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Post by PNW Dave on Jul 27, 2014 13:35:24 GMT -8
NOTE- I don't end up using either of the products in this post for the little test stove or heat riser later in the thread.I have one tube each of Fire Barrier Sealant (red) and Furnace Cement (black), Any advise on whether or not either of these products would a good additive to a fireclay and perlite mix for casting a heat riser (8" system)? The red one says it expands during a fire, I'm torn between thinking that will provide a boost to insulation and thinking it will weaken the structure and the riser will crumble. The riser will be cast in a few short sections, fired in the kiln, then stacked. I made two hockey puck sized sample bricks with a ratio of 6 parts perlite, 2 parts fire clay, 1/4 part cement or sealant and as little water as possible. First mixing either the cement or sealant with water, then using that water to mix the clay and perlite. After drying, I blasted them with a blow torch. Pretty similar performance in my "break it in half with my hands" test, the sealant one seems to heat up and cool down slightly faster (measured with laser thermometer) and there isn't really a noticeable expansion of the product. With this simple test I think they both would be a decent candidate. I should have made a plain perlite and clay puck for a control to test against. I guess I'm just checking to see if anyone says something along the lines of "NO! Don't add that!" or "Yup, that Black Furnace Cement is a good choice". Thanks Here is a pic of the products-
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Post by ericvw on Jul 28, 2014 3:18:15 GMT -8
Hello DavidEaks, I have read several posts about the use of furnace cement as an additive in the clay/perlite mix. Matthewwalker's posts and videos are a great testament to this. Search it and you will be validated. Furnace cement contains sodium silicate. I too have used this in a similar test mix, w/ fairly good results, but as matthewwalker seems to end up saying, a good commercially available refractory is the more reliable way to go. Then you have Karl, who not in any sort of mad scientist way, is publishing to the forum some geopolymer recipes which by my non educated guess would work wonderfully too. You mentioned the use of a kiln- do you have access to a pottery kiln, or is it something homegrown? I have been messing about w/ some purchased refractory(not cheap) and been trying to line up the use of kiln, as I'm not interested in some part of the system cracking and leading to some catastrophic failure which takes the house with it! I know a lot of these very experienced folks use cob and such, and I can see how their systems are essentially safe, but I need to keep my wife happy, and her mechanical engineer stepfather satisfied with the application! On with the day, EVW PS-if u use the 3M product and it heats too fast it will bubble, harden, and become very brittle! Used it often on former woodstove. But it does contain sodium silicate too.
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Post by Deleted on Jul 28, 2014 4:03:45 GMT -8
If you have access to a kiln you could calcine fire clay at 650°C to 750°C for 90 minutes to remove the chemicaly bound water and make it pozzolanic reactive. If you add by weight 10% NaOH powder and 10% lime powder to the calcined fire clay and mix it with water it will harden to a ceramic like material aka geopolymer.
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Post by PNW Dave on Aug 13, 2014 2:25:07 GMT -8
Eric, thank you for pointing me to Matt's videos. I hadn't quite put it together that some of the videos I have watched were in fact his videos. Now I owe him even more credit for all the information, inspiration and ideas!
I do have a pottery kiln. I'm holding it for at least the next 1-4 years and can use it at my leisure during that time and will still have access afterwards... But it is not yet setup nor am I completely familiar with its operation. I intend to tackle that very soon. Maybe we can work something out.
Karl, thank you for the suggestion but I'm not fully confident that I understand what to do in order to follow your advice correctly.
- To calcine the fire clay, is that just to fire a pile of dry fire clay at a temperature that doesn't sinter it into a solid mass? I read that fire clay has a fusion point above 1600*C, so that seems feasible. What sort of vessel do I put the clay in for the calcine firing?
- The 10% by weight of each Lye and Lime, is 10% of the weight of the dry calcined fire clay, correct? That seems pretty clear.
- This will be for the heat riser so I'd like it to be as insulating as possible. Can I add a whole lot of perlite to this mix?
