Building or grit sand in bedding mortar

[r896neo]

I always use grit sand based for mortar for flags but was wondering what the technical reason for not using a building sand based mortar is?

Practically its troublesome because it holds so much water its like a soup when you tap into it but i'm sure there are technical reasons why a coarse sand is recommended?

I'm talking mainly about bedding for indian sandstone here when i usually lay a full bed about 40mm deep.

[lutonlagerlout]

grit sand is coarser so is a stronger bedding material
building sand is only ever laid 10-12mm thick and although it is more workable it is useless under flags

of course the next strength up is concrete,the bigger the aggregate and coarser the material the stronger the finished job

I suppose technically you could use building sand mortar on top of a flat concrete base but why make life hard?
cheers
LLL

[mike builder/landscaper]

When I do lay paving, my mix is 5 sharp, 1 yellow,1 cement and a splash of plasterciser, 40-50mm deep, full bed, it works well for me but I'm probably in the wrong.

[lutonlagerlout]

about 20 years ago when i switched to a wetter mix we experimented with adding a shovel of building sand and it does make it more workable

but 1 day we didnt have any building sand and the grit sand worked fine on its own when wet enough

of course our grit sand may be completely different to your Mike

cheers LLL

[lemoncurd1702]

of course our grit sand may be completely different to your Mike

cheers LLL

Regional differences.

The stuff LLL uses as building sand is from the ground and is much finer than the stuff dredged from the sea. I've had no problems using dredged sand 5:1 mix, wet.

The grit sand will vary also. If I go to the merchants for a bulk bag of sharp/grit sand it ain't much different from our building sand and is useless as bedding for block paving.

Cannot get dredged grit sand anymore as dredging licence has not been renewed. The only stuff available now is recycled, looks like a ground up mixture of mortar, bricks and other shit.

Looks the same as grit sand and if there is a difference it's positive.

[lutonlagerlout]

I have loads of sand pits in a 15 mile radius of me

soft at sand pit lane st albans which is bright orange

sharp from pratts yard leighton buzzard

riverwash (grit sand ) from linslade

but its all bagged and sent to local suppliers

I cant use that red B and Q sand for love nor money

LLL

[r896neo]

I'm asking because i normally get it delivered and i get screed mixed up as wet as building mortar with a touch of plasticiser and retarder.

Because its special order its obviously much dearer. I can get render with 8 hour retarder for nearly half the price as other sites will be using it too, but the price is irrelevant if it won't be as good a job.

[sy76uk]

When I lay a customers patio I will only ever use sharp sand for the mortar because it's a stronger mortar but I put my own patio down on whatever I had lying around so it's a combination of the lot (red, yellow sharp and even KDS)
It seems solid enough to me but I wouldn't chance it with a paying customer.