Leveling a floor after the builder cocked it up?

30 Jul 2014
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United Kingdom
We had an extension built a few years ago - this resulted in the concrete floor of the extension abutting the existing wooden suspended floor in two rooms. The kitchen floor works perfectly - but the back room was/is a problem.

I recall the activity at the time when they built the back room floor floor - The builder struggled to get it level and used leveling compound 3 times.

We were so keen to get our house back that we just carpeted over the mess (mistake?). The floor always felt uneven under the carpet.

We have just lifted the carpets as they are being replaced and there are problems as follows

1) At the join between the concrete and floor boards some parts of the concrete are too high (about 5mm). 2) The builder extended the leveling compound over the floor boards - Where the leveling compound was over floor boards this has now disintegrated
3) There is a small but definite raised bulge (around 5mm) near the middle of the concrete floor

Any views on how to remediate?

Thanks in advance
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How far does the SLC go over the floorboards. How big an area is raised, and is it concrete, or SLC. How big is the extension.
Thanks - The extension is 3m off the wall along the back of the house. The back room is around 4.4m wide and is now around 5.8m long. So the space is quite large with around 50% of the floor concrete. The room also has a connecting small passage (80cm long) into the front room.

I had not thought about 6mm ply - this would need to cover both the front and back rooms. That is a lot of ply. But I can see that this may be the best option.

I am going to need a builder for that.

Any other ideas? Can leveling compound be removed and then re-applied? Or sanded level?

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If the raised section is SLC, then a belt sander will take it down. If it's concrete, then you'd need a concrete grinding cup on an angle grinder to take it down.

You could hire a medium breaker and chop out the SLC and the concrete, then we could take you through how to level the floor properly
The small lump is SLC (I believe). The SLC covers some of the floor boards to a width of around 10 cm.
If the lump is SLC, then it can be sanded down. If the SLC on the floorboards is about 10mm wide, then chip it out, and replace it with 2 part wood filler, or car body filler.

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