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Q&A with Handy Mac: Wall cracks

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Robby and Jill both problems with cracks in the wall

Q: Over the past 23 years, I have had my simplex painted five times. It’s due for another paint together with prior substrate repairs. My problem is that I have cold joint cracks in my plastered 115mm screen walls that keep reappearing a few months after painting.

These cracks have obviously come about as a result of poor bricklaying practices, such as the wetting and slurry sealing of the brickwork prior to commencing work after a weekend break has not taken place. Hence the lack of adhesion. How can I fix this?

I have thought of raking out the cracks 10mm wide to the full depth of the plaster, sealing with an agent, filling with a recommended filler, then covering with a membrane. I have spoken to a building contractor friend who identifies the crack as a “dry joint” caused by the reason I suspected.

Sadly, he has no clue how to hide the crack. The screen wall is 1.4m long, 2.4m high and firmly attached to the main house structure on one end only. If it were free-standing, a good wind would probably blow it over.

The crack is horizontal, level, and passes right through the wall along its entire length. The wall is not that big, and it might just be better to start all over again, or rebuild it out of another material? – Robby

A: The correct method of repair is to have the plaster hacked off about 100mm either side of the crack, fix metal lathing over the crack and replaster. This might not work if it is only a 115mm wall and the whole thing might collapse.

Also, you are always going to notice the repair. The alternatives are to use a fibreglass tissue and paint system or one of the more modern paints that have fibre in the paint. Fibreforce is one brand that comes to mind. Both are flexible and thus hide cracks.

As you say, the crack would need to be raked open first and filled with a flexible filler. 

Jill also has a problem with cracks. 

Q: Last year you wrote a column about wall cracks.

You said it would be best not to fix these until after the winter rains, as you felt they might have appeared because of our dry conditions, and that they might correct themselves after the rain. I was heartened by your response and have happily left them. 

However, the heavy rains we were hoping for did not materialise and the cracks from the lounge, kitchen and right down the passage on both sides have worsened. I am at a loss as to what to do about them and wondered if you and your wife ever come in our direction to give us your opinion?

A: Maybe I can consider retiring again and send Mrs Mac out to consult. Seriously, though, reports of cracks since the start of the drought seem to have slowed down.

Hopefully we have seen the worst of it but I would still recommend not rushing in to do anything until the rains do return – this is obviously going to happen because the politicians say so.

My company has been quite busy with under-pinning/crack repair contracts and I would once again like to point out that these should not be undertaken unless under the supervision of a suitably qualified structural engineer. 

We are busy with one at the moment where the whole scope has changed because what can be seen superficially does not match with what is found once you start to open up areas. As a warning to both contractors and clients, please be aware that the cost of this type of work can vary and must be priced on a provisional basis with both parties aware of the fact that the final price may well have to be negotiated.

*Handy Mac, aka Don MacAlister, is our expert on household DIY issues. If you have a question for him, please send it to or SMS only to 082 446 3859. Find Don on FB:

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