Bulk Ceramic Fiber Experiments.

I have finally pulled the trigger on a purchase of 45 lbs of chopped, bulk ceramic fiber.  Rated at 2300 degrees F. for the riser I will cast from 8 inch and 12 inch sonotube.

My intention is to use some of the material and experiment with it in regards to mixing it with various binders.  There is the traditional Sodium Silicate route.  But I have also considered mixing it with castable refractory materials to see what sort of characteristics it takes on.  I am looking to build a heat riser that will perform very well, and be very durable as to last for many years to come.  My plan is to take the cast cylinder from the sonotube and coat it, inside and out with a 3000 degree F Masonry Hot Face material.  Hopefullly, filling in the pores and giving the cylinder added strengh, protection from hot flowing gasses, and a smoothness to help reduce laminar friction.  I'm not sure how much of the bulk fiber I will need to create the riser, as I am hoping the one 44 lb. bag will be sufficient.

I was hoping anyone in the Permies community who has had any experience experimenting with bulk ceramic fiber might share that experience here so we might all benefit as it doesn't look like purchasing commercially produced ceramic fiber heat risers is really an economical option.  

Hi Thomas;
As you have thought this thru and gone ahead on the chopped fiber.  I assume that ceramic fiber blanket five minute riser is not quite long lived enough for you.
When I was casting fireclay and perlite risers , the proper mix was high in perlite.  So I would think a higher percentage of chopped fiber would be more insulative than one, say high in refractory.  Sodium silicate could be a winner .
There was a source of ceramic round 6" risers that were being bulk ordered, but I believe the source dried up.
Almost everyone at donkeys forum is now using the ceramic blanket in a pipe riser. AKA) The five minute riser.
Keep us posted on your experiments.

I believe most insulative fibers work by capturing air between the individual fibers.
Mixing them into a cement would preclude this.
Unless these fibers are hollow in structure,I don't think they will add anything to the insulativeness of the mixture.
They should help preventing  cracking.

I've used rockwool to re-enforce refractory mixtures to good effect.
I've also coated batts of  rockwool with a stucco-like refractory/perlite mix.
The idea was to give the rockwool a durable hot face.
It stuck quite well, but I haven't fired it yet.

Thomas,

"Almost everyone at donkeys forum is now using the ceramic blanket in a pipe riser. AKA) The five minute riser."

I am aware of the "Five Minute Riser" and was sorely tempted to go that route.  Has this been around long enough to gauge it's durability?  

You got me thinking about this so much I actually had to go out to the mailbox and retrieve the order for the ceramic fiber until I get t his question settled.  A fully ceramic fiber riser like I'm thinking will cost no less than $150 when you count up the cost for the fiber, refractory, rigidizer, and sonotube.  

I'll have to head over there and see what the word is on durability and what, if anything, needs to be done to improve on the idea.

Thomas;
The word I got from "pinhead" the inventor of the five minute riser, is that his original riser is still in use today and showing no signs of failing. I think it is close to two years or more.
He used #6 2300 F 1" thick ceramic blanket  wrapped inside an 8" black steel stove pipe. It doesn't get much faster or easier than that
I have a 4' long piece of 10" pipe I will use to make an 8" riser on my new stove.
Ceramic blanket unfortunately seems to be sold in 25' and 50' rolls, for around $90 so its not cheap.
I should mention also that ceramic fiber boards are also the newest best thing to make your burn tunnel out of...   That costs about another $100... Its not cheap to stay on the cutting edge.

Thomas,

Since the diameter of your 10" pipe is 31.4 inches,  and you only need 4 feet, do you think it would be appropriate to do two concentric rings to cover the inside of your pipe with a material of these dimensions.  

https://www.ebay.com/itm/Ceramic-Fiber-Blanket-2300F-8lb-Thermal-High-Temp-Insulation-2-X24-X12-5-Kaowool/251990787538?hash=item3aabd245d2:g:XDwAAOSw8RZahw5T

I see prices for 10" duct pipe at about $40 for 5 foot lengths.  I'd still be in the same price range going this route, but a whole lot less fuss.  

What do you think about using the two inch vs one inch thick blanket?

Thomas;
Not sure I understand your question?
 2" blanket I believe is more than you need .  I have not read of anyone using that thickness. Most of the blanket sold is 24" , I have seen 48" offered but it was to long a roll and way to much money. I'll use 24" and stack it for my 8" dia. 48" riser.
Now when it comes to ceramic boards its a different story.  1" is acceptable through out the burn tunnel and start of riser,  2" board on the roof has been suggested as even better.

