Castable Refractory Products (VT600)

[TARibs]

I am looking at casting a dome for my Oven. Checking sources for Fireclay I came across a place called Smart Ceramics in Woburn MA, (they apparently have changed their name to Rubix Composites) They told me the have a Castable refractory product called VT600. Has anyone ever heard of it. I'm not sure what it is exactly but suspect it is a castable cement product and from reading the Forums (Particularly david S ) I believe it would need to have crashed firebrick or some other suitable aggregate added to it. I've asked them if they have a spec sheet on it so I can get more information.

Also while I'm here when someone mentions casting the dome do you recommend using the home mix to do that or is the home mix really for the using between bricks on the brick ovens?

Thanks
Tom

[david s]

There are heaps of castable refractory products out there. If it is CAC (Calcium Aluminate Cement) then it should be labelled as such. If it is called castable refractory it should be the bagged product containing CAC, high temperature aggregates and usually with burnout fibres added which assist in water elimination more safely. There are generally two types, an insulating castable which should only be used as insulation as it won't provide the thermal mass required and results in too weak a casting unable to withstand wear and abrasion. The other type is the dense castable more suited to hot face service which is also more suited for an oven the density is in the region of 2000 kg/m2 or 2 kg/litre. Castable refractory is superior to making your own castable from home-brew, but way more expensive. If making up your own castable you should add some burnout fibres like the very fine polypropylene ones (not the thicker/longer nylon ones) used in some concrete random fibre reinforcing.

[TARibs]

Thanks for that info David, This is what they sent me

"We do not sell fireclay, however we do have an overstock castable refractory product, called VT600 for $15 per 55lb bag.

Mortar:
Heat Stop 50, Outdoor Hydraulic Setting Refractory Mortar, 50 lb bag - $68 each
3000°F Premixed Refractory Mortar, 55 lb pail - $68

at $15 for a 55 lb bag it sounds like it might be ideal.

How thick do you think I would need to make the dome if this product is what you say? And again based on what I read here it sounds like its better to do it in multiple pours (which would seem to be easier as well)

[david s]

Check it’s density., it should be heavy like a bag of cement if it’s the dense type. at $15/ 55 lb bag it’s very cheap. Also check it’s date of manufacture. Don’t use it if it’s gone lumpy. Also don’t mix more than half a bag at a time as the stuff goes off very quickly. 2” thick is the normal thickness and that gives you enough thermal mass for good cooking. Use a 2” thick floor of firebricks laid loose. The simplest way to go is to cast the dome in situ over a sand mould on top of the firebrick floor bricks. Don’t forget to insulate under them.

[wotavidone]

Chaps, I believe if this is Morgan Ceramics CEASE-FIRE VT 600, then it is a refractory expanding foam for high temperature insulation. Looks damned good for that use.

Here is the SDS for C-F VT 2000, C-F VT600
http://msvsc03-g735nw.uv.netbenefit....?id=3105&lang=

Here is the data sheet for VT 2000
http://www.matweb.com/search/datashe...9f76bc2&ckck=1

[wotavidone]

Note, if the stuff they are offering you is the insulating castable it is gunned in place, with phosphoric acid added at the nozzle to provide the reaction for the formation of the foam.
As david s says, castables are usually CAC plus aggregates. I would guess that in this particular product the aggregates would be very small size so as to promote and assist the foaming.
If I were in driving distance of that supplier, I would be sorely tempted to grab one $15 bag, mix some and make a trial cast without the phosphoric acid. Seems to be a mix of alumina, silica and CAC, without the air bubbles it might be a good dense castable.
So I'd fill a 1 litre container with it, let it set, and weigh the finished product to determine density. Hopefully the un-foamed 1 litre casting would weigh at least 2kg. Then I'd hit the casting with a hammer to see if I thought it strong enough.

The phosphoric acid would also contribute a phosphate bonding mechanism to the set, you'd have to find out if it still works without it. Though the SDS says it has "cement alumina chemicals" in the range of 10-55% so it should set well anyway.

