Deleted
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Post by Deleted on Sept 19, 2016 8:52:23 GMT -8
Plastic trays are great molds for geopolymers.
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lawry
Junior Member
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Post by lawry on Sept 19, 2016 9:41:04 GMT -8
How thick should a bench cap be? I am thinking 50mm... I need enough to carry the weight of a person? the way my one half firebox feels and sounds I think I can get away with thinner...
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Post by firewatcher on Sept 19, 2016 16:22:19 GMT -8
Time for another update...1 test puck and 2 test bricks (all three are 1 inch (25mm) thick):
Note: all 3 test pieces were VERY easy to break with my hands. Disappointing.
Test Puck - unfortunately I forgot to take a "before firing" pic so all that I have is the "after fired".
- there was no cracking in the brick before firing. It was fired with the cardboard mold still on and on the piece of plywood it was
molded on.
Puck "recipe":
100g perlite powder
35g fire clay
600g slag
13.5g hydrated lime
5g lye
1 cup waterglass (330g/L)
Was ambient dried for 7 days then "camp fire" temperature cured. Cracks developed while temperature curing.
Reverse side test results (after 10 minutes of MAPP gas torch application):
Torch side: 897F
Reverse side: 257F
Picture after temperature cure:
Test Brick #1
- there was no cracking in the brick before firing. It was fired in the plywood mold as I didn't want to risk cracking during unmolding.
Brick#1 "recipe":
200g powdered perlite
70g fire clay
800g slag
100g hydrated lime
2 cups waterglass (330g/L)
Was ambient dried for 7 days then "camp fire" temperature cured. Cracks developed while temperature curing. Brick looked a little damaged around all of the edges and there appeared to be some warping/misshaping of the brick after heat cure.
Reverse side test results (after 10 minutes of MAPP gas torch application):
Torch side: 982F
Reverse side: 227F
Picture of brick before and after heat cure:
Test Brick #2
- there was cracking in the brick on day 2 of ambient cure. It was fired in the plywood mold as I didn't want to risk further cracking during unmolding.
- after heat curing there are many hills and valleys on one side of the brick. It appears that the perlite has melted, as it kind of looks like melted hardened marshmallow in places.
Brick#2 "recipe":
200g powdered perlite
70g fire clay
800g slag
17g hydrated lime
2 cups waterglass (330g/L)
Was ambient dried for 7 days then "camp fire" temperature cured. Cracks developed while temperature curing. Brick looked a little damaged around all of the edges and there appeared to be some warping/misshaping of the brick after heat cure on this brick as well.
Reverse side test results (after 10 minutes of MAPP gas torch application):
Torch side: 965F
Reverse side: 252F
Picture of brick before and after heat cure:
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lawry
Junior Member
Posts: 113
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Post by lawry on Sept 20, 2016 0:14:41 GMT -8
" firewatcher" are you not missing some aggregate? What is the granular size of the slag?. My mixes hardly cracked. My binder was fly ash. But I had granular perlite and vermiculite, I believe that added structural support... |
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Post by firewatcher on Sept 20, 2016 2:23:32 GMT -8
" firewatcher" are you not missing some aggregate? What is the granular size of the slag?. My mixes hardly cracked. My binder was fly ash. But I had granular perlite and vermiculite, I believe that added structural support... The aggregate in my mix is the "slag". Perhaps I need something additional? Below is a pic of the slag.  |
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lawry
Junior Member
Posts: 113
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Post by lawry on Sept 20, 2016 5:17:17 GMT -8
firewatcher see below. this is the perlite and vermiculite that i add as aggregate. My mix in grams: Fly ash 322 NASIO/NAOH 152 RIVER 108 PERLITE 20 VERMICULITE 14 "River" is river sand it has aggregate 7 mm and Smaller Ok. Noted. Ta. Here is a picture with what i have access to. In the middle its salt just for comparison. Perlite (right) looks "fine". Or does it still need to be pulverized more? 
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Deleted
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Post by Deleted on Sept 20, 2016 5:18:44 GMT -8
Either you are as strong as the Hulk or something went wrong.
I am unable to break much thinner pieces with my hands.
Steam pressure can damage the inner structure if fired before completely dry.
Maybe your aggregate has not enough fine particles.
You could try to add 10%-15% very fine sand, like dune sand, to your aggregate.
lawry uses fly ash, which has a very low water demand.
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Post by firewatcher on Sept 20, 2016 5:41:31 GMT -8
I am definately not strong like the hulk. 😅
I don't understand what's going wrong though. Instead of my mixes becoming stronger with the changes I've made, they seem to be getting weaker or more brittle.
Two of the three mixes that I just tested incorporated the use of some extra lye. This is also the first time that I waited any longer than a day or two before firing. All three of these mixes were the first ones (I think) to use the red devil solid waterglass in the mix. This makes it difficult to tell which factor could have affected them adversly as well.
One of the strongest mixes that I've made thus far (the 2 inch puck) used home made waterglass with 500g solids to 1.5L water and way more lime than you recommend
The recipe for the brick that did not crack in two pieces during ambient curing used almost the same recipe except for the waterglass concentration which, this time, was 330g solids (red devil) to 1L water.
Curing could be the issue as well...i place the test pucks in the fire pit before startimg it and then just light it up. Maybe it's just too large of a temperature increase too quickly. Unfortunately it's the only allowable heat cure method that i have available as my wife doesn't want me using her oven. Even if i could use it, it wouldn't be large enough to temperature cure full sized molds for my actual stove.
