watching cement dry

have just finished my shed foundation top coat, one cement to four sharp sand; resting on a base coat of one cement to three sharp and three wickes ballast.
how long before i can start walking on it and putting up the tin shed up please? (in north london its been quite warm last couple of days temps going around 23 c or so during the day. thanks.
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should have enough strength in 3 days. May be quicker in warm weather - but do keep it damp while it cures.
NT
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You shouldn't be watching it dry. You should be keeping it wet to ensure that it continues to gain strength through hydration of the cement.
In the past, hessian sacking was placed over the work and watered regularly. Nowadays it is more likely to be cured by spraying on a waterproof membrane and/or covering it with heavy polythene or plastic tarpaulins.
Whichever way you choose, keep it wet. It will continue to gain strength for about 28 days, but will have achieved most of its maximum strength after 7.
When can you start walking on it?
How long is a piece of string? The longer you wait, the stronger it will get, provided that you keep it wet. Geddit?
If it was me, I would leave it at least 14 days. But I am far more patient than you appear.
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Bruce wrote:

And have obviously never had to work on a building site. Where you have to smash the mornings mix out of the mixer cost some bugger didn't wash it..befire going off for lunch..
In these sorts of temps it will be set enough to walk on in probably under 8 hours, 24 is reasonable.
Sure it will ge stronger with time, but its strong enough after 24..
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Hessian still is used by Carillion. There's a picture at:
http://whr.bangor.ac.uk/2008/ctrl-200408-1.jpg
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wrote:

... mmm .... I could do with some of those 'roadform' concrete shutterings they've left lying about!!!!
AWEM
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On Fri, 8 Aug 2008 17:35:25 +0100, "Andrew Mawson"

They took them away when they took the hessian up. (The procedure, incidentally, was to leave the concrete exposed overnight after it had been poured and then to put the hessian down and spray it the next day. The concrete was cured for seven days before the road was reopened.)
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Thanks! I was thinking that it was an old-fashioned technique that had gone the way of most old-fashioned techniques.
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Bruce wrote:

By "old-fashioned technique" do you mean "worked a treat"? :-)
--
Dave - The Medway Handyman
www.medwayhandyman.co.uk
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That's usually the case. ;-)
When people invent something new and highly profitable, they market it heavily, and often make a fortune. Meanwhile the old methods work just as well as they always did, and often better than the new.
I recall the claims made for spray-on curing compound, and how its everyday performance differed greatly from the claims. I only ever used it with hessian, polythene or flooding the slab with water, never on its own. Couldn't trust the stuff. ;-)
I felt a warm glow of satisfaction seeing the hessian in use by Carillion, and even more pleasure at seeing a roll of it on the right of Peter's very clear picture.
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It could be that the site foreman is a time-served guy close to retirement. Perhaps a different foreman would have had it done differently. I don't know.
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I didn't know that hessian on a roll (as shown in your pic) was still available. I haven't seen it used for years.
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wrote:

that
still
Used extensively by re-upholsterers.
AWEM
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Thanks. I realised it was still used in upholstery, but I hadn't seen it on a construction site for a long time.
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john hamilton wrote:

should be OK fetr 24 hrs. It will dust up, so if thats an issue PVA it.
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Thanks you guys. dropped mouse on the spot and ran out into the garden and sprayed it straight away. life's not easy for a novice.....sigh
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what does 'dust up' mean? PVA it..? Does that mean the PVA waterproof adhesive I see for sale in Wickes?
Since I don't have any Hessian, would it be a good idea to keep a layer of old newspapers wet on top of the cement?
Although my original post asked how soon would it be before I could put up the tin shed on it, I didn't then know anything about keeping the cement damp for making it strong. It was not made wet for the first 24 hours after laying it down. For how many more days should I best be keeping it damp? I much appreciate all the advice I am being given in this group, thanks.
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john hamilton wrote:

To be honest its been so humid it probably wanst an issue.
The PVA thing is to basically slosh thinned PVA over it - yes the normal stuff you buy in teh builders merchants. Not sure what it would be sod as, but its usually siod in 5 liter cans as PVA sealer.
It does two things: stops the cement drying out rapidly and puts a fairly tough surface on it so it wont wear to dust as you walk all over it, whne its not completely set (or indeed after,as well)
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