Advice please - natural sandstone - indoors on anhydrite screed

[frances.inglis]

Hello,
I am pretty new to this forum and would like some help please on laying sandstone indoors. I’ve read up everything I can find that looks relevant first so as not to waste your time :smilewinkgrin:

I have a 3.2m diameter circular floor area with anhydrite screed finish and am a laying Bradstone natural sandstone (pre-cut) circle kit (approx. 20mm thick).
The screed has been sanded to remove laitance and is flat. There is very LOW temperature (approx. 35 deg C) warm water underfloor heating laid below the screed.

Do I need to lay a decoupling mat?

What adhesive would you recommend? I do not need to make up any height.

I plan to seal the stones before laying with Lithofin Stain Stop until the stones are saturated. Does anyone have alternative recommendations?

What grout works well with sandstone? The joint width is 10-15mm on these kits as they are really for outdoors. This seems very wide to me.

Are there any other pitfalls I should be aware of please?

Thank you in advance.

Frances

 

[Spud]

lithofin stain stop is a great product however I found fila w68 worked better for me on the last sandstone job I did and is now my favourite product for natural stone

 

[jonnyc]

frances .
make sure anhydrite is dry as per recommendation and primed as per.
dont have underfloor heating on during fixing or at leat two weeks after completion of whole job.
heating should have been commisioned brought uo]p to temp held and brought down over period recommended.
i always use ditra on anhydite but may not be necessary for such a small area.I always use tlilemaster anhyfix adhesive which is compatible with anhydrite sceed to fix ditra mat down and then use normal flex adhesive to stick sandstone on top of ditra .
now for the sealing.
i never preseal stone as for most part it comes wet by dint of fact that it is cut witha wet saw and packed in crate wet.
if you want to pre seal then fine but make sure stone is dry before you do.
i rather fix the wet stone and let it dry and then seal.
leave seler overnight to cure and dry and then grout.

 

[jonnyc]

leave grout till dry maybe two days and then apply further seal .
with sandstone i like to apply lithofin multiseal or clear hard wax.
doa test and see what you think.
sandstone is very very porous and you definitely need something as surface seal.
i would never use a single part flex grout with sandstone as i would be worried it would stain stone.

i do my own mix of c2 ardex colour combinations with no additive.

 

[jonnyc]

sorry i have to keep posting quick as i have just spent half an hour relpying to you and got timed out and lost all the info so i am starting again.
regarding setting out and joint widths , i am not qualified to give a professional opinion but ive had a bash at loads of circular segmented ringed features and most of these we made ourselves .
you have chosen quite a challenge if this is your first if i may say so.
nonetheless it is quite doable?
were only talking maths here and being clean with not getting adhesive on the tiles to achieve what you want asthey are super porous

 

[jonnyc]

if your worried about the joint width recommended by stone supplier then there is reason for this i suspect.
10-15mm is not uncommon on a terrace. this product would be aimed at the outside terrace market which has to be competitive .
the accuracy therefore is what it is.
if you want to go inside and create a more accurate mimalist look you have the wrong product

 

[jonnyc]

this said you can achieve a closer joint and it is possible.
what you have to do is to draw an outline on your floor probably a bit like what you saw on the golden shot.!!
apologies if you are too young for that .
but tiling is alll about mathematics / symmetry and practice .
when i started i had real good maths /symmetry but no practice .
you need to find the centre point where you want your feature to radiate from.

 

[Lithofin BOB]

As above , i would lay , ensure all is clean and Fully released of all moisture , then impregnate. Whichever impregnator you use be aware that it lines the capillary of the stone and does not fill it, this stone is prone to surface contamination even if sealed. Perhaps you could gun the morta/ grout in ,as do a lot of the external guys, not sure how the guys feel about this , more time consuming but less chance of contamination which is difficult to remove . Test your grout release on a spare sealed stone to ensure your confident to move onto the floor.

 

[jonnyc]

bob agree with above.
i posted a full to do and got timed out .
i get very frustrated by this and only happens on this forum only.
i said that i thought the sandstone needed either lithofin multiseal or hard clear wax as top seal.
lithofin stain stop on its own is going to bemaitenace unfriendly

 

[Lithofin BOB]

Absolutely , I would apply 4-5 coats multi seal on top , satin sheen yes, but so much easier to maintain as you say.