Wall tie replacement in cellar

[MarkSmith]

Hi folks,

I'm after some advice on wall ties. I've just read a couple of "discussions" on them on here, but they don't answer my specific question.

I am doing a cellar conversion in my 1931 semi. The front (cavity) wall of the cellar is entirely below ground. It is currently buttressed (against the pressure of the soil outside) by a great lump of concrete about 50cm high and about 1.5m deep into the room. A structural engineer is redesigning this for me, basically to be higher and less deep, so as to give (much) more floor space.

This will mean that most of the wall becomes hidden behind a good thickness of concrete and will forever more be inaccessible, to all intents and purposes.

Now the buttress will be on the inside of the cavity wall, and the pressure on the outside - so the wall ties are all that is preventing the wall from collapsing in. Therefore I thought it might be a good idea to have some wall tie work done NOW, on this part of the wall, because it will shortly get a lot harder to do.

To be clear - there is no sign (that I can see, or that builders can see, or that surveyor could see 6 months ago when I bought the house) that there is anything wrong with the existing wall ties.

What do people think about this? Is it a waste of time/money? If I do it, should I have the old ties removed? My thinking was, there's nothing wrong with them - leave them in there and just give extra strength. Also removing them would disturb the wall - no point removing bricks and weakening the wall just for the sake of it. But I may not have considered all the factors.

Thanks!
-Mark

 

[gday2uk]

If it is taking a lot of weight from the ground on the outside why is it even a cavity wall? I'm no expert but it doesn't sound like a cavity wall would take the pressure and the wall ties would just crumple under the weight, not support anything. I would have thought a tanked solid wall would be more beneficial?

 

[MarkSmith]

I don't know the details either. It's been there 80 years, though.

Tanking won't help with the strength of it...

 

[gday2uk]

Tanking won't help with the strength of it...

Would only need to be tanked if a 'solid' wall. Solid wall (not cavity) thus helping with the strength of it.

 

[BristolBuild1]

Sounds really odd at first reading this one.
Do you have any pictures?
Cavity walls have been used to retain sail before but they are usually reinforced anyway. Have you looked outside to check what the overall thickness of the wall is?
I have replaced wall ties before but always try not to knock the wall about in so doing. (Sort one problem and cause another). It is possible to introduce a system of stainless steel ties by drilling and fixing threaded bar to ends that are configured like rawl bolts. ( A good merchant will advise).
But check what you are doing carefully.
PS.... How does water drain from the bottom of this cavity?

 

[MarkSmith]

OK, interesting questions. Sounds like I might have opened a whole can of worms here...

The wall has been there 80 years so something is holding it up.

I can take pictures. What of, exactly? On the inside it looks like a wall. No brick ends showing - it's "running bond" I think - only whole sides of bricks on show, layers offset by half a brick length.

Not sure how looking from outside would help determine the thickness of the wall. Dig down to see if it's counterforted on the outside, and gets thicker below the ground, you mean? The bit above the ground looks very much like a normal wall. Not sure how I'd go about measuring the thickness though, unless it visibly gets thicker below the ground. Any suggestions?

I have no idea how water drains. I put my hand through a vent hole, and it's soaked on the inside of the outer wall, but not too much of a damp problem inside the inside wall. (Little bit damp in one corner, that's all.) There is a french drain on the outside of it, but not at the bottom - about half way up.

Sounds like I might really need professional advice on this. Trouble is, I have just paid over £300 to a structural engineer for exactly that, and to be honest not been AT ALL impressed with what he had to offer. I suggested the "can wall ties take this amount of compression and will supporting the wall inside actually help" issue, and he basically brushed it off. So who would I go to?

Thanks for the replies!

 

[gday2uk]

TBH if you've paid for your engineers report go with what he says. If there's any problems after then it his responsibility to rectify.

Your original post was asking about replacing wall ties to stop your wall collapsing in. It will stop the two skins coming away from each other but not from the outer skin collapsing against the inner skin. You can get a specialist in to inspect the condition of the existing ties with an endoscope camera and they will tell you whether ties need replacing or not.

 

[Chukka63]

why isnt your structural engineer supplying the answers to your questions???

 

[MarkSmith]

why isnt your structural engineer supplying the answers to your questions???

He doesn't seem terribly good at providing answers to anything. I'm not really sure how I can get better answers from him. I just ask and ask and get waffle and conjecture...

I need to push him harder, I think... Or get someone who's not an idiot.

Thanks!

 

[Nige F]

Substitute waffle and conjecture for a lump hammer and a chisel ......and cut a hole in a brick .you`ll soon see how thick the wall is P.S I profess to BE an idiot

 

[MarkSmith]

I can do that on the insde - in fact I don't need to because there are a couple of missing bricks (vents etc.) which I can put my hand through. Inner skin is one brick thick, easy.

Outer wall is more of a problem. I can't get at the outisde (it's under 2m of soil) and to get at the inside i'd have to remove a really large part of the inner skin, which really doesn't feel like a good idea.

I suppose I could get a long drill bit and drill out until it pops through into something soft...

 

[stuart45]

I would guess that the outside skin is at least 9, or 13 inches thick to have held that amount of earth back this length of time.

 

[MarkSmith]

I would guess that the outside skin is at least 9, or 13 inches thick to have held that amount of earth back this length of time.

Outside skin is now confirmed as 4" (one brick). It's a mystery how it holds the weight.

Wall now has about 25 new wall ties and will soon have the newly-designed buttress. Let's hope it's good enough for the next 80 years...

 

[Deluks]

Odd setup. Wonder why Shyz hasn't chipped in on this one yet?

 

[MarkSmith]

Odd setup.

Certainly is. The wall has a bay window shape (no window of course) and the engineer thinks that probably adds quite a bit to the strength of it.

Next door (house is a semi) has no support at all in the cellar, apparently, but I still don't feel comfortable removing it from mine.