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problem with forge. Welding temp


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Beyond 2" of insulation you get diminishing returns from your investment, and increasing heat transfer into the burner's mixing tube; a poor bargain. The major heat loss in heating equipment is straight out of its exhaust.

The entire point of insulation is to help equipment interiors to reach incandescent levels of heat, by slowing conductive heat loss. The higher the incandescent level (the closer to blue-white) the greater the percentage of radiant heat transfer from the forge surfaces into your work pieces.

    Keeping this in mind, stop at two-inch thick insulation, and spend the money that a third insulation layer represents on upgrades in hard refractory flame surfaces, and re-emission coatings.

If your burner and forge are built well enough to bring the interior to orange incandescence, the right coating can take it to lemon yellow heat. Changing out your burner for the best burner you can build or buy MIGHT do as well. Which do you think will cost more?

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On 10/25/2020 at 6:53 PM, Mikey98118 said:

(3) After you have done steps one and two--not before--we need to help you retool those burners; they are heavily reducing.

Ive got the whole forge covered with castolite what would be the next steps?


one more question i i looked at pdf's of casto and there is no metion how to use it what would be a process of drying it? i have done the forge yesterday and ill let it sit for at least 48h before ill start putting any heat in to it, what would be the ideal way to start heating it up to get the cast to set good?

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Hi Miki,

Copied from another post....

From Frosty

The best cure method according to the maker is to treat it just like hydraulic concrete. It water SETS, it does NOT DRY. These are two entirely different things. Read up on working, and curing a patio or shop floor. Portland cement, concrete and Kastolite set and cure very closely to the same in time and steps. Kastolite refers to concrete procedures as THE way to cure Kastolite for maximum strength and temperature rating. 

Except for water % details the comparison is across the boards close enough to the same as to be interchangeable. 

So, when it sets close it up in a 100% humidity atmosphere for up to 7 days. We do NOT need a max strength cure, we aren't subjecting it to the kinds of forces temps and atmospheric changes a commercial forging or scrap furnace does.

Frosty The Lucky.


More from Frosty..

The cure procedure the maker recommends for Kastolite is 100% humidity @ 60 -100f. for up to 7 days for max strength and temp rating. I put mine in a plastic bag, dumped in about a gallon of water, twisty sealed it and left it for something like 24 - 36 hrs, I don't recall. It begins to set in about 30 minutes and finishes setting in an hour or so, then into a wet cure environment. Kastolite does NOT dry, it hydrates and sets the same way Portland cement concrete does and follows a cure so similar the maker uses it as the default cure method.






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5 hours ago, Mikishelby said:

ve got the whole forge covered with castolite what would be the next steps?

After it is heat cured, it's time for the heat reflective coating; several have been discussed on this group, but Plistex is cheap and easy.

Then, it's time to get together with Frosty and tune up your burners.

Don't forget the Plistex. Then, it's time to coax Frosty into helping you tune up those burners :)

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would anyone know where i can get Plistix or Metrokite. Location UK

If anyone couyld provide me with info that would be much appriciated


I got hold of Plistix but its from US and I can't buy a single bag They said I would have to get 5x bags whom is 113kg

other than that i had no luck with any of the above and finding rubber stuff for fixing driveways. or when i do find something is out of stock... 


Mikey can i run the forge for now and make some stuff before i get the ir coating, or should i hold off till ill get that sorted?


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2 hours ago, Mikishelby said:

Mikey can i run the forge for now and make some stuff before i get the ir coating, or should i hold off till ill get that sorted?

Yes, go right ahead and use the forge; it's good to thoroughly fire the hard refractory flame layer, anyway.
Plistex is a cheap and easy way to get the job done; it is far from the only way, or even the best way. There are various products made from Zircon ( crushed zirconium silicate crystals) that you can find through pottery supplies everywhere. It can be mixed with sodium silcate (water glass), that has been previously mixed into water, to form a very effective (better than Plistex) heat reflective coating. Called Zircopax and other names, it can be mixed with 3% to 5% bentonite clay to make an even better re-emissive  coating (although not as easy to use).