Yes, stacking it is what I meant to convey.

I'll take your word for it that 1" thick is enough.  Just hard for me to wrap my head around.  I always try to overbuild things.  

Regarding the ceramic fiber board.  I have just one concern regarding that, and it is related to concerns I had about the blanket.  I was watching a video Matt Walker put out regarding his smaller woodstove that uses the fiber board.  In the video, he showed the inside of the stove and it appeared to me that the velocity of the hot gasses were eroding the boards.  I can't be certain of this and I will make it a point to ask him directly, but that was the root cause of my concern, and hence the reason I wanted to use the 3000 degree F hot face refractory mix on the inside face of the riser.  

It was Matt who recommended the 5 minute riser to me and also Matt who told me 1" Cf boards backed by common red brick is good for a core but if you felt rich 2" on the roof and if richer yet than 2" on the floor as well.
I'm sure that 2" would be overkill on the riser... nobody else has done it.
With the popularity of ceramic fiber and the extreme performance of it, I see it as the new standard in rocket stoves.  Kind of getting away from building one for under $100 down to free.  BUT you still can!

Thomas,

So does that mean high velocity erosion is not an issue??

I have gone from planning an 8" batch rocket,with barrel and traditional Wisner style cob bench, to an 8" masonry bell batch rocket with  masonry bell bench, to a 8" rocket with barrel and masonry/stone bell bench.  I have certainly learned a lot along the way.
I have some space constraints that make a full fledged masonry heater unrealistic.

Yes, we pay a price for durability and efficiency.  I have seen a lot of threads where builders are constantly tearing down their rockets to repair them because the inexpensive materials can't hold up.  I'm getting a bit too old for that, so I'm trying to devise a system that will last as long as I do.  LOL.

I've started a thread for my build.  I expect to be posting more information about it as I get started on it, hopefully this winter.

I can not speak yet from personal experience as my ceramic fiber board is still wrapped in plastic...and my CF blanket has not even been ordered yet. But as I understand it , the first time you bring it up to rocket temps it hardens . I would expect some scorch markings but its good to 2300F , even in the riser we are not reaching that level... Yet...
Matt is happy to answer any questions. He has worked with all the variants of rmh's from the early days to the new riserless cores and his newly released "Continental" rmh.
If ceramic fiber board and blanket is what he and the other innovators are using then that's good enough for me.  

Thomas,

I was not aware that the board and blanket harden when brought up to temp.  That is good to know.

Thank you kindly for all your input!

Update.  I consulted Matt Walker regarding high velocity flue gas erosion.  He stated he did not see any evidence of this in his builds.  No concerns.  I also asked him if he thought a masonry cement facing such as Satanite and a layer of ceramic fabric on the ceramic fiber board might make it more durable.   Again, he stated he did not think it would provide any added benefit to be worth the effort.  

Not having yet handled this material and having no experience with it's durability, I just wanted to cast my line out once more for any opinions on the matter.  I thought I'd read that Erica Wisner had remarked that using dense firebrick in the feed tube of a J-Rocket as a means of protecting the ceramic fiber from the rough and tumble of the firewood could lead to smokeback due to the brick reversing the draw after the main part of the burn. So it might well be best to not use any firebrick in the feed tube at all.  I'm trying to get a better mental grip on how the ceramic board fares when used unprotected in the feed tube.  Can anyone speak to that point?

I took notice that there have been other inquiries made as to the durability of Pinhead's five minute riser.  2+ years and going with no discernible wear and tear.  That is encouraging!

Thank's again to everyone for all their help.

I have located a supplier for my barrels.  A build is on the horizon.

