# firebrick question



## jomama45 (Nov 13, 2008)

Lot's of questions squished into one post, I'll try to answer so it makes sense:

- You can lay the firebrick in a Type S or M mortar, no need for high-heat refractory on the back side fo them.

- You really want good, sound joints between the firebrick with good refractory. I would plan on buttering the brick right away rather than trying to tuckpoint refractory to full bed depth later. You'll never get a decent joint unless you compress the refractory as you lay it IMPO.

- Make sure you use a refractory like "Heat Stop II" or "Alsey Flue-set" that is non-water soluable for an exterior application.

- Yes, you want to use the same refractory mortar on the flues as the firebrick.

Do you have a smoke shelf or reducer figured in? I can't imagine how how you would transition from a firebox to a flue without one of them..........


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## Jason34 (Aug 15, 2010)

Thank you for your response and sorry for all the questions. I think you were the one that chimed in on that thread about setting the fire brick in regular mortar but I wanted to double check. I was going to let the brick rest in the mortar over night before using the refractory mortar. I will be using heat stop II 50lbs bag. As for the smoke shelf. No there will not be one. I'm actually copying this fireplace exactly off of my father in laws which was built back in the mid 90s and it passed inspection. We have used it hundreds of times and it works very well. I honestly didn't think I needed one since the flue length is so short and the fireplace itself is opened


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## Jason34 (Aug 15, 2010)

When I go to set the walls do I use regular mortar on the backside? I've read refractory mortar isn't a structural mortar so that's why I asked


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## jomama45 (Nov 13, 2008)

I wouldn't adhere the firebrick to the common brick back-up. It will get too hot, and likely damage the brick if there's alot of contact between the two. In a perfect world, when you have minimal back-up (3.5" of brick with holes), you'd leave a 1-2" air space between the 2 and fill with an insulating castable material, or just leave it as an airspace.

The brick get laid in Heat Stop II again (or equivalent) and should be free standing by themselves. Although the fireclay may not be listed as "load bearing", it's more than strong enough for the little weight it will carry.......


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## Jason34 (Aug 15, 2010)

Oh crap. I adhered the firebrick to the regular brick using regular mortar. The directions said that when filling in the joints there needs to be minimal 1" of refractory mortar depth for it to give its full protection. Since the brick themselves stacked on their sides are 2 1/2" thick I thought I would be ok using regular mortar to at least keep it in place. I used the same mindset when setting the floor. I know heat rises so I didn't think the side brick would get hot enough to where it would heat through the fire brick and into the backing. The directions also said the refractory mortar is not a structural mortar so to not use it as you would regular mortar


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## jomama45 (Nov 13, 2008)

Once you have your first big fire you'll know what kind of effect the direct placement to the brick will have when it comes to heat.......


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## Jason34 (Aug 15, 2010)

So its Ok to lay the floor in regular mortar but not the sides? I don't quite understand. I know heat rises so the underside of the floor bricks shouldn't get that hot but since the top of my fireplace is open thus allowing heat to escape easily won't that help my sides to stay cooler? I can understand if the top wasn't open than the heat would build up much more. I just would like a better understanding if you don't mind.


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## jomama45 (Nov 13, 2008)

When you said "fireplace", I didn't realize you were just building an open top firepit. As long as your fires don't get too big, the sides might be OK. The only way to tell is to try it out and see how hot it gets.........


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## Jason34 (Aug 15, 2010)

Ok I'm sorry but I see how I could have confused you. When I think of a firepit I think of enclosed sides. Well the front will be open. But a fireplace has the top closed off so I guess its neither a fire pit nor fireplace. I was just thinking along the lines of an open top so that I can easily cook on it plus I plan on setting a larger grate across the top for clam bakes. Well I'm too far into it now to go back. Will finish it up and give it a test. If it fails I can just fix that part.


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## Jason34 (Aug 15, 2010)

I have another question I wanted to ask but don't want to make another topic so I'll just ask it in here. Ok so I installed the chimney flue and the other day I made a form and poured my concrete for my chimney crown. I have an expansion joint between the flue and the crown which I will be caulking with high heat caulk. I also want to seal the crown and I know I need to wait a month to do so. My question is which order do I seal and caulk? Do I caulk now and then seal or wait till its sealed to caulk?


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## jomama45 (Nov 13, 2008)

Either way is fine. You may want to give the cap a little time to cure before caulking as well.......


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## Jason34 (Aug 15, 2010)

I was going to give it a full month before doing anything to it. I just wasn't sure which got done first for adhesion purposes


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## Jason34 (Aug 15, 2010)

I'm heading out to buy supplies awhile to seal everything. Would one coat be enough or should I apply 2 coats of penetrating sealer?


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## jomama45 (Nov 13, 2008)

If it's a siloxane, the directions should tell you two quotes, and the timing between them......


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## Jason34 (Aug 15, 2010)

Ok will do. I'm going cheap on sealer since its not all that important. I can't seal it till the 20th but just want to get things together awhile. I'll post pictures of it fully finished then


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## Jason34 (Aug 15, 2010)

Well here is the finished product before I go and seal it which will be in 2 weeks. I know the refractory mortar looks a bit messy but that was my first time using it.


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