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Posted: Thu Sep 26, 2013 7:28 pm
by Morti
Hi. New to site and the world of paving so please excuse my ignorance. We're having granite patio and paths laid in garden using a mixture of silver/grey and blue/black. Seen articles on here about staining, picture framing and want to seek advice and reassurance I've got the facts right.
Granite pavers should be laid using a full mortar bed 6:1 mix using silver sand & white cement and same 3:1 mix for the joints. The pavers are 20mm thick and they're being laid onto a newly laid concrete base. How thick should mortar bed be and how wide should joints be? .
If the above is correct do we also need to coat each paver with SBR mixed with white cement and paint it onto back of pavers.
Drainage/rain run off to avoid puddles. Is this avoided by laying pavers on a slight gradient or is it more involved than that?
We're not laying these ourselves are getting it done professionally by a guy who lays granite but he worried me slightly when he said "I haven't laid this type of paver before" Eek!
Sorry I'm such a div but don't want to make any expensive mistakes and I want to make sure the guy is laying them to the recommended spec
Your advice and guidance is very much appreciated
:O
Posted: Thu Sep 26, 2013 10:04 pm
by London Stone Paving
Hello Morti
1. Yes, full mortar bed
2. the silver sand and white cement IMO us OTT for granite but there is no harm in doing it if it gives you the peace of mind against picture framing. The key to avoid picture framing is not to make the mortar mix to wet. If the mix is to wet when the slabs are tapped down with a mallet, the mortar will squeeze up throught the pointing joints. This in my experience is one of the biggest causes of picture framing.
3. Dont go for a concrete base. Use MOT type 1. MOT type 1 is a graded aggregate. The moisture from the mortar bed will be looking for somewhere to go and it will always take the easiest route. If you lay on a concrete base, that easiset route will be through the stone which is more porous than the concrete base. It will pull through cementitious material along with it and could potentially make some nasty stains on your paving which will be hard to get rid of. I've seen this happen on so many occasions when people lay natural stone on a concrete base
4. Joints 6-8mm is ideal for sawn paving.
5. Mortar bed 40-50mm
6. Pavers should be laid on a slight gradient. Your man should know all about this and if he doesnt I would look for another contractor
Hope it goes well
Steve
Posted: Fri Sep 27, 2013 8:41 am
by Tony McC
The silver sand with white cement is a good option with G603, the pale granite often labelled as 'Silver Grey' which is relatively porous and prone to staining when laid using iron-rich sands in the mortar and/or cements which are not white or wholly based on portland cement.
Picture framing is more common with stone that is 'thirsty', so porous stone (G603 f'rinstance) which has been sat in a storage container or outdoors in warm dry weather for a few weeks. If such stone is soaked with clean water a day or so before laying, but allowed to become 'surface dry' before laying, the incidence of picture framing is much reduced.
Bond bridging with SBR is really only needed with sawn granite.
For pedestrian-only paths and patios, 50-75mm of mortar/concrete bedding over a sub-base or sound sub-grade. It *must* be laid to falls to ensure water can drain from the surface.
I'd be wary of a contractor who hasn't laid this paving before. Get him to lay a trial panel of a square metre or so before giving him the job.
Posted: Fri Sep 27, 2013 11:15 am
by London Stone Paving
"If such stone is soaked with clean water a day or so before laying, but allowed to become 'surface dry' before laying, the incidence of picture framing is much reduced."
Nice bit of advice Tony. I will stick that in the memory banks for future reference
Posted: Mon Sep 30, 2013 11:07 am
by Tony McC
That's what I'm here for (occasionally) 
Posted: Mon Sep 30, 2013 9:23 pm
by Morti
Thanks chaps. Very helpful. Holy moly re the concrete base!! What a disaster its already been laid and it is a huge area. Think my builder might just want to throttle me 
As stated in my original post I'm a paving novice (and female) so I must ask what is MOT type 1 and can it be laid over the concrete base that's been put down? I'm panicking...big time.
Posted: Mon Sep 30, 2013 9:27 pm
by Morti
Sorry Steve just noticed you've explained in your reply that MOT type 1 is a graded aggregate.
Morti
Posted: Tue Oct 01, 2013 12:23 pm
by r896neo
It can't go over concrete unfortunately as concrete is relatively imperveous so the MOT will hold water badly and be unstable.
There may be a technical solution here so don't get the sledge hammer out yet.
Posted: Tue Oct 01, 2013 2:32 pm
by Morti
Thanks r896. Any advice regarding the technical solution would be very welcome
Posted: Tue Oct 01, 2013 4:30 pm
by lutonlagerlout
IF i were laying onto a concrete base i would be using a 6:1 grit sand:cement mortar with plenty of SBR in it
its not ideal and what should have happened is the pavers were laid directly onto 100 mm of the above in a drier mix
LLL
Posted: Wed Oct 02, 2013 7:08 pm
by Tony McC
Why has a concrete base been laid? I think your "builder" knows buggerall about this and is making it up as he goes along.
Sett Paving is a specialist skill. It's not a job for a general builder. If he offers to service the car or neuter the hamster, don't let him!
Posted: Thu Oct 03, 2013 7:40 am
by London Stone Paving
We see a lot of architects speccing concrete bases. TBF I can understand why they do it. They mistakingly think they are providing a bomb proof sub base. Unfortunately there are other issues to consider, the key one for me being the drainage issue.
Is there a solution for this project that does not involve lifting the concrete base?
Posted: Thu Oct 03, 2013 3:10 pm
by Morti
Thanks London Stone. You're correct in your summary. Our builder genuinely thought a concrete base would be the best option. His thinking being the 20mm thick pavers would essentially be laid like tiles rather than like paving slabs. As I stated above we're going to use silver sand and white cement for the mortar and make the mix quite dry (firm enough that when you squeeze a handful in your fist it retains it's shape when you open your hand) and treat the underside with a SBR/white cement in an effort to reduce staining and increase waterproofing of the pavers. The main issue now is drainage underneath the pavers.
I echo your question does anyone know how best to lay without lifting the concrete base?
Posted: Thu Oct 03, 2013 6:45 pm
by lutonlagerlout
Morti wrote:I echo your question does anyone know how best to lay without lifting the concrete base?
already answered
IF i were laying onto a concrete base i would be using a 6:1 grit sand:cement mortar with plenty of SBR in it
its not ideal and what should have happened is the pavers were laid directly onto 100 mm of the above in a drier mix
LLL
Posted: Thu Oct 03, 2013 6:49 pm
by Morti
Thanks LLL