Granite planks

[Bob_A]

Well the missus idea of circle kits last all of 5 minutes and now the boss wants the complete opposite being granite planks 900x200x20 for an area of 15m2 where next doors Leylandii drops it bits.
I'll probably be using GFTK or Romex for the jointing and would like the joints to be narrow, how narrow can I safely go, I was hoping to go for 5mm.

There are a number of GFTK usage calculators on the web but only when I use this one I get a message saying 'joint depth should be more than depth 30mm
LINK
I do not get this warning on the manufacturers website
LINK assuming the manufacturer should know best is it safe to assume 5mm wide 20mm deep joints be ok?
Thanks

[Tony McC]

If you use the VDW 815, that's designed for 3-5mm joints, so ideal for the sort of joint you are considering.

The 30mm depth requirement is "up for discussion", shall we say. There does need to be a minimum depth, and that is probably at least 20mm. Then there's a depth at which possible failure is pretty unlikely, and that's probably closer to 25mm. And finally, there's a depth at which failure almost never happens and the supplier gets to flog lots of lovely mortar. This all gets a little complicated by the fact that the 815 is designed for narrow joints, so, while the VDW 850 at 10mm width may well last for decades at 20mm depth, with just 5mm or so of the 815, some additional depth is necessary to give the material enough 'bant' to survive.

With these planks of yours, I'd lay as directed (and be aware that some granites really need to be pre-sealed), then rake through the joints with a big nail to give a bit of additional depth and clear out any accidental debris. This should give you 20-25mm depth, and that would probably be adequate for a residential patio.

[Bob_A]

Thanks Tony and you also managed to answer a question that I had thought about but haven't asked yet.
The answer is a big nail :laugh:

[Tony McC]

Invaluable bit of kit, is a big nail!

[Bob_A]

I’m thinking about using my cheap and nasty table saw IT'S THIS ONE and replacing the blade with a diamond one to cut my granite planks.For my project I will need to make a total of approx. 20 cuts each 200mm long into the 20mm thick granite planks, I would be looking to buy a cheap blade so it can be discarded afterwards I assume I can do this?
The bore of the blade needs to be 25.4mm which really cuts down the amount that are readily available, if it were 22.2mm then they’d loads to choose from.
Most blades with a bore of 25.4mm have continuous rims, very few have segmented edges. Will a continuous edge blade be ok
LIKE THIS ONE
If the table saw gets ruined in the process then it's not a problem, it'll be an excuse to replace it :laugh:
Thanks

[dig dug dan]

How will you apply water?

[Bob_A]

I was going to very carefully tip some water out of a cup as I went along or better still get an assistant to do it. The machine will be protected by an earth leakage breaker.
I know I'm talking about making twenty 200mm cuts into granite but I got the idea of a table saw from this porcelain thread
Link
I assumed the table saw mentioned in that thread is an ordinary general purpose one? I'd imagine it would need to be kept clean all the time but that's only time and I have plenty of that.
Could I get away without using water if I can get hold of a segmented blade, I know dry cutting is frowned upon but if I'm the only one in my garden and I'm wearing PPE perhaps I could be forgiven for the small amount of cutting I need to do?

EDIT
Or maybe a tile cutter for this one off job and if it survives I could always use it as intended a tile cutter.
This one looks less plastic than the other cheapies

[Tony McC]

I'm by no stretch of the imagination an expert on saw blades, but somewhere in the back of me mind is a remembrance that cont. rim blades *must* be cooled, whereas segmented blades are better if cooled, but it's not quite essential.

I'd be loath to cut granite without cooling - it eats blades is they are allowed to get too hot.

[Bob_A]

I'm by no stretch of the imagination an expert on saw blades, but somewhere in the back of me mind is a remembrance that cont. rim blades *must* be cooled, whereas segmented blades are better if cooled, but it's not quite essential.

I'd be loath to cut granite without cooling - it eats blades is they are allowed to get too hot.

Thanks Tony I've got my eye on a 650w (rather than the cheapest 450w) tile cutter table that's water cooled. Maybe buy a segmented blade and together with the water it might just do it
If not I still have a tile cutter for an indoor project in the future

[Bob_A]

I've started and making good progress with the sub base, I'm using 75mm of type 1.
Although it's probably not necessary I've put a geo textile between the sub grade and sub base, reason being is I got it dirt cheap.
My standard bedding layer will be 6:1
Laying to a free edge will be like this


To finish the fabric at the edge I was going to bring it upwards fold it back and sandwich it between the sub base and the Class II, if that's ok does it matter how much I fold back and sandwich, just wondering if it can be too little or too much that it could compromise the job the Class II is meant to do.
Thanks

[lutonlagerlout]

Hi Bob
what kind of granite are you using?
cheers LLL

[Tony McC]

Bob - no problem with your proposal.

Possibly pre-empting what's going through the mind of LLL, but don't forget to use a good quality slurry primer bond bridge on the underside of the granite flags immediately before laying.

[Bob_A]

Hi LLL
I always do a fair bit of research on here and read that you have reservations about Chinese granite, you being a regular I always take note and for that reason I recently resurrected an old thread to find out moreLink
As you've pointed out some granites are prone to reflective staining, mine is an Indian granite and I'm going to take Tony's advice and use a slurry on the underside which will hopefully negate the effect. Fingers crossed
I may seal it from the top but will wait until the dryer weather next year before deciding.

Tony McC
The planks have a depth of 200mm so I was going to dampen the fabric, fold it back so that 75-100mm is left under the planks, ClassII and finally lay the plank with the slurry applied.

[Bob_A]

Most of the granite planks are down so it’s time to think about VDW815. It says the minimum working temp is 3C. I’ll check with the Met Office but achieving above 3C during the day in London is not normally difficult but what about if it gets unexpectedly frosty overnight, will that cause problems? The first thing that comes to mind is to cover the newly jointed patio overnight, I’ve got a thin tarpaulin, will that do? Don’t really want to buy something just for a night when it might not even drop below 3C.
Will a cheap tarp be adequate?

[Tony McC]

It really is important to observe temp requirements. It's best to wait for a suitable day, which I acknowledge are fewer and further between just now, but if it means holding on for a few days, it's well worth the delay.

Tarps work fairly well, but you can improve their effectiveness by scattering the surface with straw or scrunched-up newspaper/carboard before covering with the tarp - that traps in more of the insulating air and keeps it still.