Masonry Heater Part II

I wanted to finish the center channel of the masonry heater today before I updated the blog, but I ran out of time and almost out of mortar. I decided to do the update anyway.

Inner firebox finished.

Lintel in place. The slots underneath will hold firebrick splits to form a heat shield.

My inner firebox ended up a little shorter than my outer firebox so I used some leftover castable refractory cement to bring it up to the same level.

The 2 inch gaps form a bypass channel that runs underneath the bake oven floor.

Bake oven floor is set in a bed of refractory mortar.

The back wall is gasketed with 1/8 inch ceramic paper and it sits dry.

Firebrick walls and back wall of the bake oven is gasketed with 1/8 inch ceramic paper.

Top of bake oven in place.

Channel behind the bake oven.

Flared rear channel tilted up so you can see the cuts.

Flare bricks in place.

In order to bring the front and back up to the same level we needed to rip 5/8 inch off the top course of the front bricks.

This is the start of the angled transition header that holds the capping slabs.

This is a view from the front.

Once the angled transition header is finished we will start to lay up the side channels.

Masonry Heater Part I

Our latest project is the masonry heater. I've been excited to start building this monument since day one. We are building a 22" finnish contraflow. If you are unfamiliar with masonry heaters, think of it as a fireplace with a lot of mass and a flue that winds about a bit before leaving out the roof of your house. The mass is for heat storage and the winding flue is for gathering up all that heat. It is one of the most efficient ways of burning wood.

Here is our account thus far. The first thing we did was to make some molds in order to pre-cast a few pieces of the heater. A masonry heater burns really hot. So to make the pre-cast pieces we needed to purchase what is called castable refractory cement. When all is said and done it is basically a concrete with a very high heat tolerance.

We ended up using two different types of castable refractory - Harbison Walker KS-4 and Alsey Hi-cast. I prefer the Alsey. It seemed much more workable.

The molds were made out of lumber, but we had to take extra care to make them water tight. Castable refractory (and common concrete) get their strength by curing; the slower the better. So in order to make our molds water tight we wrapped the interior surface with house wrap tape, stapled on plastic and mounted them to a plywood sheet. A side note, use heavier plastic than painters plastic. It tears too easy.

After they were mounted, a bead of silicone was applied to all the seams.

We had to pour the slabs in my garage since the castable refractory is temperature sensitive. This was a very messy experience.

After the refractory was poured into each mold, we vibrated it by putting a piece of scrap lumber up against the mold and beating on it with a hammer drill. This proved very effective for those of us with limited tools.

After each piece was poured, they were covered with plastic to cure.

Three bake oven slabs, two capping slabs and one hearth slab.

This is the base slab laid in place in a bed of common mortar. The base slab is not refractory. It is 3 parts vermiculite to 1 part portland cement. FYI vermiculite concrete cures extremely slow.

The following photos are a course by course synopsis of the progress so far. All joints are thin and laid with refractory cement - Meeco's Red Devil (because of availability)

The space in the front middle is the where the ash box is located. The hole in the back is where the flue connection is. The two side holes are clean outs for the side flue channels.

This picture shows a port I left open in order to try to have an under fire air source to speed up the hot coals phase of the fire. It is something I read about here, but wasn't included in the plans I purchased here.

Hearth floor with ash drop.

Firebox outer shell.

Expansion joint in the rear of firebox.

Firebox inner shell.

This is the progress so far. When I am completely done, I plan to compile the total photo sequence into one link to try to make things easier for anyone building the same heater.

We Do Acid

I can't wait to see what kind of traffic the title of this blog draws. Over the past week we have tackled the acid staining of our concrete floor.

Parts of the project were as easy as I thought they would be, and other parts were much more difficult. I'll start from the beginning.

We used kona brown colored stain from Butterfield - mainly because I could get it locally. Most experts recommend doing a test spot in an inconspicuous area. So we did. Our test spot revealed a color we liked and gave us the confidence to continue.

We started by moving everything out of the room.

This is the first time we could see this much of the floor in months. Then we masked off the walls with some leftover landscaping plastic.

Next, we cleaned the floor and cleaned the floor and cleaned the floor. We used a CHO concrete cleaner that also came from Butterfield. I would not recommend this cleaner unless you have really old or dirty concrete. The cleaner needs to be neutralized with a solution of baking soda and water, which was the start of our problems. We must have scrubbed and wet vac'd the floor a half dozen times trying to clean up the remaining residue.  If I had it to do over again, I would use something like 'simple green' or another degreaser style detergent.

Once we were finally done cleaning the concrete, it was time to do some acid. I mean stain the floor. We used a hand pump sprayer, just like a garden sprayer. The manufacturer warns you not to use a sprayer with metal parts. I don't know what will happen, but I envision a MacGyver style explosion. Laying the stain down is pretty simple. You just work your way out of the room and let it dry.

Here is another mistake I made that you don't have to. Make sure your stain is completely dry before you neutralize it. It will save you some clean up time. The stuff that is still a bit wet contaminates your clean up solution and makes cleaning up take longer. It may also make some designs you aren't happy with. After it is completely dry, you need to neutralize it with a solution of baking soda and water. Then you need to work your tail off trying to clean up the baking soda residue with clean water - before the residue drys on the surface.

We ended up doing a second coat, mostly to hide some of the mistakes I made when I washed my stain off too early - but partially because we wanted a darker shade.

When all is stained you need to seal your creation.

The sealer we used was also from Butterfield. It is solvent based and very nasty stuff. Get in, get it sealed and get out. Make sure to follow the directions on the can. For example, ours said that it is highly flammable and temperature sensitive. Two things that could have made everything go horribly wrong. We used two coats of sealer followed by three coats of Halloway House floor finish. Even though mistakes were made, we couldn't be happier with our floor.

This last picture is a teaser for the next blog post.

The End of Tuckpointing

The tuckpointing is finished! It was an ongoing project for the bulk of the summer and today my wife finished off the last bit. The pointing ended exactly where the slipforming ended last year - the south peak.

We are ecstatic that we can move on from another very large project. Hats off to my wife and my mom for doing all the tooling.

Today we also started putting trim around the windows.

And on Saturday ... watermelon harvest!