Bede Clarke on tue 17 jun 97
Can anyone share experience with wood kiln floors on concrete block
foundation - top layer of concrete block is set up to promote air flow
through it. Does one 2 and 1/2 inch layer of IFB topped with 2 and 1/2
inches of hard brick sound adaquate? I realize another layer of IFB would
be good insurance in this situation, but of course there is the price of
the brick. Thanks. Bede
Bede Clarke bclarke@showme.missouri.edu
A126 Fine Arts Bldg., University of Missouri
Columbia, MO 65211
hm.(573)443-0362
o. (573)882-7120
fax. (573)884-6807
David Hendley on tue 17 jun 97
I have 3" thick hard bricks on top of my cement blocks. Like you, I
layed the cement blocks the "wrong" way, to promote air flow under the kiln.
No problems after 5 or 6 years... My kiln is a modified "fast fire", and
VERY hot beds of coals build up on the brick floor.
David Hendley
Maydelle, Texas
Louis Katz on tue 17 jun 97
The Archie Bray Foundation had a salt kiln on two layers of Hard Fire
Brick for fifteen years before the cinder block underneath gave way.
Louis
Louis Katz
Texas A&M University Corpus Campus
lkatz@falcon.tamucc.edu
http://www.tamucc.edu/~lkatz
Vince Pitelka on wed 18 jun 97
At 12:31 PM 6/17/97 -0400, you wrote:
>----------------------------Original message----------------------------
>Can anyone share experience with wood kiln floors on concrete block
>foundation - top layer of concrete block is set up to promote air flow
>through it. Does one 2 and 1/2 inch layer of IFB topped with 2 and 1/2
>inches of hard brick sound adaquate? I realize another layer of IFB would
>be good insurance in this situation, but of course there is the price of
>the brick. Thanks. Bede
Hey Bede -
First of all, I do not believe in placing any courses of foundation blocks
on their sides. Concrete blocks today are incredibly brittle, and I do not
believe they have the strength to support a kiln if placed on their side. I
like to place them with the holes facing up, surfaced with a course of cap
blocks, which are solid concrete and come in 2", 3", and 4" thicknesses. I
like to dust a mixture of portland cement and fireclay on the slab beneath
the first course of blocks, between each course of blocks, and beneath the
cap blocks. On top of that, I think that one course of softbrick and one
course of hardbrick is adequate. It has always worked well for me. The
softbrick has pretty amazing insulating capabilities, and will prevent the
concrete from getting too hot.
- Vince
>
>Bede Clarke bclarke@showme.missouri.edu
>A126 Fine Arts Bldg., University of Missouri
>Columbia, MO 65211
>hm.(573)443-0362
>o. (573)882-7120
>fax. (573)884-6807
>
Vince Pitelka - vpitelka@DeKalb.net
Home 615/597-5376, work 615/597-6801, fax 615/597-6803
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
George VanOstrand on thu 19 jun 97
Bede,
Our woodkiln was designed by George Lowe and has two layers of hard
brick on top of the cement block. Works fine. Not sure about the IFB but
should provide a much better heat barrier. What surprised me was that the
fire box floor, which is lower than the floor of the kiln, is on the
concrete pad without any protection by a firebrick layer. It works fine! No
cracking of the cement. the pad is reinforced by a steel mesh and some
other metal rods.
George VanOstrand
gvanostr@julian.uwo.ca
London, Ontario
Paul M Wilmoth on thu 19 jun 97
Dear Bede,
I have always used two layers of IFB then one layer of hard brick
for the floor of any kiln(wood & salt & high fire gas). I have built and
fired over twenty kilns (four wood fired) and have never had any
problems. Don't fool around and try to save money on this one, you may
end up rebuilding the whole kiln after you replace the cement block.
Good Luck -- Paul Wilmoth
Sheila Clennell on fri 20 jun 97
>----------------------------Original message----------------------------
>At 12:31 PM 6/17/97 -0400, you wrote:
>>----------------------------Original message----------------------------
>>Can anyone share experience with wood kiln floors on concrete block
>>foundation - top layer of concrete block is set up to promote air flow
>>through it. Does one 2 and 1/2 inch layer of IFB topped with 2 and 1/2
>>inches of hard brick sound adaquate? I realize another layer of IFB would
>>be good insurance in this situation, but of course there is the price of
>>the brick. Thanks. Bede
>
Hey Bede: Sounds like an OK floor to me. I have built many wood kilns with
concrete blocks on sides so that air can flow through. My last wood kiln
was two chambers with almost 10,000 bricks all nicely supported by concrete
blocks as you have described. We then used a layer of common brick , then
two layers of hard brick so I think the hards and softs would do a great
job.
Long may your chimney smoke!
Tony
Sheila and Tony Clennell
Gleason Brook Pottery
Box l0, RR#2,
Wiarton, Ontario
NOH 2TO
Canada
Phone # 1 (519) 534-2935
Fax # 1 (519) 534-0602
E-mail clennell@bmts.com
John Baymore on fri 20 jun 97
------------------
------------------------------------------------------------------------
=3Cclip=3E Can anyone share experience with wood kiln floors on concrete =
block
foundation - top layer of concrete block is set up to promote air flow
through it. Does one 2 and 1/2 inch layer of IFB topped with 2 and 1/2
inches of hard brick sound adaquate? =3Csnip=3E
-------------------------------------------------------------------------
Bede,
A little while back we had a discussiobn about heat flow through materials.
Check the archives. Some fundamental concepts are explored there.
Heat flows from areas of higher concentration (hot face of brick) to areas
of lower concentration (cold face of brick). The driving force for this is
the differential in temperature between the hot face and the cold face.
The composition (K value) and thickness of the materials that the heat has
to flow through determines the amount of heat passed through the wall.
