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PostPosted: Wed Aug 12, 2015 1:48 pm 
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jcls wrote:
Thanks!

Quote:
...and less than 300mm square then PVA as recommended by the adhesive manufacturer will be fine...........


Erm... They're not actually. They are 600mm x 300mm. Why would the size be related to the PVA?

Cheers!

Jules


Sorry, didn't make myself clear, the tubbed adhesive is only suitable for tiles of 300mm x 300mm Max and for tubbed adhesive PVA is OK to use as a primer.

Anything bigger than 300mm Always use a cement based (Powdered adhesive). PVA is not suitable as a primer for cement based adhesive.

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PostPosted: Wed Aug 12, 2015 5:02 pm 
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I did a bit research on the subject of pva vs dedicated primers and this guys write up I found online,kinda(to me anyway) confirms why you shouldn't use pva.


P.V.A. Versus Primers when Wall and Floor Tiling
by David Howe Tiling
Published on 26-04-2012 06:33 PM 9 Comments
TilersForums.co.uk recommends Mapei Adhesive, Grouts, Primers and Silicone for use with all wall and floor tilers.

See www.Mapei.co.uk for more information.

MANY PEOPLE THINK THAT P.V.A. IS OK AS A PRIMER ON WALLS AND FLOORS SO I THOUGHT THAT I WOULD LET YOU SEE THIS " LINK " AND HOPEFULLY IT WILL ENLIGHTEN SOME NEWCOMERS OR EVEN EXPERIANCED TILERS AS WHY NOT TO PRIME SUBSTRATES WITH P.V.A. INSTEAD OF PRIMERS.........DAVE.....


P.S. I always prime with primers and this will show you why!!!!!!!

PVA - Why you shouldn't use it as a tiling primer

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 specify 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 partly 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 crystallising 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 what's 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. They also stop a chemical reaction occurring between the cement based adhesive and a plaster substrate, a known problem know as "Ettringite failure"

I hope this clears up any misunderstandings.
So only use PVA before tiling if the adhesive manufacturer specifies it in the instructions.


Read more: http://************/content/p ... z2ITUSIzA3


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PostPosted: Wed Aug 12, 2015 5:39 pm 
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That looks suspiciously like Mudsters post & I know for a fact his name is not David Howe

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PostPosted: Wed Aug 12, 2015 6:04 pm 
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Dunno who it is tbh. I came across it whilst browsing one of the tiling forums earlier as the subject interests me as I have a bit of tiling to do in my own gaff and this guys post seems to make a lot of sense and have some very good points so I thought I'd share.


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PostPosted: Wed Aug 12, 2015 6:50 pm 
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village idiot wrote:
That looks suspiciously like Mudsters post & I know for a fact his name is not David Howe


Mudster did a more full explanation of the whys and wherefores (Sp?) of primers for tiling which used to be on the forum somewhere.............

Can't seem to find it now.....

@ OP, regardless, tubbed addy isn't suitable for 600x300mm tiles..

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PostPosted: Wed Aug 12, 2015 7:13 pm 
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Just out of curiosity guys,what tubbed addy do you guys prefer? The tiles I have are 150x150 ceramic and will be adhered to unskimed plasterboard. Or is powdered adhesive the way to go?


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PostPosted: Wed Aug 12, 2015 7:15 pm 
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wine~o wrote:
village idiot wrote:
That looks suspiciously like Mudsters post & I know for a fact his name is not David Howe


Mudster did a more full explanation of the whys and wherefores (Sp?) of primers for tiling which used to be on the forum somewhere.............

Can't seem to find it now.....

@ OP, regardless, tubbed addy isn't suitable for 600x300mm tiles..


Look at the very first post on this thread

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PostPosted: Wed Aug 12, 2015 7:24 pm 
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Yeah,it's nearly the same as the one posted on the UK buisness forum from Lawrence147 who has copied it from David Howe tiling!!
Easy seeing I never read the first post :lol:
Is mudster Lawrence 147 then from the other forum?


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PostPosted: Wed Aug 12, 2015 8:01 pm 
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On balance, I think not :lol:
I met Mr Mudd a couple of times when I was working in Surrey (I met a few forum members when I used to travel a lot with work, there are very few places in this country I have not visited over the years)
He had a daft spaniel called Dave :lol:
His company A.T.Stone is still listed on Google but I don't know if he is still trading :roll:

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PostPosted: Wed Aug 12, 2015 9:04 pm 
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village idiot wrote:
On balance, I think not :lol:
I met Mr Mudd a couple of times when I was working in Surrey (I met a few forum members when I used to travel a lot with work, there are very few places in this country I have not visited over the years)
He had a daft spaniel called Dave :lol:
His company A.T.Stone is still listed on Google but I don't know if he is still trading :roll:


Dave wasn't the original author and has never claimed to be as far as I know, but he was the one that has championed the cause and got that info out there.

The original author is still around and I think he still has his hand in with tiling but his main business is in diamonds now... the drilling sort... http://www.atsdiamondtools.co.uk/ :wink:

Which indecently are cracking tools at a cracking price :thumbright:

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PostPosted: Tue Aug 18, 2015 3:30 pm 
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darrenba wrote:
Generally you can't use tubbed adhesive on tiles of that size. You will need to buy a powdered cement based adhesive.


