Replacing fence posts set in wall

[Sickboy]

I have 6 fence posts that have been set in the brick of a retaining wall. The posts are rotten below the brick level.

Any ideas on how to replace the 100 mm posts. I suspect when I take them out it will leave a nice slot about 105mm wide to get new posts in but it will wobble and bit and there is not enough room to get concrete in.

I thought about poring a resin around them but this won't allow draining and they will probably rot quickly. I could use 75 mm posts to give room for some concrete but it won't match the others (although it is at the side of the house and I won't see it so not too bothered). Don't really want to have to rebuild the wall around new posts either.

Unfortunately some of the wall is a little crumbling so a metal post mount on top of the wall might not hold.

Any suggestions please?

 

[Sickboy]

This is the fence

 

[conny]

Is this sitting on top of the wall?
Can you take a photo from a little further back so we can get a better idea of the true set up?

 

[Sickboy]

This is from further back.

Edit: photo won't upload. Will try again in a bit

 

[Sickboy]

This is the wall. My house is on the left and the path shown leads to houses. I don't actually own the fence but it has been like this for years so I want to get it sorted as no-one knows who owns it.

The posts go about 40 cm into the wall. The wood is very rotten so I will be able to remove old posts easily and it should leave a nice 100 mm hole but I suspect it will have crumbled slightly. I thought about getting 100 mm posts to match the ones that will stay but trimming them to 75 mm for the section in the wall so there is room for some cement?

 

[JohnD]

I think you need to dig post-holes beside the wall. They need not be in the same position as the old ones and it may be easier to avoid the old lump of concrete. Can you lay your hands on a heavyweight SDS+ drill, which wil cut through the concrete?

If you plant concrete repair spurs in the ground, they can be spaced about 100mm further out from the wall and, when hardened, you can bolt the wooden posts to them on the wall side. This avoids wooden posts being in contact with the ground, which accelerates rot. It also makes it easier to replace the woodwork when it rots. The concrete spurs last about 9 times as long as wooden posts.

If you feel like it, you can use masonry paint on the concrete spur.

I like dark brown fence stain, and dark chocolate masonry paint on the concrete, which blends well.

 

[Sickboy]

Thanks John but that isn't really on option to put posts in to the ground. The area shown in the photo doesn't belong to me so I can't put anything on that side. The other side has a 4-6 foot drop to the ground.

The new posts have to go into the wall, into the existing holes, the question is how best to secure them.

 

[DIYspanner]

I replaced 15 posts last year, installing all into the original concrete.

The section of the posts set partially into the brick should easily chop out.

The stubs set into the ground, are they in soil or concrete?

Take a photo of the other side (fence to ground) and post it please.

 

[Sickboy]

This is the other side of the fence. The posts don't go in to the ground at all. The new posts will sit in the existing 100 mm concrete hole inside the wall. My issue is how to get new 100 mm posts to sit tight in the holes.

I'm now thinking I will buy 100 mm posts but trim them to 75mm where they go into the wall so there is space for new concrete around them. I'll loose the pressure treated exterior if I do that but will treat with something else first.

 

[DIYspanner]

I get the gist, like this?

You should be able to pull the stubs out by screwing in a M12x200mm coach screw with a washer and length of chain on the head and shackle at the other end to pull on with a strong bar.

If too tightly gripped, they can be chopped out with a long crow bar sharpened to a chisel edge on the straight end. Stab into the stub and use a pair of vice grips on the bar to twist into and break up the wood. It does work.

With post stubs out, sink the new ones in and bed in with some runny cement if a bit wobbly.

 

[DIYspanner]

Here's a couple of snaps from my post adventures last year albeit the post were in the ground but set in concrete. The bar is the one I used to chop the stubborn ones out. If you try and pull them out using coach screws, screw it all the way for a good bite. If the post stubs are rotten, just chop them out with the bar.

 

[Sickboy]

Thanks. I'm not worried about getting the old posts out at all. I think they are rotten to the bottom but if not I will try your suggestion.

Main issue is that I expect there will only be 2 or 3 mm clearance after I slot the new post into the existing concrete hole. That seems too small to me to get a cement slurry that will have any strength. Did you use a cement slurry and was it OK? Do you use sand in the mix or just cement and water?
Thanks

 

[DIYspanner]

I only cemented (cement/sharp sand) one new posts in because the concrete sleeve crumbled as I was chopping the post out. The rest of the concrete sleeves were fine.

For the length of post sunk into the wall, I doubt 2 or 3mm will give much wobble but try one in dry and see.

Dry or wet cement, its a small gap to feed in to.

What you could do is router two small channels down, side and rear, that would allow runny cement to go down between the post and masonry. If you've not got a router, use a wood chisel and carve a channel out, say 3/4" wide, 1/2" deep. For your job, I'd say soft sand would be better than sharp sand.

By the way, I oiled the post bases before they went in the concrete.

Put a 1/2" chamfer on the post bottom ends for easing them into and down the hole.

 

[Sickboy]

Thanks

The idea of cutting a channel seems interesting. I was thinking of just trimming the whole side off but cutting a channel would help to keep the post more upright and stable while the cement sets.

Thanks

 

[DIYspanner]

If the posts fit in the holes as is, I'd be most reluctant to plane them down. A couple of small channels to weep cement down and snug the post in helps maintain the post strength.

Try the posts in dry first. They may well be snug enough.