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Vermiculite board for hearth ?

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Dave C29/04/2013 14:04:21
94 forum posts
8 photos

I am about to attempt silver soldering and have been looking through the threads on here which have been helpful. First I have to arrange a hearth and was wondering if vermiculite board is suitable, Will it absorb the heat too much? I see recomendations for light weight refractory bricks, Are these similar material and where can they be bought from.

Secondly the first job to be soldered is a box made from 1/8" thick BMS plate. The box has no lid and is for a frame stretcher. I am concerned about possible distortion and would also appreciate advice on how best to hold this together for soldering as I have four to make.

Box dimension is approx 3.5" x 2.5" x 1.5" tall.

Any advice or tips would be appreciated. I have a Propane bottle for the job.



Edited By Dave C on 29/04/2013 14:05:24

Joseph Ramon29/04/2013 14:29:56
107 forum posts

Vermiculite board absorbes very little heat. It's not quite space shuttle tiles, but I've picked up bits within a minute of them being at red heat and not burned myself.

The problem with it is that flux residues build up on eths urfeca and can cause it to flake off.


CuP Alloys29/04/2013 15:49:31
45 forum posts

Hi Dave,

Heating - use a propane burner generating about 7 kw of heat eg Sievert 2941. Get the whole joint upto temperature

Flux - use a long life flux eg HT5

Alloy - use low temperature 55% silver alloy 1.0-1.5mm dia

Heat the joint from the outside and apply rod on the inside or cut a small length of rod and place on the inside. When the alloy melts it will flow towards the heat creating a strong joint.

If necessary hold the pieces together with soft wire to allow expansion and prevent distortion.

Use vermiculite board and/or bricks to build a small hearth.

All products readily available.

For general advice see "Best Brazing Practice" on the website



Michael Cox 129/04/2013 17:29:25
533 forum posts
27 photos

I use lightweight concrete blocks (Thermalite or Celcon) for my hearth. These are cheaply available from any builders merchant.


Dave C29/04/2013 21:01:42
94 forum posts
8 photos

Thanks for the help.

Very much appreciated. I will be contacting CUP Alloys in the morning for supplies. I hadn't considered Thermalite blocks but I will give them a try at the price. So thanks for the tip Mike.

I'm still worried about holding everything in the right place during soldering but that will add a little more to the excitement I guess.

Thanks again


Stub Mandrel29/04/2013 21:10:26
4311 forum posts
291 photos
1 articles

I'm a big fan of skamolex (a type of vermiculite).

> flux residues build up on eths urfeca

Hi Joey, I think you should see the doctor about that.


Weary29/04/2013 22:14:28
308 forum posts

I have just recently built up a similar 'open box' structure frame stretcher. I used small bolts to hold the structure together and component parts in position whilst brazing (silver-soldering). That removed all the worry of 'things moving'. Center-punching along mating surfaces established the gap for the silver-solder to flow into.

I had a bit of an advantage over your stretcher though as my materials are 5mm thick so I could easily use 8BA bolts - but I would definitely find some way to pin the parts together for brazing.



Andrew Evans29/04/2013 22:56:11
327 forum posts
8 photos

I got a small hearth from a seller on eBay, 3 pieces of vermiculite type board for about £7

bricky30/04/2013 06:09:27
445 forum posts
48 photos

Hi Dave

Celcon blocks cut with a hand saw,,why not use the vermiculite board as a base and then cut the blocks to but up to your frame,thus supporting it.If using bricks make sure they are fire bricks as house bricks soak up the heat.I always reach carrot red before the solder will flow so keep plenty of heat on the job.The celcon blocks can also be sculpted to support difficult jobs.



John Reese28/11/2017 14:12:05
847 forum posts

I just got a few insulating brick from a refractory vendor. I stack them up the way I want them for each job. I can cut channels, etc. for fixturing parts.

mechman4828/11/2017 17:27:06
2749 forum posts
423 photos

I have a small hearth made using vermiculite blocks bought off e bay, iirc 5 blocks for £15...

modified hearth (2).jpg


fizzy28/11/2017 18:38:32
1732 forum posts
116 photos
Posted by mechman48 on 28/11/2017 17:27:06:

I have a small hearth made using vermiculite blocks bought off e bay, iirc 5 blocks for £15...

modified hearth (2).jpg


That was a bloomin good deal !

mechman4828/11/2017 19:23:23
2749 forum posts
423 photos

Have a look at ...



Dave Halford29/11/2017 20:30:32
921 forum posts
9 photos

Please be careful with the definition of 'fire bricks'

Do not use the bricks sold in some old ironomgers to line the side of a fireplace. They soak up heat like house bricks (I bought some)

Thermalite / celcon are insulators and very light weight.

Bazyle29/11/2017 20:46:52
5466 forum posts
206 photos

Check your local wood burning stove shop for offcuts.

Andrew Tinsley29/11/2017 21:08:04
1179 forum posts

Make sure that the vermiculite is dry! I didn't and found minor explosions occurred when it got hot!


Mark Rand29/11/2017 22:37:46
922 forum posts
6 photos

If you use EBay, insulating firebricks and ceramic blanket are readily available. If you don't then pottery suppliers such as Bath Potters have the materials.

No connections other than as a customer in both methods!

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