Block off plate. Galvanized vs SS?

[Ogre]

I have a large galvanized sheet laying around that is probably from doing cold air return for duct work.
Can this be used for a block off plate or should I go get a SS sheet?
Where should I look to buy this 'rockwool' stuff (what is the actual name of that stuff) I see referred to as a means to insulate above the block off plate?

Thanks again for all the advice.

 

[Fsappo]

galv is fine. Rockwool, try an hvac place or your local hearth retailer

 

[Shane]

I remember one poster was able to get their local Home Depot to order some in for them a couple years ago.

 

[gpcollen1]

You want steel - not stainless or galvanized. From what I understand, galvanized off gases some bad stuff when heated too high. You may never get it that high but why mess around...

 

[theheatelement]

Stainless won't hurt... we use aluminized which is fine, here's an excerpt about it.

Type 2 aluminized steel, with an aluminum coating of about 1.5 mil on each side, resists atmospheric corrosion and is claimed to outlast zinc-coated sheet in industrial environments by as much as five to one. Typical applications are industrial and commercial roofing and siding, drying ovens, silo roofs, and housings for outdoor lighting fixtures and air conditioners.

You want steel - not stainless or galvanized. From what I understand, galvanized off gases some bad stuff when heated too high. You may never get it that high but why mess around...

 

[BrotherBart]

Use your sheet of galvy. It will do the job just fine.

 

[Ogre]

Mixed review but thanks for all the input. If my sheet will fit I will use it bcz it is here... If it does not work out bcz of size then I will follow your alls advise.

Thanks again.

 

[Jags]

If it gets hot enough to outgas the galv, you have bigger problems. The galv will work just fine.

Edit: the process of "galvanizing" happens at about 860F. Suitable for applications up to 392 Deg. So if your insulated liner (on the outside surface) gets to that point, you are probably already melting the Stainless steel liner.

 

[EddyKilowatt]

I've made three block-off plates for various houses over the years and used galvanized steel for each. No problems with any of them, which is to say, no visible corrosion and no sign of overheating.

Aluminized would probably be the top choice (cost-effective) for a hot/dry application, but you're unlikely to find it at the local hardware store. So especially since you already have a sheet of galvanized on hand, I'd use that for sure.

If you're the type that enjoys being well informed, here's some interesting reading on sheet steel coating products:

(broken link removed to http://www.galvinfo.com/ginotes/GalvInfoNote_1_2.pdf)


Eddy

 

[joe245]

After asking around I was told Galvanized metal begins to emit zinc oxide fumes at around 350-400 degs ( zinc oxide poisoning) Which should not be a issue. And for added protection you could coat it with Hi Temp stove paint

 

[Beetle-Kill]

If you decide to paint it, you probably want to "etch" it first, with either a commercial galvanizing etching spray, or nitric acid. Most paints will not adhere to a hot-galvanized finish, especially when exposed to high temps.

 

[joe245]

If you decide to paint it, you probably want to "etch" it first, with either a commercial galvanizing etching spray, or nitric acid. Most paints will not adhere to a hot-galvanized finish, especially when exposed to high temps.

Good info. Thanks

 

[Berone]

Rock wool is also called "sound and fire blanket". It comes in 2x4 sheets in a bale, which will probably be more than you need. A good lumber yard or building supply house will have it.

 

[Dune]

http://www.anvilfire.com/iForge/tutor/safety3/index.htm

Sure, it will probably be o.k., but why take a chance like that to save a few bucks.

 

[Hogwildz]

http://www.anvilfire.com/iForge/tutor/safety3/index.htm

Sure, it will probably be o.k., but why take a chance like that to save a few bucks.

Dune, your so dramatic.
Making a block off plate with galvanized, is not putting it in a forge or oven with the intentions of intentionally baking it off.
According to that site, we all better stop using steel stoves & stainless steel pipes too.

