Nearly there - final marking out done and final excavations tomorrow hopefully.
Now the plan is to lay the floor as a concrete slab to include footings - a raft.
The current dimensions are 3.5m * 7.8m.
The question of expansion joints has been raised.
Does a slab this size need an expansion joint? If so, how do you do it? A joint all the way across would effectively make two rafts. This might match up to an expansion joint (control joint) in the walls as one book says that any wall over 6m long needs a control joint. Sounds sensible as you don't want the wall flexing at one point and the floor flexing at another, I would guess.
Or am I over thinking things as usual, and the whole lot can be one big slab and any expansion can be taken up at the edges?
The book is a 2001 edition of Collins Complete DIY Manual. It says that walls over 6m should have a control joint to allow for expansion. This is basically a vertical unmortared joint bridged with metal and filled with mastic. When I looked at the illustration I understood what the brown vertical lines were in walls in a recently built hospital. Look around at recent commercial buildings and see if you can spot a vertical brown line every 6m or so.
I don't think there is any such thing in my 1930's semi (or in my 1950's semi in Berkshire) or my previous 1930's 5 bedroom detached. None of these showed signs of movement in the walls.
P576 of my recently acquired Building Construction Handbook talks about 'construction joints' which again are to allow for expansion and contraction in walls. It says max. 6m for concrete block walls and max.12m for brick walls. There are special ties to bond the wall laterally but allow longditudinal movement.
Talks about shrinkage cracks in lightweight concrete block walls and having construction joints every 6m and within 3m of any corner.
This is getting even more complicated because this suggests that I should have two joints at the back and one at each side. I would also need to provide a joint around both door frames on the front.
I am not sure how critical this all is - I suspect this has only come in in recent years - but I now have the usual dillema of following latest building practice or doing it the way it has been done for decades with the occasional problem.
So, in summary, if you have a block wall of 10m long with no joints I would check with Building Control. If it is of brick then it looks as though you are all right (at least according to one of my books).
You don't need any expansion joints anywhere, either in the floor or the walls - entire detatched houses have their floors poured in one go, and their outer walls, both brick and block, have no expansion joints
Long, unbroken lengths of wall need expansion joints at about 12m to prevent the expansion & contraction of the materials causing cracking. Lightweight aircrete blocks, IIRC, should be no more than 6m. Normal domestic walls are rarely anything like this length, and usually have windows, doors, etc., in them which will break up any expansion.
I'm not certain, but I would have thought expansion joints came in after cement mortar became common.
Surely this also depends on the type of concrete that you pour, the ability of the concrete to slide when shrinking and the way you treat the concrete after pouring. I recently had a concrete slab poured for a conservatory 7 x 3 Metres, the concrete had fibres incorporated in the mix which, I was told, reduces the tendency to crack when curing, I also made sure that the underlying surface was smooth, so that it could slide easily and kept it wet for the first 2 weeks with a hosepipe. The concrete was poured first week in Sptember, no cracks so far :-)
Why don't you get in touch with the conrete firm for advice, also the BCO
It certainly was, particularly the bit about making sure that the substrate was smooth, that's not something I had considered before, assuming that it would be fine to let the concrete take up any surface deviations.
FWIW, I don't think that was a dig, just a humorous observation, you've certainly gone further than most would in making the slab good and it is to your credit.
Thanks for that - how did you have the slab poured? Readimix and one big pour? I am contemplating the ease of pouring a slab that size in one go - if it should be poured and levelled in sections or if you just fill the whole space in one go.
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