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repairing electric kiln lids

updated sat 1 may 99


Vince Pitelka on mon 17 may 99

I have not been monitoring the list very closely over the past month or so,
because of a zillion other things going on, so this may have already been

It is not difficult to do a rebuild on a cracked lid from a toploader
electric kiln. Remove the lid, and place it on a flat surface on a heavy
plastic sheet - either on a large table-top, or on the floor. Loosen the
clamp at the back of the lid (if there is one) and/or remove the hinge
screws, and remove the stainless steel band around the lid. At all the
cracks or breaks, gently pull the bricks apart, and spread them all apart
slightly on the plastic sheet, retaining their original ordere.

You must use a very good quality high-temperature refractory cement. I like
APGreen Greenpatch 421. APGreen has been bought bought out by
Harbison-Walker, but they are still selling APGreen products, so you should
be able to get it from your local refractory or boiler equipment supplier.
When you are ready to proceed, open the can of refractory cement, and mix it
up very well - there will be standing liquid on top, and this must be mixed
into the mass.

Devise a plan of action, depending on how the bricks should go back
together. Think about this when you are taking them apart. They will come
apart in a certain sequence, and if it helps, you can number the joints with
a sharpie to help in the re-assembly. When you are ready to start
re-assembling the bricks, and have your refractory cement mixed up,
thoroughly moisten the softbricks you are going to join first. That means
DOUSE THEM WITH WATER. Let them soak up PLENTY OF WATER. Normal high-temp
refractory cements are air-setting cements. That means that they develop
great strength in curing, even before they are fired. In order to do so,
they must be allowed to cure completely before they are allowed to dry out,
and the only way to insure this is to wet the IFBs thoroughly before
applying the cement. Once you have moistened the surfaces, apply a good
layer of refractory cement, and press the pieces firmly together.
Immediately move on to the next joint, moisten the surfaces thoroughly,
apply cement and press firmly together. As you do each additional joint,
make sure not to flex or distress the previous joints at all. Proceed as
quickly as possible until the whole lid is reassembled, and IMMEDIATELY
re-install the stainless steel band and clamp it tight. If it does not have
a hose-clamp-type clamp at the back, use a carpenter's strap clamp to clamp
the band tightly in place. Leave the lid alone for at least 24 hours to
allow it to cure completely. You may then re-install it on the kiln. You
can fire it immediately, but for the first firing I would fire the kiln
empty like a bisque-firing, bringing it up to temperature over 24 hours with
a gradual overnight preheat.

A lid properly repaired as described above will last as long as a brand new
lid. But keep in mind that ANY lid, whether repaired or brand new, will be
destroyed if it is dropped shut JUST ONE TIME. Do not allow this to happen,
under any circumstances.
Best wishes -
- Vince

Vince Pitelka -
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166