Forum: Flags and Slabs
Topic: Slabs on beam and block - advice needed
started by: HelpMonkey

Posted by HelpMonkey on 11 July 2019,14:53
Hello guys
Please can you advise.
House built on a slope.  So we have a rear patio area made from beam and block - about 40m2.

Have bought sandstone slabs of mixed sizes.  Biggest 90@x600.  Wondering whether you could guide me on best way to bed sandstone onto beam and block?  The beam and block bounces and moves in small amounts, as do most, and thinking of damage to adhesion and joints.

- will a mortar bed be sufficient?
- should it be screeded first?
- should I go with a BAL type flexible product straight onto beam and block?

Any advice very welcome on how you would do it

Posted by Tony McC on 16 July 2019,09:33
I'd be more concerned with ascertaining why the B&B floor is moving, It should be more-or-less completely stable. You can sometimes get minor wobbles when a bit of grit or similar has lodged benath one of the blocks, but other than that, there should be no movement. Sort that first!

The usual process then would be to lay a DPM, insulation (if necessary) then a screed of sand/cement, and finally the paving itself.

But all this depends on the B&B being stable. Any movement therein will only be transferred through to the eventual paving layer.

Posted by HelpMonkey on 18 July 2019,22:45
Thanks for your guidance, much appreciated.
The B&B has some flexibility as it’s 4750mm long, the max span without support.You can feel small movement if you jump in the centre.  I have now screeded the surface.

Would you use a flexible adhesive or a mortar bed for the sandstone slabs?

Posted by Tony McC on 19 July 2019,10:16
Mortar bed - there's nothing to be gained by using a flexible adhesive
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