Hi Thomas;  
Thanks for sharing that information from Matt, I'm sure there are others wondering the same things you were.
As far as the dense brick in the feed tube.  Erica is a master builder, anything she has to say about rmh's should be listened to closely, as it most likely based by experience.
My own experience with my RMH, is that my mass is so warm after burning, that it sucks out matches if trying to relight it.  
I am currently amassing parts for my next RMH.  I have the ceramic boards now, I have yet to order the cf blanket.  I have brand new split firebrick to build my feed tube. I have piles of old and new red clay bricks and I have several pallets of full size heavy firebrick.  
My first RMH is an 8" J tube with horizontal mass. I built it 5 years ago. We love it ! It is in our greenhouse / studio no fire all night ,all winter!
My new RMH will also be an 8" J tube, with exposed barrel and 2 brick bells in place of the long mass. It will be in my shop.  I have high hopes how well this one will work.  Split brick feed tube, 1" CF board burn tunnel/riser , 8" C.F. blanket 5 minute riser . I'm thinking it should really roar fast and loud !
Without even making my first one. I'm already planning on replacing my walker style fireclay / perlite riser in the studio with a ceramic fiber blanket riser!

Grainger has what seem to be good prices on ceramic fiber:

1" Thick Ceramic Fiber Insulation, 5 ft. x 48", 6 cu. ft./lb. Insulation Density

$55.00 each.

Looks very expensive to me, dimensions are double width and just 5' long. That's not a full 1" thick roll I'd think.

Edit: Just checked, a full roll of 1" thickness and 2' wide is 24' long, delivered in a carton box. Weight depending on the density, #64, #96 and #128 are common densities. In the Netherlands it can be obtained for just under € 70.-, something like $ 82.- excluding shipping.

Edit2: The above price is for a cheap material that contains carcinogetic components. The real Superwool is not bio-persistent and cost €142.- or $167.- excluding shipping.

Peter;  
Could you please explain the difference in ceramic blanket ?  What components are carcinogenic ?  Bio-persistent ? Real Superwool is different how ? Is there a certain brand of blanket ? My understanding is that all ceramic fiber is carcinogenic if inhaled ?  A mask & long sleeves should be used when working with.
I agree the price William located was on the high side especially if you include shipping , I did not notice any material difference in it from other cf blankets offered elsewhere.
The CF blanket I am looking at is #6) 1" x 24" x 25' long. Cost is apx. $95.00 including shipping.

EDIT)   I started researching this on my own.  Seems Superwool Plus is a brand name and does not have/need a heath warning label... Apparently a large percentage of the available CF blanket is Chinese manufacture using substandard components !!!  I did not know about this !
I would say I have answered my own questions from the above post.

Thank You Peter, for bringing it to our attention!

EDIT #2) Peter , I located real superwool plus in a 50' roll ,$115.00 delivered  #8 density but only 1/2" thick.  Do you think I can double 1/2" up in a riser to safely get a 1" thick riser ?

EDIT #3)  Would the 1/2" #8 density alone be enough to use in a riser ?  

Ah, I didn't realize the amounts you were getting.
Granger has an outlet in my area, so no shipping.
I just looked for a minimum amount of material for the riser,but 5 times as much for just over twice the money is clearly better.

I will be building an 8" x "scandalously short riser"  myself, so I will be using this:

1/2" Thick Ceramic Fiber Insulation, 5 ft. x 24", 8 cu. ft./lb. Insulation Density


https://m.grainger.com/mobile/product/UNITHERM-1-2-Thick-Ceramic-Fiber-Insulation-54TP60?breadcrumbCatId=27785&fc=MWP2IDP2PCP



At $15.65 out the door it  makes sense for me.

I like materials I can get locally, so I can replinish on a whim,or more to the point,whenever I have the spare cash.
$15.65 is pizza for the family, easy to choose RMH over that.
$115.00 is a utility bill, so it's harder to pull the trigger on.

Careful guys, with the ceramic "felts" they are in the same league as asbestos. I have ordered superwool lately. Which is supposed to be safer.

You can use kaowool or the other ceramic felts, but wear a respirator mask, full paper body suit, gloves. Do the work outside. In France, you can't buy these, unless you are a professional.

Thomas, i don't know if half inch would hold it's shape. But if it does, you can build a heat riser from that. It would cut the bulk of the heat and excess oxygen, from the stainless steel pipe, and you can insulate outside of this riser with rockwool for example.

An excellent point. And the MSDS backs it up.


Note especially:
"Possible cancer hazard by inhalation especially when the fiber becomes christobalite at high temperatures above 1800F"


I concluded continuous prolonged unprotected exposure can cause serious problems, so I plan on immobilizing the fibers by dampening them and adding a dusting of refectory before shaping the blanket into riser.

Mind you, if you burn anything, you pretty much produce carcinogens, and I know that there are no visible signs of deterioration, but in my position, why risk it?