Floor slab -reinforcing mesh?

[Notch7]

Architect / structural engineer has spec'ed the floor slab at 125mm with reinforcing mesh.

Builder is saying why its only a 5 x 4m and an extra 2m x 4m - shape, conventional slab.

Builder is also saying mesh will make it almost impossible to walk around tamping (it has internal corner, so not easy to reach all areas.

BI says mesh not required.

 

[wessex101]

So it is a ground bearing slab, not suspended? What mesh is specified?

I do not understand why the builder says it is impossible to walk on the mesh, just how fat is this guy? or has he got teeny tiny little feet?

 

[Notch7]

So it is a ground bearing slab, not suspended? What mesh is specified?

I do not understand why the builder says it is impossible to walk on the mesh, just how fat is this guy? or has he got teeny tiny little feet?

its just a ground bearing slab.

I dont know the mesh spec, it is a 150 x 150mm mesh -the builder is saying itll be awkward to walk around with the mesh being that size, either the mesh will get trodden on or his wellies will get stuck. He says he doesnt thinks its necessary and he thinks theres a risk of damaging the dpm. Ive never been asked to do it before on a job -at least not for a normal slab. Ive done as part of a raft or ground beam.

 

[wessex101]

its just a ground bearing slab.

I dont know the mesh spec, it is a 150 x 150mm mesh -the builder is saying itll be awkward to walk around with the mesh being that size, either the mesh will get trodden on or his wellies will get stuck. He says he doesnt thinks its necessary and he thinks theres a risk of damaging the dpm. Ive never been asked to do it before on a job -at least not for a normal slab. Ive done as part of a raft or ground beam.

It is certainly awkward to walk on but not impossible. I am not familiar with a 150mm spacing mesh but it sounds like it might just be an anti-cracking mesh not a structural mesh.

If the builder is prepared to put his money where his mouth is and guarantee the slab will not crack then follow his advice. Otherwise ask the engineer/architect if it is strictly necessary or whether it is just a standard clause they put in all their designs or there was a specific reason it was included.

 

[JP_]

How long will the mesh be down before concrete is poured. I had mesh, but it went down same day as the concrete. My builders seemed to cope ok without tripping over it.

 

[John D v2.0]

Builder will just ask for what's most convenient, se will spec whatever is safest for their insurance, building inspector will go by past experience. I would ask the se, just in case they had concerns about the ground or something.

 

[tomfe]

Is this slab to be covered in insulation and then a screed?
If it is they you don't really need an anti cracking mesh (e.g. A142 is about standard for domestic), if it's your finished floor then you'll want it in.

There is no trouble standing on the mesh at all, if he's that worried about falling on his ass he can put some boards down or simply lay some concrete to fill under the mesh then it wont move.

 

[Notch7]

Is this slab to be covered in insulation and then a screed?
If it is they you don't really need an anti cracking mesh (e.g. A142 is about standard for domestic), if it's your finished floor then you'll want it in.

There is no trouble standing on the mesh at all, if he's that worried about falling on his ass he can put some boards down or simply lay some concrete to fill under the mesh then it wont move.

Yes it will be covered by insulation and screed.

I think he is worried about falling on his ass and knocking the mesh chairs over or piercing the dpm.

Its going to be a pump delivery and its being poured in extension, plus a few of the house ground floor rooms.

 

[noseall]

Pump in 50mm or so, drop the mesh in then carry on. No biggie. Piece of cake and done it many times either with the mesh positioned in situ or pushed in after. Can't see why its needed unless the ground is made up, there are drains crossing the site or there is crappy clay.

 

[^woody^]

Building inspectors are not designers and will not take any responsibility for their opinion or advice on what is or is not required.

A builder who can't work with mesh in a slab is not a real builder IMO. And they certainly should not be making these design decisions themselves, especially based purely on their convenience.

 

[Notch7]

Pump in 50mm or so, drop the mesh in then carry on. No biggie. Piece of cake and done it many times either with the mesh positioned in situ or pushed in after. Can't see why its needed unless the ground is made up, there are drains crossing the site or there is crappy clay.

There is one foul run across the slab, maybe thats it. It isnt near the surface though, but I suppose it counts as localised backfill.

The ground is not too bad, sub soil then sand stone lower down. Virgin ground not backfill.

If the mesh is dropped in after 50mm poured, then I guess it cant be stood on after as it will sink?

I think the builder is concerned he wont be able to reach the whole area without standing in the area of the pour. Perhaps he doesnt need to, I dont know.

Im asking out of interest really, the builder is contracted to the client not to me.

 

[Notch7]

Building inspectors are not designers and will not take any responsibility for their opinion or advice on what is or is not required.

A builder who can't work with mesh in a slab is not a real builder IMO. And they certainly should not be making these design decisions themselves, especially based purely on their convenience.

True, but its not unreasonable to ask the question, whether its needed or not, especially when the building inspector thinks not -I realise they arent the ones responsible to design decisions.

The guy is bricklayer by trade and does groundworks too, so he maybe inexperienced in some areas.