Repairing refractory floor in Mendota fireplace.

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TechWrench

Member
Apr 11, 2018
24
Hawley, PA
Back again, with a new problem with my old Mendota wood fireplace. Two weeks ago, while cleaning out the ash buildup, I noticed a bubble in the floor of the unit. Upon cleaning, I found out that the surface of the floor refractory is starting to deteriorate. I removed the wood grate, and found that about a 5" x 6" section of the floor surface is breaking down. I used a small tack hammer to break-up the loose surface material, and ended up with a 5" x 6" oval of missing surface cement that is about 1/8 t0 1/4" deep. I tried contacting Mendota about replacement refractory panels, but their reply was that these factory panels are no longer available (not surprised). They suggested trying to repair the damaged surface with refractory cement mix, or replacing the entire floor with fire brick or pre-fab refractory panels. Since the refractory panel for the floor isn't completely flat (it has an inclined floor about 9" from the rear of the firebox, which rises at about a 20 degree incline to meet the front door opening) It seems to me that replacing the floor with firebrick is the best source of action. But, I thought that a temp fix, using refractory mortar would work until after the heating season, when I could remove the damaged panel and rebuild it with fire brick.

I ordered a tub of Rutland refractory cement mix, and after thoroughly cleaning all the loose material, I misted the area, as instructed, and troweled in the cement to fill the depression. I let the fix set for three days, and tried using a small box (ceramic) heater to help with drying the repair. The instructions mention starting a small fire and getting it up to 500 degrees for about 1 hour to finish the curing process. Since the repair is on the floor of the firebox, I wasn't sure how it would work with the ash/coal bed on top of the repair. Well, as I feared, after the burn, I cleaned the ashes out, and discovered the repair had bubbled up (probably from residual moisture in the repair boiling up and creating steam bubbles.

I am at a loss as how to cure this type of repair without removing the entire floor piece, and using the oven to complete the cure. If I have to go that route, I might as well just replace it with fire brick instead.

I guess my question is, since the refractory section is about 1" thick, would burning for the last few months of the season be a bad idea?
 

jetsam

Minister of Fire
Dec 12, 2015
5,337
Long Island, NY
youtu.be
If it's 1" thick, it sounds like you could just pull the whole thing out and replace it with cheap old firebrick. Leave your patch there until the firebrick arrives.
 

Sodbuster

Minister of Fire
Sep 22, 2012
1,513
Michigan
What about using firebrick?
 

Sodbuster

Minister of Fire
Sep 22, 2012
1,513
Michigan
If it's 1" thick, it sounds like you could just pull the whole thing out and replace it with cheap old firebrick. Leave your patch there until the firebrick arrives.

LOL posted at the same time.
 

TechWrench

Member
Apr 11, 2018
24
Hawley, PA
If it's 1" thick, it sounds like you could just pull the whole thing out and replace it with cheap old firebrick. Leave your patch there until the firebrick arrives.

Replacing the entire floor refractory with firebrick is my plan once the heating season is over. I am just wondering about using the fireplace the way it is until then. I am assuming that as long as the floor doesn't get any worse, I should be able to use it for a while longer.

Buy the way, I noticed you are from LI. May I ask what part? I am originally from Lynbrook, but moved upstate NY in '78, and we recently moved to PA to gt away from NY politics.
 
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ShawnLiNY

Burning Hunk
Dec 13, 2018
224
Ny
Hey techwrench , fellow Long Islander here too . If repair is still intact use as is , if damaged and cracking remove the loose stuff and fill with dry play sand
 

jetsam

Minister of Fire
Dec 12, 2015
5,337
Long Island, NY
youtu.be
Replacing the entire floor refractory with firebrick is my plan once the heating season is over. I am just wondering about using the fireplace the way it is until then. I am assuming that as long as the floor doesn't get any worse, I should be able to use it for a while longer.

Buy the way, I noticed you are from LI. May I ask what part? I am originally from Lynbrook, but moved upstate NY in '78, and we recently moved to PA to gt away from NY politics.

There's actually a disproportionate number of Long Islanders on this forum for some reason. We're out by Medford. There's at least one other hearther within a few miles of me, not sure how many others!

I threw away my TV in 1991, which got me away from politics pretty well. I can recommend that move to anyone. :)
 

ShawnLiNY

Burning Hunk
Dec 13, 2018
224
Ny
There's actually a disproportionate number of Long Islanders on this forum for some reason. We're out by Medford. There's at least one other hearther within a few miles of me, not sure how many others!

