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Farm House RMH, First full in house build.  RSS feed

 
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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After a few years of planning, materials testing, scavenging, and picking up stuff on sale, design revisions, negotiations, and aesthetic reviews by the better half, I am finally constructing a RMH in our home. This will be the first full build Iv'e done in a living space so it had to meet a lot of aesthetic criteria. I will post pictures of the build to document the construction and discuss the performance.

Background
The farm was purchased by my grandparents in the late 60's. At the time it had minimal electrical and no running water. There was, and is, an old outhouse that was used and the water came from a cistern that the gutters fed into. A hand pump sat in the corner of the kitchen and pumped water into an old trough sink. My grandparents renovated the kitchen and added plumbing, electrical, and an indoor bathroom. The water comes from a spring on the property. There is no insulation in the house. There are two old brick chimneys that are both interior to the house until they go through the roof. A gas furnace was installed sometime in the 70's and vents up the chimney in the center of the house. The southern two thirds of the house has finished second floor rooms. The "attic" over the north end of the house is not insulated, drafty, and is major heat sink to the kitchen and dining room directly below. Winter utilities between gas and electric run average $200 a month the past two winters. Furnace running "winter" weather usually starts sometime in October and tapers off in March/April. Due to some leaks in the roof I have not been able find the source of and seal, I cannot justify insulating the attic floor/kitchen-Dining room ceiling at this point. It may require roof replacement which is not in the budget. The farm has approximately 60 acres of timber that I cut and sold oak firewood off of in high school and college from the dead trees that died or blew down. We annually experience power outages that range from a few hours to a week. An ice storm about 4 years ago took out power for just over a week when my sister was living there. She worked full time and had a small propane catalytic heater to use periodically in the house. I can't expect my wife an two children to do that since they are there all day.

Goals and Requirements
Big picture is to build something that burns wood (no direct $ cost to me) and will offset the utility bill enough to justify the construction cost this year. It also needs to be safe to operate and be around as I have young children. Breaking that down a little more;
- Wood Heat that burns in a safe and efficient manner. I don't feel that traditional wood stoves meet this.
- No utilities required to operate. This knocks out pellet stoves in general although I know there are passive versions.
- Relatively low cost. Buying a traditional wood stove is not really an option. Building one isn't either although I did it in high school for a welding competition. (I won 1st and the Regional level with that stove)
- Passes my wife's aesthetic check. This knocks out the remaining passive pellet heaters. It also means no typical cob/plaster surface finish.
- Can be cleanly removed if we decide it just didn't work come next spring. This means direct $$ needs to be low and/or materials that can be recycled elsewhere.
- Needs to increase the comfort level in the Kitchen/Dining room area. Hopefully the whole house.
- Utilizes the existing chimney that sits on the north wall between the kitchen and dining room.
- Small enough to not "take over" the dining room. This also ties into the aesthetic requirement.
- Does not make any more holes in the original wood floor. This ties in with the "clean removal" requirement.

Design
After reading Ernie and Erica's Builders Guide I settled on some form of Pebble Style bench and a 5" system. I acquired several grease drums some years ago and I want to use those for my bell. They are roughly 14" in diameter and 28" tall. Using the 5 Minute Riser design (7" pipe with 1" ceramic fiber blanket liner = 5" ID) I should have plenty of clearance around the sides of the heat riser for good flow.
The bench will be 22" wide and a maximum of 20" from the floor. My wife requires it to be a comfortable table seating height with a cushion on it so we agreed on 18" from the floor to the top of the bench. This will allow us to use the bench as table seating for the large table I promised to build next year.
With the bench being 22" wide I can get a full 4" of clearance from the wall and not stick out into the room obtrusively. You will be able to see this better in the future photos.
To tie the aesthetics of the RMH into the decor of the rooms the visible face of the bench will be clad in reclaimed corrugated metal roofing from a barn on my in-laws farm. It happens to be left overs from our corrugated metal kitchen ceiling project. The mass will be high clay content earth from the farm and stones from the creek.
To ensure a clean removal should we decide to remove it someday, I decided to invest in a roll of 24" wide aluminium flashing to lay on floor before mortar leveling the bricks to build the bench on. I realize foil might work, but I know with my two children something would have gone under the bench and the foil torn in the first hour had I used it. Flashing it is.
On top of the flashing will be grey pavers my wife selected. DuRock cement board went down on top of the pavers. The pavers are no more than 6" apart.
2" drip edge will be glued to the cement board with a high temperature rated adhesive to capture the box walls. The sides and back of the box will be cement board and the face will be the reclaimed corrugated metal. J-Bead makes the upper framing to hold it all in place. As fill goes in I plan to add "deadmen" to help keep the walls where I want them.
The surface is undecided at this point, but will be either a smooth plaster or tile of my wife's choosing.
Under the combustion unit I am putting a total of 2.5" of Perlite before the clay fire brick of the feed tube, burn tunnel and heat riser base. Although the system is going to be a 5" system (19.7 to 20.25 CSA) from feed tube to the top of the heat riser, the bench ducting is going to be 6". I'm hoping for a bit of stratification chamber effect. Total bench pipe run is only 7 feet to a 90 up, up 5 feet to another 90, then into the brick chimney. I'm optimistically hopeful that since the chimney is internal to the house and warm relative to the outside air, and since it's a short run in the bench, my exhaust should have enough heat left to both draft well and continue heating the big heat sink of a chimney. Worst case, I pickup some pipe and line the chimney. I have already checked the internal dimensions of the chimney for pipe clearance and I'm prepared for that possibility.

