Unibond PVA - Aaaaargh! (or is it?)

[Grace'sDad]

I just spoke with a (hopefully soon to be) customer who told me he has PVA'd his floor (heated s&c screed) to keep the dust down before tiling.

As it was Unibond will it be ok, or does Unibond still mean trouble?
I seem to remember Unibond PVA being modified to avoid re-wetting?

If this is a disaster - why? and how do I remedy?

 

[davy_G]

I dunno about unibond, give their tech helpline a call, although im sure they will tell you its OK. Maybe get them to put that in writing first....

 

[LM Ceramics]

if he has pva d the floor i would say to the customer that you cant guranntee your work as pva had been used except from that i wouldnt know what to suggest

 

[grumpygrouter]

I just spoke with a (hopefully soon to be) customer who told me he has PVA'd his floor (heated s&c screed) to keep the dust down before tiling.

As it was Unibond will it be ok, or does Unibond still mean trouble?
I seem to remember Unibond PVA being modified to avoid re-wetting?

If this is a disaster - why? and how do I remedy?

Try wetting it 'dad and see what happens..........

 

[sWe]

Taken from my guide thread

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 hydration 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.

 

[Grace'sDad]

Thanks sWe - I remember that guide (actually I saved it all into one nice document which I am about to publish and make lots of money from - JOKE!)

The thing with the Unibond is that it's supposed to be waterproof.

Best bet is I'll contact BAL technical and ask them tomorrow.

If it isn't waterproof, how do I remove it???

 

[sWe]

Mechanically I suppose... Btw, I'm gathering input on such a document as we speak If there is no negative input on it, I'll post a pdf with the posts from the guide thread later tonight or tomorrow.