Granite outdoor flags

[dave1975]

I’m about to lay some granite flags and wondered if I need to seal the tops before I start. Granite “generally” is non porous but I’m unsure how it reacts with sand & cement. I was planning on sealing them once they’re down anyway (as it’s easier) but wondered if I need to do that pre laying.

 

[John D v2.0]

Make sure the sharp sand and cement laying course is not a wet mix and it won't be a problem anyway

 

[dave1975]

I was going to lay them on 3 parts sharp, 1 builders & 1 cement with a slurry on the back. Is chucking in a bit of builders sand a problem?

 

[John D v2.0]

That's too much cement, i did about 8 to 1 sharp sand to cement. But you could go up to 6 to 1 if you're worried.
If you add that much cement you'll need more water and with more water you're more likely to make a mess.
The builders sand i can't see why it's needed. It's more likely to shrink and it needs more cement, it's designed for when you need a fine mortar for bricklaying with consistent narrow joints.

 

[John D v2.0]

Paving expert is a good site for information about laying pavingbtw

 

[dave1975]

Ok thanks I’ll have a look

 

[Agile]

I would use about 7:1 with sharp sand and probably laid dry to pick up moisture and harden later.

Given the constituents of granite I would not expect it to reactive with any concrete mix.