Cracks in Internal part of chimney

[gothiceye]

We've made 'investigation holes' in the plasterboard which had hidden the upper fireplace in our house (and in the process discovered the ring main, and water tubes and removed half of the building rubble that had been left behind there) and from our small vantage point, with the aid of a torch, we have seen what look like a crack quite high up in the chimney breast (at the point where it joins the loft.

I'm sure this is due to general movement of the house, but is it something that we need to get a structural engineer to assess? As we've only been in the house about 18 months and the fireplace has been behind plasterboard for quite some time, there is no way to know how long the crack has been there, or the rate of its progress.

 

[Penners]

As you suggest, the age of the crack is critical. If I were you, I would uncover it, and then watch it for a good while.

You can, of course, get a structural engineer in to look at it, if you want a quicker result. But it'll cost you.

Do your ceiling joists by any chance house into the chimney breast?

 

[charlie-ia]

any hints on watching walls? i heard glueing a microscope coverslip over the crack would work, as it would crack if the wall moved. and how much movement is too much? i dont think it would take much to break one of them.

 

[Penners]

That's a widely used technique. You can also get special tell-tale devices that are calibrated to enable you to measure movement. But I think they need a specialist to read them properly, and I've no idea where you get them.

A low-tech method might be to fill the crack with cement mortar, and then keep an eye on it. Cement is very brittle, so if the crack is still moving, the mortar would probably crack itself, or separate from one side of the brickwork crack.

But that's just an amateur idea. Others may have more professional suggestions.

 

[charlie-ia]

what kind of time period are we talking? ive watched my dad fill cracks, and they always reappear. he didnt appear to worry. on the other hand he has recently been told that his walls need ties.
i understand that old buildings need to move, but im under the impression that they nip off to the pub everytime no-ones looking!

 

[CHRIS]

Penners

You can get said thingies from York Survey Supplies and as I can read them you dont need to be a "specialist" to use them! (use them in Underground tunnels etc)

http://www.yorksurvey.co.uk/products/16crack.htm

Just use gripfill etc to fix them or use the studs and use some vernier calipers to measure on a regular basis.

Infact send me a PM and I will send you a handfull of the Crackmark studs

 

[Penners]

Chris - that's very kind, but actually it's charlie-ia who needs them.

Perhaps he/she will PM you.

Thanks again for the kind offer.

 

[gothiceye]

I've had another look at the wall, and I am thinking that it is more of a 'gap' than a 'crack' - in terms of the side of the chimney not being completely straight, and the wall built to join on to it being made out of square bricks that do not meet the side of the chimney?

Its the dividing wall between our house and the next, so I am thinking that whoever built the dividing wall between the two houses either did not have the means to break bricks to fit in awkward gaps, or felt it was unnecessary as it was a dividing wall rather than an exterior wall? Not sure when this wall would have been built, the house is early 1700s timberframed but was brick faced at a later stage.

There is what appears to be a fair bit of builders rubble in the gap (and a couple of smaller ones lower down - would it be worth removing this once the plasterboard wall is down? Once the plasterboard covering the fireplace and chimney is removed we also have the problem of finishing off the room - one option would be to lime plaster the bit of wall that is exposed up to where the chimney starts, then leave that exposed - but as the rest of the wall is plasterboarded, will this be OK, or would it be better to remove the plasterboard from the whole of the room, then plaster it as a whole?

Thanks for the advice.

 

[Penners]

Sorry, Chris - gothiceye, not charlie-ia.

What's my name again? Have I had my tea?

 

[Penners]

Gothiceye - it sounds as though you've got what is not an uncommon problem. The wall that abutts your chimney stack has not been properly tied into the stack, and over the passage time some separation has taken place. Anyway - as I said - that's what it sounds like from your description.

If it were my house, I don't think I would vary from the advice that's already been given. The important thing is how active the separation is today. If it has stabilised, then you may not have to do much more than fill the gap (with perhaps a bit of judicious tying between the wall and the stack). But if it's still moving, then a more drastic remedy may be needed.

I suggest you PM Chris (see post above) who has kindly offered to send a telltale or two. You can use this/these to watch the separation over a period of time, and see whether there is still any movement. I'm not sure how long such things should be left in place and watched, but at an amateur guess, I would say for no less than a year. That way you can see whether seasonal variations in groundwater, etc, have any effect.

I hope someone more expert than I am will add their endorsement or disagreement with this view.

 

[gothiceye]

I'm not sure from the second look that the wall has actually *moved* from the original spot, as there are several bricks lower down the wall that are actually pretty close - causing more of a 'higgledypiggledy' effect where bricks appear to have been put as close to the chimney stack as possible. (Imagine a slight diagonal sloping inwards where the wider chimney breast narrows to begin forming the chimney, and a wall roughly built to the side of it, which roughly follows the shape but not exactly...)

From what I saw on the link provided above, I think the gap is too large to put the guides on - but it also looks like is fairly stable (to my untrained eye). There are also no cracks on the outside of the house that would suggest that there was a movement problem in this direction.

Does this sound like a usual construction method? At the moment it is a less pressing emergency than trying to repair the damage caused by the shower, but it is something to be considered...

Thanks

 

[Penners]

Does this sound like a usual construction method?

Hmmm - define "usual"!

It sounds pretty cowboy, but then cowboy builders aren't confined to the 20th/21st centuries!

 

[gothiceye]

...possibly something we lime plaster up once we've cleared the rubbish out of the gaps?

 

[Penners]

It's very difficult to imagine this gap. Could you post a picture? This will help experts on this forum to advise you on how you should best repair it.

 

[gothiceye]

I'll try to get a picture on here over the weekend - although we've got guests stopping so getting to the computer will be difficult, so it may be early next week - thanks

 

[CHRIS]

I find if you have guests any excuse to get away is a good one!

Especially Mother in laws!

 

[Penners]

In our family, the in-laws have traditionally been referred to as the outlaws.

 

[gothiceye]

Sorry - yesterday was spent taking the shower out to see the damage! I tried to take some pics with my camera phone but it was too dark. I'll try over the next couple of days and use my proper camera