Hi,

I have started a project laying an indian sandstone patio.

So far I have put down 100mm mot subbase. A friend of mine who is a builder suggested I put down an inch of compacted sharp sand (which I have done), before applying a full mortar bed and tapping the sandstone onto that.

As I say, I have got as far as putting down an inch of sharp sand, screeding it, then compacting with a wacker. (I understand i probably should have compacted then screened, but it seems fairly level; and I am aware it will now be less than an inch deep but fairly uniform in thickness).

It seems as though most guides I've read ignore the inch layer of sharp sand step, and instead suggest putting down a full mortar bed directly onto the compacted mot sub base.

This now worries me. The questions i have are:
Will I need to remove this sharp sand layer?
If not, will a mortar bed stick to compacted sharp sand?

Thanks in advance!
Kash

@RpR. Kash, where are you geographically located?

What is your mortar mix?
An inch of sand is used for dry laying, I assume you are laying semi-dry and as you compacted it, it will make no difference.

RpR said:What is your mortar mix?
An inch of sand is used for dry laying, I assume you are laying semi-dry and as you compacted it, it will make no difference.

Planning to use 4:1 mix. Will a semi-dry mix affect the longevity of the Indian stone slabs? I've read in a few places it may shorten their lifespan.

What do you think about the alternative options?
- rake up and remove the sand, and apply 4:1 mortar mix directly on subbase and fix slabs
- loosen the sand and mix cement and little water to create mortar 'in situ' for slabs to sit on.

Which would you personally prefer?

Kash

crawgarden said:@RpR. Kash, where are you geographically located?

Oldham, England.

We have lot of rain all year round here, heavy clay soil.

Kash

You are probably fine just as you are, sand will not be a problem as you already compacted it.

RpR said:You are probably fine just as you are, sand will not be a problem as you already compacted it.

Will I still need the mortar mix on top of the compacted sand to sit the stone on?

If so, will mortar stick to the compacted sand in the same way it would to the subbase?

Yes
Yes
MOT consists of small rock to just plain dust, sand is in there also.