Sub base - lots of sand

[David 1234]

I'm currently having an old patio dug up, ready for a new sandstone to go in. The paving installer has dug down a little over 150mm, and as this area is notorious for settlement, he is going to put down 100mm Type One MOT. The problem is that even after digging 150mm, there is still lots of compacted builders sand on the ground, (yes previous patio was laid on builders sand...)

Paving installer tells me that as he has dug down so far and will be using 100mm of Type 1, and as the builders sand is so compacted, it will be ok for him to run the whacker plate over the sand and cover with 100mm Type 1.

This concerns me - in fairness the sand is very compacted and seems to go down another 200mm. As much as I dig, more comes out. The paving installer said that it wouldn't be feasable to take it all out down to clay and that I'd end up having to buy a fortune of MOT (the area is 65 SM and I'm already using 14 tons)

What do you think? Quite worried as MOT about to go down and I've put him on hold...

[Tony McC]

Have them put a sheet of decent geo-textile over the excavated sand.That will help minimise the effect of any subsequent settlement of the sand by keeping the sub-base in position.

I'd suggest excavating to 200mm or so, using the geo-textile and then 150mm of sub-base. I know it's only a patio, but if there is any looseness in the sand, it's likely to be encountered in that top 200mm.

[David 1234]

Thank you Tony. I really appreciate you answering so quickly. Off to buy some geo-textile.

[Mikey_C]

Also if you are getting 14t of type1 delivered it won't cost you to much more to fill the lorry up to the 20t it can carry, as you will already be paying a part load charge.

[David 1234]

thanks for that

[Dave_L]

Depends if it is coming in a 5 or 6 wheeler though!