Thanks to everyone for the willingness to share!
I've also made a batch of Sodium Silicate "water glass" and some perlite based test bricks, of which I'll post details soon. First impressions are encouraging.
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Post by Deleted on Aug 13, 2014 3:22:22 GMT -8
- To calcine the fire clay, is that just to fire a pile of dry fire clay at a temperature that doesn't sinter it into a solid mass? Yes. Between 480-700°C chemical water is driven off. Between 800-900°C sintering begins. Something that can resist the temperature. 10% of the dry mixture. Yes.
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Post by PNW Dave on Aug 13, 2014 5:09:32 GMT -8
Excellent, % of total dry mix. Thanks for clarifying.
Would it be beneficial to first calcine fire clay before making a mixture including furnace cement (3000F) and/or Sodium Silicate with Perlite? Or does it not really matter in that situation?
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Post by Deleted on Aug 13, 2014 6:27:33 GMT -8
It's up to you.
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Post by PNW Dave on Aug 19, 2014 10:15:23 GMT -8
For reference, neither of the products pictured in my first post were used in the following test bricks. I recently made up a 1000ml batch of sodium silicate, using Roebic 100% lye crystal drain cleaner but instead of silica gel "beads" I used a "flower drying art" silica gel that is more the consistency of sand. I found it at Michael's craft store. With some homemade sodium silicate I made several test bricks by ramming the mix into the center of a roll of duct tape so it was half full, creating a hockey puck sized sample. Mix 1) Plain perlite and Sodium Silicate mixed very dry, just to the point where it holds together. Right off the bat it seemed to harden quickly, when I removed it from the form it felt very encouraging, firm and light weight (but see below). Mix 2) Perlite and fire clay mixed dry, then I strained out the excess fire clay and the finest of the perlite particles. Then I added back a small amount of the fire clay and perlite fines. This left me with what I'll call "fire clay dusted perlite". I think I added a little too much Sodium Silicate to this mix, even though it seemed to firm up well at first and I was able to remove it from the form, it was quite sticky and seemed flexible. Mix 3) "Fire clay dusted perlite" with Oatey Furnace Cement 3000f. Mixed with as little Furnace Cement as I felt would hold it together while still keeping it light weight and insulating. I rammed this into the form and left it in the garage overnight. Mix 4) "Fire clay dusted perlite" with equal parts of both Sodium Silicate and Oatey Furnace Cement 3000f. Mixed with as little Furnace Cement and Sodium Silicate as I felt would hold it together while still keeping it light weight and insulating. I rammed this into the form and left it in the garage overnight. Then I got busy and didn't check on them the next day. The day after that I was disappointed to see that Mix 1 had not cured. It was pretty soft, crumbly and slightly damp, any slight touch would crumble off the edges. Mix 2 was sticky but not as crumbly. I think the moisture in the air was part of the problem. Curing them in a bag injected with CO2 probably would have been a good idea. Mixes 3 & 4 were feeling pretty solid but I can't remember if they felt dry or not yet. So, I gave them all a short blast with the burns-o-matic ts 8000, torching each one from various angles for a few seconds and repeating several times before flipping and repeating the process on the other side. Mix 1 hardened right up again. Mix 2 expanded wildly and unevenly when heated too quickly, growing like one of those kids "snake" fireworks. I just had some fun torching the heck out of one side and watching it expand and harden. The other side I heated slowly trying to not let it expand. Mixes 3 & 4 didn't seem to react to the heat at all. Except I could hear the Sodium Silicate in mix 4 sizzling a bit, it didn't expand or noticeably change. After leaving the samples in the garage for another couple days, I was again disappointed to find mixes 1 and 2 uncured and softening again. Torching hardened mix 1 again. Mix 2 was still at risk of expanding so I went slow. Mixes 3 & 4 were still solid and unchanged. Mix 4 still sizzled when heated. I just went out and checked on the sample pucks again, which have been left out in the garage for a couple more days and I torched them again yesterday. Mix 1 is dry and solid. Mix 2 still has not dried/cured (except for the expanded parts) and is a fragile, crumbly, mess waiting to happen. Mixes 3 & 4 are dry, solid and unchanged. I still need to do a test puck following Karl's advice. I'll also do a test puck or two with perlite that has been very lightly misted with water then mixed with fire clay to coat the perlite. Then sift out the remaining fire clay to make what I'll call "Fire Clay coated Perlite". As Matthew Walker says, adding the furnace cement really hardens up the mix. I'm sure that it will be in my final mix. For the heat riser it will likely be as little as I can use and still get a decently strong material, but with a main focus on achieving highly insulating properties.
