A friend is hoping to cast some balusters in concrete and asked me what mix he needed and whether there was any technique for not having the aggregate obviously visible on the surface.
He also asked where he could get an "explosion-proof extractor fan" for use in a home-made spray booth. He's apparently found several on the web at around the £600 mark but was hoping for something a little more reasonable!
Anyone out there offer any advice?
Thanks in advance,
Mike
Dunno about the concrete question but proper inherently safe fans or anything else to do with safety will be high priced. I don't know how much air flow you need but the sort of low voltage fans in PCs are brushless and hence cannot create sparks. you could use several in parallel ( from the airflow point of view) for greater flow.
Bob
If you seal the spray booth adequately, then you can blow air in, rather than sucking it out.
Don't know what shape the balusters are, but couldn't he do a two-stage casting process; 'line' the mould using a little aggregate-free mixture, let that set before adding the remainder of 'proper' concrete? The aggregate-free mix would obviously need to be as hard as possible; somebody else would be able to advise on sand-cement ratio (or alternatively, shoot down the whole idea in flames?!)
David
================= You can get a smooth surface by using a very wet mix of cement and water to coat the mould before pouring the concrete. Success depends on the shape and detail of the mould.
Cic.
Thanks for all the excellent suggestions, guys. I'll pass them on.
Mike
a heavily retarded mix and a way of vibrating the mould
not sure about explosion proof, but I've used these for workshop extraction
Interesting idea. How's s/he going to fix them in place? Or is it all in one casting? If so, thats gonna be a heck of a mould to construct.
I'd consider painting them afterwards with a cement and very fine sand mix to hide any visible stone. I mean much finer sand than the usual stuff, so it leaves a fairly smooth surface. Very strong mix too.
What mix are they using for this? Concrete technology is really quite complex nowadays. I'd want plenty of fibres in it as cracks become a safety issue on stairs and the like.
I also cant imagine how theyre going to get a nicely shaped and reusable mould without spending a lot of time on it. Will it just be
2x2 square? How will they decorate it, faux marble?And why not wood? Sounds far easier, and 2x2 is not expensive. Plane
1mm or 2 off the corners and varnish and it looks quite nice.Induction motors are non-sparking, as long as they dont have bimetallic thermal overheat cutouts. Another means is just to keep the motor far away and use a drive belt. Motors in sealed metal cans also cant produce external sparks. However there is always the potential of overlooking something, so they would need to really know what theyre doing in detail before trusting their life to it.
Regards, NT
PS Ohh I just noticed: did you want to cast in concrete an explosion proof fan?
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