Gunnables are mixed fairly runny, I think, so it might be a good candidate for a double sided mould that can be poured rather than just packing it over a sand mould.

[david s]

Tom, I'm not sure that your product is suitable, you may need to get further advice from the manufacturer. There are many different products available (must be hundreds) from a number of different manufacturers. The product I use and have been using for ten years is called a standard duty gunnable dense refractory castable, with aggregate size max 4mm. max service temp 1450 C, and it is also suitable to be applied by trowelling. But that does not mean the product you are being offered is also. You can, as Wotavidone has suggested, buy one bag and try it out. For most castable refractories the suggested water content as tested in the lab, is way too low for practical application. For my product it is 12.5 %, but that results in a mix too dry for trowel application. A gunning mix would have an even higher water content so just mix it to a consistency that is nicely workable. Any type of concrete mix is weakened if the water content is increased too much because the water simply increases volume and hence reduces density.

[TARibs]

So I am easily within driving distance and they've offered me a bag to try for nothing, so I'm going to see what it does, he said it is between a dense and insultating castable so not sure if will do what I need, Not even sure how I tell after I cast it? Going to see what information I can get on it as well.

[TARibs]

It looks like wotavidone may be correct, it is at least made by Morgan Ceramics but has very few marking on the bag. I went over and grabbed two bags (he gave them to me for nothing), turns out I played Soccer\Football with the owner of the place. He's going to look for more specs on it and send them over to me. He did tell me he's made castings out of it before (didn't say if they were poured) so I suspect it doesn't need the phosporic acid to bind. He gave me a few pieces of scrap firebricks (thin ones that were easy to break into pieces) as well. I figured I could crush it up (sieve out the dust) and add it to some of the mix and see what that does for the density? Now if I can't use for the dome would it work for an insulating layer (either underneath or on top), suggestions on how I can tell?

So spec sheet is attached, Looks a bit light density wise listed as 37pcf comes out to only .59 kg/cul would adding the crushed Firebrick to it improve it?? Temp rating is 1093C for continuous use though. So what would happen if I used it? Would it just not retain heat very well?

[david s]

The quoted density of 0.59 kg/ L would be the density of the resulting fluffed up product. If just mixed with water it should be far denser. But do check to find out if it’s also trowellable

[TARibs]

What about the idea of adding the firebrick to it? I was planning on making a trial casting both ways just to see what each was like? Would suggest pouring it into anything in particular to test it. Owner suggested starting with an 88:12 by wgt powder:water. He said he had made successful castings with it before but not sure for what. When you say trowelable, in what sense.

[david s]

Trowellable or “ball up “ consistency. Ie take a handful about the size of a cricket/tennis ball and throw it about two feet in the air. It should stay together. I would try mixing some and filling a cardboard milk container with the top opened right up(if you have those) waiting 24 hrs to cure then ripping off the container then you can weigh it. Cardboard is easier to remove than plastic, An ice cream container is another alternative. As the aggregate is already in the product the addition of more is unneccessary. But if you really want to you could, but no more than about 20% of total volume otherwise you’d need to add more CAC to balance it. Discard any dust because you risk weakening the mix. Also dampen any added firebrick aggregate before adding to the mix. It should be graded but nothing bigger than about 6 mm

[TARibs]

There is no aggregate in the product it is just a powder like cement hence the question about adding some to increase the density.

[wotavidone]

Slurry consistency = 66% solids on that data sheet. 34% water would be quite runny. It would be much more water than is required for the cement in the mix.
The conventional wisdom is that excess water compromises final strength.They must be assuming it won't require much structural strength, hence the 0.28 MPa compressive strength.
Owner's recommendation would supply enough water for the cement reactions, I'm guessing, so good strength.

If you don't want to just use it as is, which you could do given how cheap it is, I vote you mix a small portion of this about 1:1 with some 1/4 inch crushed aggregate for a trial.

