The wife and I are going to pull the trigger on the RMH build this week as its friggin cold up here now! Should have done this in the summer I know heh.
We have about 800 firebricks, about 600 light and the rest heavy. They come from a kiln we dismantled. Our hope is to assemble a j tube masonry heater, with an oven or at least a brick en closable area.
We also like the standard 52-7? block design we see made out of light bricks but would like to make the bell out of heavy brick.
We can lay bricks, just would like to avoid any tricky masonry work or a lot of cutting etc.
So the question is... does anyone have a plan for something like that, in english, that has a fully insulated riser. Like the first plan but larger to have a brick riser? or if you know of a better way to do this please let us know! Would a layer of the light bricks on their sides be enough insulation for the floor?
You want the core except for high-abrasion areas in the feed tube and burn tunnel to be insulating, and the dense parts surrounded by insulating brick.
The bell enclosure should not be made of insulating brick, as you want to absorb, store and radiate the heat. The floor of the bell can very well be insulating brick. The top 1/3 should be firebrick as this area sees a lot of intense heating, while the lower 2/3 more or less can be common brick or other masonry, as long as it is not insulating.
Should I build 52 brick using the light brick then an entire bell over it using the light brick and then an entire bell over that using the dense brick? Starting the build tomorrow. Ill post some pics as I still need some help
You want to use dense firebricks for the feed tube and burn tunnel, and insulating bricks for the heat riser. You could use insulating bricks for the whole combustion zone if you tend to be very careful and gentle, and you don't mind possibly rebuilding part of it in several years if it gets damaged.
You DO NOT want to use any light insulating bricks in the bell except possibly at the floor to keep from leaking heat in undesirable directions. You can use dense bricks or common red bricks for the lower 2/3 of the bell, but you should have dense firebricks for the top, as that will see some high heat.
Couldnt find mortar but did find refractory material for replacing worn bricks? I will use this as the mortar for the layup. Going to layer my wood subfloor with on edge firebrick (light ones) to make the base. Then Im going to build a 52 brick light firebrick core substituting the entry way light bricks with heavy ones instead. Then a heavy brick bell over the riser.
Im stuck as to what to do at the top of the riser. Make it light brick and then heavy over it and as to what that looks like from a masons standpoint I dont know. Also the cleanouts. I have one planned for the bottom of the bell and I can make a tool to jam a shop vac up to the endge of the riser to get anything from there but should I plan a cleanout on the top of the bell? I sorta wanted a white oven on top.
Thanks everyone and I will keep looking back for replies. Any idea how to post photos on here as I go? I dont want or have a photobucket etc.
Refractory cement would be the right material - you do not want to use any standard portland cement mortar in the hot/warm parts of the construction, as heat above around 6-800 degrees F will destroy it.
You need to use more than just a layer of insulating brick over your wood floor. It is important to have an airspace between the wood and the brick so heat can escape. Insulation slows heat flow, it does not stop it, and eventually heat would build up in the wood and char it, lowering its combustion temperature. I have seen recommendations to construct the system to keep wood below about 175 F (I think that's it). A 2"+- airspace made by spaced-out bricks, then a layer of aluminum foil shiny side down FACING THE AIRSPACE (critical), then a sheet of cement board for airtightness and ease of further construction, THEN your insulating firebricks, will do well.
How big do you expect the inside dimensions of the bell to be? You could corbel out the bricks at the top to gradually close the gap untl you can bridge over it with bricks, or you can get slabs of refractory material (kiln shelves would work fine) to close off the top.
Ok off to get a sheet of masonry board. Thank you. I get it now. For some reason I thought making it thicker would help but conceptually I was missing the point.
The inside will be the standard 52 brick core layout you see on many videos. I think its around 5-6 inches in the end. I think I have the link near the top post. I want to have a flat top so I can build a brick box oven on top that radiates from the bottom only. Or maybe line it with light brick to heat more evenly? We shall see how it looks in the next few hours, off to the hardware store to make my wife think I know what I'm doing! wheee.
Back from the store with two durorock boards and a bunch of air gap cinder blocks. Looks like a cinder block but only 5 cm tall instead of standard height. Has a nice air gap. I have 10 of them for the 5x3 base I am making for a 2.5x4 herman mass heater we decided on with a few tweeks and upgrades.
Im just unloading the car and getting half in the bag before I start the mock up. Ill get a photo cuket account or whatever so you guys can tell me all the stupid stuff Im doing. If nothing else I aim to entertain!
Thanks again everyone for your info, I feel more confident now, quote me on that when my house burns down
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
OK Im taking pics as I go along. 5x3 durorock inset into floor over 1 inch plywood. 10 small air gap cinder blocks evenly spaced over it loose. Another sheet of durorock over the whole mess giving me a nice level platform to start on. I am opting to add a lift right at the start to double insulate the bottom of this unit with light brick to try and "improve" the design. Im also thinking of capping it in light bricks to increase the heat transfer at the top to try and improve its rocketyness. Looks like the oven will be 10 feet off the ground and be able to hold an egg at this rate
Well, ended up going downstairs and putting in two beams under the unit. Had to move an electrical run of course in order to get those in , just after I dropped some plumbing lines out of the way. Just a little 4 hour side project haha.
Back to the stove today and I am mixing up a tub of refractory cement and glueing the first layer of 12 firebricks to the duroboard. Not sure if I should be doing this as Im sure it will weigh enough to not move much. I am putting a second layer of 12 firebricks on top to double up the floor thickness and put two cleverly placed hard bricks on level two to make the floor of the entry to the CC, that way the wood being put it wont damage the floor. Another at the back where the exhaust exits to keep it all hard bricks surrounding the exit for the steel exhaust plate.
Fingers crossed. I think I am supposed to be using mortar but I couldnt find any. Will this refractory cement do the job?
Refractory cement is the mortar you should be using for this. (Although you are right, it isn't really needed for this first layer as gravity would take care of it fine.) You should not be using it the way common mortar is used, with a thick layer of material; refractory cement is generally mixed thin and liquidy, and often a brick will be dipped in it to wet the mating surfaces and then put in place. The point is that the joints should be as thin as possible, 1/8" or less, so the refractory cement just fills gaps and keeps bricks from shifting. Firebricks are made to strict tolerances so they can have much smaller joints than common bricks.
Using hard bricks in the floor at the base of the feed tube is good.
I see that you are tight up against wooden walls; these will also need airgaps and heat shielding, even more than the floor, as the internal heat will be more intense at mid and upper levels of the interior. Masonry heater code calls for something like an 8" airspace between walls and the heater exterior, with a double-thickness heater wall. There are more specifics in the International Building Code which has a section for these units, equivalent to some RMHs (which are not covered by any building code except Portland, Oregon's).
Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
Thanks guys!. I will strip the wainscotting pine (read: kindling) from the wall and get some standoffs. Should I just run a duroboard sheet up behind it? Thanks for the tip on the mortar. I have imperisal castable refractory cement. I will make thin joints, I get what yer saying, keep the expansion the same so less cracking.
I will move the unit away from the way. The back of the bell (made of bricks no barrel on this build) has lots of clearance but since I am single wall masonry I will move it out as far as I can go.
I just checked and I can move it over to have 15 inches of clearance to the back wall. Is that enough or still should I run reflectors on standoffs?
Well after a review of all the code and the entire job, we are calling it off. Looks like we will upgrade the current stove and add mass to it. In the end we just didnt want to do all the real work to do it proper and make it look nice when we are selling this house. Sorry future owners,. Thanks for everyones help. Sorry to disappoint
He loves you so much! And I'm baking the cake! I'm going to put this tiny ad in the cake: