Ray Carlton on thu 29 may 97
hi all I am building a kiln [65cuft d/draft gas fired] and I am currently
bricking up the door I am using air set cement [rest of brickwork has been
done with firelay+grog mortar] and I am finding a buildup of white furry
stuff aroundf the mortar joins. I assume this is sodium silicate crystals.
I had a freind who had the same thing a few years ago and after he fired
the kiln 1st time the sodium silicate crystals had slagged badly into the
brick work. If possible I would like to avoid similar happening to my kiln.
What can be used to neutralise this material???
ray carlton.....mcmahons creek victoria australia
Kenneth D Westfall on fri 30 may 97
A scraper and a stiff brush solved it for my kiln wall. You defiantly
want to remove the crystals before firing the kiln. Those crystals will
work just like throwing in salt if you fire! It is also a indication
that you may have used to much water in the cement or you wet the brick
to much before laying them. What ever you do don't use a wet sponge or
cloth to wipe them away!
Kenneth D. Westfall
Pine Hill Pottery
potter-ken@juno.com
Don't get stuck in the mud pies K&T
Vince Pitelka on fri 30 may 97
At 11:24 AM 5/29/97 -0400, you wrote:
>----------------------------Original message----------------------------
>hi all I am building a kiln [65cuft d/draft gas fired] and I am currently
>bricking up the door I am using air set cement [rest of brickwork has been
>done with firelay+grog mortar] and I am finding a buildup of white furry
>stuff aroundf the mortar joins. I assume this is sodium silicate crystals.
>I had a freind who had the same thing a few years ago and after he fired
>the kiln 1st time the sodium silicate crystals had slagged badly into the
>brick work. If possible I would like to avoid similar happening to my kiln.
>What can be used to neutralise this material???
>
>ray carlton.....mcmahons creek victoria australia
Ray -
This can be a serious problem, and I think that lots of kiln-builders use
refractory mortars which are not really rated high enough for a cone 10
kiln. I have experienced a little of what you describe even with APGreen
Sairset, which is what APGreen usually recommends for general-purpose kiln
mortar. I have had much better luck using APGreen Greenpatch-421, thinned
with water to a creamy consistency. It works great, and still air-sets just
fine, and it will not eat away at the brick, because it is much more
refractory than Sairset.
But that does not help you now. When I used Sairset the last time, I
sponged the entire inside surface of the door generously with water, which I
imagine helped dissipate any accumulated soluble flux, and then coated the
inside of the door with a 50-50 alumina-kaolin wash. It worked very well,
and has needed no further coatings after two years of use.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Vince Pitelka on sat 31 may 97
>A scraper and a stiff brush solved it for my kiln wall. You defiantly
>want to remove the crystals before firing the kiln. Those crystals will
>work just like throwing in salt if you fire! It is also a indication
>that you may have used to much water in the cement or you wet the brick
>to much before laying them. What ever you do don't use a wet sponge or
>cloth to wipe them away!
Just to clarify what might seem like a contradiction between my advice and
Kenneth Westfall's, if the surface is allowed to dry and crystals form, you
should certainly follow this advice, and brush off the crystals before
firing the kiln. But when you initially finish assembling the bricks, go
ahead and wipe down the surface with a wet sponge. It gives a nice finish
to the mortar joints. It is of course essential that you wet the bricks
before mortaring them together, as most air-set cements rely on the
retention of moisture in order to develop maximum strength. If the bricks
are not wetted adequately, they will draw off the moisture from the cement,
preventing proper airsetting. I have always immersed the softbrick quickly
in a bucket of water. I believe it was APGreen that originally suggested
that. So, as the water evaporates from the surface, it is bound to carry
some soluble materials with it and deposit them as crystals on the surface.
I have always believed that this is completely normal and expected, unless
you use a plain fireclay-grog/sand mortar, or if you wet the bricks
inadequately.
- Vince
Vince Pitelka - vpitelka@DeKalb.net
Phone - home 615/597-5376, work 615/597-6801
Appalachian Center for Crafts
1560 Craft Center Drive, Smithville TN 37166
Ray Carlton on sun 1 jun 97
At 11:09 AM 30/05/97 EDT, you wrote:
>----------------------------Original message----------------------------
>A scraper and a stiff brush solved it for my kiln wall. You defiantly
>want to remove the crystals before firing the kiln. Those crystals will
>work just like throwing in salt if you fire! It is also a indication
>that you may have used to much water in the cement or you wet the brick
>to much before laying them. What ever you do don't use a wet sponge or
>cloth to wipe them away!
>
>Kenneth D. Westfall
>Pine Hill Pottery
>potter-ken@juno.com
>Don't get stuck in the mud pies K&T
>
>mmmm opposite advice to vince pitelka
any else want comment??
Ray Carlton McMahons Creek Victoria Australia
raycarlt@ozonline.com.au
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