Villaboard OK for floating slab?

[Wozza]

Posting this in the Aussie section as you guys would probably know Villaboard.

I'm still thinking of a floating slab for the hearth so I can put a vapour barrier between it and the blockwork walls. The compressed cement sheeting that I was going to use as a base is the same stuff you'd use for flooring in wet areas. Really solid, about 20mm thick. But quite expensive.

Then I thought maybe use Villaboard, which is, I think, compressed cement sheeting, but generally used for walls as opposed to flooring. It's thinner, but about 1/4 the price. The sheets I was looking at earlier today were 6mm thick. I think it would be OK with enough support underneath. The internal dimensions of the walls are 800mm x 1200mm.

If I were to used this stuff, the game plan would be to fill all the holes in the blockwork walls so I have a nice flat solid surface, then lay 3 or 4 layers of builders plastic on top of the walls, the board on top of that, suitably supported, with formwork around the edges as required (for a 100mm thick hearth).

I've already filled every other hole with concrete (and a reo bar) and the rest are filled with rubble so I won't have to use much concrete to top them off.

Any thoughts?

[Bert]

Re: Villaboard OK for floating slab?

Hi Wozza

So your intending to use the Villaboard/Hardi sheeting as the base for your slab formwork and then support it until the concreting goes off?

Bert

[cobblerdave]

Re: Villaboard OK for floating slab?

G'day
Properly supported that villaboard would be good. You could leave it in situ and just remove the frame.



Shows the framing. All screwed together from below with chipboard screws for ease of removal. I didn't use form work for the slab just a row of bricks. The brick and mortar is 85mm and then the slab is recessed 10mm. Then your core fill and an pour on the same day. Use the builders plastic on top of the slab underneath your insulation layer. You'll only need one thickness it's plenty strong enough

[Wozza]

Re: Villaboard OK for floating slab?

Hi Wozza

So your intending to use the Villaboard/Hardi sheeting as the base for your slab formwork and then support it until the concreting goes off?

Bert

That's the game plan Bert, yeah.

G'day
Properly supported that villaboard would be good. You could leave it in situ and just remove the frame.

Sounds good to me. I just wanted to check. I lifted some 4 x 2's out of a skip just up the road this morning, so I'll have plenty of support. The hearth is bigger than the wall so it will overhang about 150mm on all sides so I'll need to support around the perimeter as well.

Maybe post a piccie of where I'm at later. Off to watch the Roosters kick some arse now.

[BrendanLovesPizza]

Re: Villaboard OK for floating slab?

I still have my formwork ply lying around if you want some?

And there are a few tricks when forming up the area. If you need help PM me and I'll describe in more detail.

[Bert]

Re: Villaboard OK for floating slab?

I actually used metal interlocking metal suspended slab as my base, due to its strength and my centre wall I didn't use any bracing or supports when I poured.

The whole process was extremely easy. I was lucky as my father in-law had some lying around as it quite expensive, but if you know a builder or have some local construction going on you may get some cheap or free.

Worth a look as it was a breeze, some of the traditionalists may disagree with this method but I've haven't seen any structural issues with this method.

Enjoy your build.

Attached are a couple of pics.

[Wozza]

Re: Villaboard OK for floating slab?

I still have my formwork ply lying around if you want some?

And there are a few tricks when forming up the area. If you need help PM me and I'll describe in more detail.

I'll pass on the ply Bren, but thanks for asking. And if you want to share your tips for formwork, then I'm all for it. The only time I've done it was casting a beam across the front of the blockwork walls and that went OK. But the hearth will be a bit more involved.

[BrendanLovesPizza]

Re: Villaboard OK for floating slab?

builders make form work to stay in place for ever. form wokers make it easy to remove and recycle. there are a few tricks. i also have scrap form work timber as well.