Concrete for footings?

Hi,

The building inspector has just signed off the trench for our small (3m x 3m) single story extension. We've excavated 500mm wide and 1.3m deep and the BI is happy with that.

It's a strip foundation and we now need to fill it with concrete 600mm deep.

The drawings state the concrete should be "sulphate resisting unless this is proved to be unnecessary".

Is this a common requirement for concrete? I'm not really sure what it means and the architect is unavailable at the moment.

A strength of C25 or better is also required. Again does this sound correct?

Apologies for asking such basic questions but I want to have some idea what I'm talking about when I order the concrete!

As you may have gathered this is all new to me although I am trying to do as much of the work myself!

Thank you

About C25, it's hard to believe that spec won't be sufficient. You could ask the building inspector to check though.

About sulphate resisting, you could ask the building inspector about that too, however I'd start by asking the concrete supplier what the cost difference was, before doing soil samples, embarking on a lengthy bit of research etc... to try to figure out if it's needed.

When you order the concrete it normally comes with a guarantee about the mix, a good question to ask might be in what circumstances that guarantee will be invalidated, e.g. if you've added too much water, or if you've not taken into account soil conditions, blah blah blah...

Hope this helps.

For sulphate resistant cement to be specified, then you either have a lazy architect who is just covering his arse, or an architect so on the ball that he knows the specific ground make-up of your back garden or has done some tests based on a suspicion that for some reason the ground may be high in sulphates. Think about which one it may be

So, no it is not a common requirement

Ask your architect, that's what he has been paid for. Also, if he has specified it for the concrete, then he should have specified it for any mortar below DPC

As for the strength, just tell the supplier you want a footing mix. No one checks

Thanks Guys.

Having spoken to a couple of local builders who have done similar jobs in the area we reached the conclusion that we had a lazy architect!

Concrete poured this morning with the help of a few willing friends. Now having a well deserved coffee and bacon sarnie!

Thanks again.

Davey

Should have it up to damp by tomorrow eve then.

ROFL

We've got a bricky on board but we're trying to do as much as we can ourselves.

I'm sure we'll be back with many more questions before we're finished!