The Brew Cabin

Posted: **Fri Sep 05, 2014 4:43 pm**

Hi,

Iâ€™ve purchased some of the silver grey (G603) granite 600x600 slabs for a patio (75m2).

Iâ€™ve been reading up about what to use to prevent staining or picture framing to the point where Iâ€™m now a bit paranoid, so Iâ€™m looking for some advice. Iâ€™m doing this for my own patio so its not like anyone is paying me to do it for them.

Iâ€™ve already got about 100mm of type 1 down which I am just about to level out / compact. My plan is to lay the slabs on a damp full mortar bed, leaving about 6mm between slabs which I can point later.

Iâ€™m planning giving the slabs a good soaking the day before I lay them (as I saw advised here!)
Iâ€™ve also read the recommendations of using silver sand or washed sand and white cement.

So my query really is - are both of these really necessary.. Would white cement and sharp sand do? Or silver sand and normal cement? Or could I even get away with plain old cement and sharp sand?

Beyond this, Iâ€™ve also read about coating the rear of the slabs with SBR - so again, my query really is if this is necessary?

Doing this for myself Iâ€™m trying to balance out cost but also do things as good as possible so I donâ€™t end up with stains and marks!

Any help would be greatly appreciated!

Posted: **Sat Sep 06, 2014 9:47 am**

found this from earlier this year by the gaffer tony McC

"I'm fairly certain we've discussed this before. The lighter granite to which you refer is the G603 silver grey, sold under various fancy names by all sorts of suppliers, and it is notoriously porous, so much so that it actively sucks-up the resin binder from polymerics and slurries and creates the unsightly 'picture framing' effect. It can do the very same thing with cement mortars. On the most porous pieces of G603, the surface of the paving can also absorb the resin which can result in unsightly darker patches, varying with the natural porosity of each part of the stone.

There have been various attempts to forsetall this effect. Pre-sealing the granite to prevent or limit absorption of the resin is a popular tactic, but has limited success. Whenever a piece of granite is cut, the 'seal' is breached and the resin can get into the granite. Also, with *some* mortars, particular sealants prevent a really good bond between mortar and stone.

Generally speaking, by thoroughly soaking the stone prior to jointing, and I mean soaking to and beyond saturation point, the thirst of the stone is quenched and less resin (or cement paste) is absorbed, which in turn prevents or minimises the dreaded picture framing effect. It also acts against surface staining, but because we are dealing with completely natural materials, with unpredictable porosity, results can't be guaranteed. This is why many contractors opt to use a dry-ish, just-about-damp cement mortar to hand point G603"

cheers LLL

Posted: **Sat Sep 06, 2014 10:05 am**

Thank you very much. It was posts like that which made me so paranoid!

So, in light of that, is the general consensus that for this specific variety of the granite, the white cement & silver sand mix is ESSENTIAL?

Posted: **Sat Sep 06, 2014 10:35 am**

I have never laid it so cant comment but all I can say is dont get your expectations up

the thing is all the picture framing and damp spots are only of concern to the nit pickers

you have made the bed ,now you get to sleep in it

if the patio is well laid with proper falls etc and is complemented by sympathetic planting it will still look good

but if you are looking for a wallpaper like effect you may be out of luck

all the best

LLL

The Brew Cabin

Granite slabs