Mesh arrangement for slab

[oranjeboom]

I've just about completed my slab insulation for my extensions (EPS + Celotex) and old bungalow (EPS). I've used 25mm of EPS perimeter insulation and will probably stick on the 8mm roll stuff that I will get from UFH supplier. So I'm just about ready to get my 2.4x4.8m mesh sheets into place (will have to cut most of the buggers in order to get through door ways. Luckily I should at least get them through the larger sliding door at the rear.

 

The plan is to have UFH cable tied to mesh and then have a wet mix concrete pour. No final screed!

 

Before I start cutting and laying them, i have some questions:

 

1) How much overlap should I have? Is one 'square' overlap enough? The mesh has 200mm squares.

2) How far from the walls should I have the mesh? I know there should be some distance and I think I read somewhere 150mm?

3) Tying wire. As it's just a case of keeping the mesh in situ whilst concrete is being poured, would cheapo galv wired be sufficient rather than defacto tying wire? e.g. https://www.toolstation.com/shop/Landscaping/d130/Wire+Fencing+%26+Tools/sd3333/Galvanised+Straining+Wire/p40640

4) Should I continue the mesh through doorways?

5) Not mesh related, but if I am supposed to cover the celotex top layer (in the extensions only) with a poly sheet (vapour barrier) or should I use something more heavy duty like a DPM? (I have the DPM/radon barrier in already but further down the layers. My only concern with the lighter vapour sheets is that it is more prone to being punctured / ripped with the mesh (I will be using chairs) and people (i.e. me!) repeatedly tripping over the mesh.

6) I intend to tape up the celotex joins (not the EPS sheets). Can I use any tape to do this or need the foil type tape?

 

Thanks in advance.

Edited June 26, 2017 by oranjeboom
Photos

[Onoff]

Looking really good there.

 

All I can contribute is that I tied my mesh bits together with the armour from cut back SWA cable. Tend to always keep some handy.

 

Though I did foil tape my Celotex joints, in places to repair the ripped foil face I even used some decent quality tin foil stuck on with spray contact adhesive.

 

I had Polypipe trays you might remember that negated the need for a membrane and chairs. 

 

I'd go with whatever cheap VCL you have I think and repair locally with any old tape. Only there to stop the concrete reacting with the foil. Tbh you could use bin bags, rubble sacks or the carefully saved plastic bags that cement comes in!

[Gone West]

Hi Erwin,

1. mine was overlapped one square

2. no closer than 40mm to the edge to prevent rusting, mine was around 50mm

3. don't see why not

4. I would to prevent cracking

[Oz07]

Isn't it two squares then doesn't need to be tied in this scenario? Could be wrong. 

[Russell griffiths]

I would always tie it in case you get a stray end trying to pop up. 

As you walk on one sheet you may find you dip it down which causes the end to try and lift. 

 

as an aside I would really try and protect those doors before you struggle through with the sheets. 

[oranjeboom]

4 hours ago, Oz07 said:

Isn't it two squares then doesn't need to be tied in this scenario? Could be wrong. 

Two?????? Bugger! Just come in from outside cutting the buggers with one square overlap. Looks like I overbought sheets so can also recut if needed.

 

http://www.pavingexpert.com/reinfrc1.htm: "Where sheets need to be overlapped, the lap should be at least 350mm and the two layers should be lashed together with tie-wire."

 

Elsewhere on the web it ranges from 1 square to 300 or even 600mm lap! Will contact the BCO to see whether I can get a response from him this time.

 

3 hours ago, Russell griffiths said:

I would always tie it in case you get a stray end trying to pop up. 

As you walk on one sheet you may find you dip it down which causes the end to try and lift. 

 

as an aside I would really try and protect those doors before you struggle through with the sheets. 

Yes, will tie up all pieces.

 

And yes, will add protection to the new doors/windows. The weighed a tonne and I don't want to do that again!

 

10 hours ago, Onoff said:

I'd go with whatever cheap VCL you have I think and repair locally with any old tape. Only there to stop the concrete reacting with the foil. Tbh you could use bin bags, rubble sacks or the carefully saved plastic bags that cement comes in!

 

Thanks Onoff. I have plenty of plastic sheeting left from the insulation, but really can't be arsed with taping it all up and hoping it's all good. Wouldn't want to go for the bin bag option for the same reason - surely only a small gap will enable the concrete to get in and do its reaction thing with the foil??

Edited June 26, 2017 by oranjeboom
'research' added

[Onoff]

8 hours ago, oranjeboom said:

Two?????? Bugger! Just come in from outside cutting the buggers with one square overlap. Looks like I overbought sheets so can also recut if needed.

 

http://www.pavingexpert.com/reinfrc1.htm: "Where sheets need to be overlapped, the lap should be at least 350mm and the two layers should be lashed together with tie-wire."

 

Elsewhere on the web it ranges from 1 square to 300 or even 600mm lap! Will contact the BCO to see whether I can get a response from him this time.

 

Yes, will tie up all pieces.

 

And yes, will add protection to the new doors/windows. The weighed a tonne and I don't want to do that again!

 

 

Thanks Onoff. I have plenty of plastic sheeting left from the insulation, but really can't be arsed with taping it all up and hoping it's all good. Wouldn't want to go for the bin bag option for the same reason - surely only a small gap will enable the concrete to get in and do its reaction thing with the foil??

 

No use crying over spilt milk and all that but I've just looked back and appear to have NO OVERLAP on the mesh. I thought I was being clever "linking" the sheets with off cuts of re-bar  bent back at the ends. I can see how it's a weak point and defeats the object of the mesh a bit but hey ho, I'll know next time! At least thanks to you I'll know why the crack in the tiles in future occured! I was a floor virgin is my only defense!

 

 

Ref stuff getting through it's got to be more critical with a wet mix as opposed to semi dry screed. With the Polypanels above where I felt their overlaps were a bit "open" I added further duct tape. Even then I wasn't convinced. Only hope was as my wet mix went down it further compressed the panel joints.

 

I did too, gun foam all edges where the Polypanels met the UFH upstands, sunken bath shuttering etc:

 

 

I wonder in reality how bad the foil / concrete reaction is and what the result is?

 

BTW, DON'T FORGET YOUR FIBRES IN THE MIX.....I DID!

[jfb]

One square overlap should be fine.

 

A lesson I learned in doing this is to go overboard in trying to get it all as level as you can (sounds obvious I know) especially if you are trying to avoid a screed. It will save a lot of time later on when putting the floor down. Use laser level/yardstick or some way to be able to tell easily at any point in the floor how its level compares to everywhere else. Have someone with a barrow and shovel ready to add bits here and there (or to take away). Corners especially can have a tendency to get a bit high. I was doing a whole house and an outbuilding on the same day so it all got a bit hectic!  

[Mr Punter]

I think the rule of thumb is 40 times the diameter of the wire for lap.  On some slabs we have used separate lap bars to join fabric which is just butted.  This helps stop the mesh layer getting too thick.