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Building a New Lid

This old lid on my oil fueled furnace is in pretty bad shape. I need to make a new one before this one fails completely.

The only thing holding it together is the rings of wire that were cast into it when it was made.

First I made a form. I used a plastic vane from a discarded set of vertical blinds to make the outside ring and a cake frosting container for the inside. Duct tape was used to seal the outside form to a sheet metal base. This mold is about 13.5 " diameter and 3 " high.

I put a bunch of flat metal plates around the ring to help hold the shape.

A couple of rings of twisted wire help to keep the casting together if it develops radial cracks after use. The eyebolts provide a way to attach a handle. The cross wire is used to support the wire rings and to keep the eyebolts above the casting.

This is the refractory mix. I bought it from Canfield & Joseph in Kansas City. It is MINRO-FIREŽ CAST F80 made by Allied Mineral Products. It is rated for use to 3000 degrees F. It comes in 55lb bags and sells for about $42 a bag. You mix it with water like concrete mix.


After adding the wet mix to the mold, I "bounce" the surface with a stick to help settle the mix and encourage bubbles to rise to the surface. I also tap the sides with my hand to work bubbles to the surface. Do this lightly for about 15 or 20 minutes.

24 hours later I removed the inside and outside forms. Let it dry another day or so. It will need to be heated gradually to remove the final traces of water.

I let the lid cure for a few days while I thought about firing it . I was going to put it in my BBQ grill. The lid though is about the size of a large cake so I decided why not use the oven? The temperature controls are so much more precise!

I baked the lid at 200F for 2 hours, 225F for 2 hours and finally 325F for 2 hours. The idea here is to drive off the water without blowing it up with a steam explosion. This process seems to have worked well.

Wow! This is much better. Makes that furnace look kind of dated though.....

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