Sanity check: Plistix on high density ceramic fiber board?

[TommyVee]

I just bought a Diamondback series 2 (one burner) forge, having decided the price point was right and the size was good for a beginner like me --- and I could get to squishing metal more if I had one than if I spent time learning to build and tune one of my own.  The  Diamondback web site claims the sides and top of the chamber would be insulating firebrick, but when it arrived it had tops and sides clearly lined with high density fiber board instead (like their higher-end models).

Having read a bunch of articles here, it appears that everyone is agreed that coating the boards and high density firebrick floor with Plistix would be wise, and would improve performance and durability of the forge even though the manufacturer of the forge says it's not necessary.  I had decided to do so and started hunting for sources (since Glenn is out of stock).  In my hunting, I emailed Larry Zoeller about whether he had any in stock, and casually asked if it was appropriate to apply this to HD ceramic fiber board.  He replied:  "It will not bond to the board.  The only thing that I know that will bond with the board is Unifrax QF-180 or QF-180 Blue."

I already have a package of the stuff incoming from some *other* source, and given the number of times I've seen it stated categorically on this forum that Plistix is an excellent addition even to HD ceramic board, I'm inclined to give it a go despite this discouraging reply.

But can anyone corroborate or contradict Larry's statement?  I know several folks here even have Diamondback forges with the fiber board refractory and used plistix on it --- how has it held up for you?

[TommyVee]

Quote

fiber board refractory

I *meant* to say "fiber board insulation"

 

[Frosty]

I don't know how Larry applied Plistex to fiber board or more likely the person who's testimony he's relying on did it right. 

I've never opened a new box, piece, etc. of fiberboard so I don't know if it's dusty or nice and clean. Regardless applying ANY kiln wash or mortar/cement to a dry surface is dicey at best. What happens is the dry surface draws moisture right out of the kiln wash (or whatever) leaving a thin layer of uncured DRY powder between the underlayment and wash. The kiln wash can't bond well and so size change with thermal cycling causes it to crack and flake off.

Buttering the underlayment, wetting it first works by diluting the contact layer causing it to flow into nooks crannies or along fibers to intersections. This way when it cures and later fires it can bond TO the underlayment rather than just stick to it. Buttering is a mason's term and technique that's probably as ancient as mortared stone. Heck even sticking a handle on pottery wants a little buttering.

Were I building with fiber board I'd wash it with a sponge and clean water then apply the kiln wash. Mix it to a consistency like thinish latex house paint and apply it in thin layers allowing it to dry thoroughly before applying another. Remember to "Butter" spritz or wipe it with water first for the same reason as above. 

Appling a single thick coat is more likely to crack and spall from thermal cycling or shrink checking. Be patient will be rewarded.

In response to your latest post. Fiberboard is a refractory, you had it right the first time. 

Frosty The Lucky. 

[JHCC]

Try a sample in one area; if you can't get it to stick, you won't have wasted the whole thing.

[TommyVee]

Frosty and JHCC:  Thank you.  Especially regarding the wisdom of buttering and which consistency to use.  I was assuming the thin layer was the way to go, but good to have clear statement.  The guy who sold me my plistix has a video showing how to line a particular type of forge with plistix, and he does show buttering the wool liner of that forge before applying.  But he also shows mixing it into a thicker mixture and applying it more in the "trowel on" mode, but with his gloved hand instead of a trowel --- which I also assumed wasn't appropriate to my forge and its material.  Both  the issue of buttering and of consistency/manner of application were going to be subjects of a follow up set of questions. 

As for refractory/insulation, I guess the fiber board serves as both, yes?  Taking the place of an insulating firebrick in this specific design, I just assumed its primary purpose was insulation.  Still so much to learn...

[Frosty]

The manufacturer of Plistex say it's a stand alone refractory and indeed recommend applying it in different consistencies, thick like stiff plaster is fine. 

I prefer Kastolite 30 as it's locally available and reasonably priced IF you ask for our club discount. 

What we've discovered though is most furnace level refractories don't hold up as well as we'd like. Propane flame is very chemically active and erodes almost anything it impinges on. Plistex on the other hand doesn't seem to care and it's pretty impervious to caustic forge welding fluxes. 

In ceramics kilns they need something to prevent glazes and firing clay from fusing with the kiln furniture as well as improve it's useable life. Hence the name "kiln wash." Wash because all you need is a thin layer to protect the kiln. Our needs are a LITTLE different but the same products work just fine. Usually.

If you want to use his technique please let us know how it works. We're flexible in our beliefs, we adopt and adapt all the time.

Frosty The Lucky.

[TommyVee]

Nah.  I don't feel like being an innovator here.  I'm looking for guidance from people who already know what they're talking about, and I'm getting it.  Painting it on like thinish latex house paint will be what I do.  My plistix arrived in the mail today, I'll probably spend some quality time with it this weekend.  But only after I've assisted the wife with the actual latex house paint that she's been applying around the house while I'm at work all week, so that it's done before the workers come on Monday to replace all our flooring...

 

[Latticino]

Note:  While a kiln wash like Plistix may help with IR re-radiation and a bit of flux resistance, it is unlikely to add any significant strength to the ceramic fiber board walls.  This is the major advantage to adding a 1/2" - 3/4" thick layer of cast refractory insulation like the Kastolite 30.  In my experience ceramic fiberboard does not stand up at all well to multiple thermal cycles, and sags at higher temperatures depending on the unsupported span.  I hope the kiln wash does what you need, but it isn't the direction I would go for a durable forge skin.

[TommyVee]

Thanks.  I'll definitely keep that in mind.  This is a pretty tiny forge already --- the chamber is only 3.5"x4.5" in cross section already, so adding a half-inch thick layer to each surface would be reducing the volume a bit more than I'm willing to do as a first cut.  The unsupported span is just 4.5".

If I find any sign that my fiberboard is not holding up, I will reconsider the approach.