Laying porcelain tiles

[diycooper]

Ok please go easy as I have started reading before buying. I have just bought b n q porcelain tiles and got unibond extended set adhesive. I am going to be laying onto a self leveled floor. I have read you need flex adhesive but b n q told me you do not. Any advice there ? I have read seal floor with pva and read do not and help here to please ?

 

[Richard C]

Ok please go easy as I have started reading before buying.

How does that follow if you’ve already bought the tiles & adhesive & been given bum advice by a DIY shed employee!

I have just bought b n q porcelain tiles and got unibond extended set adhesive.

That’s your first mistake; take the unibomb back & get a refund, then go to your nearest trade tile outlet & buy something that will actually work; it has a notorious reputation! Use powder cement adhesive only on floors.

I am going to be laying onto a self leveled floor.

If you’ve laid an SLC what have you laid it over & which type is it? What size are the tiles?

I have read you need flex adhesive

Absolutely 100% correct.

but b n q told me you do not. Any advice there ?

That’s mistake number 2 & whoever told you that is a complete idiot; ignore whatever DIY shed staff tell you, there may be some who know what they are talking about but they could just as easily have been working a checkout in Tesco last week

I have read seal floor with pva and read do not and help here to please ?

Mistake number 3; never ever use standard PVA on a tile base, it remains water soluble. Use it in a wet are or if water gets in, it will dissolve taking your tiles with it.

Tiling isn’t rocket science but there are still many things that can catch you out & suspended timber floors need special consideration; walls can also catch you out with tile weights, prep & materials. I would advise you read the Tiling Sticky & Forum Archive posts before doing any work or buying any more materials, it could prevent you making disastrous & potentially expensive mistakes. Then post the forum for more detailed step-by-step advice if you wish.

It’s important to use only quality trade tilling materials of the correct type for your tiles & tile base; cheapo own brand & DIY stuff is mostly crap.

 

[diycooper]

Ok please go easy as I have started reading before buying.

How does that follow if you’ve already bought the tiles & adhesive & been given bum advice by a DIY shed employee!

I have just bought b n q porcelain tiles and got unibond extended set adhesive.

That’s your first mistake; take the unibomb back & get a refund, then go to your nearest trade tile outlet & buy something that will actually work; it has a notorious reputation! Use powder cement adhesive only on floors.

I am going to be laying onto a self leveled floor.

If you’ve laid an SLC what have you laid it over & which type is it? What size are the tiles?

I have read you need flex adhesive

Absolutely 100% correct.

but b n q told me you do not. Any advice there ?

That’s mistake number 2 & whoever told you that is a complete idiot; ignore whatever DIY shed staff tell you, there may be some who know what they are talking about but they could just as easily have been working a checkout in Tesco last week

I have read seal floor with pva and read do not and help here to please ?

Mistake number 3; never ever use standard PVA on a tile base, it remains water soluble. Use it in a wet are or if water gets in, it will dissolve taking your tiles with it.

Tiling isn’t rocket science but there are still many things that can catch you out & suspended timber floors need special consideration; walls can also catch you out with tile weights, prep & materials. I would advise you read the Tiling Sticky & Forum Archive posts before doing any work or buying any more materials, it could prevent you making disastrous & potentially expensive mistakes. Then post the forum for more detailed step-by-step advice if you wish.

It’s important to use only quality trade tilling materials of the correct type for your tiles & tile base; cheapo own brand & DIY stuff is mostly
crap.

Hi it was a SLC that never had any latex in and it was laid over a area of floor what had to be built up with concrete. Could you explain why I need flexi adhesive if its on concrete floor please ?

Also what shall I seal the floor with ?

Tiles are roughly as I am not at the property where they are so as a guide 45 cm by 30 cm.

 

[paul78]

use a SBR primer for that mate, much cheaper than acrylic.

Im local to you myself so you must know edge lane retail..... theres a tile warehouse there behind the macdonalds that sell WEBBER brand of adhesive, my personal opinion to use that. BAL is good but expensive. also use rapid set if experienced but if you use slow set read the bag to see when light traffic is allowed and dont be tempted to take chances as ive seen it done! (DONT USE TUBBED STUFF)

the flexible stuff you dont technically need but for the extra couple of pound i always use flexible adhesive and grout also, thats just me.

if you get stuck just ask.

 

[Richard C]

Could you explain why I need flexi adhesive if its on concrete floor please ?

Because you’re tiling over an SLC not over the concrete.

Also what shall I seal the floor with?

Check with the SLC recommendation but nothing unless the adhesive manufacturer recommends it; if in any doubt use an acrylic/SBR bonding primer.

Tiles are roughly as I ma not at the property where they are so as a guide 45 cm by 30 cm.

