Depression Refractory Mixture for Backyard Foundry.

Depression Refractory Mixture for Backyard Foundry.

This old foundry refractory mix for crucibles or domes

Ovens were taken over by financially strapped foundry owners during the Great Depression, everyone was suffering from financial hardships during this time so a lot of improvisation was done, now the backyard founder can save money by having his own brew like the old timers.

First you need to make a mixture of grog i.e. slag free old broken fire bricks, crush it into 50% pea size & 50% walnut size. Place the grog mixture in a large bucket or drum and fill the drum with water until the grog is well covered; Allow to soak until no more air bubbles are visible.

Follow the next steps carefully as quantities are based on volume, not weight.

Take “three volumes” of the now very wet 50/50 grog mixture and add “two volumes” of good fireclay. (The measuring volumes range from a small can to a large bucket, depending on the amount required) Mix thoroughly and temper it like founding sand with a water glass mixture of 50% water glass and 50% water. Water glass is the old name for sodium silicate.

The final mixture of grog and fireclay should have about 6% moisture, it should form easily into a ball in your hands, if it is crumbly it is too dry and you may need to add more water. But be careful because you don't want it to turn out like mud. Finally, place your mixture under plastic and let it sweat and age for about 72 hours, or about three days. Now comes the part where you can start installing the mixture into your cupola or gas oven.

Using the inner metal or wooden former, the mixture can now be placed around the oven wall cavity and carefully rammed until the lining is complete. Smooth it out on top and then let it air dry for a day or so.

Before you begin ramming the mix to aid in drainage and ventilation later as the refractory cures, drill a series of 1/4″ holes through the outer shell to drain moisture as the mix dries out. After a few days, you can light a small fire in the oven and begin to slowly dry and harden the fireproof lining.

The drying phase is the most important part of the entire process and needs to be highlighted in bold. IF YOU DRY THE LIGHTER TOO QUICKLY IT WILL BREAK AND REMOVE AND RUIN ALL YOUR GOOD WORK.

When the steam from the vent holes stops, build a larger fire until the melting bed or zone is located. (10″ to 14″ from the bottom of the dome oven) Turn on the fan, this will increase the heat and glaze or glaze the rammed mixture into a solid lining.

It is advisable not to use borax while glazing the liner because borax is a flux and will dissolve the liner, which you don't want. That homemade refractory liner that you made and installed in your furnace should never need to be replaced, except in the area where the melting zone is located. In which you may need to replace a small ring after each melting session.

In a gas fired oven it will last for many, many years.

Good luck.

Col Croucher.

Inspired by Colin Croucher