|
|
Post by machinemaker on Dec 9, 2010 20:30:28 GMT -8
Just a couple of thoughts: most refractory, ie firebrick mortar, is a clay slip. Typically you dip the bricks in the mortar and lay them up. It is only a thin coating that vitrifies when heated to "glue" the bricks together. I question the use of perlite in rocket stove. In most fireplaces you don't see the temperatures that you could get in a rocket stove. At the temps I see in foundry and kiln applications perlite melts and acts like a flux to dissolve other higher temp refractories.
kent
|
|
|
|
Post by northriver on Dec 9, 2010 22:02:49 GMT -8
I have been reading about the clay slip.
The Natural Plaster Book gives a very good description for making the clay slip.
This sounds simple enough.
However, on the internet some clay slip mixtures also add a deflocculant (sodium silicate or sodium carbonate). I get the impression this is done for pottery and cast items. Do I need a deflocculant for the slip?
The Rocket Mass Heater book suggests a ratio of 6-9 parts perlite to 1 part slip for the perlite/clay mixture and the proposed rocket stove code calls for a 2" layer of this insulation mixture around the burn tunnel. I am assuming that a further 4-6" layer of cob (less straw) holds this insulation mixture in place?
|
|
|
|
Post by Donkey on Dec 10, 2010 8:44:14 GMT -8
I don't see the kinds of temperatures required to melt pearlite.. At least, not often in a home heater.
You shouldn't need to add ANYTHING to the slip. It's fine on it's own.
We're not building kilns here.. (I suppose we could, but It's not the intent of a home heater)
You want your in home wood stove to be tame. It's possible to build a roaring, dangerous beast but why would you want to?
|
|
|
|
Post by Donkey on Dec 10, 2010 8:45:25 GMT -8
I am assuming that a further 4-6" layer of cob (less straw) holds this insulation mixture in place? Yep. |
|
|
|
Post by canyon on Dec 10, 2010 9:07:48 GMT -8
I have been reading about the clay slip. However, on the internet some clay slip mixtures also add a deflocculant (sodium silicate or sodium carbonate). I get the impression this is done for pottery and cast items. Do I need a deflocculant for the slip? No need on the deflocculant.  BTW I've gotten that perlite melting warning from other kiln builders and I second Donkey that we don't see those kind of temps. Could be too 'cuz we don't fire for more than a few hours at a time. |
|
|
|
Post by northriver on Dec 10, 2010 20:30:33 GMT -8
We packed the clay slip/perlite layer around the core of the stove. Found this fairly challenging ... it crumbled easily and did not want to stay in place. We added more slip until it behaved. We also started the 6" layer of thermal cob around the stove. We fired up the stove to dry out the cob so we could carry on ... this worked out fairly well. I've got pictures of the day's activities at www.darfieldearthship.com/2010/12/fired-the-rocket-thank-god-for-skylights.html. I am now starting to think more about the bench. Is there any reason not to use sheep's wool instead of straw in the cob? We have been using wool for our walls and it has been working well. Can anybody see any issues with using it in the stove bench? |
|
|
|
Post by Donkey on Dec 11, 2010 11:25:53 GMT -8
Aha!!
For future reference.. The pearlite mix isn't meant to be sculpted on like that.. As you've discovered, it's REALLY difficult to do it that way.
I've found that the best method is to build a void (pocket) out of cob and FILL with pearlite/slip. This way you don't have to keep adding slip to make it stick, the mix stays light for better insulation, and tempers remain mellow.
To the wool, why not? I haven't tried it myself but I'm assuming it will work.
Replace the word "straw" with the word "fiber", let your conscience be your guide.
Try it in a test block and apply some heat to it. I don't know how the wool will react to the heat.
|
|
|
|
Post by northriver on Dec 11, 2010 18:22:28 GMT -8
Aha!! For future reference.. The pearlite mix isn't meant to be sculpted on like that.. I've found that the best method is to build a void (pocket) out of cob and FILL with pearlite/slip. Darn ... that makes sense! |
|
|
|
Post by northriver on Dec 11, 2010 22:07:50 GMT -8
First thing this morning we laid out the ducting and argued about its placement (we needed to figure out where the ducting met the heat riser in order to place the manifold). Our walls are non-combustible (especially when they are covered in cob) but we kept the stove pipe a minimum of four inches from the wall. Additionally, we made sure the top of the pipe was under 14″ from the top of the finished floor as we want a minimum of 4″ of cob covering the pipes. Once we had the pipe roughly placed I started cutting away the cob (much to Sandra’s dismay) to create a base for the manifold. Once we had a level base to work with I laid out a base round of bricks and we cobbed around the edges of them. After that I formed a box out of brick and cob. I mortared the brick in place with the last of the refractory cement we had. I put an 8″ diameter clean out pipe running perpendicular to the heat exchange pipe and cobbed both pipes into the box. I fitted the cap to the clean out pipe before I started placing cob so that the pipe did not go out of a circular shape. We had the stove lit most of the day and it continued to dry out the clay. At the end of the day we dropped the heat riser barrel over the heat riser to direct the hot exhaust gas down onto the wet cob … it seems to be helping a lot to bake the cob. A word to the wise; cutting stainless steel is HARD work, my arms are still shaking and Katie is still vibrating from holding the barrel. I went through three sawzall blades getting the top off of the barrel. Stephen and I had fun burning off the residue of Tea Tree oil originally stored in the barrel! Tomorrow I hope to fit a cover over the manifold, place and insulate the insulation drum, and place the heat riser barrel. After that we will just have to hook up the flue! Are there any concerns with placing a vapour barrier (6 mil poly) under the cob bench? The heat should be diffuse enough at that point to not be an issue? Pictures and text of what we did today at www.darfieldearthship.com/2010/12/rocket-mass-heater-sculpting-the-manifold.html. |
|
|
|
Post by Donkey on Dec 12, 2010 15:39:32 GMT -8
Are there any concerns with placing a vapour barrier (6 mil poly) under the cob bench? The heat should be diffuse enough at that point to not be an issue? I don't think so.. But why would you want to? I've noticed that vapor barriers tend to end up as condensation points and/or underfloor ponds. IMHO, better to let vapor move through easily than try to stop it. |
|
|
|
Post by northriver on Dec 15, 2010 21:07:04 GMT -8
I've been busy the last couple of days! We did not want to light the stove anymore until we had it exhausted outside ... the house (and I) were starting to smell like a camp ground. So, over the last couple of days we got the exhaust hooked up (details and pictures at www.darfieldearthship.com/2010/12/the-rocket-lifts-off.html). Initial results are promising; the stove was fairly easy to light (I've read of some problems at this stage), and a horizontal flame was quickly established. We put a clean out at the base of the flue and made sure the flue was close to the feed barrel of the stove. This allows us to light a piece of paper and stick it in the base of the flue to encourage the stove to draw properly when first lit ... it is very effective. For the last day or so the stove has been drying out ... it is mesmerizing to watch the steam curl off of the stove. Frustratingly, I do not have any way to take temperature readings at the top of the burn barrel or the exhaust flue (an almost intolerable situation!), so I have no idea how well the stove is performing. The barrel is quite hot ... you cannot touch it! The exhaust temperature is quite low ... you could lean against the flue and feel pleasantly warm. The exhaust coming out of the chimney is clear once the fire is established, it smokes at start up. I am going to see about some sort of thermometer ... Some thoughts and observations ... The top of our heat riser barrel is 2-3/8" above the top of the heat riser. The Rocket Mass Heater book specifies a minimum distance at this point of 1.5", but there is some latitude to increase this distance according to other builders. The tighter this measurement is, the hotter the top of the barrel will get and the quicker water will boil for tea. Practically, there seems to be a sweet spot that optimizes the performance of the stove. I am not sure if I should play with this gap and hunt for a sweet spot and how I would go about doing that? The gap between the insulation barrel and the heat riser barrel is 1.5" and this is the distance specified by the Rocket Mass Heater book. We got a carbon monoxide detector and put it in the same room as the stove. It has not moved off of a reading of 0 ppm. It occurs me as I type this that I should go stick it at the outlet of the chimney and see what it reads. We have not yet * built our cob bench, * finished insulating around the stove, * installed the feed barrel * provided an outside source of combustion air So much to do! All of these steps will improve the effectiveness of the stove so I am keen to carry on. The building inspector will want a vapor barrier on the floor. I am just trying to figure out if there is a good reason to tell him this is a bad idea. |
|
|
|
Post by careinke on Dec 15, 2010 21:24:26 GMT -8
Nice Job! I just watched "Garbage Warrior" and it added new meaning to your place.