You should be OK with a thick bed trowel but large format might be better. Are they glazed or polished porcelain tiles? Polished porcelain needs sealing but some come pre-sealed, check the box or with supplier (of maybe not if BNQ). Do a water test to see if they are absorbent; leave water on the tile face for 20 minutes, if it soaks into the surface you need to seal & use white adhesive if they are light colour tiles; dark adhesive can bleed through & stain; obvioiuls dark adhesive for dark tiles!

Good pointers from paul78. BAL do good flexy adhesives with a pot life up to 5 hours if you can't manage 30 minute Rapidset.

 

[diycooper]

Thanks paul78 may take a trip up there. Richard C they are glazed I have just been to property and checked them with the water test you said and they never absorbed any water. Also out of curiosity read the back of the SLC and of the unibond tile adhesive and they both say prime the surface with diltute PVA 4 water to 1 PVA prior to tiling ?

 

[Richard C]

Also out of curiosity read the back of the SLC and of the unibond tile adhesive and they both say prime the surface with diltute PVA 4 water to 1 PVA prior to tiling ?

What you should appreciate is that Unibond also make PVA; I wonder if they also make the SLC you used? I know of only one other manufacturer that recommends using PVA as a tile primer despite all the evidence it can end in disaster.

The specification of standard PVA alone rules it out as tile base & here are a couple of articles to read but also check out the other tile forums if you’ve a mind.


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This article has been written by Alan at AT Stone who is a Professional Tiling contractor, He now mainly specialise in natural products but over the years He’s stuck up (or down) every type of tile there is.
A while ago I wrote a post for another forum which explained the reasons behind not using PVA as a tiling primer, it is posted below for your information, I've been asked to copy it to various other forums and thought it might be useful here also. I hope it is of some help.

Oh and if you do require a primer then use one suitable for the adhesive you are using, such as BAL APD or Ardion 51.

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 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 its 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.

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. Basically a moist layer of PVA is then holding the entire weight of the tiles, grout and adhesive and stopping a great deal of the mechanical grip occurring.

Ok so what’s the difference between this and Ardex or BAL primer, well basically the tile manufacturers primers are generally acrylic (such as BAL APD- Acrylic Polymer Dispersant), the chemicals don't become "Live" when a tile adhesive is applied to it and stop the mechanical crystallisation of the adhesive gripping the substrate itself. They also stop a chemical reaction occurring between the cement based adhesive and a plaster substrate, a known problem know as "Ettringite failure"

BAL and some other manufacturers also produce SBR primers, these are slurry primers for flooring, so if you're about to tile a dusty sand/cement screed, a thin coat of SBR will bond all the surface dust together and allow the adhesive to bond to the screed correctly, SBR shouldn't be used as a wall plaster primer as a replacement of APD.

I hope this clears up any misunderstandings.
Alan
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& another

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Introduction

There have been many debates on these subjects, and my intention is to, in a reasonably easily understood manner, explain the "why" of it all. I'm not an expert on this, but I have read up on it enough to form an opinion, and I wish to pass on my findings.

This post is based on a pair I did very recently, in a thread pertaining to these matters.


A Brief Summary

If you do not want to read the whole post, here follows a summary of what I'm going to explain.
• PVA is not suitable in any tiling related application.
• Cementious materials and anydrite (or gypsum) materials are not compatible, and must be completely separated by, for example, a primer.

There. Now onto the main part of this discourse.


PVA and Cementious Materials

I hadn't even heard of using PVA for anything tiling related before I came on here. Thus, I read up on it, and here follows my findings:

PVA stands for polyvinyl acetate, and it is a rubbery synthetic polymer. It is commonly emulsified in water and used as glue. Many know it simply as "wood glue", or "carpenter's glue".

Cementious materials, such as many tile adhesives and grouts, or other materials which contain cement, such as concrete, are alkaline. Simplified, that means they have a high pH.

Alkali slowly attacks polyvinyl acetate, forming acetic acid, which has a low pH. Cement doesn't dry per se; it cures through hydration, which means it binds the water you mix it with chemically. This causes the pH of the substance to rise dramatically. Introducing an acid negates that process to some extent, preventing the cement or conrete from binding all the water it needs to harden properly.

It is hydrolysis which gives cement and concrete products strength, and holds them together. Without this process, it would merely be the powder you started with.

The acetic acid which is formed when cement and PVA comes into contact, either through mixing them, or "priming" with PVA, will continually free the water bound in the cement, and that will weaken the bond and/or integrity of the material. The effect is accelerated if the material is subjected to moisture, which is more or less always the case.

PVA isn't water resistant. It becomes slightly live when exposed to moisture, and this in combination with the exposure to alkali, accelerates the forming of acetic acid. PVA which is marketed as "water resistant" or "exterior grade", has additives which makes them water resistant, but they're not alkali-resistant.


Anhydrite, gypsum, and cement

Anhydrite products are mainly composed of calcium sulfate, and gypsum products are mainly composed of calcium sulfate dihydrate. When anhydrite is exposed to water, it forms gypsum. In other words, it hydrates. Essentially, it cures, but not to the same extent as cement.

