Soft sand v sharp sand for pond surround flags - Soft sand v sharp sand for pond surround

[Kieran Bourke]

I am laying 22 flags (basic economic concrete type 30mm) to edge a pond and my gardening book states to lay the flags on 50mm soft sand. However all my internet searches state to use sharp sand. I am laying down old 30mm crazy paving slabs underneath the sand as a firm base. Can you advise if I should be using soft or sharp sand. I have already purchased the soft but can exchange the 25kg bags for sharp.

Also how do I calculate the volume a 25kg bag of sand will cover. I read that 1m3 = 1.7 tonne (1000kg) and I need 0.2m3 ie 14 x 25kg...but this seems a lot for the small project I am undertaking. Are these sums correct?

Many thanks
Kieran

[Stuarty]

Dont use soft ( builders ) sand. Use sharp sand in a 10:1 mix of sand and cement at 50 mm thick.

Cubic metres ( m3 ) should only be used when ordering volumes, not weights. You need to find out the area and not the volume of the job.

[Kieran Bourke]

Thanks very much I will use a semi dry mix then with sharp sand. How do I work out how many 25kg bags of sharp sand to use, Im only laying 22 slabs? I have the area calculated.

[Stuarty]

you have only stated the slab thickness, not the dimensions. The slabs could be 400x400 , 450x450 could even be 300x300. If i dont know the area i cannot advise on how much material you will require

[Kieran Bourke]

Sry .... 450 x 450 slabs

[Stuarty]

i reckon you would need around 12 bags of sharp sand and 2 bags of cement should do it. Good luck with the project

[Kieran Bourke]

Cheers thanks very much!

[slickboy]

As they are a pond surround-ie an unrestrained edge-I would lay them on a 'class II' or 4 sharp sand to 1 cement wettish mortar, with some bonding agent such as SBR or PVA added and make the bed 25-50mm thick.