Cracks in Walls. Canberra repairs?

The soil under most houses in Canberra is clay and these clays tend to shrink on moisture loss or swell on moisture take up. You may be surprised to hear that 30mm of movement of the ground surface is fairly typical around Canberra. That having been said it is not the total movement but the relative movement that causes the trouble and this can be due to a number of factors.

Prior to AS2870 Residential Slabs and Footings Code which was first referenced by the BCA in 1990 all footings were around 230 to 250 thick with one layer of mesh but after that, structural engineers started to better understand what was required and footings became 20 to 50 times stiffer than they were. This is why houses built after 1990 with proper site classifications and code compliant footings very rarely crack due to soil moisture changes. Some engineers around town choose to ignore some code provisions for commercial reasons so there are still some problems but the situation is much improved.

I can’t specifically comment on your cracks but there is some excellent general advice with a local flavor here http://www.structuraldesigns.com.au/faq-20

I’ve got the same problem, any other ideas on what I should put in these joints?

I’ve also got a situation where the ceiling cornice is attached to the ceiling and has moved with its movement away from the wall, can I de-tatch that from the ceiling back onto the wall?

This is a common problem, especially with concrete brick houses. Most brick walls have expansion joints filled with mastic (which after 40 years will have lost its plasticity). Cracks appear elsewhere when the foundations move farther than the expansion joints accommodate. This can happen if a season is unusually wet or unusually dry. If you fill the cracks with rigid material, you may get new problems when the foundations move back.

You can alleviate the problem by stabilising the soil moisture around the house – e.g. by building concrete paths around the house to drain water away from the foundations. You can fix sticking doors and windows by planing back the sticking edges. If the gaps get too big, you can use draught sealing tape.

You’ve done well if you’ve only just started getting them on a 40 year old house. I wouldn’t be too concerned if its only small. Our inner north house was fully renovated 7 years ago and by the 3rd year cracks were starting to show again. Unless you do major underpinning (expensive and not really necessary after that length of time) then cracks will just show again as things move back and forth and you’ll be out a ton of money from all the minor filling and repainting.

It might be your house “settling” due to drought causing the clay to shrink and shift the foundations. I got this fixed for my house through Uretek.

A structural engineer will tell you if it’s a problem (they do pre purchase inspections on them all the time). So start there before anything else, maybe $500 or so. But it’s probably just the dry weather causing earth movement.