Adhesive - riven sandstone to smooth tile

[Skyman]

Hi, I have some left over Indian Sandstone slabs, they are Riven, rough and un-regulated in thickness. I'd like to lay these over some existing exterior steps that are covered with (semi shiny ish) kind of terracotta sort of tiles. I'd prefer to avoid having to remove these existing tiles unless otherwise advised. Is there a type of adhesive that can cope with these conditions?
Rough, porous surface to smooth, exterior. Many thanks for your expert advise. Cheers

[lutonlagerlout]

if you prime the sand stone and the steps with SBR
then mix up a 3:1 sharp sand :cement mix with 100ml of sbr in the mix
they will stick like the proverbial blanket
best no more than 30mm overhang
cheers LLL

[Mikey_C]

as well as the above you could also try roughing up the surface of the tiles.

[Skyman]

Thanks LLL - I had to look up SBR and that sounds like the Mother of all methods. Are there any off-the-shelf ready mix adhesives that will do a similar job? It's just a one-off fairly small front door step. Cheers

if you prime the sand stone and the steps with SBR
then mix up a 3:1 sharp sand :cement mix with 100ml of sbr in the mix
they will stick like the proverbial blanket
best no more than 30mm overhang
cheers LLL

[Skyman]

Thanks LLL - I had to look up SBR and that sounds like the Mother of all methods. Are there any off-the-shelf ready mix adhesives that will do a similar job? It's just a one-off fairly small front door step. Cheers

[lutonlagerlout]

its only about £15 for a 5 litre pot of sbr
worth every penny
just a bit of sand and cement and you are sorted
LLL

[Tony McC]

There are 'off-the-shelf' adhesives, but when you analyse them, they usually turn out to be sand, cement and a dry form of SBR or its equivalent, and the whole thing costs considerably more than a 5 litre container of the aforesaid SBR.

Most of these 'adhesives' are intended to be used as thing layers, just 1-3mm, and so you get what seems like good coverage from a pack. However, when you realise that bedding for riven, uncalibrated flags will take 5-20mm thickness, all of a sudden you're only getting a square metre or two for every pack, which is why those in the know, use sand + cement + SBR: it's just much better value for money!

[Skyman]

Thanks LLL & Tony - you've sold it too me.

Should I let the primmer coats dry before assembling?

Thanks again

[lutonlagerlout]

let them get sticky
be careful SBR really does stick like **** to a blanket!
LLL

[mickg]

if you get any SBR on the surface of the paving you need to remove it straight away with lots of clean water and a hand held soft brush rubbing vigorously otherwise you will never be able to get it off the surface of the paving