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How to fix/fill the gaps between the stones in the retaining wall in backyard?

Just Starting Out

How to fix/fill the gaps between the stones in the retaining wall in backyard?

Hi Experts,


I am a newbie and haven't done an outdoor DIY as such. I have an issue with our retaining wall that holds the Garden and runs along 1 side of the entire house. (Check the pictures shown)


Over the years, stone in it have become loose and I also find that the GAP between the stones has increased.


I am not sure how can I fix it ? Can I just use some fast setting Cement and patch it on these GAPS or what ?

Any advice is highly appreciated. The last photo shows some cement thrown on the stones by previous owner may be.


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Amassing an Audience

Re: How to fix/fill the gaps between the stones in the retaining wall in backyard?

Hey @SuchDIY , 

Doing something similar (that's on the backburner while our current project gets completed), but we purchased a Concrete Cement Sprayer to do exactly what you're wanting + cover up the boulders of our retaining walls. It hooks into an air compressor and just shoots out your mixture, much easier than manually applying it and gets a smooth finish :smile: 


Bunnings Team Member
Bunnings Team Member

Re: How to fix/fill the gaps between the stones in the retaining wall in backyard?

Hello @SuchDIY


Welcome to the Bunnings Workshop community. It's a pleasure to have you join us, and thank you for sharing your question about fixing the gaps in your retaining wall.


One reason the mortar on your wall has fallen out is because of the water passing through it. Ideally, a drain pipe is installed at the bottom behind the retaining wall and diverts the water away. If the drain pipe has failed or none was placed at all water will push its way out of the wall. Placing mortar in the gaps will temporarily fix the issue but eventually, water will find a way through.


Generally, to comprehensively repair the wall, the stones will have to be removed and a drain pipe placed at the back of the retaining wall. The wall will then have to be rebuilt with mortar between the stones. However, if you are after a temporary repair, I suggest using Bastion 20kg Premix Mortar in combination with a Craftright 150mm Pointing Trowel


Before you begin, I propose cleaning the gaps between the stones as best you can with a stiff brush to remove moss, mould and debris. I suggest mixing the mortar to the consistency of toothpaste and using the trowel to push the mortar into the gaps. 


Let me call on our experienced members @Adam_W and @Chaks _DIY for their recommendations.


If you need further assistance, please let us know.




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Workshop Legend

Re: How to fix/fill the gaps between the stones in the retaining wall in backyard?

Hi @SuchDIY it's actually a pretty typical sort of problem.
I'm not sure if I can offer you an easy solution but I can give you some info to mull over...
The first image looks to be an original wall while the others appear to be later additions.

All of the mortar that's coming out is effectively grout, it's been pushed in to fill gaps in the face and then in the case of the original wall finished to give it a neat appearance.I couldn't be sure whether that mortar is structural or just decorative.

The walls themselves appears to mostly be what's called 'dry stone' - stone is stacked to create the wall without mortar and its weight holds it together and in place. The 2nd last photo shows how such a wall should look & work. The first course is bedded in a concrete footing but then the rest are just stacked. I could be wrong, always a bit hard to tell from photos.
Fact is that stone reacts to gravity and temperature and age and anything that's impacting the underlying soil. In other words... it moves. This cracks the mortar and it falls out. More so if just a regular sand and cement mix was used. As @EricL pointed out if you then add excess water into the mix it can get messy.
Using mortar mix, as suggested, rather than sand and cement would be a good move as mortar is a bit more forgiving of movement.
It is however a band-aid approach. Not a real fix.
Ideally all of the old material should be chipped out and then you need to evaluate in more detail what you are dealing with. Adding new drainage may be needed and that can be a laborious, although not overly difficult or challenging, job.

It does look to me that there's been a fair bit of movement in that first wall. The way the capping is all up & down is a give-away. I'd be using a level to check that it isn't leaning forwards too.

@Remarka6le 's suggestion has merit however I would suggest there's too much movement in your wall for it not crack very quickly.


I guess the bottom-line is do you want a cosmetic fix or a proper one...

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