how to prepare 2 level surface for tiling, help please

[happyhero]

Hi I am helping my mother in law out as she cant afford much but wants to do her bathroom up. Its a 1930's ex council house. The council tiled it last, years ago and I have found that most of the tiles are coming off really easy and unbroken, in fact sometimes i knock 1 off and 3 fall off, almost seems amazing they stayed on there up till now. It makes me wonder what they have done for it all to come off so easy.

Anyway in some places they are pulling of what I think you would call the skim coat ie its about 2 or 3mm thick, so that i am ending up with 2 levels. Underneath appears to be a cement based scored coating, would that be a sort of render?

I have scraped the loose stuff off, but I worry will the remaining firmer stuff support tiles? It was tiled only half way and this is where the plaster has come off, up higher when I tap it, it seems ok to me. The render surface thankfully appears to be very level.

My questions are

1. Do I have to scrape all the skim coat off?
2. will the render surface be ok to tile on?
3. what coating should I apply to the render surface?
4. as it is being tiled do I need to level it or can 3mm be covered by applying more adhesive?
5. If I should level it what should I use?
6. Out of interest what do you think the council did when tiling this bathroom for the tiles to come off so easy?
7. anything else i need to know?

Any help appreciated.

 

[tpt]

1. no, if its sound and your new tiles arent too heavy*
2. yes (sort of) pop some acrylic primer on it(not pva) then patch it with rapid set floor adhesive, assuming its just smallish areas that have come off.
3. see above
4. at an absolute push but above is easier
5 see above
6. probably new plaster and no primer, and probably dot and dabbed the adhesive (you'll be able to see if they did that)
7. have a search on here, but to help more tell us which tiles your fixing (size, type e.g. ceramic) and what adhesive you have bought (or better) what your thinking of buying

* - point one. get some gaffa tap, stick it on and yank it off, it the skim stays then itll likely be ok. do this in several areas and be honest with yourself.

hope this helps so far.

 

[happyhero]

Really grateful tpt, thats some great advice for me to go on, so I will find out more ie what tiles they want and get back on here.

You are right about the dot and dab, I saw it but it did not register with me at the time.

They are tempted with big tiles as they seem popular for the bathroom, but I will wait and see.

 

[Richard C]

Dot & dab fixing tiles is nothing but a bodge but if the skim coat is coming off with the tiles, the adhesive has at least stuck; the plaster has either blown, has poor adhesion or the tiles are too heavy.

Large format tiles are very popular now but what most folks don’t realise is that plaster has a weight limit of 20 kg/sqm (including up to 4 kg/sqm for the adhesive) for plaster in good condition so if your tiles weigh in at much more than 16 kg/sqm, plaster isn’t a suitable tile base.

 

[happyhero]

Ok just one question at this point, why the rapid set floor adhesive, is it going to be easier or stronger or both compared with maybe using some finishing plaster? OR is it even ok to use bonding plaster if the surface is only for tiling on?

The rapid set bit slightly concerns me, how quick is rapid, I could not plaster a whole wall but i am pretty good with even a large patch to give you some idea where I am coming from with my questions.

 

[Richard C]

why the rapid set floor adhesive, is it going to be easier or stronger or both compared with maybe using some finishing plaster?

If you use anything else to fill out you will have to wait around 10 days for it to dry out before tiling. It can be used in thin coats & is far better than render (if not more expensive) when correctly applied. Use an acrylic primer over the base render & over any sound plaster if using cement powder adhesive for the tiles (depends on size/weight) but the weight of your proposed tiles is also very important.

OR is it even ok to use bonding plaster if the surface is only for tiling on?

You can’t tile over Bonding plaster, it is completely unsuitable; in fact plaster is not ideal as a tile base as it restricts tile weight.

The rapid set bit slightly concerns me, how quick is rapid, I could not plaster a whole wall but i am pretty good with even a large patch to give you some idea where I am coming from with my questions.

Rapidset has a pot life of 45 minutes so only mix up enough for 30-35 minutes & do it in stages; wash your tools & bucket well between mixes. It doesn’t have to be perfect as long as it’s flat; the other alternative is to use a quickset render.

 

[happyhero]

Ok got the Rapidset and have got off all the loose plaster so that I am left with only firmly fixed stuff. I now have some questions, probably some a bit silly but hopefully you can help me out with the answers.

1. With the rapidset am I aiming for a smooth finish since I am just using it to bring the lower level up or and I supposed to put it on with a tile adhesive trowel ie leaving grooves, sorry for question but I have never used rapidset for doing this before?

2. Next the bathroom was only tiled half way up before and the top half was painted plaster, what should I do with the paint, do I need to get it off, its not flaking or anything?

3. There is a part of the wall which has an imperfection due to the fact there was a cupboard there once and is now removed The plaster was badly patched leaving a very minor difference in plaster levels either side of the repair. I was wondering would you use a trowel with deeper teeth to give a thicker adhesive level to allow more scope to compensate gradually over the distance, this is just a guess, don't know if this is a method or would even work?

4. Also I looked online at Topps tiles for acrylic primer, thinking of getting a Bal product but nothing comes up on their site for acrylic primer, can someone please give me a link to a good one that does not cost the earth if possible?

All help greatly appreciated.

 

[tpt]

1. - use a smooth trowel, no grooves - your just filling the gaps and aiming to get a roughly level surface.

2. - at the very least score the paint - if you tile on paint its only the paint holding your tiles on - so scratch the hell out of it!

