How long should a slab cure before framing?

Hey guys

Driving past house construction sites I am consistently noticing that MAJOR builders start putting up house frames with in 3 to 4 days from laying the slab. Major builder are under pressure to finish construction before a contractual due date otherwise they will be penalised, but is this compromising structural quality (the foundations is the most important component of a house)?

A quote from a CSR Ready Mix Publication "Compressive strength of properly cured concrete is 80 to 100 per cent greater than the strength of concrete which has not been cured at all".

What are you thoughts about this?

I totally agree with the curing benefits

Plastic covered IMHO is best! a week is good, particularly in the extremes we have around ATM.

It is the concrete contractors obligation but they seem to 'forget' that part

Good point onc_artisan

I've been told by a various private builders that a slab should cure for up to 3 weeks before framing. They said that the frames heavy load will create fine cracks which might get bigger over time (hence cracked plaster or doors not closing properly).

Hmmm... 7 days is fine but longer is better.

I don't agree with the other bits IMHO

guys here is a link to a guide to AS 2870 - 1996 "Residential slabs and footing contructions:

http://www.concrete.net.au/publications ... ityWEB.pdf

Refer to point 6.4. 3 "Curing"

"Curing is the process that controls the loss of
moisture from concrete after it has been placed
in position (or during the manufacture of concrete
products), thereby providing time for complete
hydration of the cement to occur. Since the hydration
of cement takes time – days, and even weeks
rather than hours – curing must be undertaken for a
reasonable period of time if the concrete is to achieve
its potential strength and durability. Curing may also
encompass the control of temperature since this
affects the rate at which cement hydrates".

Recommended curing periods are:
n Slab Surface
I nterior 3 days
Exterior 7 days
n Slab Edge
Non-aggressive or saline 7 days

Is your builder following the standards?

http://www.saiglobal.com/PDFTemp/Previe ... 0/2870.pdf

Australian Standard™AS 2870 - 1996 Residential slabs and footings— Construction

Here's some more info - http://www.concrete.net.au/publications/pdf/Curing06.pdf

Next time I'd put it into contract that the slab is to be left alone for 3 full weeks minimum - no load and definitely no driving over it with bobcat to install stormwater pipes Foot traffic only, no tools of any kind.

Lex good work.... It’s recommended to achieve the max slab strength that its covered and cured for up to 28 days. This process achieved 95% strength.... I've noticed that’s all major builder air dry the slab for 3 days and then start building the frame... this process only achieves 40% strength.... If you are wondering why your walls have cracks in them maybe it’s due to your builder not curing the slab...

That is 28 days at 20c and average humidity.
a 5 deg increase in average temp would reduce cure time by 25%
... an average summer day will be 28+ reducing the cure time.
Winter is a different story.

Don't confuse curing time (7 days is good) with design strength (after 28 days). If putting up a timber frame, 3 days is OK. If loading with brickwork best to wait 1 week for on-grade slabs and 28 days for suspended slabs (with all props removed before loading with brick walls).

I had my slab laid on a Monday, frame was started on the Wednesday... I really don't think that was enough time, they told me a week...

Hey Victoria_g06,

Builder make most of their money with the first 3 stages of the build. They just rush the job so they get paid... its all about cash flow these days, they have a business to run and bills to pay.

Hi Guys,

My slab was poured last Tuesday in 38C heat. On Wednesday (22 hours later) the frame was put up, again in 35C+ conditions.

This was followed on Friday by 189mm of rain.

I am concerned that these extremes will have impacted on the integrity of the slab, which sits on piers at one end.

Do we have any recourse with the builder if the house develops cracks over time?

Despite these conditions the slab has not a single hairline crack or crumbling edge - could the weather have created a super slab capable of withstanding the crazy weather in melbourne?!?

The rain would have helped a bit.
Give it another 2 weeks and see what you have.

The only recourse is your statutory warranty of 7 years for any structural defects. I think its poor workmanship that the builder has erected the frame after only 22 hours of laying the slab. For a slab to cure it must be kept moist and allowed to dry slowly.

I think your luck here as your slab required a pier which adds to the structural integrity of your foundation. Most people freak out when they get the site cost estimate from the builder but what they don’t realise is that the foundation is the most important part of the house. Most people would rather spend the site cost money on in house upgrades rather house than on a strong super reinforced slab.

Thanks tstr1a

We will definitely keep an eye out for any damage resulting from our speedy start and get onto the builders straight away!

best of luck with your build Arena537

cracks start to appear after 2 weeks or so - keep an eye

I was told by the concreter they will allow my slab to cure for 5 days,on the 5th day the frame was stood. The frame is relatively light and the weight of it on a slab would be negligble. The weight comes with the bricks and roof tiles sitting on the frame and by the time thats completed your slab would have had plenty of time to cure.