UPDATE(s):
Cost Evaluation
As one of the major goals of this is to offset the utility costs for the winter I will post some updates in this main post to keep it easy to find.
I already had/keep on hand things like RapidSet Mortar, perlite, ducting, etc. as we are renovating the farm house and I did not have to go out and purchase them.

Items I did have to purchase specifically for the RMH that I otherwise wouldn't have on hand:
Fire brick, I bought 25 whole and 12 splits, but didn't use all of them  - $80
Pavers, 42 new pavers - $18
DuRock Cement Board -  $30
Ceramic Insulating Blanket - $45
7" Ducting for Riser - $10
Specialty caulking adhesives - $20
Narrow Ridge Corrugated metal sheets - $45

Total direct costs(things bought for specifically this build) $248

I also tallied up everything if I had to go out and buy all new right now to build it and that total comes out to about $450 not counting any clay or sand for the mass. I won't need to buy any of that for my build, it's all available on site as is all the firewood I will need.
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Hi Caleb;
Sounds like you have a well thought out plan. I think you & your family will be impressed with it.
Have you considered a bell bench rather than a pipe bench ? A bell can be low and long for sitting just like a pipe bench and would use less fill material.
Is your floor sturdy enough for the extra weight ?
Keep us posted with plenty of pictures.


 
Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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Thomas,
I think the main reason I didn't go with a bell is time. The concept was one I was not familiar with until more recently. I learned in a previous life in the construction industry that when you put a lot of time and effort into planning an operation, and you put together a good solid plan, it is best to go forward with that plan than trying to change it last minute for something you are unfamiliar with even if it could provide a little benefit one way or the other.
Last night we got our first snow of the season. It's supposed to hit 18F tonight, and I am not able to light a fire yet, but I'm close. So I am essentially out of time for this season. The bell bench is certainly an idea I want to further research, bit for this build I am going to move forward with the pipe.

As for weight, I am comfortable with the bracing under the floor and the weight I'll be putting on it. That was definitely a concern and consideration in the sizing of the bench. I was initially unsure I would be able to access the floor joists to brace them, but I was able to once I removed the existing ducting. Another plus on that is the floor joists are old enough that when you refer to them as 2x10, they are every bit of 2" thick and 10" tall unlike the lumber they sell today. The foundation is cut Stone and is very wide. It actually extends under the two bricks closest to the wall.
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Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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Once I had a layout and certain materials nailed down, I began looking closely at clearances to combustibles. With the layout I had in mind the drum would be within 12" of the paneling covered plaster and lath wall of the house. I did a lot of research on required and recommended clearances and ultimately decided I needed to experiment. The heat shielding of choice was new corrugated metal roof panels to 1) tie into the visual aesthetics of the kitchen and dinging room, 2) have higher reflectivity over the reclaimed material, and 3) increase surface area while also having a diffusion effect on the radiant heat. To kill two birds I setup a mock J-tube that was an L-tube outside with big box store split firebrick and set the drum that I would be using as a bell on top bell fashion. I then set a panel of the shiny corrugated metal up so that it was 4" from the side of the drum. Final SketchUp design showed the drum would be 6.5"-7" from the heat shielding if I did dual layers with a minimum of 1" air gap between them and between the wall.
This setup allowed me to test the clearance for heat shielding in this application and to burn the paint off the barrel. I used a propane weed burned in the L-tube in order to achieve my target temperatures and to have a heat source I could control. Sadly, the photos and video of this died with my phone a few days after the test and I don't have any of the footage. The top side of the barrel exceeded what my Harbor Freight IR thermometer would read. If memory serves, that means the temperature was in excess of 980 F. The bottom edge of the drum read just over 700 F. I sustained that heat for 15 minutes and took readings on the back of the corrugated metal. The metal never read over 135 F. Shiny objects can tend to give off/poor/inaccurate readings with a non-contact IR thermometer, so I also had a dark board set 2" from the back of the corrugated metal. At the 30 minute mark of the test the board was 95 F.

