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What's causing the brick wall's base to have cracks and crumbling render, and how can it be fixed?

taj1
Just Starting Out

What's causing the brick wall's base to have cracks and crumbling render, and how can it be fixed?

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?

 

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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.

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