validity of ash as a refractory material

[PinguForPresident]

I've heard some mention of ash as a cheap but supposedly effective refractory material, but never any actual facts.

How well does it stick stuff together (better than clay?) I've heard it can make a mean concrete. Can it handle temperatures of 1200C, 1400C or even 1600C? Will it degrade easily (as in, how resistant to fluxes, water, etc. is it?) Does it compliment use with any other materials (such as clay, sand, flint, other ashes, grog, etc.)? Also, what type of ash should I be using for best results? Hardwood ash is supposed to consist of mostly KCO3, correct? And coal as has more silica, meaning...?

In general: why haven't we all been using ash in our refractory mixes?

Thanks for your time.

- Ginny.

[Chris Williams]

Ash is an insulator, and you can put items into wood ashes to anneal them, for example. When you get ashes hot enough (as in a solid fuel forge), they will melt and you will be removing them as clinker. I cannot answer what exact temperature ashes will melt, particularly since it will depend on what they are made of and what proportion of each constituent is present. 

[pnut]

I've mixed wood ash with clay. My clay firepot seems to  like ash from the charcoal I burn in it. When I used anthracite coal the slag/ clinker didn't want to stick to it as much as when  there was less ash in the clay.

Pnut

As far as refractory I'm not sure. I know wood ash has insulating properties as was mentioned above.

[Frosty]

You're mistaking solid fuel pan liner for a refractory. Claying the pan in a coal forge doesn't take anything more sophisticated than garden clay. Adding ash is often to stick material together that doesn't naturally stick say sandy soils or crushed clinker from the forge.

Certain types of wood ash can be used to make cement for concrete but that's sort of a special process and I'm only aware of it, not familiar. 

It might be fun to play around with but if I were interested in learning blacksmithing I'd just clay my forge with moist garden soil and go to work at the anvil. If it didn't work well, I'd dig in another spot till I found soil that worked for me.

Making refractory mixes is a beginner's sport I think we've all played at one time or another. Buying high quality refractory of known properties and application is just too cheap to worry about inventing our own. I can sweep driveways for a weekend and buy 50lbs. of top quality, water setting, high alumina castable bubble refractory.

Frosty The Lucky.

[ThomasPowers]

Note that just saying "ash" is relatively meaningingless: Fly ash? Cinders? Wood ash? Rice Straw Ash? etc and so on. Each type has a different chemical make up and differing properties. (Some of them toxic, look at the possible radiation output of coal ashes!)

[PinguForPresident]

That's exactly my question. What type of ash should I be using?

[JHCC]

If you're just adding ash to soil for the lining of a solid-fuel forge pan, regular wood ash is fine.

[ThomasPowers]

This is in the Gas Forges section and so probably NOT a simple coal/charcoal forge.

Please consider if being cheap on the refractory and then spending several times as much as you save on time and fuel is actually a savings.

(And I completely forgot about Volcanic ash! Some types of which are used for casting molds. Native american silver casting uses/used a volcanic tuff)

 

This was posted in foundry section and relocated to here

[JHCC]

One of the reasons for the strength and durability of Roman concrete was their use of volcanic ash in the mix.

[PinguForPresident]

Yes it's an oil burner. Insulation is quite important as I understand.

[Frosty]

Ginny: I don't want to discourage you but I think you don't know enough about what you want to do to ask good questions or understand the answers. This isn't a bad thing, it's the norm for anybody entering a new field. 

My advise to you is take classes or join a club that engages in casting. If you just MUST tinker with this on your own scale your melter down to minimum size, not what you think is minimum but as small as possible. A tea cup size crucible is my suggestion for size.

Just buy refractory, most of here have taken a shot at making our own and we buy commercial refractories. It's more effort and expense than it's worth and there is ZERO guarantee your best effort will work worth a hill of beans. You do NOT want a melter failure that allows a molten metal spill. Spilling molten metal is B A D on toast!

That's my best advice. Take a class, join a club and scale your project as small as you possibly can. Develop your equipment and skills before you attempt working projects, say casting a brooch rather than single rings.

Best of luck to you my friend. Be safe. 

Frosty The Lucky.