Can anyone tell me the coverage, square inches at what thickness, for a bag of Kast-O-Lite ? 

Depends upon the size of the bag.

And thickness of the application.

The density is listed as 95 to 105 lb/ft^3, so you should be able to figure it out from there.

On 5/23/2019 at 3:02 PM, jwmelvin said:

The density is listed as 95 to 105 lb/ft^3, so you should be able to figure it out from there.

You must have been misinformed, jwmelvin.................I don't have enough toes and fingers to do that kind of math, but thanks anyway. 

To the other questions:  I'm building a forge that will end up with a 7"x7"x12" interior. (after I apply the 2  1/2" soft firebrick to all the walls.)  Wayne says I need 2 "bags" (no comment on weight) at $15 each to coat a Freon tank forge.................but I've explained to him several times that's not what I'm building.  I'm just trying to figure out how  "far" the two bags he's offering will go in coating the inside of my forge.   I'm trying to find the coverage in how many square inches at what thickness.

4 minutes ago, Chris C said:

a 7"x7"x12" interior

One difficulty in calculating is that the area gets smaller the thicker you make a coat; also, the corners would represent overlap so you overestimate. But let's use those dimensions to reach a conservative number. Each wall is 7x12, so that is 84 in^2. Four walls means you have a surface area of 336 in^2. Let's go with a round number for density of 100 lb/ft^3 (as reported by a few places online). To cover 336 in^2 with one inch of thickness requires 336 in^3. That's the amount (in volume) you need for each inch of thickness. KOL is generally sold by weight, so we need to convert from in^3 to ft^3 and then multiply by density. There are 12*12*12 in^3/ft^3, so 336 in^3 is 0.194 ft^3, and once multiplied by the density we have 19.4 lb per inch of thickness in your forge. Wayne sells 5 lb. bags, so you would get about 1/2" of thickness out of two bags. 

My experience with KOL is that I was glad I bought extra.

My eyes crossed and smoke was coming out of my ears just reading that !   Is 1/2" thickness sufficient on top of 2 1/2" soft bricks?  I'm going to coat the KOL with Metrikote, by the way.

I have 2" of kaowool coated with about 3/8" of KOL. 1/2" should be sufficient since you're covering 2.5" of brick. And since you're going to be coating the KOL, 1/2" should be fine.

But definitely take some advice and get an extra bag just to be safe. I ordered 2 bags for when I relined my forge, and I'm glad I did. I didn't have to dip into the second bag, because I went thin on the roof of the forge, but I would have been SOL had I needed to up my thickness at all.

Wayne got back with me this evening and said he recommended at least 1/2".  I'm like you guys, though, in that it won't hurt to have the extra bag as a "just in case".

Since I'm going to have a square hole through the middle of my forge, would it behoove me to make a Plexiglas box as a form and just pack the KOL in-between the mold and the bricks so I get a uniform wall thickness..............or would that be a waste of time?  Also...................should I attach some kind of chicken wire or something to the soft brick to hold the KOL...................like plastering a wall?

The IForgeIron store has one 4# bag of Kast-o-lite in stock. The store also sells 5# bags of Kast-o-lite and 5# bags of Plastix 900F kiln wash. PM me if your interested.

Gas Forge Refractories and Supplies

I just bought a 50lb bag for whenever I get around to building my forge. Didn't want to do the math and it was dirt cheep, so just went that route. Should be plenty.

You must be making a pretty large forge, materman.  You gonna be forging punch press flywheels?????

Yes I know it was a bit much, but I couldn't pass up the cash and carry price. I figured extra setting around isn't a bad thing, and maybe once I get mine a going, someone else might want to build one and so I will have the ability to help them out.

"Pay it forward".....................always works for me.   Good for you!

1 hour ago, Chris C said:

would it behoove me to make a Plexiglas box as a form and just pack the KOL in-between the mold and the bricks so I get a uniform wall thickness

Definitely make a form. It is frustrating to try and shape it by hand. It’s not easy to get it in the thin form, so think about assembling the form as you fill it. Like plaster one wall then press the form against it as you move to the next wall. 

If you make the form I don’t think you will need any attachment between the KOL and bricks. 

Hmmmmm.  One wall at a time?  Does the KOL not have any "flow" to it?   If it does, I'd be surprised if I could do it without an actual box fabricated to hold back the KOL while it set up.

You do want a box to hold the KOL while it sets. I’m just encouraging you to think about how to get the KOL into the box as it is difficult to cram into a small space. It doesn’t flow much (depends on hydration).  I was thinking: cover floor, place bottom panel of form over KOL, place side panel on bottom panel, cover panel with KOL, flip up to push against side wall, place other side panel on bottom panel, cover with KOL, flip up to push against other side, the cover top panel with KOL and place against roof. If the top panel overlaps the sides they will hold it up. 

Great suggestion.  Thanks.