Advice please? Can you lay Indian sandstone on solid concrete with sand inbetween?

Hyacinth2_2

We have some pavers in to break up our concrete garden, to level, add in a step (we're on a slope) and pave with Indian sandstone. 
The concrete is hard (shock horror) and they can't get it out easily. To be fair to them the concrete is maybe 200mm thick or more. 
The area at the side of my kitchen is also supposed to be knocked out but now they want to lay sand on top and then the Indian sandstone. My gut is saying no but I'm not a paver or even a DIYer. Please could you give me advice?

Mickey666

Structurally the paving itself would be OK . . . after all, the basis of any good paving is to first create a solid 'sub-base' on which to lay the final paving and 200mm of concrete would certainly be a solid base!

BUT, a common cause of damp walls is when the outside ground level has been raised too close to, or sometimes even above, the damp-proof course of the house walls.  The ground level should ideally be six inches (150mm) BELOW the DPC of any adjacent walls.

The house DPC is not visible in the posted photo, but assuming it's about where the wall render finishes the the existing concrete path looks to be at about the right level.  Raising it by simply adding more paving on top could compromise the DPC in the walls and lead to damp problems later on.

I'd say the concrete has to go.  A good contractor would make short work of removing it if they used the right tools (ie an hydraulic breaker).  A poor contractor would make excuses and just lay the paving on top, thus raising the ground level and compromising the house DPC.

Hyacinth2_2

Hank you @Mickey666. Unfortunately they have to do it by hand as there is only a narrow alleyway to access the house. It is a horrible job to be fair to them but concrete is hard, they should have anticipated some of the challenges but it's like a surprise.
If they put eco drains around the outside of the house would that prevent any damp problems? Is this a hydraulic breaker? I thought it was a Jack hammer 

Hyacinth2_2

This is also what they are using

Hyacinth2_2

This is the 2 brick gap before the render. 

Mickey666

Yes, those are hydraulic breakers.
The DPC is not clear from the 'two bricks' photo.  It doesn't look like it is between the two layers of bricks and it shouldn't be level with the existing concrete path.   It could be that the render has been applied down to the same level as the DPC, in which case the two-bricks height above the existing concrete should be fine.  But raising ground level by paving on top is not advisable.

I'm not sure exactly what you mean by an 'eco drain' but I'm guessing it would effectively be a gap between the added paving and the house wall.  This sort of thing can certainly help, but care would be needed to ensure it doesn't simply fill up with water and act like a miniature 'moat' and that it is wide enough so that rain falling on the raised paving cannot splash up the wall above the DPC level and if it is wide enough for that then it might look rather odd in such a narrow passageway.

DPCs are built into houses for good reasons and you seem to be trying to find ways to raise the outside ground level and quite possibly compromise the DPC, all for the sake of saving a day or two labouring to remove a relatively small area of concrete so that the new paving can be laid properly.  I'd hate for you to be returning here in a couple of years because you have a penetrating damp problem caused by raised exterior ground levels.

TELLIT01

I hope they are intending to lay a bed of mortar on the existing concrete rather than just a bed of sand with the slabs laid loose on that.  Whatever the slabs are betted in, the overall level of the path is going to be raised by at least 3" and I think that is getting too close to the assumed DPC level.

On a more general point, make sure the paving is being laid on a bed of mortar, not the old '5 dab' system often used with concrete paving.  Anything other than a solid base will show as circles on the surface of the paving over time.

stuart45

Once you get through the first bit of concrete and have an edge to work from it gets a bit easier.

Hyacinth2_2

Thanks everyone. @Mickey666 I want the concrete out but they're wanting to slab on top with wet base, sand and cement (I've checked they are putting down a full bed not just spots) They are also worried about the drains and damaging them. See picture.
Eco drains/ aco drains are like guttering with a metal grid on the top. 

Mickey666

Hyacinth2_2 said:

Thanks everyone. @Mickey666 I want the concrete out but they're wanting to slab on top with wet base, sand and cement (I've checked they are putting down a full bed not just spots) They are also worried about the drains and damaging them. See picture.
Eco drains/ aco drains are like guttering with a metal grid on the top. 

Of course they do, because it's easier for them and they'll be long gone by the time you have any damp issues if they compromise the DPC.

Ah, linear drains.  Well they might help, but they'll still block ventilation up to the level of wall they cover, which is an important aspect of the damp protection, and there's still the issue of rainfall splashing above the DPC because fo the raised level.  Perhaps not as bad as solid paving but still not ideal.

I'm not sure what you want me to say.  Fact is that raising the outside ground level WILL increase the risk of future damp issues.  No one can say for sure what will or won't happen but there are very good and proven reasons why ground levels should be at least 150mm  BELOW the DPC level.

All I can really say is that I wouldn't do it if it was my house.

stuart45

Those old salt glaze pipes could be a problem. Once you break the cement joints they can leak. Also they do crack easily. They should be surrounded in concrete, But the concrete path is probably on top of it.