Flexible adhesive substitute

[Mark2000]

Just been out to get some flexible tile adhesive and was quite shocked at how much this cost, this beign that i have never really thought about prices of materials as i am only on a college course at the moment. The reason i need the adhesive is that i need to do a final piece of work for my college course which i 1m2 so dont really need a whole bag, so is there anything i could add to normal adhesive to get near the same results as flexible adhesive, someone said to me about adding pva to it, i know this is not good practice, but wll only do it this once.

 

[sWe]

I can't imagine PVA would make adhesive more flexible. Besides, cementious materials and poly-vinyl-acetate don't mix. They're simply not chemically compatible.

If you mix PVA into cementious materials, the PVA will react with the cement and form acetic acid, which will cause the cement to deteriorate and crumble. Also, if you "prime" with Pva, the adhesive will eventually lose it's bond with the substrate.

Manufacturers design their products in systems. Do not ever combine them with things, or in ways, which aren't expressly stated to be suitable. It's a liability issue.

Most good manufacturers retail latex additives which you can mix with their adhesives to make them more flexible. Check out Ardex, BAL, and MAPEI. They have two component adhesives which are highly flexible, and single component adhesives which can be made highly flexible using additives.

Read the "choosing adhesive and grout with standards as a guide" post in my guide thread for additional info on how to best choose materials. You can find the link in my signature.

Also, a good piece of advice would be to read up on different manufacturers product ranges, and their prices, and then ask around what people think about them. Read the specs and guidelines, which can normally be found on their websites. You'll learn alot, and you'll get a better overview of what can be used for what, and how the materials work.

 

[DHTiling]

You can get an additive for cement based normal adhesives to make them flexible.......but it will be cheaper just to buy a 10kg bag of flexi set...coz the additive is chance to be more to buy than that size bag of sticky...

 

[Mark2000]

cheers for the detailed advice sWe and Dave. I have managed to find a cheaper adhesive and managed to get it in a 10kg bag, i know you get what you pay for but i am only using it to tile 1m2. Cheers for all advice!!!

 

[DHTiling]

No probs.....what is the final piece you have to do..?...

 

[Mark2000]

We are given a piece of board and we have to tile it with a design that we have made up by ourselves and a design that influences us, i have dry laid it all out, and starting on it tommorow. i will post some pictures up when it is complete.

 

[DHTiling]

please do....as you know we love pics.........i look forward to it..

 

[NickH]

Besides, cementious materials and poly-vinyl-acetate don't mix. They're simply not chemically compatible.

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Now you see, I just dont get this. I've been in the building game for over 25 years and PVA has been and still is universally used as an admix/sealer/bondong agent for cement and concrete, in fact most products are recommended as such, for example
Link removed
I've personally used it a thousand times to seal and bond concrete and renders etc. and the stuff is still sound, I know because i still work on a lot of the same houses years after.
Every builder I know has a tub of this in the van and its used constantly, I just dont get the impression that its failing.
Another one that I struggle with is the "cementitous products are incompatible with gypsum products" statement, when gypsum plasters have been recommended and used over sand/cement renders for donkeys years.
I know what has worked for me over the last 25 years and i've yet to be convinced otherwise.

 

[DHTiling]

Nick....can you tell us if PVA stops the formation of Ettringite between cement and gypsum...we know Acrylic primers do but can you show us some literature that shows PVA does as well....?

Also can you show us some literature that states that PVA impregnates a substrate and not just sit on the face of it...?

I and quite a few members would like to see this.....in writing...

 

[NickH]

Dave your missing the point, I'm not saying you should use PVA as a primer for tiling, in fact I personally use SBR, its a superb product and if i'm in any doubt I'll prime, the stuffs cheap so why worry. The point i'm trying to make is that you cant just say that PVA and cement are incompatible because years of experience have shown otherwise.

 

[DHTiling]

I can't say i have had experiance of a reaction with PVA and cement ...basicly because i don't use PVA........Marcus ... can you find some info on this reaction please......?

Then it might help us understand your point.....

 

[sWe]

Cement and concrete are alkaline in nature. Alkali slowly attacks polyvinyl acetate, forming acetic acid, which has a low pH. Cement and concrete cures through hydration, which means the binding of water. 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. 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.

Furthermore, the acetic acid will continue to free the water bound through hydrolysis, and that will weaken the bond and/or integrity of the cement or concrete. 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 "waterresistant" or "exterior grade", has additives which makes them water resistant, but they're not alkali-resistant.

I'm hungry, I'll post more later.

Edit: oh yeah: http://www.tilersforums.com/tile-ad...-ettringite-formation-over-gypsum-screed.html

 

[sWe]

As for 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, or 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 hydrate; in other words, ettringite crystals. These expand, and pushes 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.

In the words of Cliff Anger:

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

And oh; I'm not an expert on this subject. I've merely researched a bit so that I could form an opinion

And oh again; 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.

 

[NickH]

Thats all very interesting but it doesn't alter the fact that statements such as "cementitious materials and PVA dont mix" are incorrect, sure there are lot of things PVA shouldn't be used for particularly with regard to tiling, but for other general building uses its a very useful product proven over many many years.
Similarly, gypsum plasters have been used over cement renders for many years and are manufactured for that very purpose, to say that cement and gypsum are incompatible products is a sweeping statement at best.

 

[sWe]

Thats all very interesting but it doesn't alter the fact that statements such as "cementitious materials and PVA dont mix" are incorrect, sure there are lot of things PVA shouldn't be used for particularly with regard to tiling, but for other general building uses its a very useful product proven over many many years.
Similarly, gypsum plasters have been used over cement renders for many years and are manufactured for that very purpose, to say that cement and gypsum are incompatible products is a sweeping statement at best.

As I said, the reaction won't be as severe on gypsum as it would on anhydrite, for reasons already stated. If you separate materials containing calcium sulfate, and cement, then there shouldn't be any problems.

"Cementitious materials and PVA dont mix" is a true statement from a chemical stand point, but real life has many variables. Failiure, nor success, can be guranteed, but the likelyhood of either can be increased or decreased, depending on what preparatory measures, and what material choices, you make.

As Cliff Anger stated, failiure isn't guaranteed, but it is a risk, and I would like to add that the risk increases if the materials aren't completely compatible to begin with.