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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.