I'm not entirely plucking that number from thin air, though it is all guess work.
My reading of the SDS suggests this stuff is about 1/3 "cement alumina chemicals".

(if you add up all the other materials in it, their maximum values total about 81%, so it is at least 19% cement I think, so 30% is probably a safe number.)

Let's assume the rest is "fine aggregates"

A pretty standard Portland cement based concrete in my part of the world is what we of a certain age refer to as "3:2:1 Government mix"
3 gravel, 2 sand, 1 cement. i.e. a paste of cement and sand coats and holds together an equal volume of gravel.

1:1 of this VT600 mix and gravel, assuming it is 1/3 cement and 2/3 fine aggregates, would give 3 parts gravel:2 parts fine aggregate:1 part cement.
At least it would be a starting point.

Pour it, cure it hit, it with a hammer. Then hit it with some serious heat.

[david s]

Slurry consistency = 66% solids on that data sheet. 34% water would be quite runny. It would be much more water than is required for the cement in the mix.
The conventional wisdom is that excess water compromises final strength.They must be assuming it won't require much structural strength, hence the 0.28 MPa compressive strength.
Owner's recommendation would supply enough water for the cement reactions, I'm guessing, so good strength.

If you don't want to just use it as is, which you could do given how cheap it is, I vote you mix a small portion of this about 1:1 with some 1/4 inch crushed aggregate for a trial.

I'm not entirely plucking that number from thin air, though it is all guess work.
My reading of the SDS suggests this stuff is about 1/3 "cement alumina chemicals".

(if you add up all the other materials in it, their maximum values total about 81%, so it is at least 19% cement I think, so 30% is probably a safe number.)

Let's assume the rest is "fine aggregates"

A pretty standard Portland cement based concrete in my part of the world is what we of a certain age refer to as "3:2:1 Government mix"
3 gravel, 2 sand, 1 cement. i.e. a paste of cement and sand coats and holds together an equal volume of gravel.

1:1 of this VT600 mix and gravel, assuming it is 1/3 cement and 2/3 fine aggregates, would give 3 parts gravel:2 parts fine aggregate:1 part cement.
At least it would be a starting point.

Pour it, cure it hit, it with a hammer. Then hit it with some serious heat.

When the manufacturers quote the chemical composition of their product, it is the total of all the materials contained,. They don’t like to quote the % of separate ingredients because they like to keep their recipes secret. Consequently you can’t assume a % of any material relates to the cementious content. Eg the uncalcined kaolin in the mix is around 40% alumina and 60% silica yet is not cementious. The quoted table in the data sheet is difficult to interpret, even more so as the list pops up differently on my iPad to my desktop, but 10-55% Silica and 20-25% Cement Alumina Chemicals is also an indication of the rather fuzzy data provided.
Adding an aggregate either fine or coarse, will also upset the balance of cement to aggregate as it increases the surface area for the cement to act upon, so will weaken the resulting product. Because the finer material increases the surface area more than the coarse material, the larger size is preferable, that is why the dust needs to be discarded. Extra cement should be added to compensate. It is probably safe to add some crushed firebrick because it’s fairly stable, but caution should be taken if other aggregates are selected as thermal expansion, conductivity as well as permeability need to be considered. “”"Permanent strain increases with the no. of cycles of heating and cooling indicating an increase of thermal cracking in the rock.”" ”
As wotavidone has pointed out the product is not a dense refractory castable, but an insulating one. hence may not contain the burnout fibres which will assist in safer water elimination. Try sieving some of the product to see if there are any tiny fibres contained in it. I suspect not in which case it would be wise to add some. You can use the fine polypropylene fibres as supplied in a two pack product used to reinforce concrete. Do not use the larger nylon fibres. CAC cement achieves its full strength after 24 hrs so there is no need to damp cure for an extended period, but it needs to be dry, so don't rush the water elimination by fire or you will risk steam spallling.
http://ceae.colorado.edu/~amadei/CVE...PDF/NOTES4.pdf