Hello... I was wondering If I could possibly get some advice from you guys.. At the bottom of my garden there are concrete slabs running along separating my land from the tarmac Road.. (slabs are on my side) and I'm wanting to build a 6ft fence on top of these if you will. I was just wondering how deep I would have to dig down into the concrete as it's really hard to dig (it's around 14 inch deep) I read that for soil it's around 2 foot but would I get away with less? As it's concrete.? The posts will be 4inch wooden thanks
If it's really 14" thick then why not just use these? http://m.screwfix.com/p/bolt-down-post-supports-100-x-100mm-pack-of-2/57289?filtered=true
Yeah i second Craig with the post supports if it is that thick, just out of curiosity why is it that thick? underground bunker?
Sorry I meant backstreet not Road.. And I'm not sure why it's that thick.. I live on a little bit of a hill if you will so maybe it's some kind of defence?
Would those supports be sufficient.? Problem is I've already dug 7 inch holes where I was going to put the posts.. I was thinking of digging down 7 inch for the post and then drilling a further 5 inch and hammering a 2ft long piece of Reed bar in and drilling and hammering the post on to the reed bar and filling the 7 inch hole with cement.. Would this work? Thankyou for your replies.
18"? In to a solid concrete base? Jeepers... Pawr, if that concrete slab is really solid and unmoving, and you shoved a 4" post in to a hole that's even just 7" deep and back-filled it with a good strong mortar mix tamped down tight, I can't see any reason why that shouldn't work on its own. I mean, if you were to put strain on that post, what exactly would give?! Not the slab, not the mortar - so you'd have to snap the post... With your added idea of drilling right through and hammering down some rebar would help further, but whether it would strengthen the fixing more than say going one further inch down all round, I'm not sure. Really - if that concrete slab ain't moving anywhere, then anything you stick tightly into a hole there ain't going to move either. So I would aim to make the actual post holes as deep as is 'easy' to do - say 8" deep - and also aim to make them as 'snug' as possible. Could you easily make them with, say, just a one inch clearance all around? And straightish-sided? If so, with a strong mortar mix (you could use 'postcrete' for a quick fix, for example) tamped down tight, that would fix that post absolutely solid. I don't think I'd bother drilling right through and using rebar.
looking at the pic, it looks to me as if you are digging down the side of an old post, it looks like two bits of rusty reinforcing wire in the concrete next to the hole, then what looks to be about six foot away behind the extension lead, is another post hole, so it not really a solid concrete slab, it just a strip of concrete between post holes. If you want your fence to stay up, break through the existing concrete and fit the posts properly.
I may be able to squeeze another inch.. Its all going to be joined and then fastened to the garages also on either side.. Ill use the rebar as an extra just because I already have it and it's cut.. The slabs are completely solid hence my struggle haha and I have kept the holes as tight as I can.. Thanks everyone.
No the slabs are solid because further down the street someone has dug the soil up to have their water mains fixed that's when I measured them because he had dug right down.. Each slab is is around 3 foot long and 14 inch deep and joined with cement.. there must have been old posts in like you say but I think they were just the small council ones but no one in the backstreet has them remaining. The land is mine it's just my gates were set so far back as they are not allowed to open out into the backstreet. Before this I had a wall than ran along the perimeter of the backstreet and dropped back to meet the gates if you will but it was low and unstable.
Cool. So these slabs are 3' long by 14" deep, by how wide? IF you can rely on the concrete slabs not moving and IF you can trust the mortar mix not to crumble (and it shouldn't), then your posts set into even a 7" deep hole will not move either. As you say, the fence making a return on to that garage wall will strengthen it hugely more as well.
The fence will be making a return on a garage either side and the slabs are around a foot.. Maybe slightly more where I am putting the posts.. Thanks everyone for the replies. Also there is no chance of the slabs moving.. They are solid.
Cool. I guess the worst that could happen is that the remaining sides of the holes you are making could break away from the slab, but I reckon you are going to be ok; that would need a hefty clump on the post. Blow/suck out all the dust & debris from the hole before planting your post, and moisten the exposed concrete before packing with mortar. I'd put mortar in the hole first too so's to level out the bottom for the post to sit on, so's there's a mortar sleeve encasing the whole post leg and keeping the slab's strength to a max - no voids left under. Come back and post the results
So I forgot to keep you posted and just remembered about this haha.. So I did as we discussed and dug about 7" into the concrete then drilled a 6" hole in the middle and placed a foot long piece of rebar? In the hole I then drilled 6"into the post and hammered the post onto the bar before using postcrete to set it. Its all seems pretty solid and has stood up to the wind thanks for your help.
Blimey - that's some drillin'! I bet it is nicely firm. Thanks for coming back - I hadn't forgotten...
Forums
Facebook
Twitter
You Tube
Instagram
Shop