Handy Mac, aka Don MacAlister, is our expert on household DIY issues

Vertical cracks are reappearing in the same place after being repaired, on walls adjoining those of an extension. There are also cracks on partition walls. The new building was built in 2016. I have noticed in some areas the cornice is pulling away from the walls, so perhaps the building is settling.

My concern is the vertical cracks reappearing. Do I insert rebar into the wall and reseal it for strength?

Hi Don. How can I fix cracks that are giving me sleepless nights? The house is only eight months old. They began appearing about a month ago, and one person said it was a settlement crack.

The picture, right, sent by Mandisa shows what bad building some contractors think they can get away with. I have asked her to send me copies of her plans and I will see what I can do to help and whether she has recourse to the National Home Builders Registration Council or the builder.

Richard’s problem is that his extension is not joining well with the original house. This happens for a number of reasons. One is that we were better builders 15 years ago. Also, there is rarely enough care taken to ensure the new foundation is tucked in under the existing one.

As this will always be a weak area, the existing foundation almost needs to be underpinned by the new foundation. There are two schools of thought about whether an extension should be tied in to the existing building, or have a clear joint between the two.

Over the years I have come to believe a clear separation joint is the best bet.

However, Richard cannot start again and I would suggest he opens up in at least three spots, namely top, middle and bottom, and installs pre-cast lintels from one side to the other. If this fails, he may have to look at underpinning.

Cracks can be classified like this: Thin crack: Less than 1mm wide. Medium crack: 1 to 2mm wide. Wide crack: More than 2mm wide.

Structural cracks: These occur due to incorrect design, faulty construction or overloading and may endanger the safety of a building.

Non-structural cracks: These occur mostly from internally induced stresses in building materials. They do not endanger the safety of a building, but may look unsightly or create an impression of faulty work. In some situations, due to penetration of moisture, non-structural cracks may spoil the internal finishes, thus adding to the cost of maintenance or corroding the reinforcement.

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