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Old 12-07-2010, 12:50 PM
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Default Top slab support what can be used.

Hi everyone great site.
I have decided to build a WFO and I'm in the process of getting most materials and equipment before I start.
I'm thinking about what I can use for the support base for my stand slab. I see most use plywood (expensive in OZ) but I would like to know if using cement sheets will do or if anybody knows any negatives of using galvanised/zinc corrugated roofing sheets.
Can MDF, fence palings (laid side by side) etc be used. I'm trying to keep costs down and don't want to spend $50 just on the support base. I realise if it's not done right it'll collapse before it sets due to the weight but with enough tempory support under what ever I use I'm thinking pretty much anything can be used.
I've never built one before so just need to be warned whether I'll be right or not.

Thanks.. Oscar
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Old 12-07-2010, 01:10 PM
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Default Re: Top slab support what can be used.

If you are designing the slab to be self supporting IE: floating with re-bar on the cinder block. I would think that any nonporous flat material would work since it will not be used for a permanent support. Just make some temporary leg supports to hold up the plywood (or whatever material you decide) until the slab is dry. There are some good photos out there demonstrating how this is done.
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Old 12-07-2010, 01:47 PM
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Default Re: Top slab support what can be used.

You can use anything. If using palings or such and there are a lot of gaps, you can line it with poly prior to the pour.

Think about how the form work has to come out after the concrete cures. This can be a real pain if done wrong. If using something like 2x4s to support it vertically, cut them a bit short and use wedges that can later be knocked out. If the main base is a single sheet, consider cutting it in half and supporting the seam.
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Old 12-07-2010, 03:03 PM
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Default Re: Top slab support what can be used.

Thanks the reply guys.

This is a great idea

Quote:
If using something like 2x4s to support it vertically, cut them a bit short and use wedges that can later be knocked out

Does the slab support need to be removed. It'll be hidden under the concrete. I was thinking that by having it sitting on the blocks it'll be so much easier to do. The concrete block I plan on using are going to be 190mm deep so if I sit the wood etc on it by 50mm I'll still have 150mm on physical concrete slab sitting on the concrete block walls. Are there any negatives it doing it this way. I realise over time wood might rot but that shouldn't be a problem with so much of the slab in contact with the blocks.
Am I missing something by doing it this way.
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Old 12-07-2010, 03:32 PM
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Default Re: Top slab support what can be used.

Wives are pretty good to use as support in my experience.
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Old 12-07-2010, 03:44 PM
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Default Re: Top slab support what can be used.

Quote:
Originally Posted by david s View Post
Wives are pretty good to use as support in my experience.
Mines not to happy about the whole WFO idea so if she keeps it up I'll try it.
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Old 12-07-2010, 05:52 PM
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Default Re: Top slab support what can be used.

Yeah, I built my under-slab form work out of shipping skids, and burned them afterwords.

Why spend money on something you're just going to throw out anyway?
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Old 12-07-2010, 06:05 PM
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Default Re: Top slab support what can be used.

Ive seen corrugated iron used with good results.
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Old 12-07-2010, 06:30 PM
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Default Re: Top slab support what can be used.

Cement board is perfect for the bottom of your structural slab form. You only need two 3x5-foot sheets. You don't even need to cut them (unlike plywood) if you're building a 42 inch oven. I ran a length of duct tape along the center joint to reduce leakage from the pour and put a brace right under the joint.
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Old 12-07-2010, 06:54 PM
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Default Re: Top slab support what can be used.

Thanks for all the replies. Looks like it's cement sheeting.
I love ebay somebody just listed a heap of offcuts for $2 buy now so how lucky was that.
Thanks azatty I read your post checked ebay and saw it.
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