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Posted: Fri Jan 15, 2016 3:52 pm
by SpitfireO
We have a paved area of 20mm Brazilian Slate that has been laid on a sharp sand/ cement base. Most of the stone has failed to bond to the base. (The installer did not use a cement slurry bond bridge as advised on this site which may be the cause....).
What is now the best solution, given that the base is set hard?. Bond with a strong cement mix on the back of the stone? With SBR or not?
Or stick down with thick bed tile adhesive?
Advice much appreciated, thank you.
Posted: Fri Jan 15, 2016 5:34 pm
by exoticpete
I'm afraid the only option is to remove bedding and start again has the contractor been paid ?
Is it casarta slate ?
Posted: Sat Jan 16, 2016 8:22 pm
by SpitfireO
It's not Marshalls but is very similar, although biggest are 600 x 600. Not paid yet, we are trying to work out the right solution.
Posted: Sun Jan 17, 2016 8:24 pm
by seanandruby
are the slabs rocking, or moving when you walk on them and are they pointed up? any photos?
Posted: Sun Jan 17, 2016 8:55 pm
by SpitfireO
Not pointed yet. No rocking really, but about half of the slabs are not stuck down- they slide and can be lifted up and are wet underneath. Nothing has stuck to the back. The contractor has suggested sticking with adhesive (although he hasn't said what he proposes) or strong cement mix.
Posted: Sun Jan 17, 2016 10:55 pm
by seanandruby
Pointing would of probably kept them in place being just for patio.
Posted: Wed Jan 20, 2016 7:02 am
by lemoncurd1702
A fairly creamy mix of SBR and cement may do it or even better if you can get hold of it Pro-Prime.
Paste it on the mortar bed and make sure to note the orientation of the slab before you lift it and relay it.
I would check the ones that haven't come loose yet also by giving them a gentle kick on the edge.
Posted: Wed Jan 20, 2016 4:32 pm
by SpitfireO
Thanks to Pete, Sean and Lemoncurd for your replies.
The contractor did a test installation with tile adhesive (Mapei Stone and Porcelain rapid). That has stuck very well (can't move it) and now has been down a week including hard frosts.
If the whole lot is re- stuck with that on a solid bed, I suppose it could be OK.
For pointing, I guess that the problem of adhesion could occur again- do people recommend SBR in the pointing mortar? At what ratio?
Posted: Wed Jan 20, 2016 10:24 pm
by lemoncurd1702
That's good news.
Regarding the pointing I don't think you'd go far wrong with Marshalls Weatherpoint 365 or similar, but the Weatherpoint out of choice.
Depends what the contractor has allowed for grouting: Target price £30+vat a tub, should cover around 7m2 give or take.
Posted: Thu Jan 21, 2016 6:31 am
by cookiewales
i would use a waterproof grout flow point or decent exterior tile grout best practice to keep water out 365 is good but permeable 