Hi – worst possible use for them. They are made to absorb heat. You need to reflect heat. Ive got a few and its very difficult to solder anything which is in contact with them.

When they get up to temperature, they will work OK. But they will have made any metal heating rather less efficient than using the right materials for the job. A larger torch will overcome any heat loss to the bricks. Likely cost you more in gas, than buying the right material, over those (many?) years.

Well I use firebricks. Cheap (about £6) easy to get (buildabase etc) heat proof, low thermal conductivity. Stack nicely into a hearth can be left outside. Never had any problem silver soldering with them.  I have seen these vermiculite slabs break easily and break down with bits under the job breaking of and sticking to jobs when the flux and work get hot.

Regards

Rich

Edited By Richard brown 1 on 22/05/2019 20:20:10

It is better to find or buy a Thermalite block which can be carved with a chisel or drilled to help hold things. Just make sure tehy are thoroughly dry if they have been in the rain, Also the ceramic elements from old gas fires work well as supports and are designed to reflect and re-radiate heat.

low thermal conductivity…..the exact opposite of what they are?

I think any non combustable material will work, just that some work better than others and may mean you need to use less gas and are able to get the work upto temperature faster which is a good thing.

Beware searching the net for generic Vermiculite or Skamolex as there are many versions available some being denser than other so may not do as good a job as the lower density blocks, also watch the sizes for example you can find blocks for a fiver on the bay but they are a third the size of the ones I linked to that sell for about £12

Yes they are a bit more fragile and the surface can get pulled off when flux sticks to it but I'm still using the ones I bought 10 odd years ago and I do a lot of silver soldered fabrications on my models. Maybe treat them a disposable cost saved in gas will more than likely pay for any replacements or simply raise the work just clear of the bottom sheet/block.

As mentioned in passing by bazyle make sure any hearth material is completely dry especially if stored outside. Once heated any internal moisture will turn to steam and could cause the surface to spall and the last think you want in the middle of that critical final heat is brick in your eye.

J

With due respect to Jason and fizzy, they have both overlooked the big advantage that firebricks and storage bricks have is that they will keep the workshop warm long after you have finished brazing. All that heat put into the bricks and not the work has to be dissipated eventually.

You have burnt the gas, shame not to get any benefit from it.

Stick to light, low thermal capacity bricks and/or kaolin clay blanket folks.

Let's do things properly

Keith.

PS Jason and Fizzy otherwise are spot on!

**LINK**

I use the storage heater bricks for silver soldering. Whilst they absorb heat they also radiate heat when hot. You can look at this in the same manner as using a charcoal pit for brazing. I start by heating up the bricks then move the flame to the work piece.The ambient heat from the bricks keeps the work hot whilst you concentrate the flame onto the joint being soldered.

The only thing that I have been warned of but not seen for real is to ensure the bricks do not get wet. I am informed that a damp brick having a torch applied to it may explode.

Elmo

An oxymoron covers a pair of word that don’t fit like military intelligence, apologies to military men.

Mike