Concrete base for patio

[jamesn6]

Thanks for replies about the air bubbles in my paving slabs. These are the least of my worries.

Builders laid all slabs and didnt point so they are now all wobbly. Have been advised they all need to come up so am now having work done 'properly' as previous builders did not remove old concrete path so we are up near dpc (although we have a linear drain).

Now got quotes to dig out, relay sub base and relay all slabs. However, one contractor (my preferred as he is a reputable local builder) wants to lay a 100mm concrete sub base and not type 1. When we questioned this he said we wouldnt have any cracking of the pointing this way.

The area is about 30 sq meters and about 2ft below the level of the garden which rises away from the house. It ajoins the house wall on one length and a retaining wall on the other.

The retaining wall is now to be redone so the contractor's idea is to make a concrete base reinforced at the edges for the wall.

Is a concrete base excessive and what about the possibility of heave and cracks?

Thanks.

[Tony McC]

IMO, a concrete base for a patio is OTT, but there's very little risk of heave (at least, there isn't in the British/Irish climate).

I'd be happier to see the flags laid directly onto 75-100mm of concrete. Construcyting a base and then mortar bedding the flags onto the base always seems like a bit too much effort for me, especially for a patio.

[jamesn6]

When you say lay the slabs directly onto the concrete what do you mean? That they are laid when the concrete is still wet?

I was thinking that at least it might be easier to replace them in the future if there is a solid concrete base underneath but if they are stuck in the concrete this would make a right mess.

Cheers.

[lutonlagerlout]

i know a few lads that use leanmix rather than type 1,if its thick enough and done right it wont let you down,just as T says bit excessive cost wise
regards LLL

[Tony McC]

Laying directly onto concrete does mean bedding them straight onto the concrete while it is still plastic (unset and workable), but you make a valid point about future replacement. Depending on the type of flags being used, and how well they have bonded to that concrete, some will come up 'clean' while others will need a bit more effort, but taking up the whole concrete base would be a very last resort.