The Brew Cabin

Hi Tony
First of all may I congratulate you on such a fantastic site - obviously a labour of love!

My questions are as follows

(a) I have a concrete "patio" outside my back door which Mrs G wishes to extend. From reading the archives you are suggesting that laying a 10:1 sand/cement (semi wet) mix is adequate. Just to confirm - I should work my way down towards the garden when I lay the slabs (rather than finish the side nearest the house first and work my way down). The new slabs are Bradstone.
(b) I have taken up a layer of slabs that were running down centre of the garden the garden. Basically I wish to use there as hardcore to extend the patio - thus I was looking to put these at the end of the existing concrete (on pretty level soil) and continue on with my 10:1 mix on top of this. Can you see any problems with this approach?
© Presumably the concrete I am using to keep the new slabs in place and I do not have to worry about slippage at the end of the patio - or would you suggest an edging all the same?

Thanks

(a) It doesn't really matter whether you lay the end or the side first - maybe I'm missing summat from your description, but I can't see how it could affect the laying process.

(b) I get worried whenever I hear the term 'hardcore'. It implies all sorts of rubbish backfill material and iffy practice. Am I right in thinking that your plan is to lay the salvaged flags where the existing concrete hardstanding runs out, and then lay the new flags on top of them? Why?

It would be better to excavate as normal at the edges of the concrete and under the propsed patio extension, and use proper granular sub-base material to build up the levels. If you really want to use up the old flags, break them up into bits no larger than 50mm and use then, along with granular sub-base, as a fill layer. If you lay them, and then lay the new flags on top, then you're at least doubling the potential for problems. The under-flags, being newly laid, may not have fully settled or stabilised before you overlay them with the Bradstone stuff. Even if they were flags that had been in place for 5 years or so, I'd be reluctant to overlay them - it's much, much better to smash them up and use them as granular fill.

© While the famous 10:1 semi-dry bedding mix is fine for bedding, it does not bond to the flags, and so is unlikely to hold flags fast at free edges. There's a number of workarounds outlined on the Flagging to Free Edges page, or you could use an edging, as you mention. The easiest solution is to lay the outer course on a wetter mix, so that the flags do bond to the bedding.

Thanks for the reply Tony
Apologies for the use of the term - I have it in my mind from books I read prior to seeing your site!
I just thought (being a complete amature!) that the "sub slabs" would be fine as a sub base - it was a contractor who originally propsed laying on these slabs (I was going to use him before the quote came in!).

I'll smash them up and buy a dry filling - hire a wacker etc for the rest

Just a question on your last comment - why would a 10-1 mix not bond to the existing concrete? Is it because the mix is not "sticky" enough? I am assuming that the 10-1 is a semi-dry mix but has some element of water or am I completely mad?

You mentioned a wetter mix for the outer course - which will now be put on the sub-base - to help it bond - would it not be better to use a slightly wetter mix on the 10-1 to ensure bonding (apart from the "messiness" you mentioned earlier

A 10:1 mix will bond to paving if it is wet enough, but because I advocate using a less-messy semi-dry mix, it tends not to bond, or, to be more accurate, not to bond strongly. There is a small degree of bonding, but that bind is easily sundered, whereas a wet mix gives a strong bond that often requires a hammer, a chisel, and a deal of brute force to separate it from the flag.

So, for your free edges, you could use a slightly wetter mix, as mentioned on the page I referred you to, as this would give sufficient bond to cope with foot traffic.