3. you can build the the adhesive up to some extent, either by putting more on the wall, or back buttering the tile (trowel onto the back of the tile as well) if you do this take your time. it depends how big an imperfection your talking about!

 

[happyhero]

With the paint you say "at the very least" so would I assume you would use something like paint stripper to remove the paint to do it properly, anything special if so, or just normal paint stripper?

Also sorry but added a fourth question above probably while you were sopromptly answering me, thank you for all your help I really appreciate all the help.

 

[Richard C]

I now have some questions, probably some a bit silly but hopefully you can help me out with the answers.

1. With the rapidset am I aiming for a smooth finish since I am just using it to bring the lower level up or and I supposed to put it on with a tile adhesive trowel ie leaving grooves, sorry for question but I have never used rapidset for doing this before?

For levelling, use a plastering trowel not a notched tiling trowel; your aiming for a flat level surface, it doesn’t have to be smooth. For tiling, use an appropriately sized notch trowel to apply the adhesive.

2. Next the bathroom was only tiled half way up before and the top half was painted plaster, what should I do with the paint, do I need to get it off, its not flaking or anything?

What size/weight tiles are you laying? To test the paint, stick an 18” length of 2” gaffa tape over the paint & pull it off quickly but steadily; if the paint stays on there, you just need to heavily score it criss-cross pattern & use an acrylic bonding primer. If the paint comes off on the tape you need to remove it. If the plaster comes off as well you have a more serious problem. But, as I’ve already said, plaster has a maximum weight restriction & if your tiles weigh in at more than around 18 kg/sqm, even allowing for a 10% safety factor, you’ve got a problem.

3. There is a part of the wall which has an imperfection due to the fact there was a cupboard there once and is now removed The plaster was badly patched leaving a very minor difference in plaster levels either side of the repair. I was wondering would you use a trowel with deeper teeth to give a thicker adhesive level to allow more scope to compensate gradually over the distance, this is just a guess, don't know if this is a method or would even work?

Providing the plaster base & filler is sound, use the Rapidset to fill out level before tiling. You can use powder cement addy (Rapidset) to fill out locally up to around 10mm when tiling but it’s best done by skimming over immediately before tiling. You cannot/should not fill out using tub ready mix; it has a maximum bed depth of around 3mm, any deeper & it will take an age to set but sometimes it never does & the tiles fall off. It’s important you use the correct size notch trowel for the tile size/type & the adhesive you are using, large notch trowels aren’t really meant to be used to make up differences in tile base levels.

 

[Richard C]

4. Also I looked online at Topps tiles for acrylic primer, thinking of getting a Bal product but nothing comes up on their site for acrylic primer, can someone please give me a link to a good one that does not cost the earth if possible?

I missed that one as well; BAL is excellent stuff & I use it exclusively because I can always predict the outcome but it’s not cheap & there are other’s equally as good.

BAL supply 2 basic acrylic primers;
http://www.bal-adhesives.co.uk/products/prime-apd
or
http://www.bal-adhesives.co.uk/products/primer
& a bonding/priming agent for more specialised applications;
http://www.bal-adhesives.co.uk/products/bond-sbr

Topps is not cheap for DIY or even trade really; try & negotiate a discount or shop on line. If not, I’m sure TPT can put together a selection of suitable products for you.

 

[tpt]

i certainly can (thanks richard) but sometimes the delivery charge can make it expensive.

However if you let me know the area and any specifics (grout colour etc) i'll happily pm you a quote.

 

[happyhero]

Ok they have selected the tiles, they went to TileGiant in the end for them. The tiles are 25cm x 33cm and are ceramic. They weigh 16kg/m2, what size trowel do you think I should use?

Also I tested the paint like you advised, I cleaned the dust off the wall first and then really pressed the tape on to it firmly and then steadily pulled it off, virtually nothing came off at all, just little specs which did not really break the paint finish even. Obviously I tried this all over to check all areas. I then scored the surface thoroughly and broke off any bits where the plaster seamed live ie like around old screw holes etc. Tomorrow I will probably use the rapid set to level and then when dry, acrylic prime all the walls. I will see what Tile Giant do in the way of acrylic primer as they are near them and seemed ok.

When they bought the tiles I asked them for Bal adhesive but they do not do it and offered Mapei adhesive as a high quality alternative. We accepted it, is this a good make?

They also offered it in a tub but I asked them for the powder instead.

 

[Richard C]

When they bought the tiles I asked them for Bal adhesive but they do not do it and offered Mapei adhesive as a high quality alternative. We accepted it, is this a good make? They also offered it in a tub but I asked them for the powder instead.

Ceramics are nice & predictable so good choice there but your getting near the weight limit for plaster, just make sure you score it well. You definitely don’t want tub ready mix for that weight/size tile let alone the background you have; surprised & a little concerned a tile shop would recommended it. Nothing wrong with Mapei as long as it’s the correct type & the genuine trade version as opposed to the one sold under the “Buildfix” label (BNQ); which one did they sell you?

 

[happyhero]

I don't have any of it yet as they had to order the tiles in, so we should be getting them mid week next week, but I will see tomorrow if it states the adhesive details on the receipt, otherwise I will wait and see when we collect and make sure it does not have Buildfix or BNQ on it.

What about trowel size, what do you recommend?

I have scored it quite well with a stiff spatula, if I press much harder I think I will go through the plaster skim and end up weakening it, and I have scored it quite a lot, what do you use for this to score it well?