Tile weight limits on plaster

[Colour Republic]

Ok so we know tile weight limits on plaster is 20kg per sqm... or is it????

I've had a 'conversation' with someone about weight limits on plaster which made me look up data sheets to back me up. What i've found has left me unsure.

The formula i've worked to is

Tile + Adhesive should be = or less than 20kg sqm.

But on checking British Gypsum's website (let's be truthful, most of the the plaster is from them) I came across the following

Tiling:
Tiles up to 20kg/m2 can be applied to directly to Thistle Multi-Finish, except where the system includes a bonding agent. As the total weight limit of tiles and plaster applied over a bonding agent is limited to 20kg/m2, consideration should be given to tiling directly over to the background. If plastering to provide a background for tiles, avoid polishing the surface. Polished plaster surfaces should be roughened and a suitable primer used.

So lets take a few snipets...

Tiling:
Tiles up to 20kg/m2 can be applied to directly to Thistle Multi-Finish, except where the system includes a bonding agent.

I read this as... If the plaster is applied over a bonding agent, then the total weight limit of 20kg/m2 is to include the weight of plaster.

So the formula would be modified to:

Tile + Adhesive + Plaster should be = or less than 20kg sqm.

Now looking at the data sheets, it says the dry set weight of plaster @ 2mm is 3.4kg/m2, that takes the weight limits of Tile + Addy down to 16.6kg/m2. I know all situations on refurbs are different and these are only guidelines but still the plaster weight adds up to what we would normally use on addy right?

so if the above quote is right then multi-finish without the use of a bonding agent is still

Tile + Adhesive should be = or less than 20kg sqm.

But if the plaster is applied with bonding agent, then it should be

Tile + Adhesive + Plaster should be = or less than 20kg sqm.


The next part of the quote could be interpreted as one of two things:

Tiling:
...consideration should be given to tiling directly over to the background. ...

either, consideration should be given to tiling on to the background plaster, OR not doing any plastering at all and tiling on to the substrate to start with.

We know background plaster shouldn't be plastered on to (execpt for one), Gyproc say this in another data sheet

Tiles should not be applied directly to Thistle undercoats, with the exception of Thistle Dri-Coat

Gyproc Dri-coat is a cement based undercoat, which explains why it would exclude it from the above statement.

Sooooooo... Discuss

 

[White Room]

Yes, tile weight should be less than 20kg m2 because of the powdered adhesive weight with larger tiles but smaller tiles weight could be increased.

 

[Colour Republic]

Yes, tile weight should be less than 20kg m2 because of the powdered adhesive weight with larger tiles but smaller tiles weight could be increased.

Sorry WB you may have missed my point, from the data sheets it states that the weight of plaster (if a bonding agent is used) should be included in the weight limit of 20kg/m2

 

[Dan]

A brilliant thread. This will teach a lot of the noobs. Nice post CR. I've added to your reputation.

 

[Dan]

It's already ranking too.

 

[Colour Republic]

It's already ranking too.

You're such a geek :rofl:


(ok, I know that's pot, kettle, black, but I don't care)

 

[DHTiling]

Yep a good post and I've upped your reputation as well..

Have you checked any other suppliers for info on this weight ratio..?

 

[White Room]

Sorry WB you may have missed my point, from the data sheets it states that the weight of plaster (if a bonding agent is used) should be included in the weight limit of 20kg/m2

I'm with you now Rob, I new that pva was only up to 20kg and plaster at 2-3mm was a minimal weight but a float and set with bonding with pva as a sealer could reduce the weight some what.

Good point there mate.

 

[Alan.P]

Mmmmm, cat amongst the pigeons, can I suggest to a mod / admin that this is moved out of public view before a stampede, at least while we talk about it.

 

[DHTiling]

Good idea Alan.. moved to arms for now..

 

[Alan.P]

Thanks mate, this could be a potential law suit for many a fixer, there is a lot to be talked about, we may need some input from certain manufactures or links to their data sheets, but it doesn't bear thinking about............... but it does. Have we / are we giving bad advice, and have we been fixing to under spec substrates ??

the mind boggles.

 

[Colour Republic]

Yep a good post and I've upped your reputation as well..

Have you checked any other suppliers for info on this weight ratio..?

