How to fix crumbling concrete slab underneath window?

Kay2016

Just ripped up old carpets today, and discovered the concrete slab underneath is falling apart at the edges, particularly underneath the windows reaching the floor. The sand from the outside can be seen when the broken pieces of concrete are removed (we live in WA). Quite concerned about rainwater getting in especially since we’re in the wet season. Also don’t want the floating flooring that we’ll be installing to get ruined by this.

Seeking wisdom, is there a DIY fix for this or do I have to call for a professional (and who to call?)

Thanks

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JacobZ

Hi @Kay2016,

A warm welcome to the Bunnings Workshop community, it is fantastic to have you with us.

I am hopeful that it will be a D.I.Y. fix, but we will have to investigate a bit further.

Is it possible to tidy up the concrete edge with a dustpan and brush and take some more photos? Could we also get some photos of the slab from the outside of the house?

Cracked concrete is not entirely uncommon with those nail-in carpet edges, and there's a chance it is just a cracked top edge of the slab.

I would be very surprised if your windows were installed over sand, so there should still be concrete underneath them.

With these extra photos, I think we'll have a better chance of identifying some steps forward.

Allow me to tag @Nailbag and @Dave-1 to see what they think.

Jacob

Dave-1

Good Morning @Kay2016

Looking at your photos I am thinking that maybe the concrete edge that sits under the windows has been added after the slab has gone down tho not 100% sure from the photos.

- Is the concrete that is under the windows the same level as the concrete floor?

- From outside in, is the concrete the same level under the window as the slab?

- If the bit under the window is raised does it continue along the wall away from the windows?

Plinth! hahaha thats the word Ive been looking for to describe what the window may be sittting on. Is it a kind of plinth?

Dave

Kay2016

Hi, sorry for the late reply.

I took some additional photos after removing the crumbling portions of concrete, it seems that there is a brick outside the window and the concrete indoors is slightly higher than outside. I think water coming in should not be a problem.

My plan is to just wet the sand underneath and then pour some rapid set mortar into the gap, I was deciding between these products that you have at Bunnings:

1. Westbuild 8kg bulk fill mortar high build course screeding mortar

2. Westbuild 8kg 10-100mm high build mortar concrete repair

3. Dunlop 5th addition rapidset repair mortar

Which product would you recommend?

I will be laying floating flooring into the surface in a few days.

Thanks!

EricL

Hello @Kay2016

Can you please tell us how deep that gap is? It will help us with the product recommendation as each of them have certain conditions for filling and repair.

Thank you

Eric

Kay2016

It’s about 1 to 6 cm deep.

JacobZ

Hi @Kay2016,

I'd suggest the Westbuild High Build Mortar Concrete is the best option for this repair.

Let me know if you have any further questions.

Jacob

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