Do you know where from?
The supplier I've found won't do anything smaller than 40mm x 40mm in 3mm. I can get 20mm x 20mm with 2mm wall, but not rectangular box sections, only square. Everything else only comes in 1.5mm or 1mm.
Christian.
[T] It's not 'strength' but 'stiffness' you need here though isn't it. I think 3 spans would be sufficient as the rear and sides are solid. I might put two near the front (where there is least supoport now) and one down the middle. [T] I think the 'stiffness' goes up exponentially with the box dimensions (that a guess not a scientific comment) so go as large as you can. I'm pretty sure the tube wall thickness on my tandem cycle is pretty thin and that takes all 16 st of me, and my not-ever-so-light missus ok and without too much flex. (you need some in a cycle) ;-)
All the best ..
T i m (Nth London)
Also, what about aluminium? Is it much weaker than steel? It seems to available in suitable sizes as solid bar or box sections. Not sure on price, though.
Christian.
If you went for aluminium you'd need solid bar to match the stiffness. And it would cost *a lot* more.
I have a place up the road that sells it - but delivery will be costly.
Look in yell for steel stockholders. There's bound to be one near you who can supply.
Yes, that sounds sensible.
Well, I'll try to get the 25mm in, although I can't be sure it will fit. It would just be a case of deciding on a suitable really thin soft material to lay over the top. Do you think a bead of dry sealant will be enough to prevent the granite smashing due to the hardness?
Christian.
[T] Lookat at a previous post 25mm sq would be ok?
It
[T] For me the 'problem' with a dry sealant is the difficulty you would have getting a uniform thickmess?I would fix all the things that were going to be fixed and then run a strip of 1mm x 12mm double sided foam tape) around all the load bearing edges of the things resting on the steel box, the wall plate, the cabinet edges etc to absorb any movement etc? If they also need to be waterproofed / sealed then add yer sealant afterwards ..
All the best ..
T i m
If you pack the centre of the steel box section with a small gravel/sand/cement concrete mix, you will find that the stiffness is substantially increased. It's probably equivalent to a 3" thick granite slab. I'd pack the gap between the steel box and the granite with something like Unibond stone repair( sets like rock, 10 minutes max working life), to ensure that the granite could not flex relative to the steel.
Regards Capitol
Are you sure about that? Granite is not going to flex at all, so fixing it with an adhesive that has no give to something that might but shouldn't doesn't seem intuitively right to me.
.andy
To email, substitute .nospam with .gl
If you're having difficulty sourcing the box section, what about a few runs of angle iron to support? With a suitable facing if any of it is on show, of course....
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
If it doesn't flex at all then the steel is redundant as it must deflect by some (minuscule) amount if it is carrying a proportion of the load. If the granite just bears on the steel you'll have a load sharing situation. If you fix the steel to the granite with epoxy or whatever and put weight on the granite it will be in compression and the steel in tension like a RC beam.
Makes sense. Since the steel, I would have thought would flex rather more than the granite, I would expect that the granite would crack. Unless I've missed something?
.andy
To email, substitute .nospam with .gl
yes, I think you've missed something in this.
The granite will break not because of the compression it suffers at the top but due to it's weak tensile strength on the underside.
If you bond steel section firmly to the underside it gives the granite the required tensile strength and therefore prevents the breakage.
The alternative is to provide a firm inflexible support for the granite and not bond it securely. You limit the amount that the granite can deflect and hence the maximum tension that it will suffer underneath. This would mean that any flexible bedding or sealant used between steel and granite must be as thin as possible, because this would allow slight movement.
One thought that does strike me relates to the expansion of the steel with heat and whether the firmly bonded solution would be problematic in this instance. Might the heat kicked out from the WM and TD be sufficient to cause problems with this? (thinking aloud here, the granite ought to provide a good thermal sink thus preventing the steel from heating up and therefore expanding too much).
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
I see what you're saying.
So it seems that the conclusion is not completely clear - one can argue either way
.andy
To email, substitute .nospam with .gl
Yes, filling the steel section with concrete gives you a reinforced concrete lintel, just turned inside out! As I said, to get the optimum effect, the granite needs to be bonded to the "concrete lintel" which corresponds to about a 3" thickness of granite IMO.
Regards Capitol
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