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Deleted
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Post by Deleted on Sept 20, 2016 6:41:17 GMT -8
firewatcher with your very limitted resources a LTGS ram mixture with only a small amount of aggregate would be the safest and cheapest way. Kaolin is more expensive than ball clay but easier tu use due to the lower water demand. I have not tested fire clay as this kind of clay does not seem to be sold here. Fire clays seem not to be cheaper than kaolin. Did you have tried to activate fire clay ? Someone has posted a ram form for a batch box, but I cannot remember in which thread.
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Post by firewatcher on Sept 20, 2016 7:17:52 GMT -8
firewatcher see below. this is the perlite and vermiculite that i add as aggregate. My mix in grams: Fly ash 322 NASIO/NAOH 152 RIVER 108 PERLITE 20 VERMICULITE 14 "River" is river sand it has aggregate 7 mm and Smaller Ok. Noted. Ta. Here is a picture with what i have access to. In the middle its salt just for comparison. Perlite (right) looks "fine". Or does it still need to be pulverized more? lawry,
A few people have shared results using fly ash in their mixes and all have had very good luck with them. Unfortunately, I've done some pretty extensive searching for fly ash and no one locally is willing to sell it to me (unless I want several tons of it). In addition to that, they only have type F fly ash and from what I understand type C is what is required. Like many of the materials that I've tried to obtain, shipping costs make getting a lot of the materials non cost effective (shipping costs 2 to 3 times what the product cost is.
From what @karl has said in the past, for geopolymer, the aggregate has to also be pretty fine. He has mentioned that even the slag that I use (for best results) could be smaller, so using the aggregates that you have pictured, probably won't work in the mixes that I've been testing.
At this point in time, I'm starting to realize that I just MAY have to go a more expensive route to end up with a strong and durable stove (use of grog - which is one of the only other materials that I can buy from somewhere fairly "local"). My concern for strength of the mixes is that I don't want to have to repair/replace the casting on a yearly basis or have it crack/break apart if a piece of wood is accidentally dropped on it or something like that. At the same time, since this is a "for fun" project, I don't want to spend hundreds and hundreds of dollars on it either as money is fairly tight.
Thanks for your input...any help along my journey is always welcome.
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Post by firewatcher on Sept 20, 2016 7:35:17 GMT -8
firewatcher with your very limitted resources a LTGS ram mixture with only a small amount of aggregate would be the safest and cheapest way. Kaolin is more expensive than ball clay but easier tu use due to the lower water demand. I have not tested fire clay as this kind of clay does not seem to be sold here. Fire clays seem not to be cheaper than kaolin. Did you have tried to activate fire clay ? Someone has posted a ram form for a batch box, but I cannot remember in which thread. @karl, I have just recently tried a LTGS test puck (using the bentonite dessicant clay that I got for free), but have not yet fired it. I made a post regarding this but mistakenly put it in this thread rather than in your LTGS thread. You can see this below...
link
I'm honestly beginning to think that the fire clay that I'm using is not a good material to use. I took some of this clay the other day and mixed up a small batch with water to try and patch some gaps on my concrete test stove. After firing up the stove and burning for a little over an hour, the fire clay was dry but not hard at all...I could put my fingernail into it and it would crumble. It was also not abrasion resistant at all. Maybe this material is playing a part in the poor results that I'm having.
I will have to try and make a trip to Rovin Ceramics and pick up some known good quality material to test with to see if my "fire clay" could be what's causing me issues.
I don't know if it's the mold that you're talking about, but Lawry had posted a pic of his mold a while back.
link
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Deleted
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Post by Deleted on Sept 20, 2016 7:42:38 GMT -8
Type F fly ash is the required one. LTGS ram mixtures without aggregate become very hard, like fire bricks and can be applied like cob around an inner form. US prices are insane. If I buy 25kg the price per kg is usually lower than the US price per lb. Clay about 0,27 €/kg, kaolin 0,54 €/kg, grog 0-0.1mm 0,71 €/kg Rammed batch box donkey32.proboards.com/thread/1350/first-tries-batch-box |
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Post by firewatcher on Sept 20, 2016 8:04:36 GMT -8
Type F fly ash is the required one. LTGS ram mixtures without aggregate become very hard, like fire bricks and can be applied like cob around an inner form. US prices are insane. If I buy 25kg the price per kg is usually lower than the US price per lb. Clay about 0,27 €/kg, kaolin 0,54 €/kg, grog 0-0.1mm 0,71 €/kg I still have quite a bit of the bentonite dessicant laying around, I'll have another go at making a mix that is more dry and compact it into a larger sized mold than the 25 mm thick one that I've already done. I'm very concerned about using bentonite though as it seems to be VERY prone to cracking during even ambient drying. I'm honestly expecting the puck that I've made to pretty much fall apart when I fire it. I think it's been about 5 days of drying on the puck and it's still pretty soft. I removed it from the plastic bag 2 days ago and it has already shrank to the point where I could lift the cardboard mold right off it (the high shrinkage is also a concern for use in making a stove). |
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Deleted
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Post by Deleted on Sept 20, 2016 8:15:11 GMT -8
Bentonite has an extremely high water demand and is thus very prone to cracks.
I have found the rammed batch box and already liked it above.
Fire clays need temperatures around 1000°C or above to sinter.
It is not possible to fire fire clays to ceramic in a campfire.
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Post by firewatcher on Sept 20, 2016 10:17:41 GMT -8
Bentonite has an extremely high water demand and is thus very prone to cracks. I have found the rammed batch box and already liked it above. Fire clays need temperatures around 1000°C or above to sinter. It is not possible to fire fire clays to ceramic in a campfire. Here is a picture of the bag of fire clay that I've been using...  I can't find any information on their site as to what kind of clay it is or what it's content is. |
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