Having satisfied myself that a single layer of corrugated metal should be sufficient heat shielding, I proceeded with installing two layers of heat shielding where the drum was within 18" of the wall. I used 1/2" aluminum tubing cut into 1" and 2.25" lengths as standoffs. One piece of shielding was mounted 1" off the wall. With the corrugations that means the metal is 1" to 1.5" from the wall. I next mounted 3 full 8' sheets of metal 2.25" off the wall to ensure I had a 1" air gap between it and the secondary heat shield nearest the drum. The sheets have a minimum 1.5" air gap at the bottom to promote air circulation.
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Secondary heat shield going up
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Primary shielding
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Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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A couple of notes on the photos in the previous post.
- I used 2" drip edge attached vertically to the walls to protect the edges of the heat shielding and to keep little ones from reaching back and getting cut.
- The black cord on the left side between the heat shielding and window is the cable for a digital temperature sensor that I secured to the wall under the secondary heat shielding and is 4-6" bellow the top of the drum height wise. My plan was to connect an Arduino based microcontroller with an alarm and some sort of led or lcd to show the temperature. I would then be able to set a maximum safe temperature and have the alarm go off if the wall surface reached that. SPOILER: I wont need it. We've been burning the last day and a half and the heat shielding closest to the drum has never gotten warm. Even when the dragon is roaring and the drum thermometer boarders on the red (600 F) the heat shield is cool to the touch.
 
Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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After getting the heat shielding in place I started on the support structure since this is being built on a suspended floor. The joists below the floor were braced. I didn't really get any photos of this due to how tight the space was. What few pictures I tried to take didn't show anything meaningful and crawl space bracing is going to be more site specific than your RMH is. The main thing I can say is if you are going to build on a suspended floor, do the math. Have someone else do the math, then you do the math again. Then double what you think you need. Do not cut corners. At this stage in particular I didn't want any thoughts of "man, I wish I'd added a little more" once the construction is done.

As I mentioned in my original post I opted for aluminum flashing in lieu of aluminum foil for durability. I rolled out the flashing and secured it at the combustion end with drip edge to form an all metal fire protection layer. If a coal or ember somehow pops out and falls down behind the heater it will land on metal. I then laid out the charcoal colored concrete pavers and spaced them to where they need to be. Long way they are 6.5" apart and approximately 4.5" edge to edge. I really only focused on getting the face pavers even as you won't see the others and a quarter inch one way or the other is not going to compromise support on this spacing. I used a laser level to check for drop and discovered the floor slopes about 5/8" from the chimney to the outside corner, the corner being lower. With this in mind I mixed up some RapidSet Mortar Mix I had on hand and began setting the pavers. I started at the heat shielding corner and tried to set that set of 4 pavers high with extra mortar using the laser level sitting at the chimney. Having these set, I worked from that end towards the chimney using my 24" level to get the remaining pavers to a consistent height by setting the face paver level to the previous paver on the right and then setting the paver in that column closest to the wall level with the face paver. The paver closest to the wall was set 22" outside face to face from the facing paver. The middle two pavers were then eyeballed in and pressed down to level with the outside pavers.

I was questioned on my measurements, or lack there of, during the process. When I got to the end of the run and all the pavers were set, I went back and measured both the spacing and the levelness of the entire thing. all measurements were less than 1/8" off of design including levelness from one end to the other with the chimney end still being high. Perfect. This means if I keep my measurements consistent I will end up with an ever so slight rise from the manifold to the chimney.

