Ground Instability

Addressing wall cracks: know your soil types

Cracks are very common, particularly in houses that are more than 20 years’ old. Although many people can see cracks in their walls, they don’t know why the cracks are there.

Wall cracks develop over time as a home’s foundations move. When this happens, the situation rarely resolves itself – the cracks will continue to get bigger.

While extremely rare, a house with severe wall cracking may eventually need to be demolished. If you can put your little finger through a crack, then it should be addressed urgently.

Seasonal shifts cause walls to crack

Seasonal changes are the most common causes of ground movement, which in turn cause walls to crack. As rain sets in, excess water causes the ground to swell and when warm weather arrives, the ground shrinks again as it dries up.

The most important thing to do if there are cracks in your walls is to check for stormwater or sewer pipe breaks or leaks, as water around the house can cause its foundation to move.

Know your soil type

As part of addressing cracks in walls, you’ll need to find out what type of soil your house is built on, as this affects changes in water level and how the foundations shift over time.

Contact a local geotechnical engineer or council engineer, who can advise on what soil is typical to your area. Be aware that their advice is general, and that the site in question may have introduced soil, which is commonly referred to as fill. To obtain advice specific to your site, you will need to engage the geotechnical engineer to take soil samples from your property.

There are four types of soil – sand, clay, silt and peat.  The most common in Australia are sand, silt and clay.

Sandy soil creates fewer foundation problems because water can flow freely through the soil, helping to keep the foundations stable.  If a house built on sandy soil has a severe crack in a wall, it’s important to act quickly as it can be a strong indication there is a broken sewer or stormwater pipe nearby.  The first thing you should do in this instance is call a plumber.

Clay soils on the other hand can be highly reactive, which means they change volume and shift when moisture levels change, causing the ground to swell easily.  This makes a house more susceptible to seasonal movement.  For houses built on clay soil, wall cracks up to  five millimetres are most likely to be seasonal.

Mainmark’s team of ground engineers can provide expert advice on closing cracks in your home’s walls. Contact us on 1800 623 312 or tell us about your problem via our online enquiry form and we’ll call you.

By James O’Grady

James O’Grady is the Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years’ experience in structural engineering, construction materials and ground treatment.