After a bit of noddy advice...will be mixing concrete for a 6x4 shed base about 100-150mm deep. Having a bag of ballast delivered and cement. - how many shovels of ballast for 1/2 bag cement? - which order is best when putting in the mixer? Assume some water needs to go in early to damp down the cement dust. Any other advice?
Standard 5-1 should be ok. If you are new to mixing you may want to make up something like this. Fill it up, level it off and then shovel it, into the mixer. You are moving it twice but at least you won't lose count when you start throwing them in - plus the kids can help as well
About 12 shovels of ballast to half a bag. Lay bag of cement on floor, cut across the top/middle with a Stanley then lift it up quickly from the bottom so it folds in half. Cut through remaining paper then you can just whack half a bag straight in the mixer.
Water, 6 shovels of ballast, half bag cement, 6 shovels of Ballast, top up water as required. For a shed base 100mm will be more than enough, could even drop to 75mm in the middle.
Thanks both. I read that 100mm is needed to ensure the slab binds properly..at least mine should do that. Should I wash the mixer out between mixes?
Its only a wee shed base...doesn't matter if it cracks a bit, just didn't want it falling apart due to too shallow depth. I'll put 4x4 treated posts on top on which the shed will sit, so its all away from the ground and damp. DPC under the concrete too.
DPC on top of the posts, DPM under the concrete. The DPM serves several uses - stops damp rising but also increases the working time of the concrete and helps it cure more evenly
Yes DPM is what I meant. Was going to put DPC under the posts (between concrete and posts), but I can see its more useful if put on top. Thanks.
Always worth doing though, even on a small base. For a few pounds - and no extra time an easy option.
Shed base just laid, took 7 mixer loads and I added the fibre. Glad I was able to borrow the mixer, what a life saver! Mixture might have been a bit on the runny side, hard to tell. Should do the trick for a few years anyhow.
It was probably nearer 150mm in places, thought I might need to rush to a Wickes for more cement but had enough with 4 bags.
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