Need to investigate this solution.

We need the thinnest possible layer of concrete to go under some pavers. This will be strictly light foot traffic only, and it's a small area (maybe 3 m2 max).

Can we just put some builder's VB plastic, then some 4cm thick concrete layer, and then some 1cm sand and then the pavers? (or even just glue the pavers onto concrete) ??? Or is this still way too thin??

Any thoughts?

100mm will be plenty Lex

Its probably easiest to lay the pavers on a thin sand layer ( I would tend to add 5% cement to the sand to stop it settling over time)

I was hoping less than half of that, like 40mm maybe

Would such thin concrete (40 mm or less) actually be useless (eg. would it crack quickly under the weight of pavers when walked on) ??

You don't actually need any concrete. 100mm of well compacted road base will be as good. But make sure you use a compacting plate.

Lex 40-50mm is more than enough. As long as you get a flat finish on it you just lay the pavers straight on top and then use a good tile glue to stick down the header coarse.

Once you have them layed mix some dry fine sand and cement, broom this over the top then hose off with low pressure while you broom it.

Thanks guys.

Well, what we want is to make the paving base (be it concrete or sand only) as much water proof as possible, but not really 100% a permanent soultion because this area runs over a miriad of shallow placed water tank and other pipes. And given our experience with anything to do with water-related installations, we figure that it's better to allow fairly easy access for repairs of the pipes in the future - therefore we did not concrete over this area in the first place, but it still needs to be covered with something fairly water proof because this is a very flat area where the house foundations are most at risk and there is no natural fall.

So we thought that a thin concrete bed would be OK as it would be more water proof and also easier to break up - need be in the future. And pavers on top of the concrete are not that hard to remove (and reuse later on).

Obviously, the easiest would be to just use sand under pavers, but we noticed that it allows most of rain to get and stay under the pavers, so it's not a good solution for this particular case.

Your foundation could also move if there is no moisture in the soil and you have a reactive soil.. But you could still use a flexible system with a compacted sub base and sand but fill the paving joins with a flexible grout so if the pavers move the surface will still be water proof.

If your going to lay a concrete base it really should be reinforced and thick enough as once you go over the sand base with a plate compacter you might end up cracking the concrete base. Personally I would not bother with the concrete base.


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Thanks guys

Well, we suffer from too much moisture - ATM. But this could all change dramatically if it dries out well one day ... which just got me realise that excessive drying would probably not be that good for the slab .

BK, did you mean to suggest one of those "Pavelock"-type products, instead of plain sand??

Hey Lex,
No more like a silcon you would use on expansion joint. If you pave over a profile of crushed rock and sand on re active soils (clay) the pavers will move around. A solid join will crack and leak water through where a flexible joint wont.

Here is a recomendation

1. Excavate the existing material to a depth of 100mm+ the depth of the pavers leaving a slight (say 1:50 fall)
2. Compact the soil with a vibrating plate ( any pavement is only as good as the base and the trenches for those pipes will mean that there will be areas of uncompacted soil)
3. Lay the builders plastic.
4. Lay a 100mm layer of cement stabilised sand (5% cement you can add it yourself as you barrow the sand in)
5. Compact the sand and finsh to the required level not forgetting the slope.
6. Leave overnight to harden
7. Another sheet of plastic then lay the paver blocks
8.Brush in the paverlock

That sounds good, Bash
We were also thinking of using the palstic (a lot!), plus then somehow seal the edges of plastic to house wall/slab. We also thought to somehow "incorporate" some rubber sheeting in that area, as we noticed that it withstands the sun and rain really well. Maybe even use rubber instead of plastic ?!
Just one thing - did you mean to just lay the pavers directly over that top layer of plastic, or do we still need some bedding sand on top of it (and directly under the pavers)?

BK, so what sealant / silicone are you thinking of? Yep, any rigid seal would quickly break.

Black plastic is better than rubber for a long life.

Because of you concerns I would lay the pavers directly on the plastic. If you do this there is no need to use a flexible sealant between the pavers. as the amount of water in the joints between pavers will be negligible and quickly evaporate.

Brian

Makes sense! Thanks, Brian.