Gypsum always has a proportion on anhydrite crystals left in it.

Cement has a proportion of calcium aluminate. Calcium aluminate reacts with calcium sulfate, which is the main component of anhydrite products, and which is present in gypsum. The reaction forms hexacalcium aluminate trisulfate hydration; in other words, ettringite crystals. These expand, and force away anything which is fixed onto where they form.

As I've previously explained, cement cures, which means it binds water through hydrolysis. That means water is always present in cement. If anhydrite is put into direct contact with cement, there will be a reaction. The reaction won't be as severe with gypsum, as it's already hydrated most of the anhydrite (the dihydrate part), but there is still some present.

Thus, if you want to tile onto such products, you will need to separate them entirely. This is best done with a products which seals, and which is also water resistant, such as acryllic dispersions.
Even if you use water resistant "PVA", the separation will deteriorate with time, due to the chemical reaction between the cement, which is alkaline, and the polyvinyl acetate. If the bond of the cement onto the substrate hasn't already been compromised because of that, the formation of ettringite crystals will very likely cause complete debonding.

Rapidly curing cements may have some gypsum added when manufactured. It accelerates the curing, but does not affect the integrity of the product, because it's present in such small quantites, and during the early stages of curing.


Final Notes

PVA is not suitable as a primer, sealer, impregnator, or admix. The uses of PVA may be many, but they do not include anything tiling related. Use proper manufacturer approved primers and additives instead. Using PVA will likely cause liability issues when problems arise, and that is bound to cost alot more than buying proper materials to begin with.

If you want to tile onto anhydrite or gypsum, make very sure to properly separate the substrate from the adhesive. There will likely be tears otherwise.

Finally, I would like to quote Cliff Anger:
Calcium sulphate and portland cement are not compatable - whilst a failure is not guaranteed, it is a real possibility. Over time, ettringite crystals may appear, and as they expand, they will cause the tiles to lift and de-bond. It may well take several months to determine how bad the reaction might be.

 

[diycooper]

Thanks for that not even worth the chance. Winds me up though the way they right it on the packaging no wonder people make mistakes.

Will this sbr be ok as I am getting a toolstation delivery already ?

http://www.toolstation.com/shop/Roo...ound & Waterseals/SBR Bond/d250/sd2809/p18528

 

[paul78]

i cant open the link my end mate, but i use everbuild SBR comes in a yellow tub for approx £15 for 5litres.

Pick them up from JEM'S on green lane tuebrook or lowerhouse lane norris green if thats convenient for you.

 

[Richard C]

No don't use that it's for waterproofing render/screed mix. This is what you want;
http://www.bal-adhesives.co.uk/products/bond-sbr

 

[diycooper]

No don't use that it's for waterproofing render/screed mix. This is what you want;
http://www.bal-adhesives.co.uk/products/bond-sbr[/QUOTE]

Great what Bal adhesive shall I use also looking in the b n q trade book at them and it does not say the coverage of them any help there so I know how many I need for a 20m2 area. thanks

 

[Richard C]

You need to check the SLC manufacturer’s recommendations for priming; currently I have no idea what it is & would stick with an acrylic primer;
http://www.bal-adhesives.co.uk/products/prime-apd
2 ½ litres should be enough, diluted 1:1.

Rapidset flexible is what I mostly use; http://www.bal-adhesives.co.uk/products/rapidset-flexible but it has a short pot life of 45 minutes so don’t mix up more than you can use in 35 – 40 minutes. The big advantage with it is you can grout after 3 hours.

SPF; http://www.bal-adhesives.co.uk/products/single-part-flexible will give you a pot life of 5 hours but you must leave at least 16 hours before grouting.

Coverage on floors is around 0.25sq/m per kg or 5sq/m per 20 kg bag; for 20sq/m you might get away with 4 x 20kg bags but you might need another 10kg bag. Use a large format trowel - 20mm round notches, 13mm deep, at 28mm centres.

 

[diycooper]

It says on the back of the SLC packet to prime with pva before tiling bit as discussed this is a no go ?

Think I go with the SPF but this is not flexible as I have been advised is better. IS there not one with a longer pot life but also flexi ?

 

[Richard C]

It says on the back of the SLC packet to prime with pva before tiling bit as discussed this is a no go ?

Yes you did, sorry; don’t use PVA, use acrylic primer.

Think I go with the SPF but this is not flexible as I have been advised is better.

Sorry I don’t follow, of course it’s flexible; look at the link I posted Single Part Flexible is about as flexible as you’ll get without moving to expensive latex based products.

IS there not one with a longer pot life but also flexi ?

You must be misunderstanding; Rapidset Flexy has a pot life of 45 minutes but SPF has a pot life of 5 hours!

 

[diycooper]

Ok Thanks Richard going to go and change material sat and start job, thanks