Laying stone on concrete bases - Should it be done

[London Stone Paving]

Whats everyones thoughts on laying natural stone on to a concrete base as opposed to an MOT base.

This subject comes up quite a bit for us with customers phoning up for advice. A bit of a generalisation but it seems like construction companies prefer to use a concrete base while landscapers generally use MOT.

Would be interested to know if there is any serious flaw to using a concrete base. The main flaw that springs to mind for me is that the subbase is not porous

[seanandruby]

I would of thought it depends on the thickness of the flag, etc:

[London Stone Paving]

Outdoor paving, so 25mm and beyond

[lutonlagerlout]

all depends on levels and the integrity of the slab
LLL
in theory it would be fine if levels etc allow

[seanandruby]

maybe this will help

[haggistini]

your customers may be wondering if they can overlay what is there already there i wont advise this for a host of reasons then again it is commercial spec for full bed of conc but not overlaying!

[Suggers]

In my day, we were usually asked to to lay a "no fines concrete" as the sub-base. When set, reminded me of rice-krispie biscuit....
"Just show it the dust suggers"
Bit like the best martini, where you are told to "just show it the vermouth"
We did revisit some '70s jobs, last year before total re-vamp - can say the construction had held up no probs.

[seanandruby]

your customers may be wondering if they can overlay what is there already there i wont advise this for a host of reasons then again it is commercial spec for full bed of conc but not overlaying!

Surely it is in your interest and theirs to advise a client and let them know the alternatives. I expect the reason people ask contractors for their opinion, is because, as experts, we can advise ??? If they then go against your advise, then get them to sign a waver. We can only tell a client what works and what does'nt, because we have tried and tested and hopefully done to compliance. To not advise would be throwing work away. That is my opinion.

[cookiewales]

as lll says its fine to overlay on concrete if levels allow but have come across this very rarely. but when working on clay in winter and wet times i will use semi dry lean mix instead of type one mot so we can carry on working happy days

[seanandruby]

I reckon our wires are crossed. I am thinking LSP meant new concrete installation, as opposed to existing ??? . Hopefully he make it clear.

[London Stone Paving]

The reason for the question is that we get customers calling all the time saying that their builder has specified that the paving must be laid on top of a concrete base. I am from the school which says paving should go on type 1.

I was wondering if there are any serious flaws to laying on a concrete base?

In my experience precise concrete bases for natural stone with varying thickness is asking for trouble. I also think its over kill but thats just personal opinion.