Horizontal crack round house - an update

[Martin Wiseman]

Hi,

Over the weekend I hacked some of the plaster off to see what was going on with the bricks underneath. As promised here is the results of that investigation.

Photos at:

appears that the crack represents a transition in the style of construction of the wall. Below the crack the wall is a conventional cavity wall with bricks laid side on in the normal way. Above the crack the bricks are all end on. The soffit on the outside is level with the crack so it is impossible to see what is at the other end of the bricks, however my drilling verified that the bricks are full length so they presumably cross the cavity and end 2 inches short of the outside line of the wall.

The widest part of the crack which has opened up represents an unmortered joint between the bricks and the end of the lintel and hence an obvious weak spot in the wall.

There is a slight difference in the plane of the wall above and below the crack - above the crack the plaster was slightly proud - i.e. it appears the top of the house has shrunk or the bottom of the house has expanded.

I checked with a plumb line and the two external walls of the room do appear to be acceptable vertical so the house is not obviously leaning.

There was another vertical crack from the bottom corner of the window down to the floor. This was clearly an old crack since it appeared to have been filled (with pink plaster) when the room was originally decorated. This crack was originally about 1 to 1.5mm wide and does not appear to have opened significantly further in the 20 years since it was filled.

Do the photos help anyone explain the construction of the top of the house and/or a reason for the cracking?

I did wonder if there could be a wooden beam round the house (the wall plate?) which bears on the back of those horizontal bricks and which expands and contracts through the seasons due to moisture. Does this theory sound plausible to anyone? If this is the case the ongoing cracking could be a cyclic thing and not an indication of continuous spreading - or am I just suffering from wishful thinking?

Regards, Martin.

[dg]

It appears that there has been some differential movement.

Possibly, movement of the timber roof rafters has slightly pushed the course of headers (the bricks long-ways) and as these are overhanging the cavity, then they have dipped slightly. The lintel has been rotated slightly too, causing the crack at the bearings.

This is a design or construction issue, and does not appear to be a major structural concern.

The crack should be filled with a flexible mastic or epoxy resin. Either fit expanded s/steel mesh across the crack prior to replastering, or fit plasterboard to the wall to hid any further movement cracks

dg

[Cicero]

================ Well, you were right about the lintel - it is concrete and not wood as I originally suggested. It appears to be quite a hefty one too - about 9" x

9" judging by your pictures.

One possiblility is that the lintel was put in place too soon during the building, that is before the mortar under the underlying brickwork had gone off or the mortar might not be strong enough or thick enough to support the brick and lintel. This would probably explain the obvious break in the brick. It's also possible that the lintel was too heavy for the job and this could explain the other crack you mention from the bottom corner of the window to the floor. It would probably take two strong men to lift that lintel whereas you could hold a modern metal 'catnic' lintel in one hand and still get the same strength.

If the mortar under the broken brick appears to be solid then you probably don't need to do anything other than the cosmetic work suggested by a previous poster. If it is very crumbly then you may have to think in the long term about re-bedding the lintel but this could be quite difficult for the average DIYer.

As far as the other horizontal cracks are concerned you could do a test scrape to see what that shows up. My guess is the same as before - plaster movement on the wooden wall plate.

Cic.

[Martin Wiseman]

Hi,

Thanks to everyone who contributed to this thread, we now have a much better understanding of the possibilities and options. Due to time constraints it looks as if this room is going to have to have a quick patching up job done for now and then be sorted out properly next year.

Regards, Martin.