive solidly stuck to the tile but came clean a whistle off the ply.

We had Ardex Technical down to the site to compile a report, the basis of which was it's the PVA that causes the problem.

When you treat a surface with PVA it partly soaks in and parlty sits on the surface of the substrate much in the same way as wallpaper paste.

If PVA gets wet it becomes slightly live again, it doesn't completely return to it's liquid state but it becomes sticky.

When you spread tile adhesive onto the wall, the water in the adhesive makes the PVA live and stops the adhesive from penetrating the substrate and providing a mechanical grip. Basically your tiles, grout and adhesive are being held to the wall by a thin layer of PVA.

Most tile adhesive works by crystalising when it sets (some are slightly different such as epoxy based ones) but generally they all work the same way. Once the adhesive starts to set crystals from and expand into any imperfections in the substrate surface (at a microscopic level) to create a grip. PVA stops this process by creating a barrier between the substrate and the tile adhesive.

Ok so whats the difference between this and Ardex or BAL primer, well basically the tile manufacturers primers soak right in to the substrate and stop the sponge like "draw "effect but they don't coat the surface in any way, they are an impregnator as opposed to a barrier.

I hope this clears up any misunderstandings.................



thanks to mudster for the above
dj.

Cheers everyone,
I thought you must be able to get away with bending plasterboard somehow.  I think I will order a couple of extra sheets just to be sure.  As I have to build the frame to fix the plasterboard to I will build it in my workshop and lay it down and use as a former.
Thanks for the advice.
Big-e

So does that mean that if you form a stud partition from marine ply - you just tile straight onto it using waterproof tile adhesive ?

Marcos I wouldn't worry. You thinned the PVA down 1:5 so it will have soaked into the substrate. I think you will find that most problems arise when undiluted PVA is used as it forms a film over the surface rather than soaking in.

Plus you followed the manufacturers instructions, which is usually a good idea.

Thanks lads