Cement Block off Plate

[Fivehorizons88]

Has anyone made a block off plate using wire mesh to fit the damper opening and then skim coating it with sort of mortar or cement? I've seen a few examples are seems like an interesting concept. What are your thoughts?

thanks!

 

[mellow]

Why not just use cement board, I used Durock, a lot easier to work with.

 

[Fivehorizons88]

Why not just use cement board, I used Durock, a lot easier to work with.

how did you secure the cement board to stay in place? meaning, with a lack of a "flange" of some sort to screw into the wall.

 

[Mr. Jones]

I used caulk around the outside, and high temp silicone around the liner. Cut it tight, and it will stay in place to caulk it. I also propped it up with a couple of 2x8 until it dried.

 

[Fivehorizons88]

I used caulk around the outside, and high temp silicone around the liner. Cut it tight, and it will stay in place to caulk it. I also propped it up with a couple of 2x8 until it dried.

Did you use Durock or Hardieboard? Is Durock "dustier" to work with?

 

[mellow]

I used tapcons to hold it in place.

 

[begreen]

how did you secure the cement board to stay in place? meaning, with a lack of a "flange" of some sort to screw into the wall.

A flange could be made of angle metal. FWIW, it's usually easier to make a template first, then cut the plate out of sheet metal with an extra 1" border around it that gets folded down to form the fastening flange.

 

[Fivehorizons88]

D

A flange could be made of angle metal. FWIW, it's usually easier to make a template first, then cut the plate out of sheet metal with an extra 1" border around it that gets folded down to form the fastening flange.

Thank you for the suggestion - do you see any issues using cement board? Will it be able to handle the heat, etc?=

thanks!

 

[begreen]

As long as it's non-combustible it should be fine. Note that some cement board uses cellulose as a filler and another uses styrofoam pellets so be sure it is either pure cement board or uses a filler like pumice that is non-combustible.

 

[Fivehorizons88]

As long as it's non-combustible it should be fine. Note that some cement board uses cellulose as a filler and another uses styrofoam pellets so be sure it is either pure cement board or uses a filler like pumice that is non-combustible.

Ideally, a block off plate should be made out of stainless steel, correct?

 

[Nick Mystic]

Mr. Jones,
Where did you find high temperature silicone caulk that could take the heat up against the ss flex liner? I haven't seen any silicone caulk rated that high?

 

[Ashful]

Mine are both galvanized perf angle, fastened into the masonry with Tapcons, and stainless panels set into them and fastened with sheet metal screws. My chimneys are granite and field stone, with natural mud (not a euphemism) bedding mortar, and 240 year old lime (no Portland) pointing and daubing. If I can properly fasten angle into mine, you have no excuse for short cutting this.


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[begreen]

Ideally, a block off plate should be made out of stainless steel, correct?

Sheet steel or aluminum would also work. The point of contact with the liner is minimal.

 

[Fivehorizons88]

Mine are both galvanized perf angle, fastened into the masonry with Tapcons, and stainless panels set into them and fastened with sheet metal screws. My chimneys are granite and field stone, with natural mud (not a euphemism) bedding mortar, and 240 year old lime (no Portland) pointing and daubing. If I can properly fasten angle into mine, you have no excuse for short cutting this.


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I'm having issues finding stainless steel sheet metal - any suggestions?

 

[begreen]

I would just use 24 ga galvanized sheetmetal, but if you want stainless, try a bigger sheetmetal shop.

 

[Ashful]

McMaster Carr. Or just buy galvanized at Lowes Depot.


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[Fivehorizons88]

McMaster Carr. Or just buy galvanized at Lowes Depot.


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doesn't galvanized create a dangerous gas when heated?

 

[begreen]

This is not like welding or heating the whole sheet up to 900F. The point of contact with the liner is minimal so the heat will be distributed quickly.

 

[Fivehorizons88]

If I had some left over sections of black stove pipe, could I unroll them so they are flat and use that as my block off plate? I figure that metal can handle high heat.

 

[begreen]

I guess but it's going to be a challenge to get it to lay flat.

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[bholler]

we always just use galvanized sheet The problem with the mesh and cement idea is it is not easily removed if there is ever a problem. We do that when we are lining a fireplace for use as an open fireplace to shape the smoke chamber and tie the liner in but never for an insert.

 

[jscs.moore]

Sheet steel or aluminum would also work. The point of contact with the liner is minimal.

Hey Begreen...just had the dealer install my block off plate about two months ago in preparation for this burning season. They did a nice job and used a fairly heavy gauge aluminum sheet metal and adhered an insulation blanket (kaowool) on top it. So in your opinion...no problem with them using aluminum for the block off plate? I only ask because everyone on this site tends to use regular sheet metal?

 

[bholler]

So in your opinion...no problem with them using aluminum for the block off plate?

No problem with it. It wont get enough heat to hurt it.

 

[jscs.moore]

No problem with it. It wont get enough heat to hurt it.

Thanks bholler...that's basically what the dealer said when I asked about the aluminum. But since they were the ones who told me a year ago (at the time of install) that I absolutely did NOT need a block off plate...I wanted to get some feedback from the experts on this site

 

[Ashful]

Most folks don't need a block-off plate, just like no one really needs low-E Windows, but it is nicer having both.


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