I bought a very heavy cast Iron sink for $10 to use as a forge, due to the lack of 55 gallon drums at the time. I hooked up the blower pipe, and raised the bottom of the sink with clay I dug up and washed. It's been about 2 days, and the clay is still wet. Can I use the forge wet, or should I wait for it to dry, and how long should it take? Any tips for speeding the drying process?

what do you mean by wet?

Was the clay wet like you would use for making pots etc? Or did you ram it in like you could casting sand?

Firing it wet could result explosions of clay and steam. Put it in a warm room, hang a light bulb over it, etc. Slow gentle heat is best to avoid cracking, but after all any cracks are going to fill up with ash and fines anyway.

I built a small wood fire on a grill suspended above the clay to drive the last bit of moisture out.

Hope this is enough to get you thinking, it's based on my experiences with clay, including diy forge building.

To get a definite answer for the more experienced smiths they will want to know what type of clay, how it was applied and what sort of depth etc.

Have fun with it, and show us some photos.

Bob

Edited June 1, 200917 yr by Bob JS
revise

When I line a forge I tend to walk away from it for a couple of weeks in summer. By then its well and truely dry, in the meantime I work on one of my other "projects". SWMBO says I have too many "projects" :)

Washed clay is WAY too wet, it'll shrink check like crazy while taking weeks to dry.

Dig it all out and make up another batch of clay with 1 or 2 pts in 4 sand and only damp enough to make a clump when squeezed hard in your fist. It should break cleanly without crumbling or leaving your hand dirty. If it crumbles it needs a LITTLE more water if it leaves dirt on your hand (a little dust is okay) it's too moist, mix in some dry, let it sit over night and test again.

The idea is to have only enough moisture to get it to compact hard when hammered in. The less moisture the less it'll shrink as it dries and the fewer cracks will develop.

Once you have it rammed in till a wood mallet bounces without leaving much if any mark smooth it and burnish it with a piece of burlap or other course cloth. Smooth and burnished will help prevent clinker from sticking and make it more gouge resistant.

It's going to crack while it dries anyway so using a dull blade like a butter knife score the clay. This will cause it to crack along the score lines in a controlled manner.

Let it dry for several days for every inch of thickness if you live in a dry climate. Mi isn't known for it's desert like climate so hanging a lamp over it is a good idea. A small spot light to direct the heat works well on an open piece like yours. If you have a magnetic engine heater to stick to the bottom that might work even better.

The sand will make it more porous and will allow it to dry faster as well as reducing the chance of spalling. (popping with heat) How long it will ultimately take to dry depends on local conditions.

Let us know how it goes.

Frosty