Next I cut my DuRock cement board to size and laid them out dry. They sat in the house upright for a few days a developed a slight bow, so I set bricks on them and left them a couple days to try and take some of that out. Using more RapidSet Mortar, I buttered the tops of all the pavers and laid out the DuRock, then pressed them in and set all my clay fire bricks out on top to keep them flat while the mortar set. I kept my level during this process as well.
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Dry layout and level checking
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All set. Going back with the level for sanity check.
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Dry fit check
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Curing
 
Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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I gave the mortar a few days to cure out even though the rapid set was good to go in an hour. With my base complete I then started on the box. We want the face to tie in with the Kitchen ceiling so I cut strips of corrugated metal roofing 14" long. The DuRock for the base comes in 3'x5' sheets. With the overall length of my RMH I was able to cut all three of the sheets lengthwise at 22" leaving 14" for the back. I put a 5' panel at each end and then measured for the middle gap. From the remaining pieces I was able to cut all I needed fro the back and side walls and still have a piece 1/3 of a sheet left.

To hold the sides in place I used an outdoor fireplace adhesive. It said not to use it in the fire pit area of an outdoor fireplace, so I reasoned that along the perimeter of the RMH base would be within it's heat rating even though it doesn't actually give on on the tube. I used the adhesive to glue down 1.5" drip edge left over from the corrugated metal shower wall remodel last year. It comes in 10' sticks and the bench is over that. Since I was going to have an overlap on the face anyway, I measured and cut the drip edge so that the overlap is right in front of the barrel. That seemed like the the location to get the most "people clearance" and reduce chances of a cut from the edge even though it's smoothed. To hold the drip edge down securely while the adhesive cured I lined up my fire bricks on it. Worked spectacularly.
After it cured, I used the 14" wide pieces of DuRock to make the back and sides by gluing them down on edge with that same adhesive. I did each end/corner first, then glued in an overlap piece in the middle. Then came the next trick. 1/2" J-bead was cut and bent to create the top edge to hold the top of the box together. I secured it to the DuRock with the adhesive and then began fitting in the face panels. That was an exercise in patience and small adjustments. I used self tapping pan head screws which are domed instead of the hex head style to secure the corrugated metal to the drip edge at the bottom. Screws were placed every 5th rib.

This was done on my birthday after my lovely wife took me to get coffee and donuts. She discovered a newer local place carries my favorite coffee. She's amazing.
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Drip edge glued and weighed down
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Back, sides, and J-bead placed, face panels going in
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Box completed!
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Stumptown. Blueberry muffin, and a bag of Hair Bender for the road.
 
Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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Not wanting to lose any time and with the weather turning I jumped in on getting the firebox set. I somewhat arbitrarily decided to build the perlite insulation pad as wide as the heat shielding on the wall. Although I had 2 bags already, I picked up a new bag that was completely dry. The two I had got rained on and waterlogged so I will use those elsewhere. I used a few fire bricks to create a form on the one end, then poured about half the bag of perlite into a wheel barrow. The rest of the bag went into the box dry and was lightly tamped to "set". Using the rest of my RapidSet Mortar Mix (1/3 bag?) I mixed it with enough water to form a slurry and the blended it into the perlite in the wheel barrow. Once the perlite was covered and I wasn't seeing white spots of unmixed perlite I dumped it into the box and spread it out, then used a brick to tamp it down to just firm. The idea was to get it to the point that when I set two firebricks on it they wouldn't compress the perlite, but I could still push them into it with a little pressure. This worked out to being a total of 2.5" of perlite under the bricks. I used my 24" level to get the perlite as level as possible, then laid out my firebrick base pad.

My core design worked out to:
Feed Tube: 11"
Burn Tunnel: 18"
Heat Riser:33" (Final is taller, more on that later)

I decided that for the feed tube I would use splits on the bottom to make a pit of sorts. This meant cutting bricks, but as it turned out I only needed to cut one brick in two places instead of cutting two bricks.
I used my laser level on the far end of the box to set my center line for the build and used a chalk line to snap a line the length of the box. I gave the perlite an hour or so to setup before doing a full dry stacking of the burn tunnel. To pass the time I sanded the joints in the base pad with some fine silica sand.
For the Split that I had to cut for the feed tube base I cut 2" off of one end then split the larger piece lengthwise.
Another note, my original plan was using firebrick for the riser, so I bought enough bricks for that. After deciding to go with the 5 minute riser I had extra bricks. I decided to place two more bricks across the end in the base pad. It's not shown well in the photos, but if you look you can see them in a couple of the photos with the manifold.
Clay slip was mixed, a pan of water used to pre-wet the bricks and the stacking commenced. Sorry, clay covered hands don't make for good camera work.
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Dry perlite base, about 1.25"
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RapidSet Mortar perlite
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Base pad layout
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Lasers!
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Cut pieces dry fit and sanding
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Dry stacked
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It ain't pretty, but it's tight and it works
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Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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The Manifold.

