Brazing Hearth - castable refractory material

For some time I have had it in mind to make a small brazing hearth for silver soldering. Nothing too complicated, just a few fire bricks held together by an angle iron frame.
However the only fire bricks I have been able to find in this part of the world - West coast of Canada, are the hard absorbent kind. Whereas what is needed are the soft bricks that reflect heat back into the work. So, given the impracticality of mail-ordering bricks from elsewhere, I have had to put my plans on hold until I can find something suitable.

While reading the "Building a small electric furnace/kiln" thread I came across the link to mikesworkshop which describes the construction of a furnace using a liner cast from a refractory mixture consisting of Portland cement, clay cat litter, and perlite.
This got my thinking that it may be possible to cast my own bricks using a similar mixture, or better yet cast an actual hearth itself using scraps of wood for a mould.

Some years back I cast a few "hypertufa" planters for the garden using a similar mixture (Portland cement, peat moss, and perlite) reinforced with fencing wire. These are reasonably strong, and despite have stood outside exposed to the elements for a few years they have held up well, so I think that it may be a practical proposition to use a similar method for the hearth.

I was wondering firstly if this refractory mixture would reflect heat rather than absorb it, and also if anyone has tried something similar?
Any thoughts would be appreciated,
Thanks,
Clive

I've mixed my own refractory to that recipe or something similar and it worked well. It does reflect the heat but it's a little fragile once it's been used a few times, at least mine was. Give it a try, the ingredients are cheap enough.

Over here we have "Celcon" blockss. These are light grey aeriated concrete blocks that are extremely light and are used fro the inner skin of houses for their insulating properties. They also can be cut with an old wood saw. They are cheap and degrade slowly with hearth temperatures, though I would not recommend them to line a Bessemer converter.

Frank

The castable refractory on mikesworkshop would be very suitable for making a brazing hearth. I would not want to store the hearth outside in a Canadian winter!!!.

However, if you can get the aerated concrete blocks that Frank suggests (Celcon, and Thermalite are brand names in the uk) they would be ideal for a brazing hearth. Indeed this is what I use if I does any brazing. Here in the uk they are very cheap compared with refractory bricks. An 440 x 215 x 100 mm block typically costs around £1.80 if purchased individually. They can be sawn, carved and drilled very easily.

Mike ( of mikesworkshop.weebly.com)

i also use Thermalite and Celcon blocks as a brazing hearth. for miniature loco boiler silver soldering i make up the hearth out of these bricks to suit the size of boiler and joint i am doing and have never bothered with a steel framework. there are numerous pics of this sort of set up in my album pics on p.3 under "5"g STEPNEY terrier boiler"

for ordinary silver soldering jobs a piece of Thermalite gets plonked on top of the bench vice with another brick behind.

cheers,

julian

I built myself a blacksmiths hearth & made a lining out of pearlite & fire clay not portland cement, it's had qiute a few burns & it's still ok, as stated above thermalite blocks are good for reflecting the heat back & cheap enough I use them myself but gradually burn away,I don't recon much to night storage heater bricks as they absorb heat befor radiating it out.

For brazing and silver soldering the recipes for furnaces are completely inappropriate and will be heavy heat suckers. Just go to a woodstove fire shop and get some of the offcuts or new boards of compressed vermiculite used nowadays for lining stoves. These are long lasting lightweight very good insulators and less fragile than the lightweight proper insulating bricks. Even if you decide to use the thermalite blocks mentioned above you can protect them and reduce heat use with a half inch layer of this board.
Then to prop up awkward shapes on the hearth visit a scrap yard and get the ceramic elements from a broken gas fire. this material is specifically designed to be a good heat radiator.

Thanks everyone for the very useful replies.

Unfortunately this area of Canada is the land of cardboard houses, so I have yet to come across anything resembling Thermalite or Celcon aerated concrete blocks locally.

The compressed vermiculite boards for lining wood stoves could be a possibility, however as the closest wood stove dealer is a good distance away, it will have to wait until the weekend before I can do any investigating in that regard.

