tiling onto thistle one coat plaster??

[paul78]

just wondering if an area approx 2m2 has been patched with thistle one coat plaster 6mm depth can it be directly tiled onto, obviously primed 1st (not PVA)

hear so many different views and never actually come across it until now.

thanks

 

[Richard C]

Probably not the best choice of plaster product for a tiling base as it’s only marginally better than filler but what base did you put the “one coat” plaster onto, was it sound? What size/weight are your tiles?

What are the "different views" you've heard & from where

 

[paul78]

rich mate the walls went down back to the block, just poking all the loose bits away.
the tiles are ceramic 600x300 so i know theres a little weight issue there.

heard other tilers in the past saying they patch with one coat.....

i know skim finish is ok to tile to (less weight though) heard bonding plaster is a no no.

just never used the one coat until now and the are is approx 2m2 at the very most.

 

[Richard C]

Most base coat plasters including Bonding are unsuitable for tiling & one coat would not be my choice for patching/levelling repairs. It’s surprising how little some tilers know about plaster & its limitations regarding large format & natural stone tiles but having a foot in both camps, I have a fairly good knowledge of plaster & render. Whose one coat plaster did you use? Thistle plasters (including Multi) will accept up to 20 kg/sqm (but that includes up to 4 kg for addy & grout) but some of the DIY products are very soft & powdery & little stronger than Polyfiller, how yours will stand up is difficult to say without seeing it. You must use powder adhesive with tiles that size & use an acrylic primer over gypsum plaster to avoid it reacting with the cement in the addy.

Conventional sand/cement render is a good choice & will take around 40 kg/sqm. but the problem with using both render & plaster for repairs is the time you have to wait before tiling, a skim should be left 10 days & a 15mm base coat/skim or render base repair can take up to 4 weeks; again many tilers are either oblivious to this or just ignore it which can lead to all sorts of problems. On small areas, powder cement adhesive is probably the best bet or for larger areas, a quickset render; both can be tiled over the next day but neither is a cheap option. Sometimes you’re better to remove the lot, re-board & tile straight onto that.

 

[paul78]

i used thistle one coat to patch it up.

could i thinly skim coat this with rapid set addy ready for tiling, surely got to be safer option than tiling straight over the one coat??

 

[Richard C]

Thistle one coat will be better than most & should be as good but no better than Multi (20 kg/sqm). The tile base can only ever be as strong as the weakest substrate (link) & there is no point in going over it with rapid addy or anything else, it won’t make any difference; in fact could even make things worse.

 

[paul78]

thanks for your experience rich, this forum would be nothing without good chaps like yourself.

i didnt go with the addy route over one coat iv just primed (no pva for me)and made a start on the tiling today..... fingers crossed