This was honestly one of my biggest mental hurdles. How to do a manifold for this size drum and have air flow clearance put me through a lot of design revisions. Ultimately I decided I was just going to have to cut one of the barrels. Since I do not have a lid or ring for this kind of drum I was going to have to do a top down bell. Rather than cutting the bottom out of one drum and then trimming it to length I went with cutting off my manifold barrel at the lowest rib then hammering it out to make a socket of sorts for the top barrel to sit into. This also gave me a lot more height than I originally planned for. A little concerned I started searching Permies and came to the conclusion that extra bell height above the heat riser is not necessarily a bad thing. From what I gathered on the subject, as long as it doesn't cause too much draft you could make the bell as tall as you like, within reason, and should not experience issues. The biggest issue seems to be having too little gap. Armed with that knowledge I decided to leave the manifold "full height" as well as the drum. I measured the burn tunnel for height and width post clay bonding and mad the requisite cut in the drum with an angle grinder fitted with a cut off wheel.

For the ducting connection I used a stove pipe 8" to 6" adapter and cut off the bottom of the 8" side so that it would sit flat to the pad, and be 8" wide and 7" tall on the intake. Of note, these things are crimped together in a way that if you cut through one section is may pop off the rest of it, so strategically adding some self tapping screws is advised. Once the adapter was cut to shape I opted to leave the ring of the barrel intact. I placed the adapter on the drum and sharpied the outline as close as possible. Enter the angle grinder with a cutoff and some tin snips and few minutes and a couple inappropriate words later I had a well fitted piece of ducting. To secure it to the drum I used the snips on the inside and cut the adapter as close to the drum as I could to make tabs about a half inch wide. I then bent those over and ran self tapping screws through them. I will seal this all up later with high temp silicone sealant and furnace cement.

With the manifold built, and not needing to cut on the top drum at all I set it in place with furnace cement rated for 2000 F and began connecting the ducting. Ducting joints and seems were sealed with Hi-Temp Silicone Sealant and foil tape I only used one T clean out given the single run and it's short. I already figure I'll have to pull the barrel, so I didn't see the need to add one near the manifold.
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I set the manifold slightly offset to the riser centerline to gain some flow around the base.
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Caleb Mayfield
Posts: 26
Location: Western central Illinois
10
hunting trees wood heat
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The Riser

Having read about Eric Hammonds bad experience with refractory blanket I was a bit concerned about the blanket I had just ordered the day before. It turns out that the manufacturer has a lot to do with it. I ordered a piece of 1" ceramic fiber insulation blanket from Morgan Ceramics and CM off of Amazon. It's 24"x31" and rated at 2400 F and is really nice. It cut cleanly, there were no stray fibers, no itching, and it went as well as I could have hoped. For a 5" system, this should line a piece of 7" ducting. My original plan was to make a 24" riser, but after finalizing my plan design for the manifold and bell I realized I could go 31" with no problems and a taller heat riser is better. So I cut down a piece of 60"x7" ducting to 32" and joined it. Now the tricky part. The diameter of a circle is pi times the diameter. So;

5" x 3.1416 = 15.71"
7" x 3.1416 = 21.99"

That's a difference of 6.28". A pretty big gap. I opted for the middle ground and used 6.25".

6.25" x 3.1416 = 19.63"

This would mean the inside edge will be compressed while the outside has a gap. Maybe.
I reasoned that the difference would work itself out if so long as the blanket isn't too compressed and it squishes enough to fill the gap. I think I did pretty well as it worked exactly as I wanted and I only had to make one cut. In a perfect world I would have taken the time to figure out the angles and made the cut to have a perfectly smooth overlap. But this is supposed to be a 5 minute riser afterall.

