Laying blue black granite paving - Mortar bed

[Stu 101]

Morning,

I have recently purchased some 800x200x20mm blue black granite paving slabs and am looking for some advise on the mortar bed. At present I have laid a 100mm MOT type 1 base and have allowed 50mm for the mortar bed. My question is do I need to use white cement and silver sand to reduce the chance of staining or is this only required on the lighter slabs?

I do plan to apply an SBR slurry to the back of the slabs prior to laying and reading through the helpful posts on this website some suggest wetting the slab the night before laying.

Any help will be appreciated.

Stuart

[r896neo]

Your on the right track. The slurry bond bridge will help mitigate any staining and making sure the flags are not bone dry will also help.

I can't see any advantage using silver sand or white cement if using a bond bridge.

[Stu 101]

Thanks for the response.

In terms of joint size what would be the most recommended. I do like the contemporary look of the thin joints however with issues such as picture framing and the like would 5-6mm be sufficient to reduce this risk and still achieve good aesthetics?

[r896neo]

Is the paving sawn? If not you may struggle to get joints that tight.

5mm is the absolute minimum for a pointed joint in my book. 7mm is a little more generous but still tight and looks neat.

You obviously will only be able to point with some sort of slurry product with joints that size.

When jointing the same rules apply. Make sure the paving is saturated before jointing (but not too much water sitting in joints)

[Stu 101]

Yes the paving is sawn if 7mm is preferable I will go with that would rather do a proper job.

For the jointing compound are there any recommendations I was looking at the weatherpoint 365 however a few seem to be complaining about staining at present even when keeping everything wet. Is there the same issue with GftK 850. I know it's a bit expensive but don't want to skimp on the last bit.

[Tony McC]

I've heard many, and seen for myself several of the complaints about staining with Weatherpoint and, despite the protestations, I reckon at least three-quarters of the issues reported are down to installation error, and the most likely of these is people emptying the product onto the paving and *then* applying loads of water, when the correct methodology is to abso-bloody-lutely saturate the paving long before putting the mortar anywhere near the surface.

I've seen the same problem with other products, including the GftK products, Romex, and a couple of others.

There's a GftK product that works with 3-5mm joints which revels in the charmingly unforgettable name of VDW 815. I've been playing with this and sawn granite/honeds sandstone/porcelain paving for the last frew months and I'm very impressed.


As for the bedding, the darker granites tend not to be adverseley affected by doscolouration in the same way as the awful G603, so no real need for silver sand and white cement, but the bond bridge slurry primer is an absolute must.