Hello, I calculated that I need 21 bags of concrete per fence post - this seems a lot to me! Could someone double-check my calculations? Hole area: 0.25 m2 (0.5 m x 0.5 m) Post area: 0.01 m2 (0.1 m x 0.1 m) Hole depth: 0.9 m Volume = 0.216 m3 (0.25m - 0.01m x 0.9m) Each concrete bag fills 0.01 m3 in volume Therefore I need approximately 21 bags of concrete per fence hole. BTW, I plan to use this concrete: https://www.selcobw.com/products/bu.../cement/carlton-general-purpose-concrete-20kg
The calculations seem ok. But think the specs for the concrete is wrong. Holes seem a bit too big 30-40cm wide is more than adequate. What lenght of post will you be using? are they wooden or concrete?
Mix your own. 3 sand. 3 gravel. 1 cement. Post hole needs to be small. Use post hole digger. Hire all the stuff so you can take back I mixed in wheelbarrow easy enough
Calcs are not correct giving you a cost of approx £100 per post! just for a moment imagine stacking 21 bags of concrete and how that would wrap around each of your posts! There was a good thread on here a little while back concerning postcrete V concrete, have a read of that and you will see that perhaps 2 bags of postcrete per post would probably do.
Those holes are very deep nearly 1 m deep!, unless you have very high posts thinks its a bit overkill.
You are way off pete. Your holes want to be 200/300mm square and about 600mm deep. You will probably need 2/3 bags of the stuff you want to use.
Some essential information I missed out: Post length: 3.048 meters (selco link) Number of posts: 15 The 0.9 m depth is due to the "general" recommendation of putting 1/3 of the length in the ground. It was also recommended to use C10/GEN1 concrete as I will be retaining about 0.5m of soil on my neighbour's side. It looks like the post holes are too big, I'll reduce the size and recalculate. I'll also do my sums on mixing my own concrete to see how much it will save. Thanks for the responses!
Definitely want 900mm in the ground,400mm-500mm square,use proper concrete, get dumpy bag of ballast,will work out cheaper.
So they are essentially 10ft long posts. When you go above 10ft the posts get thicker dimensionally so will be 5"x5" and a lot heavier. Put in 5 of these this year and thick they costs about £70 each. I would have thought a 1/4 of the length of the post would be sufficient, and a lot depends on the ground condition. So if using 10ft post, 2.5ft would be in the ground. Are you planning on putting up gravel boards?
+ for dumpy bag, the sand is likely to bet wet this time of year. Would rapid setting cement be a better option?