To seal or not to seal....before laying - Laying smooth sandstone

[reg]

Hi all.
I am laying a brad stone (Ivory)smooth sandstone patio on a Screeded bed that has been down some months .

After reading this factual website, i would like to check that the way I intend to do it is correct .

SBR slurry the back of the slabs (for adhesion and try to stop any effervescence)

Use white cement and silver sand in a 8-1 dryish mix. ( to avoid any marks coming through the slabs)

Point up with Larsen (white)gun grout.
From what I have read the combination of using SBR slurry and white gun grout on unsealed smooth sandstone seems like asking for trouble, as far as messing up the face of the slabs while laying the slabs I would like to seal slabs first with Lithofin stain stop MN or similar.

I called Lithofin re sealing before laying and was told that they would only recommend sealing after 8-12 weeks to allow for effervescence to take place.

We are in the middle of a heatwave at the moment so I can be sure that the slabs are bone dry. I can lay them out in the garden which makes sense to seal them now before laying.

I can’t find a definitive answer to my question, a question that that must be relevant to many people out there .
SHOULD I SEAL BEFORE LAYING PLEASE?
Thanks for your time in reading my post.

[KeburDave]

We've laid smooth Bradstone Ivory a number of times and I wouldn't lay it unless it had been properly pre-selaed as it is very prone to staining. We pre-seal all our smooth/honed sandstone with Drytreat Stainproof which is a breathable solvent based sealer, it will actually prevent the emergence of Efflorescence and if you do get any coming through it is always extremely fine so easy to clean off. You need to be careful when applying sealants in direct sunlight and with the Honed sandstone we always apply a fine mist spray first.

[reg]

Hi David,

Thanks for your reply.

Have you ever used the Lithofin Mn stain stop on the sandstone pre seal?.

I was thinking of using this product as i have a few litres of the stuff left over from the interior limestone sealing that i have done on the same project, although

i want to do it right first time ,so if i need the dry treat, i will get it.

Do you use the sbr / white cement to slurry the backs?

Which grout do you use on these slabs. I was thinking of using the Larsen white cement gun grout, and sealing the grout afterwards.

[KeburDave]

We use Instarmac Pro Prime to slurry the back of our slabs but you can make up a Slurry using SBR and Cement if you want, never found the need to use white cement before. We've used a number of products to grout the smooth honed slabs before, Ultratile Flexjoint and Gftk vdw 815 both worked well but only on pre-sealed slabs. I haven't used Lithofin stain stop before but I think it is a very similar product to the Drytreat Stainproof, i.e. a solvent based breathable impregnating sealer. There are also a lot of reasonable water based sealants around which still do a decent job and are a lot easier to apply but will need reapplying after a few years. We've even applied a water based sealant first as a pre-install to initially protect the stone from mortar staining or compound staining and then applied the Drytreat Stainproof at a later date. As long as the sealant is a breathable impregnator you will be fine its the cheap Acrylic surface sealers you need to avoid.

[KeburDave]

We use Instarmac Pro Prime to slurry the back of our slabs but you can make up a Slurry using SBR and Cement if you want, never found the need to use white cement before. We've used a number of products to grout the smooth honed slabs before, Ultratile Flexjoint and Gftk vdw 815 both worked well but only on pre-sealed slabs. I haven't used Lithofin stain stop before but I think it is a very similar product to the Drytreat Stainproof, i.e. a solvent based breathable impregnating sealer. There are also a lot of reasonable water based sealants around which still do a decent job and are a lot easier to apply but will need reapplying after a few years. We've even applied a water based sealant first as a pre-install to initially protect the stone from mortar staining or compound staining and then applied the Drytreat Stainproof at a later date. As long as the sealant is a breathable impregnator you will be fine its the cheap Acrylic surface sealers you need to avoid.

[reg]

Hi Dave,

Thanks for all your advice.

Best to ask the questions and get it right first time