How to fix brick wall cracks and crumbling render?

taj1

Hello, everyone.

I've seen cracking and disintegrating at the bottom of my external brick wall, where the bricks meet the concrete footing. In some sections, the render/mortar is broken and slightly hollow, while in others, I can fit my finger between the brick and the concrete base.

I have attached photographs that show:

Horizontal cracking on the mortar line

Vertical fissures on the corner.

Areas where the render sounds hollow when tapped.

Minor white residue and degradation at the base.

I

am not sure what is causing this. Possible things I'm considering:

Water coming in from rain or poor drainage

Old or failed renders and mortars

Normal home movement and settlement.

Efflorescence or moisture passing through the concrete

My primary questions are:

What's the most likely cause of this issue?

Is this cosmetic or structural, and should I be concerned?

What is the proper technique to repair it?

Should I remove any loose material and replace it using repair mortar?

Do I need to apply a waterproofing or sealant after patching?

Is flexible exterior sealant a better option than cement in this case?

Which Bunnings items would you recommend for this repair?

I'm hoping for a DIY solution, but I don't want to merely cover it up if moisture is the main problem.

Any advice is much appreciated. Thank you in advance.

MitchellMc

Welcome to the Bunnings Workshop community @taj1. It's brilliant to have you join us, and many thanks for your question about brickwork.

From what you’ve shown, most of the issue seems to be a superficial layer of render or cement applied over the concrete foundation that has broken down. This is largely an aesthetic problem rather than a structural one, and it can be addressed by removing the loose or hollow sections and patching them. I would start by chipping away any render that is flaking, hollow, or poorly adhered. For the small cracks and recessed mortar, a quality exterior render patching compound will allow you to fill in and smooth over those areas.

The only part I’d pay extra attention to is where you mentioned being able to fit your finger between the brick and the concrete base. That could indicate a small gap that might need filling with mortar. If it’s just a minor void, patching with mortar should be fine, but if it’s a larger gap, it could be worth having a professional inspect it to ensure there isn’t a deeper structural concern.

Once the loose material is removed, fill the gaps and cracks with the render patching compound, smooth it out, and allow it to cure as per the product instructions. In most cases, that alone is enough; you don’t necessarily need flexible sealant unless the area is subject to movement or frequent moisture. Adding a waterproofing coat is optional for extra protection, particularly at the base where water splashback might occur, but it’s not essential if the patched render is sound and well-bonded.

Let me tag @Nailbag for his thoughts.

Please let me know if you have any questions.

Mitchell