Quote:
# METALS Stainless steel contains nickel and chromium. Nickel can cause asthma. Nickel and chromium can cause cancer. Chromium can cause sinus problems and "holes" between the nostrils.
# Mild steel (red iron) and carbon steel contain manganese. Manganese can cause Parkinson's disease, which cripples the nerves and muscles.
# Zinc in galvanized metal or in paint (on welded surfaces) can cause metal fume fever. It feels like the flu and goes away in a few hours or days after exposure ends.

Of all the folks on here that have used gal. to make block off plates, I have yet to hear of any getting sick or dying from them.
By all means, anyone who has speak up.

 

[Dune]

Like I said, to save a few bucks. Zinc starts outgassing at 400 degrees. Overfired stoves get much, much hotter than that. Anyone who did die from it would hardly have reported back here. Aside from that extreme, the effects of zinc poisoning are cummulative, the symptoms resemble common illness, why bother with all that to save ten bucks or whatever?

 

[joe245]

Dune, what is your recommendation or preference for a Block Off

 

[Dune]

Plain steel.

 

[Hogwildz]

But steel may cause you Parkinsons according to the supplied website.

So since prolly 99% of the members here use all 3 of these components in our systems we are all going to:
Die of cancer and holes between our nostrils from the S.S. liners we use, develop Parkinson disease from the steel stoves, and get metal fume fever and feel like we have the flu from the Galvanized block off plates.
Hmm, I'm thinking the galvanized is the least of the worries.

 

[Dune]

Yeah, but the difference in melting temp between zinc and steel is over 1900 degrees F.

I am just trying to be helpful and give back some of what I have gotten here. Galvanized metal doesn't belong near wood stoves, that is why you don't use gavly smoke pipe for your woodstove right?

Just because some or many people get away with doing a certain thing most of the time, why ever risk fate if it is unnessasary?

 

[Cedrusdeodara]

I used regular steel for my BO plate, then hit it with a couple of coats of black stove/furnace spray paint. I didn't want it to rust or give off any fumes. You can buy the stove spray paint in the paint section of HD. It even comes in other colors if you want a gold or silver blockoff plate.

 

[Cluttermagnet]

I used steel, and pretty thick stock at that- like maybe 0.080 to 0.1" or so. It's secured to the metal rim of the smoke chamber above with a whole bunch of Tap Cons. Big brick inside chimney. It's not visible unless you get down on hands and knees, and look up, so I didn't paint it. That plate is not going to come loose, even if Santa Claus falls on it. It probably wouldn't outgas many nasties, even during a chimney fire.

 

[Retreadsme]

Not wanting to start an argument or cause ill feelings here. I saw a response to the OP "After asking around I was told Galvanized metal begins to emit zinc oxide fumes at around 350-400 degs ( zinc oxide poisoning)" and it made me wonder where information like this comes from or whether someone failed to fully explain. Since Zn has a melting point of 787.15 deg F / 419.58 deg C and a boiling point of 1665 deg F / 907 deg C I can only assume the 350-400 deg C was intended. Admittedly it's been a while since I was in the chem lab, but honestly I can't remember ZnO being in a gaseous form before reaching Zn BP. (I could be wrong though - I'm old !)
The question crossed my mind also when installing my insert. My galvanized blockoff plate is approx 9" above the insert outer plate (not firebox) and the SS flu is insulated with ceramic blanket; thus if that plate gets anywhere near the temp required to "off gas" ZnO, I've got several serious issues to deal with!

 

[Ogre]

Hey all,

As the OP here I really do appreciate all the input... but boy I did not know this would open such a can of worms. Goes to show just how much there is to know (or assume) about this endevor. I'm going to take my chances with the Gal. If Idie I'll have my wife log in for me and pass along the news...

But since we are on the Backopff plate as a topic can we add insulation materails to this too. I hear everyone suggesting "Rockwool" what are the other alternatives for insulation above the backoff place and also to use just under the top cap to create a dead air space between the liner and the masonry chimney??? And where can I get it, I'm having a hard time finding it locally.

Thanks for all the input, from all sides and the passion. Nothing better than a good passionate debate and conflict to bring out the big guns (and old text books to verify these things...)

 

[Jags]

Ahhh heck, if given the opportunity, we would argue about whether or not the wheel is round. :lol: