Block off plate

[Ctwoodtick]

Hi all, I’m thinking about adding an after the fact block off plate in my masonry fireplace, which has a wood insert. A previous installer had done a bit of a hatchet job on the back fire brick wall of the fire box and I do not have an even surface there to attach a block off plate on that back part of the block off plate.I’m wondering if other folks have run into this and how to compensate for rough uneven masonry when doing a block off plate.

 

[EatenByLimestone]

Can you smooth out the masonry? It doesn’t have to be pretty. You can probably use tapcons partially driven in to give you something to key into.

 

[begreen]

How bad is it and how wide of an area? Is it something that a gasket could fill?

 

[Ctwoodtick]

I’ll try to get some pictures up by tomorrow of the area. But to answer your question, it’s a fairly wide area and fairly “bad“. The previous guy roughed up the area and the surface of that old fire brick looks like jagged rock could find in nature.

 

[stoveliker]

Mortar it flatter and then plate, gasket or silicone caulk?

 

[Ctwoodtick]

Thank you for responses. I took a better look at the back wall of masonry firebox and it was not quite as bad a I thought. I think it would be worth it for me to try to smooth masonry out as much as possible. I saw that using mortar was good. What type of mortar is best for this? Also, do I need to prep the rough surface in any way?
Also, I was wanting to add wrap insulation to the bottom part of the liner (it was installed with wrapped insulation but it starts at 18 inches up the liner. Currently the liner comes within millimeters of the old steel damper frame of the fireplace. To add insulation wrap in the area, I’d need to have the liner pushed back the half an inch for the insulation. My thought was to nudge the insert a tough to gain the room. It’s listed at 550 pounds so very heavy. Would you think moving the stove with the liner (heavywall) connected would damage anything? I was thinking that it would not if only moving that tiny bit, but wanted to ask. If it’s OK, I’d be curious about best to push the insert back on my own.

 

[EatenByLimestone]

If you’re using regular mortar, say type S and can’t get it to stick, making it into a slurry and painting the slurry onto the rough stuff can help. A chip brush will work for this. It doesn’t need to be a fancy brush. Like sticks to like. Also, driving in tap cons where the head isn’t seated will give the mortar something to hold onto in addition to the old brickworks.

 

[Ctwoodtick]

If you’re using regular mortar, say type S and can’t get it to stick, making it into a slurry and painting the slurry onto the rough stuff can help. A chip brush will work for this. It doesn’t need to be a fancy brush. Like sticks to like. Also, driving in tap cons where the head isn’t seated will give the mortar something to hold onto in addition to the old brickworks.

Thanks! Silly question, do I put the tapcons in before or after applying the new mortar?

 

[Ctwoodtick]

Thanks! Silly question, do I put the tapcons in before or after applying the new mortar?

Also, was curious if me trying to move insert back about half an inch with liner attached would be ok or risk damaging. Currently damper frame is right up to liner and need room to try to add insulation to that lower part. I’m hesitant to try to cut out part of the damper with proximity of liner.

 

[EatenByLimestone]

Tap cons go in before. They’ll be covered in the mortar. The idea is that they’ll solidify around the screw head and hold the mortar in place, even if the patch pulls away from the brick.

So the liner is touching the front side of the hole the damper used to be in and you want to move the liner and insert back a half inch? How wide is the damper hole? Is there enough room to slide the insert back a half inch? It sounds like it should be fine. Even if you dimple the liner a tad it shouldn’t hurt it. It can’t be any worse than those corners in singlewall that shrink the one side by forming wrinkles in it.

 

[Ctwoodtick]

Tap cons go in before. They’ll be covered in the mortar. The idea is that they’ll solidify around the screw head and hold the mortar in place, even if the patch pulls away from the brick.

So the liner is touching the front side of the hole the damper used to be in and you want to move the liner and insert back a half inch? How wide is the damper hole? Is there enough room to slide the insert back a half inch? It sounds like it should be fine. Even if you dimple the liner a tad it shouldn’t hurt it. It can’t be any worse than those corners in singlewall that shrink the one side by forming wrinkles in it.

Thank you for the information on use of tapcons. I’m a newbie with masonry.
There is plenty of room for the liner and stove to be pushed back. Glad to hear that line should be fine if I shove the stove back half and inch. It’s heavywall so I suppose that is good.
I guess my next question would how to best push it back that half inch. It’s a heavy insert so not sure of my ability to independently shove the thing for the needed space.

 

[EatenByLimestone]

I’d push it with lever and fulcrum, or pizza plus beer and friends.

 

[Ctwoodtick]

OK, so much for assumptions. So I took a better look after pulling the surround on my insert today. It looks like there’s no room for me to push the insert back the half inch needed to get the bottom of the liner insulated. My thought would be at this point to disconnect the liner from the insert and hopefully be able to push it out of the way somewhat so that I could try to cut out that portion of the damper frame that is currently abutting it. I’m not sure how much the liner is
Going to give in this situation. I prefer to not completely pull the liner. I also don’t wanna accidentally damage the liner while cutting out the damper frame. Is there any guidance on how to “shield” the liner while it’s pushed slightly out of the way while I can cut out some room from the damper frame?

