Browse Forums Building A New House 1 Jan 22, 2009 8:09 am Hi all,
I have heard that if your slab is being poured in hot weather (ours is being poured next week when it is meant to be high 30's) that it is good to hose down the slab at night to slow down the curing process and avoid it drying out really quickly. Can anyone confirm for me if this is correct and that we won't do any damage to our slab if we do that? Thanks, Craigburn Re: Slab question (calling all engineers) 2Jan 22, 2009 8:23 am Hello there,
I just had my slab poured last week on a 40 degree day....... we did hose the concrete down as this is meant to slow down the drying process and prevent shrinkage cracks. We hosed it down about 3 or 4 times that afternoon and by the morning most of the cracks had disappeared but sure enough once it got warm again the cracks re-appeared and now we have heaps. We are assured its bound to happen and its nothing structural but still i would prefer if the cracks weren't there at all! In answer to your question you should hose it down anyway, it wont hurt the concrete and anything to prevent cracks is worth a try....... good luck where are you building? Oh i should probably point out that I am no engineer Re: Slab question (calling all engineers) 3Jan 22, 2009 8:44 am Hey there, there are two parts to concrete drying.
One is drying and the other is curing. When the concrete curers it become hard and stronger, the longer it curers the harder it becomes. When drying it relates to moisture being removed from the concrete. (nothing to do with hardness) Trouble is that when moisture is removed from the concrete it shrinks and you have cracks if the concrete has not cured yet. Early on in the curing process the slab is still not strong enough so it is more susceptible to cracking. Therefore you keep wetting the slab don’t let it dry out (and shrink) until the slab is strong enough to protect itself from cracking due to shrinkage. Re: Slab question (calling all engineers) 4Jan 22, 2009 8:47 am Hi Borg,
How long does it take until the slab can protect itself from cracking? Should I be wetting it down for the first week, two weeks etc? Also, how often should I be wetting it down? I am building in SA in Craigburn Farm. Thanks, Craigburn Re: Slab question (calling all engineers) 5Jan 22, 2009 8:52 am Err good question. Bit hard to tell. Basically after the slab is ppoured dont let it go white. So i would be looking at wetting it the same day. Then in the morning,, then after noon for a couple of days.
Its a case by case bases. Just dont let the slab go white. Keep it gray for as long as possible. It becomes a case of what is practical. My slab was poured on a nice 22 degree winters day and I still have cracks. In simple terms unavoidable, to many variabales, and in the end it doesnt really matter. Just consmetic!!! Re: Slab question (calling all engineers) 6Jan 22, 2009 9:29 am I have a question, as my slab is being poured next week also.
do those cracks you are all talking about do anything to the house, cause cracks or anything structurally bad? because australia is in a drought, especially melbourne and i don't want to be wasting water like that. Building first home in Melbourne - Hilton NBG 24E (changed dramatically) inspection done... just waiting now for finalization!!!!!!! Re: Slab question (calling all engineers) 7Jan 22, 2009 9:34 am If it's cosmetic is it really worth wasting litres and litres of water?
The small cracks are nothing at all to worry about. They are going to be covered with floorcoverings anyway. I think pouring water over the slab to stop cosmetic cracking that does nothing to compromise the integrity of the slab is irresponsible and ridiculous. There's a drought and such a thing as water restrictions. I leave you to fend for yourself, figure things out yourself. Terrence Malick Re: Slab question (calling all engineers) 8Jan 22, 2009 9:42 am I know what you mean joles. So thats why you should just do if for a day or two. Still important for the garage alfresco etc.
In saying that have you ever thought how much water goes into making a slab. it would be in the 10's of thousand litres. Dont think an extra 2000 litres wil make that much difference. I know not everyone will agree. Re: Slab question (calling all engineers) 9Jan 22, 2009 9:43 am Hi Joles,
I'm asking the question because I have been advised by a few different building inspectors in SA that even small cracks in the slab are weak points and that, whilst it might pass the Australian Standards with cracks, as they are weak points if the ground moves (and in SA we have clay highly reactive soil) it can affect the structural integrity of the slab. If people can guarantee otherwise I am more than hapy not to traipse up to my block multiple times per day. I'm just basing my question on what I have been told by so-called experts in SA. Craigburn Re: Slab question (calling all engineers) 10Jan 22, 2009 9:56 am Agreed that if there is the likelihood of structural cracks. My point was about cosmetic cracks which had been mentioned.
And as you point out, soils and the history of the area will dictate what is advisable in each situation. There was just a few comments in this thread basically saying "hose away it can't hurt".... I just felt those particular comments were irresponsible because it's not going to make an ounce of difference in most cases. And I had visions of everyone with a slab doing this. Craigburn, shoot off a PM to to_do_list....... he is our resident engineer and will be able to give you some great advice. I leave you to fend for yourself, figure things out yourself. Terrence Malick Re: Slab question (calling all engineers) 11Jan 22, 2009 9:58 am There's also some great links in this thread.....
https://forum.homeone.com.au/viewtopic.p ... lab+cracks I leave you to fend for yourself, figure things out yourself. Terrence Malick Re: Slab question (calling all engineers) 12Jan 22, 2009 10:03 am I've researched that before my slab was poured. There's good stuff on curing on www.concrete.net.au. Ponding is said to be best, but labour intensive - you have to make a small clay dike around the perimeter, then flood the slab with water and top it up continuously. Clay/sand will discolour the conrete though. Covering with the polyfoil is supposed to be good too, but it should be white or reflective and secured well. Concrete should not be wetted if the temperature difference between it and water is greater than 5 degs, it can lead to "thermal shock" and flaky surface.
BTW, I've ponded and wetted, but the !@* slab is full of cracks all the same. Chris My father rode a camel, I drive a car, my son flies in a jetliner, his son will ride a camel.Saudi saying Re: Slab question (calling all engineers) 13Jan 22, 2009 10:49 am A little word of warning here:
Really no one should be wetting down the concrete slab except the builder himself, or yourself, but only on instruction from the builder / grano supplier or a structural engineer. You are opening yourselves up to serious liability here, if its the case that you over water the concrete slab and effect its integrity, you may be responsible for the resultant defects, and later rectification costs. Careful now! Pat Re: Slab question (calling all engineers) 14Jun 13, 2011 10:56 pm Digging up an old thread, but when we had our house built (A V Jennings, 25 years ago) they sprayed the slab wit "purple" as soon as it was laid, with faded off over a few weeks ?? Is this something we should ask about for our new house ?? Thanks, P_D . Block settled 07 June 2011 Our little piece of the Interwebs on HomeOne....... viewtopic.php?f=31&t=48577&start=0 Thanks. I wish there was a youtube video explaining this concept. 10 27139 I’m not a structural engineer but I’m free. you still need an engineer for the plans. I only have part of your plans, but you seem to have a 850mm drop from the side… 3 9897 |