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Re: [hobbicast] Re: homemade refractory

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  • michael.a.porter@comcast.net
    Steve, Perlite is super light, insulating, and able to bear weight (so long as the load is spread evenly over its surface). However, no it isn t springy ; for
    Message 1 of 19 , Jan 23, 2011
      Perlite is super light, insulating, and able to bear weight (so long as the load is spread evenly over its surface). However, no it isn't "springy"; for that you need vermiculite. On the other hand, metal shells expand from heat faster and further than any refractory tapped within them.

      ----- Original Message -----
      From: Dan Brewer <danqualman@...>
      To: hobbicast@yahoogroups.com
      Sent: Mon, 24 Jan 2011 03:19:48 -0000 (UTC)
      Subject: Re: [hobbicast] Re: homemade refractory

      Portland cement is hygroscopic. This means that it never releases all of
      the moisture in it and kin fact it will trap moisture. So every time you
      heat this furnace do it slowly.
      Dan in Auburn

      On Sun, Jan 23, 2011 at 7:07 PM, Steve Squier

      > Thank you for your comments, wow the experience and education in this group
      > is amazing!
      > I wondered if what you're talking about isn't the purpose of the perlite.
      > It seems this is light enough to give an insulation quality, and soft enough
      > to perhaps allow for heat expansion- but these are just guesses.
      > Steve Squier
      > Sent from my iPhone
      > On Jan 23, 2011, at 6:57 PM, "Lyle" <CREEPINOGIE@...>
      > wrote:
      > The 28 days is the accepted period of time for it to reach it's design
      > strength. In actuality, concrete continues to get stronger way beyond the 28
      > days. We'd ram up test cylinders and break them after 3 days, 7 days, 28
      > days, etc. to see when we can put construction traffic on a section of
      > roadway. Usually we'd see 3000 psi within a week.
      > When making a refractory, make sure you only add enough water to ram the
      > mix between the inner and outer forms, You don't want to be able to pour it
      > at all. It should almost feel too dry.
      > I might add the air entrainment has a lot to do with how the concrete can
      > handle differences of temperature. The air forms little micro-pores that
      > acts as a stress relief for thermal expansion. How to do this in a
      > refractory is a good question and I believe most commercial refractors have
      > this built into their system. On a construction project, we'd shoot for
      > about 6% by volume and tested it right at the site. The air entrainment
      > chemical is derived from a certain tree sap although there's more than one
      > additive.
      > I've never made homemade refractory, but the last bag of commercial I
      > bought was about $80. Ouch.
      > --- In hobbicast@yahoogroups.com , "Don"
      > wrote:
      > >
      > > Steven,
      > > According to Widipedia:
      > >
      > > Type I Portland cement is known as common or general purpose cement. It
      > is generally assumed unless another type is specified. It is commonly used
      > for general construction especially when making precast and
      > precast-prestressed concrete that is not to be in contact with soils or
      > ground water. The typical compound compositions of this type are:
      > > 55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0%
      > Ignition loss, and 1.0% free CaO.
      > > A limitation on the composition is that the (C3A) shall not exceed
      > fifteen percent.
      > > Type II is intended to have moderate sulfate resistance with or without
      > moderate heat of hydration. This type of cement costs about the same as Type
      > I. Its typical compound composition is:
      > > 51% (C3S), 24% (C2S), 6% (C3A), 11% (C4AF), 2.9% MgO, 2.5% (SO3), 0.8%
      > Ignition loss, and 1.0% free CaO.
      > > A limitation on the composition is that the (C3A) shall not exceed eight
      > percent which reduces its vulnerability to sulfates. This type is for
      > general construction that is exposed to moderate sulfate attack and is meant
      > for use when concrete is in contact with soils and ground water especially
      > in the western United States due to the high sulfur content of the soil.
      > Because of similar price to that of Type I, Type II is much used as a
      > general purpose cement, and the majority of Portland cement sold in North
      > America meets this specification.
      > >
      > > (Probably more info that you wanted, but hey...cut and paste is easy!)
      > >
      > > As for fireclay, try one of your brick or concrete block
      > manufacturers/dealers in your area. Here in Raleigh, NC, I called around to
      > a couple of each and found they have it in stock for about $15 per 25lb.
      > bag. It is not usually a product that will be carried in your home supply
      > depot... and there is a BIG difference between bentonite and the fireclay. A
      > wiki search will provide you with a wealth of information about both.
      > >
      > > The problem I see with bentonite (others, please correct me if I am
      > wrong...) is that it will capture and hold water until it evaporates or is
      > driven off by heat. Concrete needs free-water in order to start and complete
      > the chemical process of curing. (Concrete does not "dry" to become hard, it
      > "cures" through a complex chemical formula that entrains some of the water
      > in the process) Therefore, the water that you added was absorbed by the
      > bentonite before it could activate and sustain the chemical process
      > necessary for the concrete to cure. It takes 28 days for the curing process
      > to complete and for concrete to reach its maximum density/strength even
      > though it seems hard as...well concrete... after only a couple of days, it
      > is still undergoing the curing process of combining water into this matrix
      > that will eventually be a very hard substance.
      > >
      > > Hope this helps a little...
      > > -DON-
      > >
      > > --- In hobbicast@yahoogroups.com , STEVEN
      > SQUIER wrote:
      > > >
      > > > Now this concerns me.
      > > > �
      > > > First, when I was at the hardware store, I was looking for a bag that
      > indicated TYPE I, II like is in the phote where I got the recipe.� When I
      > got there, I found only either one or the other.� I have no clue (nor did
      > the in store help) what the difference is, so I went with the WHITE TYPE I.�
      > Does anyone here know the difference, and if it will be a factor in our
      > applications?
      > > > �
      > > > Secondly, the site where I found the recipe had a side note that hinted
      > about bentonite but indicated the aurthur was not able to obtain any in his
      > location.� I already had the bentonite, so I used that as I cannot find
      > anything called fire clay in my area.� Does anyone know if that will make a
      > difference in the refractory?� I mixed it as per the instructions- adding
      > the first three components (minus the clay) and adding the water to mix it
      > well.� Then added the clay (and more water as needed to make a thick mix) to
      > complete the refractory.� I hope that the portland already soak up enough
      > water for it's curing before I added the clay, but I have little knowledge
      > on how these things work.
      > > > �
      > > > It's a learning process- if this one doesn't work, I already have the
      > one from the website constructed in sonotubes and waiting for another try at
      > the home made refractory.� The one I built last week is just a 12" tube with
      > a 8" tube inside with a 2" bottom.� I added a wood dowel in the bottom to
      > make a hole in case of crucible failure (something I found in another
      > website).
      > > > �
      > > > All suggestions are most welcome.
      > > > �
      > > > Thanks again
      > > > Steve
      > >
      > [Non-text portions of this message have been removed]

      [Non-text portions of this message have been removed]


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