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Replies
Have you considered using frost proofing addative in the muck? I use use in patio pointing it work a treat.
Honey Badger Thanks for the reply but as far as I know frost proofing additive is just for white the muck is setting not for frost heave the following winters. Frost heave is caused by water in the soil underneath the patio expanding and causing the cement/ stones to crack.
Didn't know that! Ever days a school day.
Re-enforced concrete base.
are you going to put a hardcore bed down first before the sand and cement
David Benson Yes! We always put down a 100-200mm of MOT Type1 hardcore minimum depending upon type of traffic (pedestrian or vehicle).
Increase depth of dig and depth of foundation stone, put drainage round edge of patio area to try keep water away from under patio
Would you still bed it on mortar or let it move with the freeze and thaw on a bed or sharp sand?
I agree and that's why we have quoted for 200mm of Type1 but I am unsure of laying in on a mortar bed.
I would still lay on mortar bed, too much rain in Scotland for bed of sand, would never last. I have done plenty of sandstone paving scotland and so far no problems with frost heave, I would say his previous patios probably not been installed well on heavy clay soil.
Have look at American websites. I forgot I watched a youtube video years ago where a American bricklayer was saying it was a big problem there. I think that's why they all have concrete driveways.
Hello.
If you are being affected by freeze thaw heave it is indeed because the sub soil is retaining moisture. The way to counteract it would be to increase the excavation depth and use type 3 mot. A Type 3 sub base will not aid the wicking effect whereby the moisture in the soil is absorbed by the fines in the sub base material. A type 1 will act as a wick, transferring the moisture upward toward the mortar and on into the slab itself. This will cause expansion in the sub base,staining of the slab and possible failure of the mortar. Consider the use of a permeable mortar such as steintec and sbr bond the back of the sandstone before laying.
a concrete reinforced base may be used if laid over type 3 sub base with a dpm layer between the two.
If in doubt doubt I would consult an engineer. You will give your client and yourself piece of mind. I'm sure the client will be happy to pay for it. All the best.