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Posted: Wed Nov 13, 2013 2:47 am
by TMASCO
I have a slate walkway being laid on a concrete base which goes below the frost line to avoid any movement with the surface which will be 1.5' thick slate.
I requested that all joints be tight - slate against slate and slate against belgium block borders/edges.
The mason has started to lay the slate and since he is having difficulty cutting the slate to make a tight joint between the slate and belgium block he is now telling me that all edges need some sort of grout line in order to keep water from getting underneath the slate and lifting the slate in the cold weather - the slate is sitting on a semi dry cement base on top of the concrete slab. My question is how can we keep a tight fit and avoid having to use grout between the block and slate.
sorry for the long explanation - i just want make sure all of the specifics are noted.
Posted: Wed Nov 13, 2013 6:59 am
by lutonlagerlout
your mason is correct
even natural stone shouldnt really be butt jointed
you need at least a 5 mm joint
you can get grouts or pointing compounds in basalt or dark colours to complement the slate
cheers LLL
Posted: Wed Nov 13, 2013 9:32 am
by Tony McC
Butt jointing (0mm wide) never works with natural stone unless you have hours and hours to waste sanding down edges to create a tight fit.
And what would you gain? Water will penetrate a butt-joint far more easily than a mortared joint.
I do quite a few layout designs for US-ian clients and there does seem to be an obsession with but-joints but I nearly always convice clients to accept a 3mm (1/8") joint to give some tolerance for the inevitable over- and under-size pieces that always occur with natural stone. And once the stone is laid, the clients usually comment on how effective a narrow joint looks, as it frames each stone, emphasising the design.
Slate, however, needs either a wettish bed or a bond bridge otherwise it *will* lift in your winters.
Posted: Wed Nov 13, 2013 9:46 am
by PavingSuperstore
The other thing to note if you are using a standard mixed size pack of paving, is that the slabs are generally cut to tesselate with around a 10mm joint. Even then, natural stone is never precision cut and there will always be a tolerance that you need to work with.
Also, it's not really normal practice anymore to lay paving on a concrete base. I know some contractors still opt for this method, but the usual approach would be to use compacted MOT Type 1 with a wet mortar bed on top in which to bed the stone. Being just a walkway you may be OK with the concrete, but certainly over a larger area you wouldn't want to use this method.
In terms of the jointing compound, we find the GftK 840 is a good option - here's a link if we can help you at all: http://www.pavingsuperstore.co.uk/gftk-ba....0-p.asp
Each tub covers around 12m2
Posted: Wed Nov 13, 2013 5:04 pm
by lutonlagerlout
i fear the postage may to be a little high to Connecticut George
:;):
LLL
Posted: Wed Nov 13, 2013 6:17 pm
by Tony McC
Actually, there is a GftK distributor in the US. I know this because he robs the content from my site, technically paid for by UK-based NCC Ltd, and uses it to boost his meagre sales in Utah.
If I was NCC, I'd be billing him, but they are much nicer people than me, so they let him get away with it. Fools!
Posted: Wed Nov 13, 2013 8:36 pm
by DNgroundworks
Tony, is the NCC you mention the NCC in Chorley, as in Gary? Or is NCC a nationwide set up? Gary's a nice fella see him often.
Posted: Wed Nov 13, 2013 9:06 pm
by msh paving
^^^^^^its the NCC in chorley, with Gary Ken MSH 
Posted: Thu Nov 14, 2013 11:06 pm
by London Stone Paving
This is actually one of the most common questions we are asked by clients. Its usually people who are looking to create a contemporary garden and they think in order to do so then they need to have a 2 or 3mm joint. Not only is it completely unfeasible due to dimensional tolerances but its also very difficult to get any strength into such a small joint. 6-8mm is the absolute minimum we would reccomend, anything less and you are asking for trouble
Posted: Sat Nov 16, 2013 8:48 am
by GB_Groundworks
PavingSuperstore wrote:Also, it's not really normal practice anymore to lay paving on a concrete base.
Says who?
They're are plenty of occasions where a concrete base is adventitious over a compacted mot base.
I see plenty of specified works called for paving laid on concrete slabs or cbm.
Posted: Sat Nov 16, 2013 10:30 am
by Tony McC
DNgroundworks wrote:Tony, is the NCC you mention the NCC in Chorley, as in Gary? Or is NCC a nationwide set up?
Yes, it's Gary from Chorley (well, he's a Sandygrounder, really) but he does travel the length, breadth and depth of the country with the GftK stuff.
Next time you;re with him, see if you can get him to stand still for more than 5 seconds. He's *always* on the move!