Uneven founds

[Selfbuild2345]

After some advice. I am doing a garage extension and have dug the founds out, garage founds were 450mm to bottom but i went down to a more solid ground of about 750-800mm then had concrete founds in then will be using trench blocks to bring to floor level before concrete pad gets put in.

My question is my concrete founds are level to a point where it dips around 100mm for bout 2m on one side where i didn’t order enough. Can i build this up with cementing cuts of trench block so it’s level?

 

[Scarlet Pimpernel]

After some advice. I am doing a garage extension and have dug the founds out, garage founds were 450mm to bottom but i went down to a more solid ground of about 750-800mm then had concrete founds in then will be using trench blocks to bring to floor level before concrete pad gets put in. My question is my concrete founds are level to a point where it dips around 100mm for bout 2m on one side where i didn’t order enough. Can i build this up with cementing cuts of trench block so it’s level?

You've posted your query in the wrong place, both times.
It should be posted in the Building Forum. I've asked the mods to move it for you.

I suspect any responder will need to know how thick is the thinnest part of your foundation, also how wide is it?
I believe foundations can be as thin as 150mm, and should be three times wider than the intended wall.

 

[Dangee]

Foundations depend massively on ground make up (as well as proximity of trees etc) I was under the impression that if it’s chalk below the top soil, foundations can be as shallow as 300mm.

 

[jeds]

You've not got a lot of choice. It's not uncommon to make up levels with cut blocks. Just make sure you course them so you don't end up with stupid little thin wedges.

 

[Selfbuild2345]

Was told to make the founds 150cm deep of concrete and 450mm wide would be fine and build up to floor level with trench blocks. My build is a single skin block work and will be studding it out inside and will have a concrete floor in. I so if i cement bricks in where it dips would that still be fine? Concrete is 100mm deep where it dips down one sude

 

[SpecialK]

Concrete it or dense blocks on their sides?

Or Trench fill the whole thing...?

 

[Selfbuild2345]

What i have done is dug 750mm trench down to a gd solid ground and whackered. Poured 150mm thick of concrete around apart from one side where it dips, from the concrete i am using 440x300x215 trench blocks to build to floor height. Between the trench blocks either side will be a 150mm concrete pad. I’m worried my founds are not good? But surely trench blocks will help the founds?

 

[SpecialK]

What i have done is dug 750mm trench down to a gd solid ground and whackered. Poured 150mm thick of concrete around apart from one side where it dips, from the concrete i am using 440x300x215 trench blocks to build to floor height. Between the trench blocks either side will be a 150mm concrete pad. I’m worried my founds are not good? But surely trench blocks will help the founds?

A strip foundation should be a minimum of 150mm, so top up the concrete you have poured already if its too thin?

Or you could trench fill - Saves you working in a hole

 

[Selfbuild2345]

I’m building off with trench blocks to floor level. I was going to pack the 100mm dip with bricks i have lying around. Surely that will have the same strength as concrete

 

[SpecialK]

How wide is the trench meant to be? 600mm? The trench blocks are smaller..

 

[Selfbuild2345]

Trench is 450mm wide

 

[Selfbuild2345]

Just don’t want it all to move in a years time. It shouldn’t fall down

 

[SpecialK]

The best option would be to break out that concrete that is too thin and replace it with a 150mm+ layer.

Personally I would just top the concrete up to level.

The concrete should be making a continuous structure on the ground, the trench blocks wont do this and part of the foundation could sink, this is why you cant directly lay them on the soil....

 

[Selfbuild2345]

What i think am going to do is make some concrete up, grind marks into concrete and pva before pouring new. I started laying bricks in. Should i take them up or will they be fine.

 

[jeds]

450 wide is fine, 150 thick concrete is fine, 100 thick is not enough. As suggested above, I would make up levels with concrete and forget the trench blocks. Pouring concrete is cheaper than laying blocks anyway, which is why most people trench fill these days.