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How to landscape a sandy slope with rocks to reduce house moisture readings?

Hi Everyone,

need help with a solution for a steep site down the other side of our house, causing high moisture readings in the walls.

Very sandy and has a layer of limestone rocks that are not cemented in.

I've partly removed the rocks planning to remove the rest.

Top two level sections - installing drainage solution with existing and new plastic and covering with existing stones. Water will be piped down the slope. (refer images)

But what to do with the slope.

My concern is anything I do will be a temporary fix and then break down, eg plastic liner ripping.

The source of the water is all surface and want to stop it going into the ground and move it all to the front of the property.
Planning to take out all the stones, remove some sand from the left side, to create a slope away from the house.

Relay the stones and cement all the stones to create a seal/hopefully keep the sand dry.

Against the side of the house: I don't want to put stones right up to to the side of the house/damage the wall, plan to have a gap of a few inch's and fill with cement with water proof additive, then a bead of sika.

What I've suggested sounds okay or anything else you would consider?

Would you cover the whole site with plastic before laying the rocks?

What plastic is not going to rip apart and if I did put a plastic down, it would help the rocks slide down in time/crack the cement?

Would be nice to seal the house wall but its too deep, 3 meters or more at the top and at the bottom 1.5m to the pad. ( no existing seal from what I can see - build in 1975 approx)

(The other side of the house is similar - but has already had the rocks cemented, with multiple crack repaired over the years and I will be repairing as recommended in the forum with sika along the edge)

Thankyou for any suggests that can help me fix this challenge.

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Comments

JacobZ

Hi @bob11,

Some more context for a few things would certainly help. Allow me to ask a few questions to help myself and our readers understand what is currently happening.

Do the second and third photos show the top of the slope or the bottom behind the location where you were standing to take the first photo?

Where are you experiencing the most moisture in the wall?

Is the existing black plastic coming up from under the concrete footing of the house?

Where do these drainage channels expel water?

Is the aim to emulate the slope on the other side of your house that can be seen in your post titled How to seal cracked retaining wall?

If so, I would start by, as you've mentioned, excavating the sand on the left side of Image 1 so that it slopes away from the house.

I would then add a thin layer of drainage gravel, around 5-10mm thick, over the sand and compact it with a tamper. This thin layer is there to help lock the sand in place and prevent erosion.

I would then lay builder's plastic over the slope and add a thicker layer of drainage gravel, around 50mm thick and once again compact it with a tamper.

You should then attach 10 x 100mm Abelflex Expansion Joint Filler Foam to the wall so the top edge is in line with where your mortar will go. This will act as a protective barrier to prevent damage to the wall as well as cracking in your mortar from expansion.

You can then relay your larger stones over this compacted base using mortar mixed with Bondall Silasec Waterproofing Cement Additive, ensuring you maintain the negative slope away from the wall.

Once the mortar has dried, seal the edge to the wall using Sikaflex Pro+ Polyurethane Sealant like you planned to do on the other side of the house. This sealant should be applied over the top of the Abelflex.

Let me know what you think. There may be other solutions to the issue that a little more context would help us come up with.

Allow me to tag @Nailbag, @TedBear and @Dave-1 for their thoughts.

Jacob

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/50044#Comment_50044

Good Morning @bob11

Subsurface water entering via the ground is a pain 😕 One I know well.

I actually shifted the soil away from my wall, even went wide enough for a path in one instance 🙂

Fixing water ingress issues in garage Is the project.

I went down the path of how and what to use to stop water entering the garage and also the side of the house. Both had watercomeing from outside and ending up under the house 😕

Stormwater rectification stage 1

So the best way I can suggest to stop water traveling subsurface wise is to creat an air gap between the wall and your side. Even 100mm air gap is enough. I Really like Gabion cages as they allow free drainage through, are strong enough to self support and also look great 🙂

Plastic sheeting against the wall only works up to the point it may be perforated. The rear of the walls has some fine material (I have used upholstery wadding) to stop fines from entering the baskets. You could do a two step or even three step cage up that slope depending on what you want step wise and includ in it a tall airgap on the right handside.

Here is my current project and note that its off the wall and allows free flowing drainage as well.

01 27-04-2024.jpg

What was

02 17-06-2024.jpg

The purpose built cage

03 06-10-2024.jpg

Full cage installed and I have also installed a grate styled drain and pavers across the front of this.

Dave

bob11

https://www.workshop.bunnings.com.au/discussion/comment/87123#Comment_87123

Thankyou @Dave-1 for information on your solution and this is a great idea. I'm just not sure this will work for me today, but keen to explore for other projects in the future. My challenge is at the bottom of the paving, the sand depth to the house pad is about 1meter and quickly rises at the top of the slope to about 4.5 meters of dirt/to the base of the of the house , I'll add some extra detail to new images and comments in my message, cheers. Bob

bob11

https://www.workshop.bunnings.com.au/discussion/comment/50044#Comment_50044

Hi Jacob,

Thankyou for your reply, I like the plan and the details that I had not considered/wasn’t aware of, all I knew was I had a big problem to solve.

