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Thread: Steel for below ground use
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17th July 2013, 09:36 PM #1Senior Member
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Steel for below ground use
Hello
I'm want to insulate the edge of slab of an existing building. My idea is to insulate it with rigid polystyrene or polyurethane board the board would extend from near the bottom of the weather boards to the ground level (~125mm) and below ground (~350-400mm). To stop the foam from being damaged I want to face the foam with something that will last and look reasonably attractive. The soil is highly reactive clay so it will experience extended periods where it is wet.
I was thinking about using Corten steel ~2mm thick, bent to slide under the weather boards, across the top of the insulation and down one face into the ground protecting the insulation. However when I've read up on Corten steel it seems its protective qualities are based on wet and drying cycles (i.e. exposed to air). This wouldn't be happening for the section that is below ground. So there's probably no benefit in using this.
I've thought of colourbond but I'm not sure how that will last. I've seen the bottom of fences look pretty ratty in no time. I've stored some "ordinary" hot rolled sheet under the house for a while and that's turned into sheets of rust. So I'm not sure how that's going to go. However I've seen steel used for retaining walls along water courses and the building is on steel screw piles. So it is used below ground. I'm wondering if there's a grade of steel that specified for below ground use?
Christian
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17th July 2013, 09:53 PM #2Philomath in training
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You may be better off with plain steel bent up and then hot dipped galvanised. The other option (or even additional option) is an epoxy paint - the sort they use on boats.
Michael
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17th July 2013, 11:39 PM #3.
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316 Stainless sheet. And maybe a coating below ground of bituminous epoxy. I ask around tomorrow at work Christian.
BT
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18th July 2013, 09:11 AM #4Mechanical Butcher
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I want to do that around my slab too, but only up to ground level.
Actually, as there will be paving, up to just under the pavers.
The slab edge is 30cm high, and I'll leave a few inches of the edge visible, so I can see if termites try to come up.
I've painted the slab edge with bitumen.
Jordan.
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18th July 2013, 10:35 AM #5SENIOR MEMBER
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Galvanised or 316 stainless. 304 if you must, it'll probably be ok.
Depends on how long you want it to last.
PDW
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18th July 2013, 03:07 PM #6SENIOR MEMBER
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Just to throw another option out there maybe some plastic sheet in a colour that would suit. Dotmar have some interesting stuff.
-Josh
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18th July 2013, 03:28 PM #7
Hi Christian,
Interesting problem, I agree with BT and PDW that stainless might be the best choice, if you can find someone manufacturing food handling equipment, like restaurant kitchen stuff, they might have scrap material. and offcuts, or maybe a laser cutting place?
A few strategically placed folds could add rigidity and allow thinner sheet?
Of course if you wanted to go a little upmarket you could copy the Guggenheim in Bilbao which used titanium sheeting to clad the entire building...
Regards
Ray
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18th July 2013, 04:20 PM #8.
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How about fibre cement sheet. Corrosion free. Cheap.
BT
Edit. Would require a neat zed flashing tucked up behind the boards.
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18th July 2013, 06:48 PM #9
Christian,
the place I work for uses lots of steel poles buried in the ground. We have tried for a lot of years to prevent the corrosion that happens at the ground line. Galvanising doesn't work (or at least the gain in time is only very small). The bits above ground and those that are deep down will be protected, but exactly where you want the protection at the surface level, not so good.
Now, without any actual experience to back it up I would go for stainless steel or something non metallic as has been suggested.
If you do use metal, a bitumen finish will help a lot as Jordan and Anorak Bob have indicated. A company called Denso make various tapes for corrosion protection, they might have something of use, either over your metal or direct onto your polystyrene (in place of the metal).
Regards
SWK
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18th July 2013, 06:57 PM #10SENIOR MEMBER
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18th July 2013, 07:01 PM #11
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18th July 2013, 07:31 PM #12.
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How about a combination of cheap FC sheet below ground with a more durable sheet metal buried a shallow (less expensive) depth, protecting the exposed above ground expanse?
Villaboard is compressed FC sheet , supposedly impact resistant but with a soft foam backing that resistance may be tested when Christian's kids take up cricket.
Cheap, thin Hardieflex would be up to the subterranean task if provided with secondary protection above ground.
Over here, I'd be nervous about plastic Peter. Over in your necks of the woods, sun damage would hardly exist.
BT
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19th July 2013, 10:18 AM #13SENIOR MEMBER
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It was my Sydney house where I found out the f/c won't last.... and the black plastic does.
Strips of Villaboard might do it.
One of the really nice things about Tasmania is, no f*****g termites. Just as well too or half the city would disappear. I used all treated timber for the bottom plates etc when I built my house.
My big power poles are 125mm RHS galvanised and they're wrapped in Densotape at the ground level before the hole is backfilled with concrete. The ones I had to pull out for bigger ones when I upped the wires to 3 phase were all fine. Not practical for this purpose though.
PDW
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19th July 2013, 11:05 AM #14Senior Member
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Thanks for all the suggestions.
I was thinking of adding some sort of bitumen coating to the steel to add some extra protection especially at ground level due to that's where its going to cop corrosion.
Part of the project is vanity as i'd like to hide the exposed slab and insulation. So I don't think cement sheeting is going to do it. Plastic is probably the choice in terms of lasting in the ground but.... i'd probably prefer the look of rust. I guess for the same reason I don't like plastic tools....
The cost of 316 is probably going to be a deal breaker but I might use a narrower section for the exposed section and use plastic behind it going underground pretty much as BT suggested.
BTW I think cricket is the least of my worries, my kids are into backyard science I'm more worried about them blowing something up ).
Christian
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19th July 2013, 11:45 AM #15
I would imagine that the cost of SS would be very high. If you don't like the idea of plastic then that is out. I did however just think of fake plastic weatherboards. They are very nice looking. Very natural looking etc. Just joking. I have a couple that I have been saving for that perfect job. They are quite thick and very strong. The problem is they are white and plastic.
Hardies wall planks are FC but are thick and from what I have seen quite strong. I also have a couple of them LOL. They are available in woodgrain surface and colours these days.
Dean
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