Concrete shed base dipping 20mm in one corner. Any remedies?

[lonnat]

Hello,
I would be grateful for advice.
Our concrete shed base is not level, one corner is lower that the other three (20mm diference). We want to put a strong wooden shed on that base and would like it to last for a long time, The tradesman who just made that base says it will not be a problem to put a shed on it (he spoke with a 'mate' who is a carpenter, who confirmed it). I wish that what he is saying is true, but am worried that it is not.
Any advice on how to level it will be greatly appreciated.
Thank you

 

[freddiemercurystwin]

Is the concrete slab top surface not level or has the whole slab sunk in one corner?

 

[lonnat]

freddymercurystwin
well, it seems to be dipping to one side, but measuring it with a leveler the surface is not even in few other places, bit patched up all over, differences several mm, but the main concern is the corner visible at the top of the image, between the fence and the wall

 

[oldbutnotdead]

Is this sturdy wooden shed designed to bolt to the slab or does it just sit on it?

If it bolts to the slab then you'll have a bit of a faff with shims under the bearers. If it just sits on the slab then same thing- if it wobbles, put packers under the wobbly bit.

And have you paid the 'tradesman' who laid the slab yet? Did you specify any tolerance to be worked to or any specific instructions for quality of surface finish?

20mm runout in a corner isn't good, nor are the surface level variations, but if you went for the cheapest quote you possibly got what you paid for.

As long as the slab is on a properly prepared subbase (well compacted hardcore) then it'll be an irritant, nothing more. If the subbase has not been properly prepared then the slab may sink more and may also crack.

 

[lonnat]

Thank you oldbutnotdead,
We have not paid yet. Not the cheapest quote (the cheapest was the half of this quote)

 

[oldbutnotdead]

Well if you paid proper money you should have got a proper job- hard to tell from your pic but it doesn't look disastrous, if you'd done it yourself you'd probably be quite happy but it isn't really a professional job.

One problem with the low point is you'll get rainwater collecting there- if that wall is part of the house you might want to build it up a bit (not sure how well levelling compound performs outdoors though)- ideally on a slab like that you'd have a slight fall away from anything you care about (so rainwater doesn't pond under your shed but runs off into the garden.

But end of the day as long as the slab is at least 50mm thick and its on a proper subbase then your shed will be fine. If there's no DPM in it then think about protecting your shed timbers from damp concrete- strips of DPC where the bearers go will do it

 

[lonnat]

Thank you oldbutnotdead,
the builder constructed this today in order to remedy the problem. He saiid that this is now ready for the shed. We are not sure about it and are thinking whether we should remove it before it sets.
We paid for the old base to be removed and for new concrete one to be installed. The builder convinced us that the parts of the old base were OK and that he will work around it. We thought that someone with 20 years experience in building would know better than us. That is how we ended up with this.
Is this a good sollution?
View media item 84415
Agree, if we have done it, than it would be OK. Disappointed with it, not professional job, but I think that this buiilder is not able to do it better. We were not lucky this time to find someone who takes pride in their job.

 

[WabbitPoo]

No - the shed needs supoort all over, not just the perimeter. The guy is a clown.

 

[lonnat]

Thank you WabbitPoo
That confirms our suspicions, unfortunately. The repointing on the wall behind, is also left with lots of holes full of cobwebs,, didn't even brush before repointing, He has been paid and is gone. Unfortunately we are left with this.

 

[WabbitPoo]

rip out that ring and just use the slab. shim as required when the shed comes. unless its of superior quality its doubtful the shed will be supremely flat underneath anyway!

 

[lonnat]

We have a builder coming tomorrow (hopefully a real and one. Recommended by friends) to tell us whether he would build a shed on that slab - with or without the ring. The ring has a thin layer of fast setting concrete underneath. Not sure whether to rip it off asap or wait til tomorrow and see what the new person can do with it (if anything). 2cm of concrete, below the ring, I suppose we can chip off even tomorrow. Or we can use it to pour concrete in it and level it to the edge of the ring to get the level surface. Would you advise to rip asap?
Thank you.

 

[WabbitPoo]

personally, yes, but I can't see the original slab either! If you use the ring then your shed is going to be quite high off the ground!

 

[lonnat]

Thank you. We will have to sort it out somehow. Not happy at all.

 

[SittingBull]

Is that ring made of timber? Silly - rip it out - you can work off the slightly uneven slab and pack underneath it. I don't think all hope is lost Good luck tomorrow!

 

[lonnat]

Thank you SittingBull. Frame made of timber, stack on the top of thin layer of concrete(2cm or so), over the original concrete surface.. Thank you for giving hope.