# Forum Home Renovation Tiling  Blueboard as tile underlay?

## Haveago1

Is there any reason I could not use blueboard as underlay for 400 x 400 polished porcelain tiles in a foyer area?  
I have some left over blueboard sheets so would rather not now have to buy additional underlay if it was not necessary.....

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## Bedford

I'd use it, as long as the little extra in height isn't a problem. :Smilie:

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## Haveago1

I have enough room, but have now been told tile adhesive will not stick to it....bugger.

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## Damo182

depending on how big the area is you try roughing it up with an angle grinder. but for the cost of a few sheets of underlay the hassle might not be worth it.

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## Haveago1

_but for the cost of a few sheets of underlay the hassle might not be worth it._  
Yep, I'll go with the line of least resistance and get the underlay. Thanks

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## Bloss

I've used various adhesives on blueboard and they are still holding up after some years. Can't see why the blue dye (as that is all it is) should make any difference to the underlying fibre board. In any case you could lay with the face side (blue) down. I remove the recessed edges, but other than that can't see a problem. 
But as other have said you are not saving much.

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## Haveago1

_But as other have said you are not saving much_ 
True, but my real interest was in the bigger sheets of blueboard compared to tile underlay - 3000 x 1200 compared to 1800 x 1200.  
I am doing an area that goes from T&G to a slab and was hoping that the bigger sheet would cover the join in the substrates with a single sheet offering a much larger, unbroken 'transition' area from wood to concrete than the smaller underlay sheets.  
Tile people say it won't stick and manufacturers do not warrant their adhesives to stick to blueboard, notwithstanding it all appears to be fibre cement any......may try a test piece on some offcuts...its either going to stick or not....

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## Bloss

Tile adhesive manufacturers no doubt have evidence or at least enough doubt not to warrant their product on a coated surface - and that's understandable. Why that would apply to the uncoated side I can't see. 
In any case adhesive failure is rarely accepted by a manufacturer as a reason to refund anything or accept liability (and even then they' just give you new product!). 
Mostly I use common sense - but only for work my own place not a client - if it fails for me then it's me that has the problem. But mostly I do what the manufacturers say unless it seems especially dumb or clearly is CYA for them. 
Wat doesn't add up to me is that various finishes go onto blueboard and many of them are based on the same materials as adhesives - but your call.

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