Thanks darrenba,

So I'm going to buy some Bal CTF4 (seems like that is superceding CTF3) and some Bal APD Primer too. What size comb trowel would i need for that adhesive? I have a 6mm one that I bought to apply the tubbed adhesive but do I need anything different for the cement based Bal product?

Jules


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PostPosted: Thu Aug 20, 2015 4:36 pm 
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So it turns out I've done pretty much exactly the wrong thing because I had already PVA'd all my walls in the bathroom in readiness for tiling. After talking to both Bal, Mapei and Everbuild (Aquaseal), I know mostly what I have to do but I might have to 'wing it' with regards to my tanked areas.

So my bathroom has/had three basic surfaces in it.
    1) Walls that were previously emulsioned (now with two coats of PVA on top)
    2) New plasterboard boxing-in (also now with two coats of PVA on it)
    3) The shower area that I replastered first, then applied two coats of PVA, then later discovered that the Aquaseal tanking kit had a primer that also needed to be applied. So this area now has plaster plus PVA plus tanking primer, plus two coats of tanking membrane with and sealing tape where appropriate

I don't think I can fix area 3 at this point (but I'm not sure if I really need to tbh)
Area 1 and 2, I am told that I have to remove the PVA 'mechanically' - ie. sand it off. I also must sand off the old emulsion paint apparently. Once that is done, i will not need a primer to coat either surface and can apply the tile addy straight on.

BTW - I had mentioned to the person from Bal that I was going to use CTF4 and they instead advised me to use "Max Flex Fibre". However, I already have purchased Mapei Ultracolor Plus Grout in both white and cement grey and so Mapei gave me their recommendation to use "Kerraflex Maxi White" on all my surfaces.

Finally, I have a question about the Kerraflex Maxi that someone may be able to help me with: I have seen two products with this name 1) Kerraflex Maxi White and 2) Kerraflex Maxi S1 White. Are these the same and can i use either? The price of those with the 'S1' in the name seems quite a bit cheaper.

Thanks all!

Jules


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PostPosted: Thu Aug 20, 2015 5:37 pm 
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Basically the S1 designation (Or S2...whatever) are used by some manufacturers to designate the amount of flex in the adhesive once it has set.

In your case you'll be fine with a tile addy from any of those manu's..

As for the pva and paint, yes remove/sand/scrape off.

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For this message the author wine~o has received gratitude : jcls
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PostPosted: Fri Aug 21, 2015 2:55 pm 
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One more question please?

What size trowel teeth/comb would I need for Keraflex Maxi S1?

Thanks!

Jules


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PostPosted: Fri Aug 21, 2015 4:44 pm 
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jcls wrote:
One more question please?

What size trowel teeth/comb would I need for Keraflex Maxi S1?

Thanks!

Jules


The size of trowel comb is less to do with the adhesive you're using and more to do with the size of tile and the evenness of the background you're tiling.

As a general rule thumb you would use a 3mm trowel for mosaics. The reason for this is because when you press the tiles home some of the excess adhesive will migrate to the grout joints and fill these, if you were to use a large bed trowel such as an 8mm or 10mm. Therefore this is also the reason for making sure the background is even and flat when using mosaics before you start.

Standard wall tiles, say 100x100 up to 600x600 would normally be laid using an 8mm trowel. However if your walls are bad to start with then you may want to think about using a 10mm trowel.

Large format wall tiles, say anything bigger than 600x600, you want to be using a 10mm trowel to start with. This is because the tile is bridging a larger surface which is likely to have more deviations in it and you want the tile to have as much contact with the adhesive as possible. Again if the walls are bad then you may want to think about going to 12mm, 15mm even 20mm. Keep in mind though that you are now using a lot more adhesive and when using something like Mapei Keraflex which is anything between £18-£25 depending on where you are buying from, there becomes a oint where it is cheaper ot sort out the substrate/background, than using excessive amounts of adhesive.

Floors which are generally more uneven then walls, a 10mm trowel is the most common to use. But once again if the floors are bad then you can go up to a 20mm trowel

As a general rule of thumb again. a 20KG bag of adhesive will cover 5sqm using an 8mm trowel. This figure builds in some wastage of adhesive, so deeding on how you use it, you could end up with a meteage of between 4-7 sqm per bag.

Lastly most adhesives will state a maximum depth of bed and this is generally calculated by halving the trowel size. So if you use a 6mm trowel the finished bed size will be 3mm, an 8mm trowel would be 4mm, 10mm is 5mm, so on and so on.... Keraflex from memory has a a bed of 25mm (but don't quote me as haven't looked at the specs in a while) so you'd be having to sort out some seriously rough substrates to go that deep. Ready mixed tub adhesives generally have a max depth of 3mm and therefore the max trowel you can use is 6mm. Just goes to show how limited ready mixed addy's are. (that said i'm sure there re 1000's of meters of tiles fixed using an 8mm trowel which are still stuck fast, but technically it is using it's limitations to the extreme.)

Blimey i'm boring! :lol:

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