paving slabs

[jumbo55]

i have just had a builder looking to make a quote for a patio. they are flag stones, the patio will be going wall to wall at the bottom of the garden, so it wont be stuck in a patch of grass, he said he will put membrane down then a dry mix of sand and cement. why would you put membrane down when the whole area will be sealed.i mean if its done properly, no water is going to get through and if the substrate is compacted as it should be, surely no weeds are going to get through. i would appreciate your thoughts. i thought you only put membrane down when you were putting loose aggregate like bark or shingle.

 

[r896neo]

Your right there is no need for a membrane under properly laid paving.

The only scenario would be to use a geotextile membrane under the sub base to stop mixing of the sub base and a heavy clay soil for example. Or when overlaying sub base onto an area of rubble fill or anything that mya have voids.

In 95% of cases its not needed

It sounds like your builder does not intent to put in a sub base which would ring alarm bells for me.

Some flags can be laid on just a mortar bed without a sub base but its not a great idea and doing it properly is not that much more expensive.

 

[jumbo55]

thank you for your reply r896neo. i am not confident of doing the job myself as i fractured my back last year, but when i advertised the job on my builder, i asked anybody that was interested to give me a method of operation, my idea is to level the ground which has got a topsoil mixed with stones, i would put mot 1 on the top and compact that down then put a layer of sharp sand and cement, lay the slabs and put a dry mix of sand and cement for the joints. does this sound right, would welcome your opinion.