Botched internal concrete floor in extension

EvilGrin

EvilGrin

EvilGrin

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Joined
12 Oct 2004
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1,432
Location
Aberdeen, Scotland
Hi all, am having difficulties with the concrete floor laid in my new extension. There have been numerous issues with it, firstly the concrete poured into the extension hardened before it could be levelled off properly.

Our builder promised that it wasn't an issue and attempted to fix it after the house was fully built with self levelling compound, but it just made the floor even more bumpy, uneven and unlevel. He's accepted it is unacceptable and hired a local groundworks professional to dig up his bad screed and level off and fix the floors.

He's finished the floor now, and although it is better, it still isn't within NHBC tolerance (4mm over 1m) in many areas with hollows and lumps and bumps. Also he's used a sand and cement mix, it has been about 5-6 days since it was laid and when you rub your foot over the floor, it rubs off sand. For example, our fridge was a dragged across the floor by the workers leaving marks along the floor, I rubbed over the marks with my foot and they sanded away.

All we want is a floor that is fit for purpose for us to lay solid oak/engineered oak/laminate on and not come into any problems in the future.

We've been moved out of the house for 2 months while he's been trying to fix this and we're desperate to move back in. We've given so many chances to our builder to get this right, and now I'm concerned that we have another bad floor laid. Who should I turn to to check over the work, as I really have no idea what is acceptable beyond tolerance guidelines, and have no idea if it's a failed floor? Any advice very much appreciated, thanks guys!
 
Decent floor screeding is fairly specialist, and builders that I know will not attempt it.

We had an extension built last summer, and the floor was fine to walk on after 24 hours. Sand should definitely not rub off.

I'd advise getting a reputable plasterer in to taker a look and advise, but it sounds like it needs to come up again and be done properly.

Hope you get it sorted soon :)
 
I'm a bit confused, you say concrete then leveling compound then screed.

It should be

150mm concrete
Insulation
DPM
Screed min 45 mm if unreinforced

Screed dries at a rate of 1mm a day if ventilated well and you won't want to be laying any engineered flooring over a wet screed it will buckle and warp. Applying a self leveling compound over a screed may just lock in the moisture and eventually the screed will just crumble.

Any hollows in the floors will result in bouncing floors and needs to be sorted, a latex is fine if applied after the screed is dry.

You should get a report from a Building Surveyor or ask for an inspection from the manufacturer of the engineered floor but this may not be possible with a small extension.
 
https://www.thesolidwoodflooringcompany.com/nbs-specification-template

These guys did lots of work for me and their specifications are spot on.

Substrate: Cement and sand screed
Preparation: Clean, dry substrate with a moisture content of less than 2%. The cement and sand substrate needs to be firmly secured, Smooth, even, and free from abrupt changes in level. The surface regularity when checked with a 3 m straightedge with 3 mm feet at each end, placed anywhere on the surface, will have no gap greater than 6 mm, and straightedge not obstructed by the substrate.
Relative Humidity: The relative humidity above the substrate when tested with a hygrometer to BS 8201, Appendix A must be a maximum of 75%.
DPM: As designed into the floor
Click to expand...
 
Yes, not planning to lay the floor any time soon which is another frustration as you're right I don't want to fork out a few grand for nice new floor and have it bow and warp. I'm pretty confused about everything myself, and probably not using the correct terminology, but he laid the concrete slab to very near the existing floor level, this was botched, unlevel and uneven, and he attempted a thin levelling compound (it was latex I think, can you call this screed, or is a screed something different?) on top of this to rectify it which was around 10mm at its thickets I believe.

Anyway latex levelling compound/screed/whatever has been dug up now and he's used a thick sand and cement mix, I'll try and dig out some pictures.

At the worst I think it was was probably around 35mm out total from highest to lowest point across 5 rooms. This was across Dining Room (existing) and new Sitting room (which are open plan), then through door threshold from sitting room to playroom which then leads to Utility room and Study. I believe it's now around 15-20mm out across the new surfaces, and up to 20-25mm out with the existing dining room.
 
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maccapacca said:
You can't use sand and cement under 40mm (50mm if UFH)

http://www.concretecentre.com/technical_information/building_solutions/floor_screed.aspx

So if they've used a self leveling modified screed that performs perfectly adequately under 40mm and replaced it with a un reinforced sand and cement screed less than 40mm then it's only a matter of time before it breaks up and turns to dust.
Click to expand...

Ok, that's exactly what I didn't want to hear, yes the thickness of it is most certainly under 40mm and it is also un-reinforced. Thanks for confirming my suspicions though. I think I'm going to hire a quantity surveyor to report on the floor, and charge the cost of it to my builder.

The spec of the concrete slab from our building spec is 150mm fill, radon membrane, 130m kingspan tf 70, 125mm concrete, finish and mesh. This was up to a max of 25mm lower than our existing finished floor level, but it is so bumpy and uneven some areas may be as little as 1-5mm lower. Is there any sand and cement screed mix that would be suitable for this finish, or would it just be latex/anhydrite screed that's necessary?
 
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I am a Builder and plasterer but we get someone in to do our screeded floors. That is all he does and it is perfect everytime. Level and flat. Our screed comes ready mixed with fibres in it also and it certainly should not be building sand and cement. It should be screed (grit) sand and cement. 50mm ideally but our guy says he can go from 30mm to 100mm if needs be.
Sounds like you have a bit of a bodge job there :(
Without seeing how bad it is it's hard to suggest any solutions.
You can walk on our floors next day but not in high heels :D
 
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