Internal crack around window

reasonableman · 4 Jul 2016

I live in a 1950's three bed semi ex-council house. There is some cracking around the window on the first floor. It seems reasonably big to my inexperienced eye. I've attached some pictures below; the window is just out of shot to the left. There are no signs of cracking on the outside but it is a cavity wall. I've looked around for different crack information but not seen anything similar to this type of crack.

There is cracking to a lesser degree on the other side of the window, so I suspect it is due to the installation of PVC windows. However I have only recently moved in so do not now how long they have been there.

I'd be very grateful of any comments anyone has (ideally not 'lol your house is falling down'!).

^woody^ · 4 Jul 2016

Looks like a board crack between plasterboard

reasonableman · 5 Jul 2016

Thanks for the swift response.

That doesn't sound too serious. Can I just replaster the wall or will the plasterboard need to be replaced?

^woody^ · 5 Jul 2016

Look at some of the threads about repairing plasterboard cracks. They have a tendency to reappear if not repaired in a certain way.

reasonableman · 5 Jul 2016

I've had a search and think I've found the following information. I'd appreciate any comments on this plan.

This looks like it's a reoccuring problem as it looks like someone has already had a go a repairing it and it's back.

According to this thread:
//www.diynot.com/diy/threads/repairing-a-crack-ín-plasterboard.302517/
it could be these problems:

skimping on board thickness (12.5mm minimum for everything these days)
wide gaps between boards
insufficient support &/or fixings
unsupported board edges
poor/no joint taping
movement of the building structure itself

I'll try to measure the board thickness with a pokey thing.

I've got a pipe/wire detector so might see if I can find the fixings and have a look at one.

If that all fails I'm planning to tape the joints and re-skim. If it happens again I'll have to rip back the plaster to look.

Some more info here: //www.diynot.com/diy/threads/joining-new-plasterboard-to-old.311635/

vinn · 5 Jul 2016

Go round the room and knock on all the walls and reveals to see if they are dot & dabbed plaster boards.
If you remove the small square of board thats proud of the surface in photo 1. it might show exactly how the board is fixed, & what, if anything, is behind it. Release it by lightly cutting the paint & prising off.
Has cavity insulation been injected?

reasonableman · 5 Jul 2016

Thanks for the comments vinn.

Some more details. The board is there to cover an air brick - I guess they didn't like the draft.

Cavity wall insulation has been fitted, don't know how they did it so could have been injected. It was in 2009.

I've got a ruler and poked in the crack. It slides all the way it - 15 cm. Also looking at the wall I think I can see breeze block behind the plaster layer.

Starting to think this could be an issue with the blocks...I've also noticed similar cracking on the other side of the window that was repaired but hasn't cracked.

vinn · 5 Jul 2016

I'm still not clear: is the "breeze block" 150mm behind the plaster board - ie. there's a 150mm void?
You say "plaster layer" what do you mean?
If you've removed the vent cover how far back from the plasterboard surface is the wall?

Is the external wall surface rendered?

reasonableman · 5 Jul 2016

As far as I can tell there is no plasterboard - the plaster was applied directly onto the blocks.

The 150 mm is how deep the ruler goes into the crack, from the surface of the plater, but it is only 150 mm long so I can't tell if there is more space (I guess there is as the only thing that would stop it is the far side of the cavity).

The external wall is rendered.

vinn · 5 Jul 2016

Fair enough, I had wondered about that given the odd "crack lines" and rough crack edges in the photo's, & the lack of tape.

Here's a couple of possibilities:
You might be getting simple thermal movement.

The rendering might have been applied as an attempt to prevent cold/damp difficulties.
Cavity Insulation might have been injected to provide some warmth.
Blocking the air brick might be thought to assist by cutting out drafts.
Maybe the cav insulation failed & has acted as a cavity bridge thereby creating various difficulties on the inner wall?

All above is speculation however, so here's what could be done:
Hack off plaster at all the suspect areas and expose the bare masonry surface.
Post photos of what you find also post photos of the external rendered surface.
Read up on here & google about thermal movement, & possible cav insulation difficulties.

reasonableman · 7 Jul 2016

Thanks for the suggestions.

I've attached a photo of the outside render. The window in question is on the right.

I hopefully will get around to looking under the plaster, however not for a few months. This is in the 'spare' room which we're using as the main bedroom while we do up the other rooms. I'll get severely told off if there is no respite from the dust and mess. Will research thermal movement and stuff.

vinn · 7 Jul 2016

You have concrete gutters (aka Finlock gutters) - they are almost always bad news.
They could be leaking down into the cavity &, if cavity insulation is present, soaking the insulation.
Damp cav insulation could be affecting the inner wall.
Concrete gutters tend to leak at the joins between sections. All kinds of weird & wonderful remedies have been tried to seal them - in the long run the only solution is to remove them.

Your render looks to be in good condition.

The window heads show timber battens fixed as some kind of cover or filler or perhaps as drip hoods.
To profit from them as drip hoods some kind of cover flashing is necessary or they will rot.

reasonableman · 10 Jul 2016

Yeah, heard lots of bad things about Finlock gutters and it's on the list of things to sort. Apparently they can also act as a thermal bridge. As you say, I need to look under the plaster to figure out more. Will update when I can get around to it.

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Internal crack around window

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