DIY hearth

I've got a bag (100 litres) of vermiculite granules left by builders. I'm wondering if I can use them to make a solid hearth, eg for brazing, by mixing with some suitable binder. I have plenty of standard Portland cement and also hydraulic lime (NHL 3.5). Would either of these be suitable, or would they disintegrate when heated can anyone advise?

I'll spring for proper firebricks if necessary, but if I can get away with using stuff I've got it would be good.

Rob.

Have a look on the net for home made refractory recipes. I made a forge some years ago using cat litter (bentonite) cement and either perlite or vermiculite (I can't remember which) and it worked quite well. The bentonite cat litter needs to be mixed with water first though and left until it forms a slurry.

I've not created a hearth, but an aluminium melting furnace. For that I used cement, sand & gravel. Nothing fancy. It has lasted 20 firings to yellow/white with some spalling. If you are happy to do occasional re-plastering, then cement based refractory should be OK for a brazing hearth. Possibly not up to being a proper hearth for a forge, but good for a brazing hearth.

If you've got the stuff, it would be worth trying before paying for anything extra.

Regards

Richard.

Cement loses its strength about 600 degrees Celsius. It is dehydrated.

Plaster of paris is more usual as a binder, but not ideal. Portland cement, I would say, is inappropriate for anything over a few hundred degrees.

Cement does loose its strength over 600C, and melts around 1000-1100C. I agree.

The question is whether it'll last long enough at brazing hearth temperatures to be useful for more than one job. Having had a concrete furnace last a bit (and in a couple of areas at the top, the refractory has melted due to the ferocity of the fire I got from pallet timber) I think that the experience could be carried across usefully and applied to something else that is also unlikely to be subject to frequent & sustained heats. Don't want to rule out something that could be useful because the 'best' option is much better, when 'adequate' would work well enough to last a few years.

Regards,

Richard.

I have used a mix of 1 part clay (cat litter), 1 part portland cement and 7 parts perlite to make my furnace. It has been in use ,on and off, for several years for melting aluminium. Preparing the mix in the right way is important. For more detail, see:

http://mikesworkshop.weebly.com/furnace.html

Mike

My employer is currently making wood fired pizza ovens using a perlite or vermiculite & Portland cement mix. The cured shells have proven to be quite weak, prone to cracking & appear to be hygroscopic - the initial experimental attempts that didn't crack during production have failed after a few firing cycles, possibly due to getting damp during periods of non-use & then heating up too quickly when next used. IIRC he did try adding ground-up oil-absorbent clay granules as a binder at one point, but I think the recent builds have been without. The shell wall for these items is around 40 -50 mm thick. I think he is on Mark 5 or 6 at the moment - the latest "mod" being to tile & grout the outer surface to try & improve rain resistance (earlier versions had several coats of masonary paint). The earlier variations were experiments with the mix to get better consistency after failures either during manufacture or after a few uses. He is using a Belle cement mixer to mix the stuff & allows it several days to dry out before removing the forms & an intial gentle firing.

Don't know if that will help or not - but may point towards having to experiment with mixes etc. to get an acceptable result.

Nigel B

Much easier to use lightweight foamed concrete building blocks ["Celcon" or "Thermolite"].

Cheap, cut to shape with a handsaw, last a reasonable time and thow away and replace as necessary.

Visit Alloyavenue website forum .Lots on there

I made a small hearth using vermiculite bricks similar to link below... served well so far for the small amount of soldering I've done...

http://www.ebay.co.uk/itm/8-x-Vermiculite-Villager-stove-fire-brick-4-5-x-9-/280835077430?hash=item4163133536:g:nK0AAOxy3HJTI0B6



George.

vermiculite is a good base material to use.

if you've got a bit more money I would go for an upgrade I was considering to my hearth, which was to line it with what the americans call "Kaowool" or ceramic woven fibre. It's more reflective of heat than vermiculite.

Which means less absorption of heat away from your work piece. 

My hearth is very similar to mechman's I call it a soldering "sofa", like the shape of it, and I just put mine together with wood screws. Also handy to have a few blocks you can move around to support different shaped work pieces. 

Michael W

Edited By Michael-w on 25/05/2017 11:53:50

melts around 1000-1100C. I agree.

Not so. Cement clinker is formed in a kiln at around 1450 degrees Celsius. The kiln charge could easily become molten, probably over 1500 C, but that would be a production disaster - quickly scours away refractory linings, potentially blocks the cooler, is nigh-on impossible to grind into cement powder - and is avoided like the plague. Seen it all, after working in the industry for umpteen years.

...'if you've got a bit more money I would go for an upgrade I was considering to my hearth, which was to line it with what the Americans call "Kaowool" or ceramic woven fibre. It's more reflective of heat than vermiculite'.​..

I do have a ceramic fibre 'blanket' that I bought at the Doncaster exhib' last year from 'Cupalloy' stand, usual disclaimer, but never got around to cutting & forming it to suit. I believe that you can dampen it, form it, then it will hold it's shape, hmm; will have to check on their site ​ ... unless some member has already done this & can confirm / deny ?

George.

Thanks for all your suggestions - it seems that some experimentation is called for if I go for casting my own hearth. As (surprisingly) I found 5x 8 litre bags of cat litter in the 'bags of miscellaneous stuff' section of the cellar I'll start with Mike Cox's recipe as I have all the ingredients to hand.Thanks Mike - it must be getting on for 20 years since our last cat died, but I'll be able to say 'I told you it would come in handy for something one day' to the wife!

I'd not thought too much about aerated concrete because I assumed it would explode if heated because of the expansion of gas in isolated voids. A bit of Googling suggests that it soaks up water 'like a sponge' though, so I suppose the pore network is continuously connected, and heated gas will find its way out. I'll give that a go as well.

I was in the vicinity of a Wickes today and dropped in but the aerated concrete brick shelf was stacked with something else entirely. 'I could call the store manager' said the lad stacking the shelves, but the tone of his voice and the look in his eyes seemed to say 'not that it'll do any good', so I left it. I expect I can find some somewhere though.

Thanks again, Rob

Edited By Robin Graham on 25/05/2017 23:23:18