Another side effect of our cardboard houses is just how quickly they come down. Houses literally disappear from one day to the next, bulldozed, loaded into trucks and taken to the dump. Nothing is salvaged and nothing goes to the scrap yard, making the likely hood of finding ceramic gas fire elements an impossibility. Unfortunately the well heeled foreign buyers who have turned Vancouver into the city with the world's most expensive housing don't have the patience for salvaging anything, they want their brand new monster houses with the minimum delay.

Clive

May I recommend that you try Pottery Suppliers. I have just Googled Pottery Suppliers Canada and a number of suppliers have turned up. I am sure that most of them will stock kiln bricks.....lovely soft material, easily cut and shaped and just about the ultimate in heat reflection bricks.

Mick

If you wish to cast a material use Ciment Fondue with an aggregate of vermiculite. Ciment Fondue is freely obtainable from Pottery Suppliers and vermiculite ash from garden centres. The ciment is the binder and the vermiculite is the insulating material.

CIMENT FONDU® is used in a wide range of applications:

• as a reagent in formulated products
• as a hydraulic binder base for refractory and specialty concrete
• as an accelerator for Portland cements.

When it is used on its own or as a hydraulic binder base for specialty concretes, CIMENT FONDU® can produces a number of specific properties:

• quick setting
• excellent resistance to heat, thermal cycles and abrasion.

When CIMENT FONDU® is used in combination with specialty aggregates, such as ALAG® synthetic aggregates, superior performance can be achieved.

Unlike Portland cement, CIMENT FONDU® does not release lime during hydration. This property gives it good chemical resistance to acid corrosion and to a large number of aggressive substances.

The flow characteristics of CIMENT FONDU® are suited to all types of application processes, in particular casting and spraying.

Numerous applications in the civil engineering sector include:

• industrial floors
• replacement of road slabs
• unloading and transfer bays
• dam spillways, channels, etc.

In refractory applications, CIMENT FONDU® is primarily used in concrete insulation. When used in combination with suitable aggregates, it can be used at temperatures of up to 1,250° C.

regards Martin

I found a picture of my forge with home made refractory, you could easily get up to welding temps with a just a few handfuls of charcoal. The nice thing is you can cast or mould it to any size/shape you want and it doesn't need to be very thick. I think I used Perlite in my mix.

I forgot to add, if you do use Bentonite (cat litter) in the recipe you'll need to let it sit in some water for a day or two to make it workable! I think though that fire clay is freely available in the US so perhaps you could use that instead?

People are making forges out of nothing more than a steel shell lined with ceramic blanket. It's extremely efficient at keeping the heat in. One of myfordboys video's shows it held in front of his hand with a propane torch heating it to red heat. There is also fluid about for rigidising it. This can be dried out at 90C or just air dried more slowly I suspect. The amount put on determines the depth.

If you want to mix your own refractory it should be easy to obtain a bag of vermiculite from a decent garden centre. It's normally mixed with soil to increase it's ability to hold water. It's mostly air and can also be bought in a board form. It's generally rated at around 1100C

Charcoal - it's capable of melting cast iron with a blower. Not sure about the one posted by Vic but in furnace form a hair drier will do it. The ones with a nozzle type attachment are best for this as they can be kept away from the heat. They just need to blow into a hole in the base of the furnace.

There are details of a burner and forge here

John

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Edited By John W1 on 18/12/2015 09:44:44

For those that want rigdiising fluid.

**LINK**

SIG = Sheffield Insulation Group

Thanks for that link. The COS sheet clears something up for me. That rigidisers are colloidal silica I had seen a comment that ceramic board lasts longer if treated with colloidal silica and wasn't sure if this was the same thing as the rigidisers.

John

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Hi

I made up a small brazing hearth using a pack of vermiculite bricks bought off the 'auction site' & it has reflected sufficient heat to solder / braze a couple of small jobs I had ...

**LINK**

Possibly try a wood burner supplier near you for some bricks or board offcuts.

George.