Hearth material

Hi,

What is the preferred option for hearth "bricks" that is easily obtainable? I wish to make up a small hearth for silver soldering 16mm scale boilers and read somewhere that the lightweight aerated (Celcon?) blocks work. Is this correct? Obviously I do not want something that could harbour some dampness only to explode at a critical soldering moment!

cheers

Paul

I blocks and a blanket held together in a metal frame - all bought together from here -**LINK**

The ones to avoid are the very heavy solid ones sold for kilns which absorb a lot of your heat. Thermalite and such building blocks work ok. Lightweight blocks are best but expensive. Compressed vermiculite board is used for lining wood stoves. You might try a stove shop to see if they have any broken bits they have replaced in customer's stoves to use for lconcentrating the head in corners and for proping bits up. Also the white clay elements from old living room gas fires are said to be good for proping things up as they are designed for radiating heat.

I have found some soldering plates which work well and you can cut them or use as the come. I bought all three sizes and used them to silver solder the boiler recently.

https://www.cousinsuk.com/product/square-soldering-boards

Not conected to supplier.

David

The compressed vermiculite boards are very good - lightweight and easily cut to shape for odd jobs. The thin boards do become very brittle and prone to breaking. The spun kaolin blanket is also handy stuff to have around for insulation and for odd small jobs.

Both are quite expensive for occasional use. I mostly use a hearth made of standard firebricks which I assemble to suit the job, on top of a Workmate, I got eight of them from Travis Perkins for less than £1 each. Local branch didn't have them and said would deliver - a large truck arrived next day with a neat pile of bricks the only thing on it. That was a few years ago though.

I bought some vermiculite blocks from eBay some time ago, & a blanket from CupAlloy's when last at Doncaster show & made myself a small hearth. I'd already made the metal frame some years ago but was using the firebricks from a coal fire which didn't reflect heat too well. What I have now is much better.

George.

p.s. Usual disclaimer applies.

Edited By mechman48 on 26/07/2020 11:29:29

Hi George,

Could you take a picture of the blanket?

Sure', I'll be in the cave later on today; hopefully.. will post when done.

G.

Thanks guys for the timely replies.

Beware of Firebricks because there are two sorts, exact opposites!

One, as used in Night Storage Heaters, is designed to soak up heat and release it later. They're dense and tough. Don't use them in a hearth because they soak up heat like a sponge, starving the job being brazed or soldered of heat, cooking flux, creating oxides and wasting lots of energy.

The other is an insulating firebrick, exactly what's wanted. They reflect and contain heat, allowing the job to come up to temperature quickly with minimum waste. They're usually light, not very strong, and can be cut with a saw.

As high temperature bricks are structurally weak, many general-purpose insulating bricks trade-off insulation and temperature for strength. Not so suitable. Insulating bricks sold by Builders Merchants are unlikely to be best choice, but they are cheap! (Unlike the gas they waste, but this may not matter for occasional use.) Ordinary breeze blocks and house bricks poor and scary when damp.

I bought my bricks from a Pottery Supplier, but ebay is another possibility - look for Vermiculite.

With hindsight, I'd have saved bother by ordering a hearth from Cup Alloys. It's made of the right materials, decently sized, and portable. Instead, I take several minutes to fashion a hearth out of crumbly bricks and white powder goes everywhere. And I didn't save loads of money! Home-made brick hearths are more attractive for permanent and bigger hearths, but I work with smaller stuff. I'm all for getting jobs done on the cheap but false economy is always a potential booby trap. If a home-made hearth proves difficult to use, or demands a bigger than expected torch, suspect the bricks.

Dave

As said pics...

Usual disclaimer applies...

George.

Thanks George, I've actually got some of that stuff and the blocks too.

I used the wool to insulate under my 3D printers bed. I didn't realise it would stand up to silver soldering.

Neil

I use the same Kaolin blanket - and it is possible (actually quite easy) to heat it to the point where it becomes powdery and very friable. Apparently the resultant powder/dust is not at all good for you. There was a thread that mentioned this hazard a few months ago - but I cannot find it at the moment.

Anyway - I'm a bit more cautious in my handling of it these days and wear a mask & gloves to move or rearrange any 'used' blanket - with any badly burnt/fused bits getting bagged and binned rather than re-used - e.g. the blanket is viewed very much as a consumable.

Regards,

IanT

Are these useable for a hearth?

https://shop.vitcas.com/insulating-fire-bricks-vitcas-grade-30.html

Pete

Yes. Only they'll probably be a bit soft and powdery as mentioned above. Mine work well as a hearth, just slightly messy tidying up.

This sort of brick is somewhat like florist Oasis in texture and weight but stronger and - of course - heatproof. They can be cut with a wood-saw. As far as I know, no health hazard cutting or using them.

I use several bricks to build a floor with a sort of half igloo fitted to the job on top. The idea is to contain as much heat as possible whilst allowing space for manipulation. The igloo makes it possible to get away with a smaller torch, but it feels cramped. I think many jobs would be easier with an open hearth and a bigger torch. Mine is 900W and I only solder and braze smallish lumps of metal up to 200 or 300grams.

Dave

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I wonder if we have to import all the pulverised fuel ash (PFA) used to make Celcon blocks now we have closed all the coal fired power stations down. Good example of the law of unintended consequences. Same goes for all the Gypsum we used to make as a by product from desulphurisation plants on coal fired power stations.

Peter

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Phil

No not clinker blocks, the much finer grained aerated blocks. The blocks are made from cement, lime, sand, pulverised fuel ash (PFA) and water. PFA is mixed with sand and water to form a slurry. This is then heated before being mixed with cement, lime and a small amount of aluminium sulphate powder. The aluminium reacts with the lime to form bubbles of hydrogen.

Peter