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Have you talked to a pottery supply? Kiln washes are typically used in ceramic kilns and if they don't carry them will know who does. High alumina products work well if they fire hard.

Plain bentonite mixed with water to latex paint consistency works pretty well. Apply many thin coats or it'll peal and flake off. That's true of any kiln wash. 

An iforge member, Maarten in the Netherlands I believe was doing some good experimentation with bentone and zircopax. He was making refractory tiles for forges I think, maybe melters, regardless he was having some good results.

It takes astoundingly little bentone bentoite, etc. in the mix to make a seriously HARD surface.

Bentonite is also carried at pottery supplies.

Frosty The Lucky.

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  • 2 weeks later...

Mikey and Frosty Thanks for reply

I have located all the ingredients for kiln wash

there is two Sodium Silicate i have found...

~Sodium Silicate 140o TW~ and ~Sodium Silicate 75o TW~

Which one i will need?




so Ill buy:


Zirconium Silicate

Sodium Silicate

Thats all I will need?

would you know how much of which I will need and what will be mixing ratios and prep for them? 

Thanks a million. at the momnet Me and My friend are making a 2x72 grinder so not really using the forge at the moment ... would be great to do that kiln wash while it sits idle.

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It is more than you will need. Bentonite and sodium silicate are both used as binding agents. You can use either one, or use both of them in separate layers, but I don't know how well they would combine together with zirconium silicate, in a single layer; or what benefit they might bring.

You need to search out the original posts from guys who have used them, for ratios.

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Twaddell units are a hydrometer density scale: the higher the number, the greater the density. Both are solutions of Sodium Silicate in water, as far as I can tell. Either will do the job: you'll (almost certainly) dilute it with water. I think I used the 140 Twaddell and it was seriously thick and viscous as it came. It's probably "about" twice as concentrated as the 75 Twaddell. 

Be careful with Sodium Silicate. It seems to melt somewhere around 1100 degC, 2000 degF. Used as a rigidizer for blanket, it is ok up to its melting point, but then it becomes a lubricant for the fibres allowing them to flow away from where the flame impinges on the blanket. 

It might work ok in a forge design that doesn't involve the flame impinging on the blanket.

I gather a Bentonite/Zircopax (Zirconium Silicate) mixture has been successful for one or two folk. My limited experience of Bentonite in other fields causes me to feel it's not something I wish to experiment with. I would expect massive shrinkage on drying and I'd expect it to take a long time to dry (though I'm in the wet bit just North of Manchester, England and don't have a climate that's particularly conducive to drying: YMMV). I seem to recall posts on its use by someone who already had experience with pottery/ceramics and it's my guess that they'd already traversed that particular learning curve. I also have a vague recollection of them using Veegum/Bentone, rather than Bentonite, though I'll confess I have no real knowledge of the differences.

I have used Zircopax/China Clay without much success (largely due to shrinkage on drying) and commercial Rigidizer/Zircopax, which was more successful: it dried without cracking, albeit slowly, and held up to welding temperature pretty well. I used a fairly thin mix of Zircopax in rigidizer, sloshed it on liberally so the rigidizer soaked into the blanket carrying some of the solids in to a depth of maybe 1/8"-1/4", but leaving most of the solids as a surface coating maybe 1/8" thick. I let it dry slowly for 3 or 4 weeks (in a Lancashire summer) before sticking the whole thing in a slow oven for a morning, turning it up in stages over an afternoon before removing it and carefully cleaning the oven before the wife came home in the evening.

Commercial Rigidizer is usually a suspension of fumed Silica in water (there are also Alumina rigidizers). There are probably wetting agents and something to modify the pH (it felt like it might be mildly alkaline when I got it on my hands and washed them off, not unlike washing soda), but the main factor in determining how much Silica can be held in suspension seems to be the particle size.

The commercial rigidizer will use the "best" particle size for creating a high-concentration suspension. Other uses of fumed silica include as a thickening agent for epoxy resins, and it seems reasonable to assume that these will use the best particle size for thickening resin. I tried using resin thickener to make rigidizer and the best I could manage was a Specific Gravity of 1.015 against a commercial rigidizer measured at 1.08. Clearly the Silica concentration was much lower and I surmise the particle size was different.

