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How to remedy concrete erosion and sinking?

Hi,

I have noticed that the front patio of my house has concrete eroding gradually. I have also noticed that the bottom of the house render has been eroding as well. This all started to happen after the big rains in 2022.

I think our stormwater drainage is not that effective so we are getting our stormwater drains checked. What are the possible fixes for the concrete?

For context, we live in the Gold Coast, SE Queensland.

Thank you very much for the help!

Regards,

House photo 1.jpg House photo 2.jpg House photo 3.jpg House photo 4.jpg

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Comments

Jason

Hi @junzuniga,

Welcome to the Bunnings Workshop community and thanks for joining in the discussion. I'm sure you'll get loads of helpful advice and project inspiration from our wonderful members. Feel free to post anytime you need a hand.

Our resident Bunnings D.I.Y. expert @EricL will be happy to assist you when he is back on the site later today. Let me also tag some other experienced and helpful members in @Adam_W, @Jewelleryrescue and @MikeTNZ to see if they could share their thoughts.

I also wonder whether you could share detail about what it looks like on the other side of this wall? Is that area under the house accessible? Is there drainage problems evident under the house?

When you say you are not sure if your current drainage is being effective, can you please elaborate on what the impact has been in the past? You are right that you would need to tackle any drainage issues first otherwise problems will keep reoccurring.

Jason

EricL

Hi @junzuniga

Thank you for sharing your question about concrete erosion. Looking at the pattern on your concrete walk. It's clear that it has been worn away by running water. When water comes together, it forms a small pond and flows to the lowest point on the ground.

If there is a lower spot where the water can settle it will flow into that area. In this case it has gone under your concrete walk which has slowly softened the soil underneath causing the concrete slab to sink.

To begin with, I suggest investigating where the water pools and flows in your area. Once you've determined where the water pools you can then implement a drainage solution that will prevent the water from eating away your concrete walk and preventing it from flowing underneath the concrete base.

In regards to repairing the concrete surface, I suggest using Lanko 20kg 173 Floor Leveller in combination with Bondall 1L BondCrete Cement Additive. This is an easy-to-use repair compound and will fill gaps up to 25mm deep.

If you have any other questions we can help with, please let us know.

Eric

junzuniga

https://www.workshop.bunnings.com.au/discussion/comment/26687#Comment_26687

Hi Jason,

Really happy to be part of the community.

One of the downpipes, I found, is not fitted properly.

It is only now that I am realising that the stormwater drainage may be damaged underneath. Not sure yet as I am waiting for a video inspection on Monday.

Here are some photos of the other side of the wall.

House photo 5.jpg House photo 6.jpg House photo 7.jpg House photo 8.jpg

junzuniga

https://www.workshop.bunnings.com.au/discussion/comment/26696#Comment_26696

Thanks Eric!

Very valuable insight.

On another note, how can I fill the gaps between the render and the concrete? Should I use a gap filler?

Thank you very much!

Kind regards,

EricL

https://www.workshop.bunnings.com.au/discussion/comment/76023#Comment_76023

Hello @junzuniga

If you are planning to fill the gaps, I suggest using Sika 600ml Concrete Grey Sikaflex Pro+ Polyurethane Sealant in combination with Paint Partner Aluminium Caulking Gun.

Please make sure to remove any dirt and debris on the render and concrete base before applying the sealant.

Make sure to wear personal protection such as gloves, goggles and a mask when using the sealant.

If you need further assistance, please let us know.

Eric

junzuniga

https://www.workshop.bunnings.com.au/discussion/comment/26696#Comment_26696

Hi Eric,

Sorry for the follow up question.

I forgot to ask if you suggest mixing the Bondcrete to the Floor Leveller?

Thank you very much!

junzuniga

Hi Bunnings Community!

Good day!

I am humbly asking your thoughts on the reasons why this is happening on my front concrete slab and House Mortar.

It looks like its eroding from the top. There is no water runoff when it rains on this part.

Curious if it is a rising damp problem?

Here are the pictures.

Thank you very much!

Kind regards,

Jun

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/78251#Comment_78251

Hi @junzuniga,

I'd suggest applying the Bondcrete to the surface before the floor leveller. Alternatively, you can use Lanko 1L Ultraprime 124 Surface Primer. Mixing the Bondcrete in is an option for cement and concrete, but the Lanko 20kg 173 Floor Leveller is not designed to have Bondcrete mixed into it.

The wear to the concrete is oddly spaced out from the wall around the same distance as what the gutters would be. My first thought is that it's from your gutters overflowing and falling on that area. Are the gutters flowing to the downpipes as they should and not overflowing? It could also just be a poor concrete mix where the ratio of sand/cement and water was in the wrong proportions creating a weak slab that is not resistant to erosion. I wouldn't have thought the degradation of the concrete was due to rising damp.

Mitchell

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