To help with more detail of the site I have included new images, I think these will confirm the steps you mention to solve the site issues.

I'm unable to seal the whole outer wall of the house due to the depth of the dirt, but planning to remove the majority of the surface water down and exit to a soak well at the front of the property.

Sealing the outer wall - I can probably seal to about a meter below the dirt level.

The aim is to emulate the slope on the other side of your house that can be seen in my post titled How to seal cracked retaining wall?

(Top level) Re: Is the existing black plastic coming up from under the concrete footing of the house? There was some weave plastic under the rocks before, I have installed the top level drainage and extra plastic to the edge of the house.

Thanks

Bob

1974 plans.jpg View of middle level.jpeg View of the top level.jpeg View from middle level.jpeg Ground Level.jpeg

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/87172#Comment_87172

Afternoon @bob11

Im just trying to get the information right 🙂

Have you had an indication of water comingthrough to under the house?

If you have what are the indications?

Sandy soil should really be helping the moisture/water head down hill.....

Going through those photos and reading your words raises a question. Is there only one outlet pipe per wall for the drainage behind it? And if so is it supposed to take the water from the grill drain behind the retaining wall as well?

Waiting to hear back but think I know why you have high moisture readings, and wouldnt be doing anything to the side of the houe just yet (as in waterproofing)

Dave

EricL

https://www.workshop.bunnings.com.au/discussion/comment/87172#Comment_87172

Hello @bob11

It is difficult to tell if the plastic is originating from the footing of the house, you'll need to manually check and confirm by slightly tugging at the plastic to make sure it is clipped under the masonry. If it is not integrated with your wall, odds are someone has placed the drain matt in the hopes of diverting rainwater away from the house and into the Easy drain channel. To lock the gravel in place and prevent it from spreading about, I recommend using Landscape Lock 2L Concentrated Garden Glue.

If you need further assistance, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/109067#Comment_109067

Afternoon @bob11

I have a sneaking suspicion that each of those retaining walls are acting as dams. With the small outlet in them and thats for the grate styled drain its nowhere near enough to allow free drainage.

Id be digging out behind each wall and installing some course gravel (10mm size at least) with a 100mm ag drain at the base with multiple large outlets through the walls. The water should drain a lot easier that way. Im guessing at how the walls are built and configured 🙂 If the water drains then it wont want to go through the brick work into the house.

Dave

bob11

https://www.workshop.bunnings.com.au/discussion/comment/109066#Comment_109066

Hi Dave,

no problem, for background info, a plumber two months ago completed a water pressure test/checked for leaks and used a metal spike where the top level is looking for damp soil, all was okay as I was wanted to check if there was any pipe water leaks, there is no water coming in or moisture reading concerns under the house on the bottom level/garage coming into the house.

The drain grills were installed last week on upper and middle levels - the pvc pipe outlet at the bottom of the retainer wall is connected to each drain grill, there is no additional agri pipe behind the retainer walls that I could see. 90mm pipe was the plan but challenges with the retainer walls rebar was a problem.

I agree it should all soak away, last week there was a good downpour, this soaked the bottom level soil and went deep against the house wall, I cannot see any existing moisture barrier (1974 property).

Cheers

Bob

bob11

https://www.workshop.bunnings.com.au/discussion/comment/109067#Comment_109067

Thanks Eric, yes this is something I installed last week with the plastic connected into the drain to take the water away/keep it on the surface (rather than a french drain), thankyou for the landscape lock suggestion, cheers.

Bob

bob11

https://www.workshop.bunnings.com.au/discussion/comment/121849#Comment_121849

Thanks Dave, this is a good idea and will consider/see how the new drainage grill/pipe work to keep the water on the surface, it could be the second stage of the project.

There was no existing outlet or drain in each wall until the recent work, just a wall with nowhere for the water to go since 1974. Water banked up behind each retainer wall/into the corner near the house wall on the top two levels, with a gap between the retainer wall and house wall for the water to pour down against the house/soil. Plan being that the retainer walls should have little water behind them/ keeping it on the surface with the new easydrain grates. But I need to allow for the agri pipe and I'll use 90m pipe down the bottom slope or two 40mm to allow for any extra work I need to do in the future, cheers.

Bob

bob11

https://www.workshop.bunnings.com.au/discussion/comment/50044#Comment_50044

Hi Jacob,

sharing my progress where some details have change, can you help with how to make a cement slope where you can see the plastic?

all the way from top to the brottom, like to avoid cracking etc

like the idea of exposed aggregate/small stones.

The site is now stable and decided to use the rocks for a steps to the top but decided I don’t want these rocks all the way across like the original plan, I agri pipe installed.

Just keen to know what would be ideal to cover the plastic eg am I on the right track like the steps but with smaller rocks? Anything else that anyone has seen as a solution, thanks.

Bob

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/87583#Comment_87583

Any chance of some images of the area for a bit of context @bob11? You can typically mix up sand and cement into a consistency that will hold position on a reasonable slope. You might need to add some rebar to ensure it doesn't crack. Adding aggregate or small stones before it sets is an option.

Mitchell

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