I threw away my TV in 1991, which got me away from politics pretty well. I can recommend that move to anyone. :)
Jetsam I’m in Patchogue
 

TechWrench

Member
Apr 11, 2018
24
Hawley, PA
Jetsam I’m in Patchogue
Hey, Talk about a 'small' world. Growing up, I had God Parents that lived in E. Patchogue, and I spent almost every summer with them. Some of my best memories growing up.

As for my fireplace issue, I plan to clean up the refractory floor tomorrow, and see how much of the repair patch remains intact. I may try your suggestion about using sand to fill the void in the floor.
 

Sodbuster

Minister of Fire
Sep 22, 2012
1,513
Michigan
Hey, Talk about a 'small' world. Growing up, I had God Parents that lived in E. Patchogue, and I spent almost every summer with them. Some of my best memories growing up.

As for my fireplace issue, I plan to clean up the refractory floor tomorrow, and see how much of the repair patch remains intact. I may try your suggestion about using sand to fill the void in the floor.


Not much heating season left, I think you'll be fine.
 
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TechWrench

Member
Apr 11, 2018
24
Hawley, PA
Thanks for your input. I think I will go ahead with my 'plan'.
Well, it's been a while, but a lot has been going on in my life. Anyway, I finally decided to replace the bottom and rear refractory panels with firebrick. So, over the summer I removed the panels, along with some broken firebrick used to line the two sides near the back. I bought nw firebrick from Vermont Castings, and built a new floor, rear wall and both sides. I used a masonry cement that Vermont castings recommended to adhere the rear and side vertical bricks in place. Once I did a preliminary cure burn, and let it set for a few days, I started using the fireplace in November. So far it is working great. I also replaced both the blower fans in the bottom of the unit with new fans that are a lot quieter than the old ones. It is much easier to hear TV with them on now.

Now the only remaining issue is getting a positive draft started after the fireplace has not been in use for more than a day. I finally settled on using a heat gun inside the fireplace, with the doors closed, to get a draft started. It can take between 15 to 45 min before I can see a draft at the chimney cap. If I rush it, and try to light the fire too soon, all I get is smoke from the bottom chamber in the house. Wife doesn't appreciate it when it happens. Once I have a positive draft, the fire will light and start easily, and there are no further draft issues until the next time. Since I have an oil fired hot water baseboard system, I do not rely on the fireplace for round the clock heat. I only fire it up in the afternoon and burn it until we retire for evening.

I suspect that because the flue pipe goes up the outside of the house, inside a wooden clad chase, once the flue cools, it starts to reverse draft. The fireplace has an outside air supply, but there is no way to close that pipe into the stove, so I am assuming it may be the cause for the reverse draft when the flue cools. So other than the initial draft issue, and having to clean the glass doors about every week or so, I am happy with the way the fireplace works.

If anyone has any suggestions on how to make my initial draft issues easier, I would appreciate it.

Thanks.
 

ShawnLiNY

Burning Hunk
Dec 13, 2018
224
Ny
45 minutes to establish positive draft seems like a crazy long time , my stove is in my basement so I too get reverse drafting after stove is cold , perhaps you could install a clean out T with a cap to give you direct acces to the stove pipe rather than trying to warm the fire box .
 

TechWrench

Member
Apr 11, 2018
24
Hawley, PA
45 minutes to establish positive draft seems like a crazy long time , my stove is in my basement so I too get reverse drafting after stove is cold , perhaps you could install a clean out T with a cap to give you direct acces to the stove pipe rather than trying to warm the fire box .

I agree that 45 min is way to long, but the amount of time is apparently affected by how cold it is outside and the humidity level. As for your suggestion about a clean out T, it wont work in my situation. As I said in my post, the flue pipe is enclosed in an outside chase. From ground level, the lowest section of flue pipe that would be available is about 10' above ground, and inside the house, there is a stone faced wall surrounding the fireplace which extends to the ceiling.

I have tried using a MAP torch to start a draft, and it is faster than the heat gun, but it requires me to sit in front of the fireplace with the doors open and hold the torch until I think I have a draft, which can still take 10-20 min. Using the heat gun, I can build my firewood stack in the box and place the heat gun inside so that it aims up toward the flue opening in the back of the fire box. I can then close the doors and wait until I see I have heat waves at the flue cap. Fortunately, I have a fixed skylight in the cathedral ceiling which allows me a view of he flue cap from inside the living room. The only drawback to this process is I have to do this while it is still light out. Otherwise I can't see the heat waves at the cap.

The way the fireplace is designed, I do not have a flue damper to close, and even if I did, I am not sure that would help.

But, thanks for your reply and suggestion.