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How to fix a sinking outdoor patio?

The situation:

Outside my living room door, there’s an outdoor patio. Recently, I noticed water flowing towards my property because the outer edge of the patio seems to be higher than the joint of my house and the patio. The joint also has a gap and some residual marks suggesting the patio was roughly 3 cm higher before, but now the house settled and the slope is tilting towards the house.

I noticed some sealant residuals near the joint, indicating waterproofing sealant was applied several times to address this issue.

The ask:

My current plan is to use backer rod to fill the gaps and apply sealant to waterproof the gap again. However, since this solution was previously applied and the settlement of the house seems to continue and will eventually widen the gap, I’m hoping to get some options on how to fix this.

I would appreciate advice on:

- A temporary fix: maybe use sealant again to prevent water from flowing back.

- A more permanent fix: maybe suggestions on installing something in the joint as a flashback

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Tools and Materials

Decking and Paving

Repairing

Building and Construction

Tiling

Comments

EricL

Hello @Vincero1

If the patio has just recently started to sink or move more rapidly, it's highly probable that water is running underneath the concrete slab and is being carried away the by the shifting soil underneath. I propose looking around the perimeter of your house and looking to see if any of your down pipes or storm water drains have been damaged and is releasing a large amount of water in the vicinity.

The patio slab can be lifted back into place by engaging the services of a slab restoration specialist. However, it's important that the source of the water running under the patio be addressed first before you have the patio repaired. Unless this issue is fixed first the slab will continue to move and sink.

If you need further assistance, please let us know.

Eric

AlanM52

Hello Vincero1,

Even allowing for movement (everything moves) I am wondering why the patio wasn't laid with a decent fall away from the house.

Can you confirm that is a concrete slab.

What quantity of flowback are we dealing with and does it tend to flow to one side, or does it simply seep away into the gap.

If substantial I am thinking of a drain and if not maybe something like this:

Colorbond Corner Flashing.jpg

Cheers

Vincero1

https://www.workshop.bunnings.com.au/discussion/comment/53320#Comment_53320

HI @EricL and @AlanM52,

I finally got a plumber to look into this and drew a stormwater diagram. I have marked the blockage and also the gap area. Along with photos of roots that blocking the drainage.

I won't be sure it is a concrete slab under the tile but it should be. The flow back it not that serious since the roof of verandah catches most of rain water. I understand lifting the concrete might be the most permanent solution but I am cost conscious.

Given the blockage has been cleared, should I start to seal the gap? My plan was using backing rod to fill the gap and use Polyurethane Sealant from sika (https://www.bunnings.com.au/sikaflex-600ml-grey-400-fire-polyurethane-sealant_p0036456)

Screenshot 2025-07-06 at 11.32.20 am.png

EricL

https://www.workshop.bunnings.com.au/discussion/comment/89332#Comment_89332

Hello @Vincero1

It's good to hear that you've manage to deal with the blockage in your drains. I propose using Sika 600ml Concrete Grey Sikaflex Pro+ Polyurethane Sealant instead, as it is designed for use with masonry.

If you need further assistance, please let us know.

Eric

AlanM52

https://www.workshop.bunnings.com.au/discussion/comment/110458#Comment_110458

Hi @EricL & @Vincero1,

Good to hear it's all sorted out (y)

So many choices today in the past I would have simply done the mortar thing.

Photos: June 1999.

That was not a good choice to plant in the small mailbox garden bed.

Main stormwater exit to street.

Within arms length of where she runs under the footpath.

The kids loved playing with that, the younger one was running round... 'snak daddy snak'.

Cheers

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