Do you need subbase/sub base and sand under a screed kitchen floor?

[DIYRuthie]

Hi!

We were quoted for a floor to be smashed up and replaced with a new floor. The estimate described there being a sub base, sand then DPC, insulation and 65mm fibre screed.

We were away the day it was prepped for the screeder, but when we had a peek under the dpc just before the screeder arrived, we noticed it was just the soil that had been there under the original concrete.

When we questioned the builder has said that there was no need for a subbase or sand as he used a 1600 DPM, but we were wondering if:
a) will this be enough to provide structural support to a kitchen floor? We will have a 90cm range cooker, cupboards full of stuff, table and chairs, dishwasher, washing machine (which will likely move around) and the area is about 5m by 3m.
b) this meets BC

He is chasing for the full amount but I want to check this before we pay. At the end of the day, we don't mind if it's structurally sound, watertight and meets regulations.

Cheers!

 

[Notch7]

You are talking about a solid concrete floor which has to be on load bearing stable ground.

It needs: 100mm or more of well compacted type 1 MOT, sufficient sand to blind, DPM, insulation, screed.

you cant make a load bearing concrete floor straight onto soil -I'm sorry but your base is no good

The work falls under building regs part L and you need minimum 70mm PIR insulation.

 

[DIYRuthie]

Thanks again Notch7. Even if the screed is fibre reinforced? The ground underneath was very compacted as it had cement on it for many years.

There is at least 70mm insulation and dpm

 

[23vc]

Wasn’t the original quote wrong too though? Surely you still need a concrete slab somewhere rather than the only structural component being a 65mm screed (which isn’t concrete)
[question for others not the OP]

 

[^woody^]

Even if the screed is fibre reinforced?

Fibres do nothing to reinforce a screed, they are only to control cracking when it dries and shrinks.

All floors need a base. The question is whether the one there already is good enough or not.

Was something wrong with the floor or just the screed?

 

[DIYRuthie]

The floor was a little high once we took down a wall between two rooms. We were going to just have the cement floor channelled and ventilation put in, with us hacking off the floor tiles. But there would have been a 2cm step. So, we decided to pay the extra to have the floor broken up and re-done as there had been a lot of unexplained damp and thought it would be better to start again.

Do you think it would be reasonable to hold back payment for 6 months to see if there are any complications?

The floor was probably really compacted to be honest. Just questioning if there needed to be concrete as well then?

Photo shows the floor before they put the dpm down. They may have dug down more as I was away the next day, but I know they didn't put any new subbase or sand.

 

[^woody^]

Do you think it would be reasonable to hold back payment for 6 months to see if there are any complications?

Only if your contract/agreement allows it. Otherwise the builder is rightly expecting to be paid in full.

On a similar note, what did you actually instruct and agree to have done - a new floor or a bit if insulation and screed topping? The two are completely different.

 

[DIYRuthie]

The description was 'dig down to allow for a new sub base, sand, dpc, insulation and 65mm fibre screed'.

Do you think we should expect significant problems with the floor cracking, say with the washing machine?

He said after he had done it that we didn't need a sub base as he had put a higher strength dpc (1600). I asked for a guarantee in case of any cracking and he said we should expect cracks with settlement...so I have asked for reassurance that these would not be more substantial because he omitted the sub base but not had a clear answer yet.

 

[^woody^]

He said after he had done it that we didn't need a sub base as he had put a higher strength dpc (1600)

That alone indicates that the builder is clueless and trying to blag you. A DPM (polyphene!) has nothing to do with the strength of a floor now will it stop a floor sinking if the sub-base is inadequate.

And the cluelessness is confirmed if he said that you should expect settlement.

TBH, I would have doubts that you can trust what he did or trust him in his comments about why he didn't do the sub-base. Digging and removing the spoil and then barrowing a load of stone back in is a lot of work. Did he reduce the bill by around 30% to reflect the work not done and materials not purchased?

You could either chance it, try and retain some money, involve a local surveyor/structural engineer to inspect the work and comment - see how the builder responds to that suggestion - he should welcome it.

Has an application been made to building control regarding the replacement and insulation? Have they inspected?

 

[DIYRuthie]

Thanks so much for your advise Woody! I feel like you are hand holding me/us through this slightly uncomfortable situation (hate confrontation), which is very comforting.

I like that idea. I was starting to think that myself and was going to get in touch with BC. Nervous to create a situation where they turn round to us and say we have to break it all up and have it re-done with lots of cost.

We have given notice to the council and paid for one of the between xxk and xxk and it's still within that financial bracket. Just need to update building control that we changed to having a floor replacement, rather than just ventilation put in.

I think I will suggest to the builder that he gets confirmation from BC that his changes are acceptable and then we will transfer the rest (we paid part of the floor so he could pay his screeder). We need to know this before we start to get the kitchen delivered and installed.

He has not suggested any money off, just implied that this is how he knocked the price down for us (he said he did it to 'help us out' in the email alongside the revised estimate). We had a choice of ventilation chased in and us hacking of old tiles for weeks, or paying 2k more to have it redone. He knocked it down by 1k which made it seem more worth us not having to take off all the tiles. Description remained with the sub base included though, otherwise we would have considered doing it ourselves or living with the step.

They inspected for the structural beams with no problems but not the floor or doors. Builder said he would get them back once they are in and things are plastered and second fix electrics done.

Trying to keep it fair but can't pay for something that isn't OK for BC. Lived in a damp house with bodged problems for too long, not going to accept a potentially new bodge!!

Do you think my approach mentioned above is fair?

 

[^woody^]

I think I will suggest to the builder that he gets confirmation from BC that his changes are acceptable

I would suggest that you do this, and not rely on the builder to tell you "Yeah, I've told them and they said it's OK"

Ask the inspector to visit and go through it with him, or at lease speak with him on the phone and describe what has been done accurately. Photos of the exposed base and insulation would help the inspector.

You'll need to be prepared for the potential that it is not correct and may need to be redone, but then you will be confident that it will be done correctly. Or it may well be deemed OK if the existing base is adequate. And there may be an extra fee for this.

 

[Notch7]

I'm a bit confused.

Did the builder put down a damp proof membrane onto the soil, then insulation, then screed?
No hardcore, no concrete sub base?

If that's what you've got, it is highly likely you will have future problems. If you tile over that, you risk wasting the cost of the tiles too.

Screed itself has little strength. The purpose of screed is the equivalent of plastering walls - it turns a rough uneven surface into a flat one. It is cosmetic not structural.

The odds area against it being ok.

 

[23vc]

As above, I don’t understand why the original quote didn’t include a concrete slab. And I understand even less why they’d then cut corners and not even put hardcore down. I can’t see Building control OKing it in a million years unfortunately

 

[Celeronmanuk]

As above, I don’t understand why the original quote didn’t include a concrete slab. And I understand even less why they’d then cut corners and not even put hardcore down. I can’t see Building control OKing it in a million years unfortunately

Neither can I. If a builder doesn't even know how to put a floor down correctly, I wouldn't trust him to do anything else.

 

[DIYRuthie]

Thanks all. Quick update. Rang building control and they are sending an inspector round Monday. Will se what they say and take it from there.

I'll use the time they are here to also see if there is a way we can take the course of bricks down for the patio doors as well. This was something the builder said would take us below the damp proof of the house, but I am not so sure. Maybe just didn't want the extra work or maybe it's because the floor is so thin!! That's another thread on here!!

Thanks again