One trick I did figure out when you roll it to put it into the tube is to roll it from one side then the other and then both sides to the middle then put it in the tube. As the two edges unroll towards each other they will press on each other. I was able to reach in from each end of the riser tube and gently press on the ridge and it popped out to form a nearly invisible seem that required no stuffing.
I also noticed that my pipe seemed slightly out of round and by squeezing it in several directions it seemed to even out the blanket.

For those keeping track, the blanket was 31" long and I cut my tube at 32". Once the blanket was in place I used tin snips to make cuts from the end of the ducting towards the blanket then bend them over to create a flange of sorts for added stability and bonding surface. After a test fitting I used more of the Furnace cement to glue the riser to the fire bricks and fill the gaps.

With the riser done, I made a clay slip and mixed it with perlite to use as fill around the combustion unit, from the end of the box to about half way around the manifold. This was made with the water logged perlite and it was really wet.

To seal the two drums together I used the Hi-Temp Silicone sealant. I placed a heavy bead on the rim of the manifold and set the top barrel in place. I could see it squeeze around the barrel rim so I knew I had a full seal between both drums.

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I used a wire brush on my angle grinder to brush the upper barrel then wiped it with flax seed oil.
 
thomas rubino
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Everything is looking great Caleb!  Keep them pictures coming.
 
Caleb Mayfield
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Location: Western central Illinois
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Primary Ignition sequence initiated.

The natural draft is strong. Some very dry oak and Red Elm with a wad of newspaper and off she went.

 
Caleb Mayfield
Posts: 26
Location: Western central Illinois
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With the RMH operational I have started the process of massing. The soil we have here seems to be high clay for the top 18"-30" then it turns into mostly clay. Most fence posts are set no more than 32" for a good reason. I did a jar test on the location I plan to collect my dirt from. I dug and discarded the top 4" or so to get past the sod layer. I collected a sample from that soil then used a post hole digger to go down 30" where I hit the clay layer and took a sample there. I tamped some of that in around the manifold as is with no extra water and then added water and sculpted in more around the feed tube basically covering all the perlite. That material has shrunk a lot and cracked.

Would it be fine to let it dry, then patch the cracks, dry, patch, and so on until it stops cracking? (Just the area around the barrel and feed tube) Any specific reason not to? It's not structural and our long term thoughts are to add a decorative tile over it some day.

For the major fill of the bench, I plan to use as much rock as I can. We have two creeks on the property that will provide all the rocks we need. My question here is should I add sand to the clay soil if I'm rock loading the mix? None of it will be seen as it's in a box. The surface will be covered with appropriate blankets and cushioning.

The photos of the jars are taken after they sat for a generous 24+ hours.
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The workzone
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Sculpted and keyed with a fork so the next layer has something to bond with.
 
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Caleb Mayfield wrote:With the RMH operational I have started the process of massing. The soil we have here seems to be high clay for the top 18"-30" then it turns into mostly clay. Most fence posts are set no more than 32" for a good reason. I did a jar test on the location I plan to collect my dirt from. I dug and discarded the top 4" or so to get past the sod layer. I collected a sample from that soil then used a post hole digger to go down 30" where I hit the clay layer and took a sample there. I tamped some of that in around the manifold as is with no extra water and then added water and sculpted in more around the feed tube basically covering all the perlite. That material has shrunk a lot and cracked.

Would it be fine to let it dry, then patch the cracks, dry, patch, and so on until it stops cracking? (Just the area around the barrel and feed tube) Any specific reason not to? It's not structural and our long term thoughts are to add a decorative tile over it some day.

For the major fill of the bench, I plan to use as much rock as I can. We have two creeks on the property that will provide all the rocks we need. My question here is should I add sand to the clay soil if I'm rock loading the mix? None of it will be seen as it's in a box. The surface will be covered with appropriate blankets and cushioning.

The photos of the jars are taken after they sat for a generous 24+ hours.



Hi Caleb!   First off, thank you for all your hard work in compiling your build with descriptions and pictures. I have enjoyed watching your creation grow.

As for the addition of sand, I would definitely say YES!
I don't think it would ever stop cracking with the expansion and contraction the stove will experience through its life, in particular around the hotter areas your putting it in. Sand will mostly keep this from happening as it is inert and doesn't shift the way clay does.
There is no magic formula for how much sand to put in but it sounds like you have a lot of clay. I use 3 sand to 1 soil (clay) with good results. Experiment....
Also, if you do plan on putting a layer of tile or other material over this base, your going to want it nice and stable. Nothing like a nice building over a crappy foundation!
 
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