: Pres - Viewing Profile

A tip or two for ya' on kiln building and design............

One of the common causes of cold floors on kilns revolves around the mistaken understanding that so many people have that "heat rises". That preception being some sort of a "law" comes from our experiential understanding of our lives....where we experience that HOT GASES rise (like in heated structures). Hot gases rise when suspended in colder gases. Heat energy....... not true.

This mis-understanding is a core concept that I deal with in my Kiln Design and Construction classes.

Heat energy ALWAYS moves from areas of higher concentration to areas of lower concentration. Basic law of thermodynamics. Entropy. Water flows downhill. (Yes... a heat pump can move heat energy seemingly "uphill",...... but that is a separate subject.)

If you want the kiln to fire as evenly as possible using as little fuel to accomplish that feat as possibe........ make sure you don't under-insulate the floor. Otherwise you'll have to adjust the heat DISTRIBUTION pattern in the unit to send more of the overall energy into the floor area than otehrwise necessary.... some of which to also be lost out of the underinsulated floor..... and costing you money in every firing.

So if you decide that the walls and roof structure of a kiln has to have a specific insulation value (heat loss in BTS/ Sq. Ft. / hr.) then the FLOOR should have the same level of insulation. (See * note below also) So if your walls are 9" of brickwork compoised of a 4 1/2" hard brick hot face layer, backed with a 4 1/2" insulating brick layer (of some specific use temp rating) then the floor should also have about this same rating overall.

This can be a little different due to the typical layout of floor bricks being set in the 2 1/2" high layer and the walls being in the 4 1/2" format..... but you CAN lay floors with the brick set in the same (or similar) configuration. The common choices to "match" up to a 9" wall section oftten comes to a decision between a 7 1/2" thick floor and a 10" thick floor. If you understand the insulating values of refractories, you can achieve the SAME insulating value (BTU / Sq. Ft / Hr. conductivity) out of a thinner floor wall section than the side wall structure using DIFFERENT materials........ so the thickness is actuall irrelevant.

The important concept is that the INSULATING value be similar.

The old Rhodes book showing so many 5" thick hardbrick floors in kilns is responsible for SO many kilns with cold bottoms it is amazing. This is something that I commonly end up fixing on a kiln when I am called in to troubleshoot some kiln firing issues.

And if you decide to use fiber in the floor area........ make sure not to compress the fiber too greatly (difficult in a load bearing situation). The more you compress the dead air spaces... the more the loss of insulating value. There is an optimum level of compression for fiber...... used in stuff like Z blocks. Best (easiest) to use "hard versions" of fiber for floors....like board forms.

best,

......................john

(*NOTE: Because there is typically less free air circulation across the cold face of the floor structure, technically the amount of heat energy disappated into the surrounding environment off the cold face is lower than on the vertical wall surfaces and off the roof or arch. So the BTU /Sq,. Ft. / Hr. loss values there is slightly less than the same construction in a wall or roof. But this factor is so small in the overall picture ...as to be inconsequential.)

Today I had five people ask for 'honey pots'.

Ignoring the obvious smart-arse potential, I figured out that they meant 'medium sized jars with an aperture in the lid'.

I had none. Nor do I plan to make any. Oh well...

Marcia Selsor, on 19 May 2013 - 10:07 AM, said:

Thanks, I'm just having fun. The only stress I have is my rooster with 3 inch spurs keeps hiding in bushes so he can jump out and stick a spur 2 inches into my leg while I'm carrying a wareboard full of mugs to the kiln. But I am a bit concerned about you. The last time I was in school semesters were quarters.

Jim

Dear All,

I just wanted to let the group know that I just went out to my studio to glaze a large batch of pots using my Arbuckle glaze. Not sure what happened but am guessing that I put in too much water in during the initial mixing as it was pretty runny. It would not adhere without being transparent on the pot even with a 5 second dunk.

At the point of me using this glaze, it has sat for about two month and has been sieved twice. It was mixed well today before I started to consider alternative ways to thicken the mixture.

To make a long story short, the addition of just a small amount of epson salts mixed with some glaze (in the same way you would thicken a soup) worked beautifully. I added it bit-by-bit and voila, it passed the glove or finger nail test.

While there are still some drips on my pieces from my dunking technique, I know I can work with them.

I learned this technique on THIS forum. Thank you to who ever posted this information. I think someone once mentioned using molasses but am not sure how this would work.

No need to respond. I just wanted to let the group know that valuable information is transmitted on this forum that I DEFINITELY USE.

Nelly

mmhpottery, on 17 May 2013 - 04:48 PM, said:

I should add that I also pack a separate "artist card" which is like a business card but without any contact info other than my website. This card contains my short artist statement and the "dishwasher, microwave safe" language. I keep them in a stack on my checkout table so customers can take them, and I also pack them with the sold pots. That way I don't have to squeeze that info onto the hang tags. The hang tags only say my company name, plus the name of the pot.

Mea