Page 1 of 1
Posted: Mon Apr 25, 2011 8:55 am
by Spyvi
I laid my sandstone circle yesterday on a semi dry 4:1 sharp sand and cement bedding layer, buttering with a building sand and cement mortar. I can lift the flags this morning.
When the flags are laid, are they supposed to be fixed in place? Am I waiting to joint or for a longer curing process before the flags are fixed permanently?
Do I need to start again and if so, what should I do differently?
Posted: Mon Apr 25, 2011 9:11 am
by Pablo
If it's only a circle then yes start again and make the mix wetter. You could apply an sbr/cement slurry bond bridge to the underside of the flags before laying but I don't usually do that if the mix is good then it'll be fine.
Posted: Mon Apr 25, 2011 9:17 am
by Spyvi
Thanks Pablo: can you explain what an sbr/slurry bond bridge is? Also, are you saying that the flags should be fixed down when the job is completed? Should I leave the sharp sand/cement bedding layer down and make the building sand/cement mortar wetter?
Posted: Mon Apr 25, 2011 9:32 am
by Spyvi
My main difficulty is trying to work out how a non-fixed bedding layer (ie. semi dry sand and cement) is ever going to 'fix' the flags. Surely, whatever mortar I use on top of the bedding layer is going to fix to the flag, but not the bedding layer?
I'm now very confused.
Posted: Mon Apr 25, 2011 9:34 am
by Pablo
Mix a trowel load of cement with SBR (it's like PVA ony better) until you get a tile type adhesive consistency. Then paint it onto the back of the flag before you bed it. It'll stick like buggery so get it right first time. If you can get away with increasing your levels then just relay on top of the old bedding otherwise bust it out. The pointing will not make the flags stick if thats what you're asking.
Posted: Mon Apr 25, 2011 9:43 am
by Spyvi
Pablo - if I were to start again without using sbr (I'm convinced it isn't fixed properly because I'm inexperienced!) - would I do what I did before (semi-dry sharp sand and cement to bed) then butter with a much wetter building sand and cement mortar? I did both on a 4:1 mix.
Posted: Mon Apr 25, 2011 10:29 am
by lutonlagerlout
i think the problem is in the definition of a semi dry mix,it still has t be wet enough to hold its shape if you make a ball of it in your hand
also the pointing helps hold flags in place
LLL
Posted: Mon Apr 25, 2011 10:39 am
by Spyvi
OK thanks Pablo and Lutonlagerlout. I'm going to take the flags up and semi-dry the bedding layer as LLL suggested (wetter than I've been doing it) and mortar with a wetter mix.
I might buy some SBR too!
Posted: Mon Apr 25, 2011 11:00 am
by Pablo
be careful with the pointing if it's to wet or sloppy then the flags will stain.
Posted: Mon Apr 25, 2011 11:04 am
by London Stone Paving
It is also important that the mortar mix is well compacted down. The harder the mortar is compacted the stronger it will be.
It would be easy to lay a sandstone circle level for example by putting your slab on top of the mortar mix and making a few gentle taps with the mallet to make it level, but that would not be sufficient. I am not saying you need to smash the hell out of it but you do need to make sure the mortar is well compacted.
Posted: Mon Apr 25, 2011 11:50 am
by Spyvi
Thanks for the further advice - I'll make sure I position firmly! I'm also paranoid about staining - the gear cost a total of £900 odd (2400 setts and two circles) so I don't want to ruin them.
Posted: Mon Apr 25, 2011 2:46 pm
by London Stone Paving
Obviously you need to take care but you dont need to go overboard. Stone is hardy stuff.
If you are worried about mortar staining just get a bucket of water and cloth close to hand, that way you can wipe off any mortar spills as you go.
Posted: Mon Apr 25, 2011 3:25 pm
by Spyvi
Thanks to everyone who replied - I count myself lucky to have access to this forum cos it's only experts who can help when you're attempting to do something like this!