Keeping clay/adobe/refractory etc dry? Do I need to?

[Bob JS]

Hi,

I have been doing a bit of forging recently with a thrown together arrangement (offcut of 5 inch dia pipe sitting on a grille with the blower pipe underneath) it does the job but I would like to build something more suitable and more 'forge like'.

Im inspired by the washtub forge idea.

I have got access to my natural local clay (which is brown like milky coffee, and fires to a nice reddish terracotta colour) charcoal ash and portland cement.

My question is:

Would I need to make sure the forge was free of moisture every time I fire it up?

I do my forging outside, I could store the forge in my workshop, but that is still a damp environment.

I am concerned that Im going to end up with exploding clay and flying coals.

What do you think?

(sorry to drag up the forge lining discussion again, but I dont think this has been covered)

Thanks

[nett]

My forge has a nice clay liner. I have been parking it outside in the elements for over two decades. A simple cover (tarp, tin sheet, or plywood) keeps most rain off. High humidity is all you can expect, and that has never been a problem. Oh, I am on my third clay liner and expect it to last at least another eight years.

[Bob JS]

Thanks! Thats exactly what I wanted to hear.

Did you mix anything in with your clay to pad it out?

I forgot to mention I have also got builders sand, and sawdust.

[nett]

Mason's clay (fire clay) and clean hardwood ash mixed maybe 50-50. Trick is to work it stiff - adding as little water as possible. For last liner, I actually used a hammer to pound the mix into place - it was that stiff! No sand.

Still, making it as dry as possible, I let it dry throughly for a week, then built a small wood fire to harden the clay. I experienced a little bit of spalling, but no cracks. Much better than my first one many years ago that looked like a Triple A road map.

[Frosty]

If you add up to 1pt in 4 of grog, crushed ceramic, fire brick, flower pots, etc. it will help prevent spalling when you fire it the first few times.

Frosty

[BeaverDamForge]

I build the oven(s) for my gasifier forge from red mud, perlite, and straw, and after a day or so fire up the gasifier. I try not to get it too hot until the mud is back to it's dry color inside the oven, but the outside may be dark (damp) for a couple sessions of forging. My smithy is a lean-to and newspaper left in it sometimes gathers enough moisture it doesn't want to burn readily, but it doesn't seem to affect the mud.

I tried wood ash at first, but the perlite gives much better insulation. I've read here that coarse sawdust may work even better, haven't tried that yet. The straw holds it together and minimizes cracking.

[Bob JS]

Thanks for the good info,

No prizes for guessing what Im up to this weekend...

[Frosty]

Shall we call you Mudpie Bob then? Hmmmm?

Frosty

[Bob JS]

Well I suppose its not the worst iv'e been called...

at the moment Im wondering if I would be better making some bricks out of the mixture, for a bit more versitility, filling gaps with ash etc. hmm?

[Frosty]

I don't, I line the whole thing.

I mix clay as dry as possible and still have it compact hard. Take a handful and squeeze it in your hand hard. When you open your hand it shouldn't leave a stain or be sticky but it should break cleanly without crumbling.

If it's sticky it's too wet, add some dry clay. If it's crumbly it's too dry, add a LITTLE water, mix and let it temper in an air tight container. Preferably for 24 hrs or so but you're not tempering green sand for casting or making pottery so an hour or two should be okay.

Spread the tempered mix on the forge and hammer it till it's hard with a wooden mallet. If it's too thick simply scrape some off but if it's too thin you have to do some serious scoring so the additional material will stick. Dampening it will NOT work very well.

So, make it thicker than you think you'll need and scrape to final shape and contour. Once you have it how you want it use a piece of coarse cloth like burlap and burnish the surface. The smoother it is the nicer it will be to work in, less stuff will stick, tools and stock won't gouge it as easily and it'll just plain last longer. It isn't actually necessary though, you can just slap damp dirt down and fire it up so there's plenty of range for you to choose from.

Okay, it's rammed, shaped and burnished, now comes the important part scoring. Take a butter knife or similar dull metal blade and score lines in the forge liner. I like a spiderweb like design in a round forge pan and score it like bricks in a square table. This is to control shrink checking. It's going to check (crack like a dry lake bed) as it dries, even using such a dry mix, scoring it makes it check where you want it and makes for a more durable and better looking liner.

Let it dry, times will vary from place to place and season to season. You may want to hang a light bulb over it to help if it's humid where you live. Once good and dry start a small fire and warm it up. Let it cool, then light a larger fire for a longer time. Let it cool then build a good hot fire for a longer time, (hour+?) over as much of the pan as possible to cure it.

I know this sounds like a lot of work but it isn't as much as it sounds and will result in a pretty durable forge pan.

Frosty