Two levels of Concrete Foundation

[Chathura]

Hi everyone,

 

The below diagram depicts the trench-fill foundation of our house extension. Our builder introduced this groundwork contractor who did the trench-fill foundation and the oversite. The levels of the two segments that I have marked as 'Concrete A' and 'Concrete B' are very different. Concrete A is about 113mm taller than the Concrete B segment. Is this normal in the industry? or is that a poor job?

 

Our builder who introduced them to us said that he could match the levels when doing the brickwork of the footings up to the damp. But it felt like he was also concerned (when thinking of how to lay the lintel), but did not tell me that because they are friends who work together on similar projects.

 

The funny part is that this contractor who did this was laughing at one of our neighbours on a previous day saying whoever did their driveway had done a bad job and that driveway isn't properly levelled.

 

Edited November 4, 2023 by Chathura
update details

[Canski]

If it's below ground it's not an issue. A cut block flat with a chunky mortar joint will be 113 mm. This would be built around concrete B which would then bring it level with concrete A.

[Chathura]

1 hour ago, Canski said:

If it's below ground it's not an issue. A cut block flat with a chunky mortar joint will be 113 mm. This would be built around concrete B which would then bring it level with concrete A.

 

The builder will have to cut the blocks to lay along the entire length of concrete B, won't it? If the builder just lays the blocks normally along Concrete B and cuts the block in the Concrete A side to match the levels, that shouldn't be a problem, right? I am not sure about the block manufacturer's instructions about the structural integrity of horizontally cut blocks. We are about to use 3.6N concrete blocks for the footings.

 

 

Edited November 4, 2023 by Chathura

[Canski]

First of all the builder will need to work his levels out from DPC down. This will determine what size block / brick goes on then concrete. We normally use 7 kn blocks below ground cutting these is not a problem. Any bricklayer worth his salt should be used to dealing with the difference in levels. I think you are overthinking this and should let the guys get on with it. It’s very rare that we get a perfectly level concrete foundation and we are used to using several methods to get the blockwork level before it comes out of the ground. 
 

The worst foundation I ever had was over 400 mm out of level. It still wasn’t a problem to get the masonry level. 
 

[Chathura]

29 minutes ago, Canski said:

First of all the builder will need to work his levels out from DPC down. This will determine what size block / brick goes on then concrete. We normally use 7 kn blocks below ground cutting these is not a problem. Any bricklayer worth his salt should be used to dealing with the difference in levels. I think you are overthinking this and should let the guys get on with it. It’s very rare that we get a perfectly level concrete foundation and we are used to using several methods to get the blockwork level before it comes out of the ground. 
 

The worst foundation I ever had was over 400 mm out of level. It still wasn’t a problem to get the masonry level. 
 

 

Thank you very much. I wish my builder was as clear as you on this. He is the person who asked me to order 2.9N blocks and then 3.6N blocks later. Surely, I am overthinking. But that's mainly because he himself told me that he has to work a lot in order to understand how to match the levels.  Then I asked him if that meant that the groundwork contractor (his friend) did a poor job; then he panicked and started to say that this was not a problem. So, I thought I needed opinions from a wider audience.

Edited November 4, 2023 by Chathura

[Mr Punter]

I assume this is an extension and that is an existing drain?  Looks like a wide opening for a 110mm pipe?

[Chathura]

41 minutes ago, Mr Punter said:

I assume this is an extension and that is an existing drain?  Looks like a wide opening for a 110mm pipe?

 

Yes. This is an extension of a semi-detached property. The extension is being built over a public sewer (with a diversion). 

 

It costed me £15,500 already for the foundation concrete, MOT oversite, and the sewer pipes diversion. To fill the oversite fully with MOT and complete the work, the groundwork contractor is waiting until the wall is built up to the damp by the main builder. The main struggle is to get them on-site to continue work and to get any updates on what's going on. They are nice people—but don't keep me informed about the work schedules. So whenever I check, one party is waiting until the other party completes something. This is why I try to involve.

 

 

Edited November 4, 2023 by Chathura