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Builders warned to avoid pouring concrete in the heat

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Photo: Belinda Pratten

This week will be much better than next to pour the slab for your new home, according to the ACT Master Builders Association.

With temperatures only predicted to reach 30 degrees on Thursday, conditions for pouring cement should be good.

The MBA deputy executive director Jerry Howard has warned builders and their clients to resist the temptation to pour a slab in the heat just to meet a deadline.

''If it reaches 30 degrees and there is any sort of wind, the concrete will dry out too quickly,'' he said. ''It is impossible to prevent the chance of shrinkage cracking in the concrete later.''

Given that in most new homes the slab is the major structural element or foundation on which the structure is built, this can be disastrous.

''It is very hard to fix a slab once it has a house sitting on top of it,'' he said. ''Even minor damage can prove very costly with the growing popularity of hard finishes such as tiles. If the slab cracks or moves these are damaged and can be very expensive to replace.''

Thursday will be Canberra's hottest day this week when the mercury is expected to reach 30 degrees. Monday's maximum is forecast to be 23, rising to 28 on Tuesday.

Forecasters are predicting three days above 30 degrees, including 35 degrees on Friday next week.

Mr Howard said once concrete was poured it had to ''go off''. This is a process that generates heat which has to be dissipated throughout the slab and into the air. If the air temperature is too high the cement dries quickly and, despite reinforcing, will be weaker than otherwise.

''Problems are not obvious immediately,'' he said. ''They become apparent over time and, in the worst case scenario, the slab can fail.''

With the curing process taking up to three days, it is important for builders and homeowners to be aware of the weather outlook for the whole of a week; not just the day on which the concrete is going down.

Cement is not the only building material that can be heat affected. Timber frames should not be left exposed to the elements for extended periods, especially in hot weather.

''Seasoned timber should have a moisture content of about 12 per cent,'' Mr Howard said. ''If it is left exposed for several weeks in the heat it can dry out and split.''

Summer is also a challenge for landscapers working on new construction given that many building contracts now include lawns, trees and shrubs.

''Lawns need to be growing and trees need to be healthy,'' Mr Howard said. ''If plants aren't in good condition then the builder won't get sign-off which will mean the last payment is delayed and this will then cause other complications.''

Older homes are not immune and, as the subsoil dries out, subsidence and wall cracking can become a problem - especially in older, solid masonry homes.''

The good news is that as the moisture is replenished (either by watering or by rain) the cracks will usually close up.

5 comments

  • And this warrants an article in the Canberra Times because...? Must be a very slow news day. :-(

    Commenter
    Karina
    Location
    Belconnen
    Date and time
    January 28, 2013, 1:07PM
    • Surely builders should know this already.

      Commenter
      Ed
      Location
      Melbourne
      Date and time
      January 28, 2013, 4:58PM
      • I think that most people would agree that this warrants coverage as news only if it was prompted by something such as a structural collapse due to an inappropriate concrete pour. Simply issuing professional information to builders (which, as Ed says, is something that any credible builder would already know) looks like desperate space-filling.

        Commenter
        Karina
        Location
        Belconnen
        Date and time
        January 28, 2013, 10:39PM
        • Thank Goodness for the Canberra Times. Concretors will now know when they should and should not pour concrete and builders will no longer have to repair homes that have concrete slabs that have been poured in too high a temperature. They should have reported this years ago. Anything else that tradesmen and builders need to know about their trades??????????????

          Commenter
          Felix
          Location
          ACT
          Date and time
          January 28, 2013, 10:44PM
          • Any competent builder knows how and when to pour concrete. They would also know how to cure said concrete to ensure that the temperature is controlled, eg by placing hessian sacking over the concrete and keeping it wet as the concrete cures. The people who need to heed this article are not contractors, they are either honest and competent or cowboys, but the clients. This, of course, is very difficult to ascertain if you are buying a new property through an agent and you have no control over the construction process.

            Commenter
            Chris, Southside
            Date and time
            January 29, 2013, 6:02PM
            Comments are now closed
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