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Posted: Thu May 09, 2019 5:37 pm
by Freddy871
Hi all, first time post to this forum so hi and please be patient with me. I am by no means an expert, but feel with some time and effort this is not out of my reach and ability. Anyways decided I would like to lay my own Patio, and under the instruction of my luvly wife she has decided on Silver Grey Granite or Kandla Grey sandstone sawn in a 600 x 900 brick pattern edged with dark grey brick/cobble sets. I have looked through many posts re both type of slab and was hoping for some solid advice to try and ensure I have the best chance of a nice finish. From reading and although not ideal I have an existing concrete slab base that I would like to extend with MOT to give me a larger area. that looks like this
My Webpage
First question - Am I OK to lay over the concrete base without issue and then continue to new area with mot sub base.?
Hopefully should the above be OK , I am planning to use a 5/6 to 1 sharp sand mix across both with a full bed allowing water to run towards grass.
Second question - Reading across many posts I see horror stories of picture framing. I really would like to avoid this. Is coating the back of the granite and sandstone with an SBR prior to laying adequate or is there other precautions I should be taking . If SBR i OK can you advise on brand.?
Bear with me please, nearly there. With some luck and assuming we have made it through the above questions, I am now nearing the pointing stage
Third question/s - Anything I need to consider before pointing, again to avoid any staining, as was planning to use Azpects easypoint. And once finished how long to leave before sealing , or should i refrain from sealing at all.
I am sure I have missed some crucial elements here, but appreciate your time to read and hopefully provide some guidance. 
Posted: Mon May 13, 2019 9:23 pm
by alrat
Hi, sounds like you're about to embark on the big project with all the enthusiasm I did a few months ago. Firstly, if you're doing it alone like I did, with a full time day job, prepare to give up a good few weeks of your life and put in some seriously hard graft. As well as taking a few days off, when there's good weather forecast, or you've hired a cement mixer (which you must!) and need to get your full mortar bed laid before it goes back. Persevere, as the result at the end will give you some serious satisfaction with what you managed to achieve. It sounds like you've done your research though, which is a good start.
Tony's website here is invaluable, you'll find all the information you need, but the level of detail can be overwhelming as it's for serious pros. Follow the rules these guys have been kind enough to share and you'll be fine.
Minimum 75mm sub base, the real tradesmen on here will have a better idea of whether you can keep your existing concrete area as a base, but from experience in other DIY projects, shortcuts rarely work out in the long run. Eg. You're unlikely to know what mix was used and it really needs to be permeable. Won't it cause you level issues too?
30mm full mortar bed, I used a 5:1 sharp sand and ordinary Portland cement mix. If I was to do it again, I'd consider white cement and a 6:1 mix. 6:1 is recommended by many jointing product manufacturers, as it's permeable and you risk limiting your choice, I think I was just lucky my 5:1 mix is permeable. Assuming you use silver granite like me, perhaps white sand is best (if you can afford 3 times the cost), as I've one flag with a crack, that has a dark grey mark along the crack even when dry, this could be the grey cement transferring through the crack from the base, although more likely just darker deposits coming to the surface.
When laying your flags, make sure you slope away from your house to an area the water can run off. Very importantly use an SBR slurry primer on the back of each flag before laying. You'll need a 5 litre canister of SBR and the mix to make up a paste to brush on the slab is 1 part SBR, 1 part water and 5 parts cement. I made just enough for one or two flags at a time, as it dries really quickly. If you have to re-lift a flag or the SBR dries before laying, re-paste it before laying.
Some tips from someone who learned the hard way.
Just bite the bullet and hire a whacker plate and cement mixer, you might think you'll manage without, but you won't!
Get a proper line builders line and rods and set your lines well so they last.
A small hand held angle grinder will more than suffice for cutting even granite, but you must get some good diamond blades and go easy so as to not overheat them as they'll go blunt faster.
Keep your gaps between flags clean and clear as you go, it's so much easier than having to revisit after the mortar has hardened. Run round each flag with a bit of wood the right width after laying each one.
