Hi,
I've started installing a patio this week and have encountered a problem.
I've dug down six inches and tamped down the earth ready for a 4 inch layer of dolomite. When I did this a pool of water formed in one area. (Patio is 2.4m x 2.1m).
I dug down here to find a heavy clay pan about ten inches further down. I filled this hole with dolomite and left for the day. I returned to day to find an area approx 1m2 very soft underfoot. I spoke to a friend with extensive paving experience and he advised as it was a light use patio it would be ok to spread a bag of cement over the area then compact dolomite on top.
This is what I have done today, rained off for afternoon (patio covered) and will return tomorrow to see the result. I now suspect that as the area is still moving when stood on that this will not suffice. The movement is only slight but definitely noticeable.
What are my options?
I think dig the soft area down to the heavy clay pan and fill with dolomite then lay as usual, or, would a 2-3 inch layer of mortar support the patio correctly? I've attached a picture of the hole I dug yesterday.
Many thanks in advance,
Justin
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Replies
Hi Justin
Can you be sure that there isn't a burst water pipe in this area. I'd also consider the possibility that there may be a soakaway there too.
If your problem is either of the aforementioned then you really ought to consider fixing the problem otherwise anything you lay above may have its own troubles very soon.
Possibly a high water table, with the claypan underneath.
Never used dolomite, but if the sub-base is unbounded and water getting in from the sides, or from below, will likely cause problems in time.
Drainage to lowest point of garden, a soakaway/rain garden, might be worth considering.
If it is confined to the one area and not a leaking pipe or soak-a-way overflow I would suggest you excavate and infill with clean stone.
You then need to overlay the whole area with a heavy duty Geotextile membrane to the whole patio area before you lay the base.
We lay a Geotextile membrane to all areas as standard before we lay the base materials. This gives the base additional strength and and spreads the weight of the surface over a larger area.
As it is such a small patio and assuming there isnt a leak somewhere, I would excavate, lay membrane, clean aggregate, wacker plate, 100mm reinforced concrete base(which would form a raft) and lay slabs on 6/1 mortar mix.