I know others have used Silica suspension with Zircopax successfully. I think Tinkertim used a Silica investment binder (Morisol), rather than a proprietary rigidizer, and posted on here.

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Bentonite is a type of clay that has the unusual property of swelling substantially when wet and contracting when dry.  This makes it suitable for various commercial applications like stopping leaks but really bad where that quality is not wanted such as around foundations of houses ("heaving soil").  I think it would cause a lot of problems somewhere that starts out wet and then dries.

"By hammer and hand all arts do stand."

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  • 1 month later...

Hello again guys i have put up 2 layers of Zirconium Silicate in the forge. but i think i have done something wrong...


this stuff is very easy to rub off, flame itself is peeling it off as well when youll turn the forge on. just add the betonite on top and that will solve the problem?

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On 10/30/2020 at 6:42 PM, tinkertim said:

If you looked at the top of page 2 of the link I attached in my previous reply, you will have seen the Google searches needed to find the Zircopax and Colloidal Silica solution you need, to do the flame-face coating I've used.

GOOGLE: scarva en gb zircopax

GOOGLE: ulster ceramics morisol x30

Read all 3 pages of the link I sent you, as there is important information about how to mix & apply the coating, and only mix as much as you need, in a disposable cup, as the Zircopax will harden at the bottom if left.

Hi Miki,

As I posted on page 2 above (and page1), you need the Zircopax for the IR flame face and the Morisol X30 (Colloidal Silica) as the binder, so that it sticks to the lining and minimises flake-off.  Without the Colloidal Silica or some other binding agent, the Zircopax will flake away with the slightest touch or breath of flame.

The Morisol X30 I got from Ulster Ceramics, so should be easy for you.

Give it a try.


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Thanks Tink


it was a while since ive got the stuff and then ive red so many threads that i got confused .


i have the forge lined up in pure Zirconium Silicate at the moment. red you topic (I've red your topic before but got confused with other topics) and i know i have to buy mirsol x30 from pottery supplies as well, same place ive got Zirconium Silicate. great Tip a while back on trying ulster supplies , Thank you .

one thing i still dont understand is Fumed Silica... Do i need it?

my forge is completely covered with castolite... no ceramic exposed


. what should i do with the layer of  pure Zirconium Silicate that i have in the forge at the momment? (rub it off and make the proper mix containing mirsol then apply it?)


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Hiya Miki,

The fumed Silica, when you mix a spoonful into a squirty bottle half full of water and a few drops of food colouring, gives you your blanket rigidiser.  It worked really well for me.  If you have already already coated your blanket with Castolite/Refractory then you don't need the rigidiser any more.

As far as the Zircopax coating on the inside of your forge, if there is no binding agent mixed in with it, then it will flake off, and anything you paint over the top will come off as well.  The best thing to do is sand or wire-brush the inside of your forge to remove as much of the flakey layer as possible. Vacuum out the forge, to remove as much dust/flakes as possible.

When you are ready with your Zircopax/Colloidal-Silica (ZCS) mix, dampen the inside of the forge (known as "buttering"), before applying the ZCS mix, so that the Castolite doesn't suck out too much of the moisture from the ZCS mix and stop it from binding to the surface.

Once a thin coating is applied, you can dry it out with repeated short bursts of a burner.  Once the moisture has slowly been driven off you can then ramp up the temp.  I put 4 initial coats over my rigidised blanket to give it some physical protection.  As you have used Castolite, 1 or 2 layers should be fine.  Give it a try and see.  If you mix the ZCS too thick, and it forms thick layers, then it can curl away from the surface as it dries.  I'd suggest doing more layers with a thinner mix. Take your time with the drying out and firing, so that it will bond well.

Good luck.


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Cheers Matey,

I like to explain the reasons behind suggestions and advice, and not assume knowledge too much.

I've spent too many years explaining techy designs to non-technical managers and new-starters, that I automatically give the full name for things and show the abbreviation, before then using that abbreviation in the rest of the text.

Nerdy habits from an old design engineer.  :)


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