Dis-similar construction will result in varying rates of transmittance in
various parts of the wall, and a non-linear temperature gradient withing
the wall..
If the hot face of the floor is assumed to be at 2300F (like the walls and
arch), then the same amount of heat will go DOWN through the floor as goes
sideways through a wall and up through the arch. Heat does NOT rise. Hot
gases rise. If you plan to fire the floor area of your kiln to the same
temperature as the top (which I assume you do =3Cg=3E), then the driving =
force
to move the heat through the floor walls will be the same as in other areas
of the kiln.
(There are a few minor other factors invloved in the actual
construction..... but that concept is pretty fundamental.)
The formulas are availible to do these calculations from companies like AP
Green. (Unless you want to spend a lot of time, assume =22steady state=22
conditions....... inside at a constant temp, and outside at constant
temperature.) Run the math on a hot face of 2300F and a cold face of say,
200F through 2.5=22 of HB backed with 2.5=22 of 2000 degree IFB, and then
compare with the figure (in BTU/ sq. ft./hr.) for your side walls and arch.
You will then understand why the floor has to be just as well insulated as
the walls.
As another interesting note.......... you also need to keep track of the
interface temperature in walls made of varying materials............ it is
possible to construct a wall where you exceed the use rating of the backing
insulation materials. But that's another subject altogether.
In your case, you also need to be concerned about allowing too much heat
through the floor refractories, since the concrete blocks will deteriorate
and get brittle and start cracking. Calculate the interface temperature
between the outer surface of the 2.5 IFB in your proposed floor (2.5=22 HB =
+
2.5=22 IFB) and the 1=22 thickness of concrete (typical) that might be in
contact with the blocks laid sideways. Where the =22columns=22 of the block
are the concrete will be thicker..... retaining more heat and increasing
the interface temperature. Basically, it'll get pretty HOT=21=21=21 Hotter=
than
concrete is intended to be.
So those air holes lined up will be necessary to cool things down for sure.
However, what you are cooling down is heat energy which is escaping from
your chamber=21=21=21=21=21=21=21 I don't think you really want that heat =
to get out in
the first place.
So...... as a professional kiln builder of 20+ years....... nope. That
floor configuration is not adequate. In my opinion the MINIMUM
configuration would be 2.5 =22 of K20, topped with 2.5=22 of G23, topped =
with
2.5=22 of high-duty hard brick. If your construction techniques are really
good, you can JUST go with 5=22 of K20 and 2.5=22 of HB (just make sure =
there
are NO cracks open to let the backup 20's just behind the hot face HB layer
get too hot=21) The 2000F rating is for continious duty.... so there is =
some
margin there.
Preferable to that would be to top the hot face with Greenlite 28's coated
with a sealing coating like ITC 100. Then the second layer can easily go
to K20's also. The Greenlite 28 is a good comprimise between density and
hardness for a working surface, with a far better insulating value than HB.
The Greenlite 28's would not be suitable in the actual firebox floors. The
physical abrasion of the wood landing there, the action of the volitiles
from the wood ash, the slagging action of the ash melting, and the extreme
reducing conditions would cause the brick to deteriorate more quickly than
you would want. There you want to use hardbrick....... preferably
something better than typical high duty........ like maybe KX99's.
You will see plenty of kilns built with just 5=22 of HB as floors (thanks to
Rhodes =22Kiln's=22 book =3Cg=3E). That doesn't make if good practice.... =
it just
means that the kiln was built without regard for the heat loss through the
floor. So they waste heat. In worst cases, they cause the concrete to
fail. In these kilns, there has been an adjustment in the design, the
burner placement, the =22bag walls=22, and/or how the kiln is fired to =
direct
more heat to ther floor area to compensate for the greater heat loss and
the tendency caused by this for the floor area to fire colder.
I have built many kilns directly in the ground with =22dirt=22 for floors. =
NO
BRICK. It works. Plenty of climbing kilns are built this way. However,
in this case the floors tend to lag behind in temp...... the kilns do fire
unevenly. That is part of the effects desired..... and it is worked with.
Plus the moisture (and soluble materials) =22wicked=22 into the kiln from =
the
ground water is considered by a number of Japanese potters I have talked
with to be an essential part of the proper maki-gama (wood kiln) design.
(Got into a long discussion about this concept with Sato-sensei while I was
in Mashiko.)
With enough wood fuel input, you can compensate for the cold areas at the
peak and bring them up..... hence one factor in the LONG firing cycles in
larger anagama and noborigama kilns. But the heat penetrating into the
dirt floor is just going deeper into the earth....... not deteriorating
supporting concrete=21 So if labor and wood is cheap..... no big deal.
Do yourself a favor and insulate the floor well.
Best,
..........................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086
603-654-2752
JBaymore=40Compuserve.com
Tracy Dotson on sat 21 jun 97
Indeed concrete hollow blocks are stronger sitting with the holes up but
through experience I have always used them sidewise to keep any heat away
from a concrete slab floor under the kiln. There has been alot of discussion
about "heat" lately and the direction it travels which is "all" directions.
I now put just as much insulation in the floor as I do the walls. 5 inches
of insulation fire brick (IFB) usually 2300, covered with a good firebrick
for strenght. I question the use of fiber blanket below the brick in your
kiln. Blanket is a hot face material, reflecting heat to the interior of the
kiln. Even if you use this blanket under the brick floor, it will work but
since it will be compressed you will loose much of its insulation guality.
Price wise a layer or two of the IFB would be cheaper and stronger than the
blanket. Your suggestion to use the blanket and the hollow concrete blocks
will work. If you have not ordered the materials yet, check to see if it
would be cheaper to use the IFB in the floor.
Good luck
Tracy Dotson
The Pottery
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