Quote:
Originally Posted by sadia
Hello everyone, I am considering to build a Pier in my backyard. Reading through the threads I understand that at least 25mpa concreate is recommended for pier footing. I have one initial query:
Where do i source the premixed 25 mpa concrete because bunnings one seems to be 20mpa premix.
Regards
Sad
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Sad,
Pretty much all pre-mix will be 20mpa or less. The higher mpa is reached by more cement powder being added but with no additional water.
The mixture should be wet right through, but stiff, not runny. Too much water & the finished concrete will be brittle & very dusty.
When 'Finishing' the surface, try to get it to the required smoothness as quickly as possible. The more you trowel the top, the more water will be drawn up to the surface. Too much water on the surface will have the powdering effect as noted above after the concrete dries.
Also, a higher strength is acquired by the mix curing slowly. If the cement dries too quickly it will crack.
Eg. If you mix & lay the concrete in the morning at say 8am, as soon as you finish trowelling the surface you should cover the concrete with a hession bag or similar & keep it moist.
This will;
1) keep the sun off to stop it drying too quickly
2) The wet bag will help to keep the concrete damp & dry very slowly.
Hose the bag lightly every hr or so for a couple of days.
