Chalky calcium silicate board?

[Poppin]

I have recieved my Calcuim Silizate board of the construction of the hearth. I planemned to tile directly on top of it. However the board is quite messy and unexpectedly chalky. White powdery residue comes off on your hands when touched. 

 

I would imagine no tile adhesive would work on this. Is this normal? Should I screw on some tile backer?

[blackrose]

Give it a wipe over with a damp cloth and then give it a coat of PVA. If you're using high temp silicone as your tile adhesive you might not need the PVA. If using silicone you don't need to cover the whole tile, just a blob in each corner and maybe one in the middle. 

[gatekrash]

We've literally just done this 2 weeks ago. Spoke to someone that does this stuff for a living and he said get some decent primer from a tile shop, something like BAL all purpose, first coat on at 4 to 1 water to primer, wait half an hour, repeat at 2 to 1 dilution and then tile.

 

We've done that and the tiles are stuck like the proverbial to a blanket.

 

Originally we were going to prime in dilute PVA but he said on calcium silicate it runs the risk of peeling, and every tiling forum I checked also strongly advised not to use it, although I know many others haven't had a problem with PVA.

[Poppin]

43 minutes ago, blackrose said:

Give it a wipe over with a damp cloth and then give it a coat of PVA. If you're using high temp silicone as your tile adhesive you might not need the PVA. If using silicone you don't need to cover the whole tile, just a blob in each corner and maybe one in the middle. 

 

38 minutes ago, gatekrash said:

We've literally just done this 2 weeks ago. Spoke to someone that does this stuff for a living and he said get some decent primer from a tile shop, something like BAL all purpose, first coat on at 4 to 1 water to primer, wait half an hour, repeat at 2 to 1 dilution and then tile.

 

We've done that and the tiles are stuck like the proverbial to a blanket.

 

Originally we were going to prime in dilute PVA but he said on calcium silicate it runs the risk of peeling, and every tiling forum I checked also strongly advised not to use it, although I know many others haven't had a problem with PVA.

Thanks!! Will use BAL all purpose. What heat silicone would you recommend for tiles? Was going to use envirograf for flue but not sure that's also an adhesive?

[Cas446]

On 17/09/2023 at 10:20, Poppin said:

 

Thanks!! Will use BAL all purpose. What heat silicone would you recommend for tiles? Was going to use envirograf for flue but not sure that's also an adhesive?

 

Use proper heat resistant adhesive.

https://shop.vitcas.com/vitcas-heat-resistant-tile-adhesive.html

 

[TandC]

I see VItcas also do a dedicated primer https://shop.vitcas.com/pva-adhesive-sealer.html - although the other stuff mentioned above will be just as good.