You mentioned in your PM that you were keeping a keen eye on my sealant and jointing choices, if I procrastinate for a while longer perhaps you can do this first and tell me how you get on :laugh:
Posted: Tue May 14, 2019 6:58 pm
by GavP
Wow - you have just answered all my questions...just about.
I am almost working on an identical project - 6m * 5m with silver grey granite in 600mm * 900mm slabs.
I want to edge my tiles with black slate...I've edged the area with a 2 brick high red brick retainer and am attempting to edge with the black slate laterally but even after two days drying the slate is loose.
Is 'bond bridge' the answer? - or am I on a hiding to nothing trying to stick slate to a brick wall with mortar/anything....Should I abandon this idea and just run to the edge with the granite?
Only problem I can see with granite is that I'll have a half slab ever other row and it'll be a pig to try to cut accurately enough with an angle grinder.
Has anyone successfully adhered slate [22mm] to course of bricks as edging...or should I give up and perhaps remove the top layer of red brick and replace with black engineering bricks...?
Not sure what to do...
Posted: Fri May 17, 2019 1:28 pm
by Tony McC
Freddy:
First question - Am I OK to lay over the concrete base without issue and then continue to new area with mot sub base?
Yes, but make sure the Type 1 is thoroughly compacted to refusal.
Is coating the back of the granite and sandstone with an SBR prior to laying adequate or is there other precautions I should be taking . If SBR i OK can you advise on brand.
That's the best practice you can take to minimise the risk, but, as we are dealing with natural materials, it's impossible to state with 100% certauinty that picture framing will not occur.
As for SBR brand, look for a recognised name, such as Sika or Everbuild. Avoid 'bargains' and DIY sheds' own brand products, which tend to be diluted forms of brand name products.
Third question/s - Anything I need to consider before pointing, again to avoid any staining, as was planning to use Azpects easypoint. And once finished how long to leave before sealing , or should i refrain from sealing at all.
I would only countenance using a quality two-part resin slury mortar. I have lost patience with the shortcomings of the one-part products. With a good 2-part, as long as you use lots and lots and lots and lots of water, before, during and after, there should be no staining.
If you must use a sealant, I would wait a minimum 6 weeks to ensure any problems that are going to develop can be identified and rectified before applying the unnecessary varnish.
Gav P:
Yes: slate most definitely need a bond bridge.
Half-flag to give you a neat-looking stretched bond - cut one flag in half using a steel edge as a rule. A piece of old angle iroin is ideal. And then place the cut edge to the inside where the jointing will hide any minor discrepancies.
To "stick" the slates to the bricks, use a SBR primer on the underside of the slate and add more sbr to your mortar bedding mix.
Posted: Sun May 19, 2019 8:31 am
by GavP
Tony McC - Many Thanks!! (sorry to hijack a post!) - I don't know why I didn't think of reversing the cut edge to the inside :p
Posted: Sun May 19, 2019 2:18 pm
by Freddy871
Thanks for your wisdom Tony, however just when i thought it was safe , my wife has now changed her mind, which being my wife she is allowed to do.. We are now looking at tumbled limestone from local supplier (supplier being natural paving i think) with a sort of shot finish.
Not to waste your valuable time, but does sbr/slurry and and jointing for limestone still apply.? and is limestone better/worse or same for potential staining , picture framing.? and other tips for this type of stone .
Posted: Wed May 22, 2019 9:25 am
by Tony McC
I think the limestone is a more forgiving stone than the granite.
A primer is not essential but it can't do any harm (if used properly).
The only real issue with limestone is that you really MUST NOT use an acid or acid-based cleaner, as it will dissolve the stone itself. Keep it clean with a good quality biocide and regular washing down with soapy water.
Picture framing tends to be less of an issue with limestone than is the case with some granites and sandstones.
If staining is going to be a real problem, consider using an invisible sealant, such as Dry-Treat - I think wet-look limestone is awful, but you may feel differently about it.