 

[EatenByLimestone]

@bholler


Do you really need to insulate the bottom of the liner? Are you overthinking this? Throw some spun slag insulation up there where you can, install the block off plate, and enjoy life. That’s going to be the hottest part of the liner. I doubt there’ll be creosote forming there.

 

[bholler]

@bholler


Do you really need to insulate the bottom of the liner? Are you overthinking this? Throw some spun slag insulation up there where you can, install the block off plate, and enjoy life. That’s going to be the hottest part of the liner. I doubt there’ll be creosote forming there.

The issue is that it is also an area where there often isnt nearly enough protection between the inside of the smoke chamber and framing on the outside. I always make sure my insulation starts right above the block off plate . And usually stuff the smoke chamber with rock wool just to be safe.

 

[Ctwoodtick]

The issue is that it is also an area where there often isnt nearly enough protection between the inside of the smoke chamber and framing on the outside. I always make sure my insulation starts right above the block off plate . And usually stuff the smoke chamber with rock wool just to be safe.

I appreciate the info from everyone. What is the best tool to cut out an area of the damper frame? I’m thinking of something that can effectively cut the frame without damaging the liner. I realize a lot will depend on me being steady and careful. I’m ok with the cut going slower if less risk to liner. If possible I’d like keep liner installed and cut damper around it. Not sure if maybe there’s a way to cut the thing in half and remove the trouble area.

 

[bholler]

I appreciate the info from everyone. What is the best tool to cut out an area of the damper frame? I’m thinking of something that can effectively cut the frame without hitting the liner. I realize a lot will depend on me being steady and careful. I’m ok with the cut going slower is less risk to liner. If possible I’d like keep liner installed and cut damper around it. Not sure if maybe there’s a way to cut the thing in half and remove the trouble area.

I cut as far as I can with a grinder then smack it with a hammer

 

[Ctwoodtick]

I cut as far as I can with a grinder then smack it with a hammer

Any tips for cutting the damper back while not removing liner? Trying to not disconnect it while also not wanting to accidentally damage it.

 

[Ctwoodtick]

How bad is it and how wide of an area? Is it something that a gasket could fill?

So here are some pics of the back of the masonry firebox. The back firebricks had been altered to allow for insert to fit. I would be installing block off plate against the currently rough lighter colored masonry. The block off plate would be below where the installer had cut back part of masonry and damper. I will apply mortar to the rough masonry to try to get as smooth a surface as possible. The back corners are uneven- the old installer did not chisel anything out on the sides of firebox. I think I will have my work cut out for me with accommodating the rough and uneven parts when fitting the block off plate.

 

[Ctwoodtick]

If you’re using regular mortar, say type S and can’t get it to stick, making it into a slurry and painting the slurry onto the rough stuff can help. A chip brush will work for this. It doesn’t need to be a fancy brush. Like sticks to like. Also, driving in tap cons where the head isn’t seated will give the mortar something to hold onto in addition to the old brickworks.

From the pics I put up, wondering if i fit the blockoff plate as well as possible on the current rough masonry surface on the back of upper firebox and then jammed in gasket material in the gaps would be ok. It’s already going to be a bit of a project dealing with cutting out damper frame. Looking for anyway to cut down on time, but still have it be a good blockoff plate.

 

[EatenByLimestone]

Obviously the smoother and more tight fitting the plate and masonry are the better, but any plate you put in there, and any extra (non flammable) insulation you can stuff up there is going to make the situation better.

If it’s not perfect I think it’ll still give a noticeable improvement. You’re still reducing the opening up the chimney.

 

[Ctwoodtick]

Another question guys- I would like to attach the front part of the block off plate to the underside of the first course of bricks going across the front of fireplace. These are held in place with an angle iron. I want to see if there was a recommended way of attaching block off plate to the underside of the angle iron. Thank you!

 

[EatenByLimestone]

How tight is the angle to the brick? Could the sheet metal fit between the angle and the brick? A good bit can drill into the angle. You could attach right to the angle. I’d probably pre drill then run a screw into the angle. I’m not sure if that’s a preferred way, just how I’d tackle it. Maybe use a brake to make a nice finished edge so it looks nice for the next yahoo that gets up into the fireplace!

 

[Ctwoodtick]

How tight is the angle to the brick? Could the sheet metal fit between the angle and the brick? A good bit can drill into the angle. You could attach right to the angle. I’d probably pre drill then run a screw into the angle. I’m not sure if that’s a preferred way, just how I’d tackle it. Maybe use a brake to make a nice finished edge so it looks nice for the next yahoo that gets up into the fireplace!

Thanks for the info-I’ll look at the angle iron better to see if there is any ability to put sheet metal into that space. I included a pic for reference. You can also get an idea of the back wall of firebrick having been altered by previous installer. Rough but I think I’ll go for it with attaching the block off plate to it and then adding gasket to any small gaps. Was thinking of stuffing gasket into any gaps and then putting high heat RTV silicone on as well to help seal gaps up. As it turn out the back corner of the firebox will probably be the challenge with the uneven corners/
Thanks for the info on possiby attaching right to angle.
I may get myself a cheap sheet metal brake. Future yahoos are on their own but it sound like it would be helpful in make good right angles.

 

[EatenByLimestone]

If you need to, you can use a couple pieces of angle iron to pinch the sheet metal and then either lightly turn the edge with a hammer and block of wood.