|
|
|
|
Post by Donkey on Dec 16, 2010 18:22:27 GMT -8
Sorry for removing your images.. They're just too big! I'm on dialup here and it takes a crazy long time to load 'em. In the future, please DO NOT post images over about 800Kbytes. Thanks! Some thoughts and observations ... The top of our heat riser barrel is 2-3/8" above the top of the heat riser. The Rocket Mass Heater book specifies a minimum distance at this point of 1.5", but there is some latitude to increase this distance according to other builders. The tighter this measurement is, the hotter the top of the barrel will get and the quicker water will boil for tea. Practically, there seems to be a sweet spot that optimizes the performance of the stove. I am not sure if I should play with this gap and hunt for a sweet spot and how I would go about doing that? To find the "sweet spot", you'll need a helper. Start your stove with the barrel off and get it hot. Put the barrel over the heat riser (wearing gloves) and move it up and down slowly. Pay attention to what you're hearing, you will notice a place (a small range) where the stove sounds "right" When you've found the spot, have your helper chalk up the barrel so you can let go of it. Cob it in. It can be larger if you wish, though not smaller. Well.. Seems to me bad policy. When I build earthen floors, I make sure there's at least a 4 inch layer of crushed washed drain rock underneath which provides a moisture break, keeping moisture from rising up, it ALSO allows water to leave downward if it does get in. I NEVER use a vapor barrier, as it tends to become a condensation point and/or a blockage to water getting out. I doubt that my arguments will hold sway with your building dept. however, so probably better just to do what they ask for. |
|
|
|
Post by northriver on Dec 16, 2010 19:17:15 GMT -8
Sorry for removing your images.. They're just too big! I'm on dialup here and it takes a crazy long time to load 'em. In the future, please DO NOT post images over about 800Kbytes. Thanks! Sorry! Won't do that again. |
|
|
|
Post by northriver on Dec 19, 2010 20:53:39 GMT -8
No pictures as it has been a busy couple of days, but I have made progress ...
I've attached the feed barrel (1' in diameter and 11 inches high. I cut a 4" diameter hole in the side of the feed barrel (centred approximately 5" from the bottom of the barrel and attached an outside air supply pipe (4" in diameter running through the roof of the building). Does 4" diameter seem reasonable for size?
It seems to work fine. When I cover the top of the feed barrel the combustion noise level does not change. When I completely block the air supply line with the feed barrel covered the fire dies. It is amazing how much condensation builds up on the outer surface of this air supply pipe. Outside air temperature is running around -10 celcius this last week so there is quite a difference between inside and outside air temperature.
We are now working on the bench. I hope to have the heat exchanger covered in the next few days.
I inspected the manifold for the first time since sealing it, and it is still clean (almost no ash).
The stove lights easily (more so now that it is warmer and the moisture is out of the cob surrounding the core). It draws nicely and I have only seen back-drafting when the stove is first lit and the flame is getting established.
|
|