No, not yet. TBH I can't think of many suppliers and I can't seem to find a datasheet for Knauf FP90

 

[Colour Republic]

Thanks mate, this could be a potential law suit for many a fixer, there is a lot to be talked about, we may need some input from certain manufactures or links to their data sheets, but it doesn't bear thinking about............... but it does. Have we / are we giving bad advice, and have we been fixing to under spec substrates ??

the mind boggles.

I ment to put links to the source in the opening post

Multi-Finish - Broken Link Removed

Bonding - Broken Link Removed

I believe Hardwall, Tough coat and browning all have the same specs re tiling as Bonding

Dri-coat - Broken Link Removed

Now on the Dri-coat data sheet it doesn't say what the weight limit is when tiled directly to Dri-Coat. It says the same as the data sheet on multi-finish but the important words are 'Tiles up to 20kg/m2 can be applied directly to Thistle finish...', as Dri-coat isn't a 'finish' it's an undercoat, then I assume the weight limit might be different?

 

[DHTiling]

Ok.. I have emailed the TTA to get them to clarify this with BS 5385 standards and british gypsum.. something is wrong and needs amending ASAP..

 

[Gazzer]

Nice one Dave, all very confusing IMO

 

[DHTiling]

I want to clarify who is wrong all this time..LOL..

Plus i have asked if this is the limit to base coat with skim then does this apply to skim on plaster board.. lets get a final answer and if wrong BS 5385 needs amending.. ASAP..

 

[DHTiling]

Ok.. According to the TTA, the advice is not really correct from british gypsum, we as tilers should use BS5398 as our guidance and not notes by others.

Hi, I have emailed you ( TTA) direct as you might have this answer quicker than just going to independent adhesive suppliers.

BS5385 states that tiling to a plastered background has weight limitations of 20kg per sqr mtr to include tiles and adhesive/grout.

This we take is a skim coat to a base coat.. BS5385 does not differentiate between a skim coat to plaster board or a skim coat to a base coat, so as fixers we use the same weight limit on both so to coincide with BS5385 standards.

Now getting to my reason for the email, it has been pointed out by a member of our Tilers forum that this weight should also include the weight of the plaster over the base coat, this is the recommendation from british gypsum and if this is the case then BS 5385 is giving the incorrect advise , along with the TTA and also we as members of Tilers forums.co.uk.

Now this could have some difficult implications if a person were to have a weight failure don’t you agree.

I have added a link to the PDF from bristish gypsum and if you could take a look please and see if you as the tiling body of the uk read this the same way we have. Broken Link Removed because if this is the case then BS5385 needs amending as does any other data published.

I do hope this is just an over sight on british gypsums side , I look forward to any advice or anything to clear this up ..

Many thanks ..

and the very speedy reply from the TTA.

Thanks for your email.

British Standard BS5385 is the code of practice for fixing wall and floor tiles and is the basis for all tiling works carried out. In part 1 where reference is given to tiling to a plaster background it states
"The plasterwork should be firmly bonded to its background and be sufficiently strong to support the specified tiling. The maximum weight of tiling which should be supported by a dry, firmly adhered plaster background is 20 kg/m2"

This statement should clarify the matter in terms of what is included in the weight restriction. There has been discussion over the definition of "tiling" in the above phrase, and it has been agreed that this refers to the tiles and adhesives.

TTA has published a guidance note on tiling to gypsum plaster. Click here to read full details.

The point that tilers need to understand is that the use of a skim coat will reduce the weight limit on plasterboard, for example, from 32 kgm2 to 20 kg m2. I agree that the comment in the Thistle sheet could be seen to be ambiguous, so the advice to any tiler is to use British Standard BS5385 as their "bible".

We would suggest you also let your forum readers know about the guidance document we published, which is freely available on our website

The Tile Association
Forum Court, 83 Copers Cope Rd., Beckenham,
Kent BR3 1NR, United Kingdom
Telephone 020 8663 0946
Fax 020 8663 0949
Email [email protected]
Website For tiles, tilers, tiling and the tiles industry : The Tile Association
Click here to subscribe to Tilezine, the free online magazine for the tile industry

The Tile Association is a company limited by guarantee. Registered in England and Wales, Company Number 3896624

So i hope this clears this up and we stick to advise BS5385 as OUR standard for Tilers forums.co.uk..


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[diamondtiling]

Great Dave, that was something that needed clarifying asap.

 

[Alan.P]

Nice one Dave, great to know, I can sleep at night again lol

 

[White Room]

Good information there.