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How to waterproof a timber retaining wall?

Hi all, most recent property purchase and first time poster here. When we have rain water is pooling at the back right hand corner of the pictures attached. We then see the side garden bed dirt and debris flow under the pool coping leaving staining in the pool. Hopefully that can be seen!

I want to remove the side garden bed all together and have no vegetation/garden bed what so ever along the fence line, if possible. I will also likely get some updated coping at some point in the future however want to fix the pooling water/drainage issue first. The staining is removable, its just constant issue. Now, I believe better drainage would be suited to behind the retaining wall at the back end of the pool firstly, remove garden bed and then run some form of drainage down the side of the pool (fence line). Capture water and then focus on moving it away, is my thoughts. The wooden bed sleepers are all wet and rotten down below and I'm just looking for some thoughts and possible ideas. I do have plumber and landscaper mates however want some advice from the forum before we start brainstorming.

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Comments

JacobZ

Hi @P738952,

A warm welcome to the Bunnings Workshop community.

Apologies for the delayed response.

I can't see any other great ways of managing the problem besides what you've already discussed.

Removing the timber garden bed along the fence line would certainly be a good start as it would create a path where drainage can be plumbed to bypass the pool.

Adding drainage behind the retaining wall is a great idea. A French drain can be installed in a gravel trench behind the wall to collect and redirect the water. This would capture water before it reaches the pooling area and help direct it away from the pool.

Once this drainage is installed you can run it along the fence line and connect it into the drainage pit that you can see on the left of your second photo.

I'm not sure there's too much else that can be done, but some closer photos of the stone-clad retaining wall and the area behind it might help our members come up with some ideas.

Allow me to tag @JoeAzza, @Dave-1 and @Noyade for their thoughts.

Let me know what you think.

Jacob

P738952

https://www.workshop.bunnings.com.au/discussion/comment/46835#Comment_46835

Hi,

Thank you for the info.

I have added some photos of the wall. Can see a section has obviously been changed in the past. The pit noted, also does have drainage running up to and likely along the fence line. I would assume its likely broken/full of dirt.

look forward to further replies

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/85475#Comment_85475

Good Evening @P738952

This is going to be a hardish one I think.

The retaining wall you are asking about looks like its also holding back soil from your neighbours yard.

Removing the garden bed totally is a good idea but you will need a decent retaining wall (I do have an idea 🙂 )

Looking at the last few photos you have supplied I also have questions about the state of that rear retaining wall next to the black pole fence. This is where you could be getting a bunch of that water coming from, especially coloured by soil ect. The timber? looks like it has tiles on it? It may be worth investigating how solid this wall is. I am not sure where that grill drain in your last pic is tho?

For a retaining wall for both sides I am suggesting a gabion wall. Something at least 400mm wide if not a bit wider (because of the height and what it is retaining) The wall will allow free drainage through it and be strong enough to hold back the soil. (take a look at my bookmarks and you will see a large range of types you could use)

I am thinking of a grill drain along the length of the retaining wall (for whatever type you go with 🙂 ) next to the wall/s This will stop water from overtopping and flowing into your pool. Believe me when I say I know how you feel, my pool has that happening at least once a year lol The grill drain is what I intend to use to fix my problem,

Dave

P738952

https://www.workshop.bunnings.com.au/discussion/comment/107939#Comment_107939

That section of the retaining wall you have noted near (black fence) would also need to be altered.

Any ideas on best option to replace that section? And ideas on best way to waterproof a wooden retaining wall? What type of membrane would be best. Liquid or sheet etc?

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/121230#Comment_121230

Good Evening @P738952

My first preference is a gabion styled retaining wall 🙂

I prefer allowing water through things as holding water back means you ahev a bunch of extra things to consider.

To give you other options, My second preference would be a timber retaining wall, easy to install with treated pine and manageable lifespan wise. I am not sure waterproofing it is wise as the overall water push will want to push your wall out of true.

You could go the route of a concrete base foundation and the interlocking retaining wall bricks Brighton Masonry 295 x 180 x 100mm Charcoal Eziwall Block I do like this option especiallya round the pool. You will still need drainage behind the wall but it wont rot. 🙂

Dave

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/121230#Comment_121230

Hi @P738952,

Waterproofing a wooden retaining wall is a challenging task, especially after it has already been constructed. Ideally, this should be addressed during construction by installing a drainage system behind the wall. Typically, a plastic sheet or membrane would be placed against the back of the wall, with an agi-pipe (perforated drainage pipe) laid at the base. The area would then be backfilled with gravel to create a free-draining zone.

This setup allows water to hit the plastic sheet, filter through the gravel, and be directed away by the agi-pipe into the stormwater system. Without this drainage system, simply waterproofing the wall from the front or back will not prevent water buildup. The trapped water will accumulate behind the wall, creating hydrostatic pressure that can weaken the structure and potentially push the wall over.

Since you're dealing with an existing wall, retrofitting proper drainage is the best solution to address both waterproofing and structural stability.

Mitchell

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