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Post by ericvw on Aug 19, 2014 14:01:37 GMT -8
Hey there D-eaks, Nice post! Pretty thorough effort I should say... Please keep us newbs and everyone else informed? Nice work... Eric VW
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Post by PNW Dave on Aug 20, 2014 13:11:27 GMT -8
Thanks Eric, I will continue to update as I go. This being the beginnings of my first build, I'm a complete newb as well!
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Post by PNW Dave on Sept 1, 2014 11:45:00 GMT -8
I made a small, 5 gallon, rocket stove to see how the refractory/insulation mix held up on a larger scale than a little puck. The mix I used was a little different then any of the pucks above.
- 15 parts Perlite - 2 parts fireclay - 2 parts furnace cement (1/2 Gal) - 1 part Water Glass (home made) - about 40oz of water was used throughout the process
First I lightly misted the perlite with water, then lightly dusted on some fire clay, then mixed it. I repeated this until all the fire clay was used up.
Second, I mixed the furnace cement and water glass with some very thin clay slip. Then I had a helper slowly drizzle the wet ingredients while I mixed it into the dry.
Then I rammed it into the form, removed the inner forms and started applying heat over a couple hours. That night I boiled some water on the new stove.
Here's a video of the process-
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Post by ericvw on Sept 2, 2014 2:44:37 GMT -8
That's impressive, David, Very nice, well done and the video itself is really good! Your post indicates homemade water glass... Can u share the process? Thanks and can't wait to see what you cook up next! Eric VW
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Post by matthewwalker on Sept 2, 2014 7:26:29 GMT -8
That's awesome David! When you scratched at it with the hookaroon I was really surprised. That stuff is really hard! Good job man.
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Post by PNW Dave on Sept 2, 2014 9:58:16 GMT -8
That's impressive, David, Very nice, well done and the video itself is really good! Your post indicates homemade water glass... Can u share the process? Thanks and can't wait to see what you cook up next! Eric VW Thanks Eric, I followed the video below to make the water glass. I used the same Roebic lye drain cleaner, the silica gel I used is a fine sand like product for drying flowers that I found at Michaels craft store (even though employees said they don't have it, I continued looking and found it. A fairly common occurrence in many stores). The video covers the process pretty well-
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Post by PNW Dave on Sept 2, 2014 10:39:50 GMT -8
That's awesome David! When you scratched at it with the hookaroon I was really surprised. That stuff is really hard! Good job man. Thanks Matt! I'm quite happy with how it turned out. The hardness surprised me too, even shortly after removing the inner forms when I hit it with my knuckle. It was still damp and pliable but really firm at the same time. I feel that there is very little concern of this mix cracking as it dries as well. Let me know if there are any hardness/durability etc. tests you'd like to see. I want to take the angle grinder to it and see how it takes to cutting. Also the working time with this stuff is pretty long. I just looked at the empty tub of furnace cement, I had left the lid partly open for several days. I expected it to have completely hardened, nope, it's sticky. And my home made water glass doesn't seem to ever dry on its own. I mixed all of the materials in one big batch and was a little worried it would harden before I could finish ramming it into the form. Not at all, but apply some heat and BAM, like a rock. Much like you said in your core video, the furnace cement likes the heat. I'm pretty confident this is the mix I'll use for the heat riser and core. Maybe a little higher perlite ratio.
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