Some tips on working with fireclay
Mixing fireclay was something that I experimented and refined as I went along. It proved to be one of the most challenging parts of the process. The fireclay dried out very quickly if not used right away. Of course, it was the hottest part of the summer when I reached this stage in the build so that did not help matters.
Here are a few tips, I hope they help you avoid some of the hassles I had:
Mix small batches, something you can use in 20 minutes or less. I used a small plastic bucket and a paint mixer in a 1/2" drill. You want to have a consistency somewhere between peanut butter and mayonnaise. Mix it thoroughly, making sure you don't have clumps. Add small amounts of water if you need to thin it.
Clean the mixer, trowel and bucket between batches. You don't need to have everything spotless, just get the majority of the residue. I found that if there was any fireclay left from a previous batch it tended to accelerate the drying rate. This led to the clay thickening and becoming difficult to work.
Dip the firebrick in a bucket of water before you butter it. You will be amazed how much water the porous brick will absorb. Use a spray bottle to wet any bricks you have already placed that will have new brick set next to it.
I also used the spray bottle to moisten the fireclay in the bucket if it started to set before I was done. It will not help a batch that is setting up because you did not clean the tools and bucket between batches.