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Stonemason
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Hello All,
We have a few Rumford fireplaces on the horizon. In the past we've used pre-cast components supplied by Superior Clay, Buckley Rumford, Rumford.com et al.... This time around, I'd like to cast our own throat systems with refractory cement/concrete. I know there is probably a learning curve to this, but I've got time to practice, so to speak.
I'm wondering if anyone can offer any advice or tips on how you would go about this.
What refractory materials would you recommend? Do you cast in place or prefab the throat/lintel elsewhere and then install? Do you use re-bar in refractory castings? etc. etc.
Thanks for any help you can offer.
 

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Vendor
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I just went outside and looked at one to see how they molded it. It appears that the outside is formed and the inside is not. That means they use an exterior form and hand apply the material to it. Doable, but that is a complex shape. What would you use for a mold?

If I were going to do it, I would cast the quarter round throat pieces and the coving. Much easier to do.
 

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This may be a dumb (or ignorant even) question, but have you used the 12" throat sections they offer before? They're a ton cheaper than the one piece. I've never actually cast them before, but always was under the impression that they were cast in place. I'm sure Buckley has some pics somewhere on his sight.

As for another alternative, when I built the one on my patio last year, I used a section of concrete culvert pipe (removed from my own ditch a year earlier, I considered it my contribution to the "green" moovement :laughing:) & plastered to layers of Heatstop II onto it. I found the curve of the 15" I.D. pipe matched almost perfectly to the Buckley throat. I don't burn this FP that often or very hot, but the throat has held up fine so far. As a matter of fact, when checking temps with the infared gun, I don't think it ever really even gets that hot when compared to the backwall.
 

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Stonemason
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Discussion Starter #8
Thanks everyone... I was thinking along the lines of tsscarborough... forming and casting a 1/4 round, a more 'solid' version of jomama's picture. I would obviously build up the side and back walls higher with the firebrick and fill in the voids between the firebrick and the 1/4 round cast piece with cut firebrick/refractory cement. As jomama says, similar to the 1/4 round segments that Buckley Rumford sells. What I was hoping though, is to make it a one piece structural lintel. ie. for a 3' firebox opening, I would cast something say around 52" long, by roughly 12" high by 12" wide with the radius on one side... This raises a question about the introduction of re-enforcing steel into the mix... would the buildup of heat eventually cause metal and refractory to expand at different rates? I'm encouraged by the fact that jomama's infrared gun didn't register too much heat buildup. I'll certainly keep you all up to date on anything i find out...
 

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yeah very nice. I have a different way when I want to build what I call a "modified rumford".

I set a plywood form and then lay in split firebricks dry. I then place a grid of #3 rebar and a couple buckets of concrete mix. This doesn't give you that curve, rather an incline, but it works fine, looks good, and is not that difficult.

Dave
 

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If your asking me, I do have this that shows the firebricks which were laid on the plywood form. Opening was crossed over with a 4"block, then a 6" bondbeam. I coated the firebricks with fireclay then filled in behind with cement and rebar.

Now keep in mind this is not something I claim will work in any other situation. I just had a woman who wanted a 50"X50" opening and the traditionally shaped rumford wouldn't work because of some built-in bookshelves and other considerations in the room.


Dave
 

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Its been a while since I have used an exact level, I miss the days of looking sideways into the bubble on my 2 footer :no:
 

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To chirp in on this old thread, anyone looking to build a Rumford without the kit should look at how Bytor finished off the top of his firebox in the last picture post he made. Stepping the brick and continuing the firebox is exactly how it should be done. Then all is needed is simply building the front of the throat, hammer cut an angle brick and parge it off nice and smooth.

The only thing is an angle iron is needed to span the opening, and the standard dampers wont fit on the top.

Solution would be to order the Rumford dampers, have them specialty made like Bytor, or use a lemance damper.

It is worth noting that if the measurements of the firebox is altered radiant heat loss will result. Once the side walls begin to get straightened out, the amount of radiant heat that reflects into the room goes down drastically.

It is tough to say that home made versions of a Rumford work just fine without having first hand experience with a Rumford on a daily basis.

In my previous house I had a 36" Rumford and I was VERY concerned that our couch would catch fire from spontaneous combustion, or at the very least melt the fabric. The couch was positioned 5' away from the opening as well.

If any more then 1 log and some hot embers were burning the room would get too hot to even sit in.

Dozens of my friends have had me build various fireplaces with the standard 20" box 10 courses tall, and none of them have ever come close to producing this kind of heat. Some would feel warm, but thats about it.

So, no disrespect, but when people say that build a Rumford without using any of the firebox dimensions or the throat system, I am weary of putting it in the same BTU category of a true Rumford without first hand experience from both a true Rumford as well as the modified version.
 

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They used to make those Exact levels near where I went to school in New Jersey. I don't use them myself anymore either, they don't make them like they used to.

I looked and the picture you mention of Bytor's is no longer there for some reason. I too liked the construction and especially the flat damper.

I will say though that I had to copy a fireplace in a Frank LLoyd Wright designed home in Escondido CA and the throat was parged and it had crumbled away a lot. The guy would burn really big logs in what is kind of a 3 sided fireplace.

Anyway, copying that 3 faceted throat I used a form and firebricks rather than plaster hoping it would hold up better.

Though I understand what you're saying about the dimensions of a classic Rumford I would just point out that the fireplaces I build here in California aren't about being in the same BTU league as a Rumford. Most are outdoors and lots of my fireplaces never even see a real log. :)

Dave
 

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When i was in school and we were doing "fireplace week" or whatever, we had a very reputable guy come in and give us some very good info. One of the lessons was on casting rumford throats. Unfortunately I wasn't on the team that was doing that I was on the team building one using brick and parging however we did get a demonstration and did a lot of on looking.

The technique was to use very wet sand in a box and make a reverse of the throat. Pour in the castable refractory, no steel that i can remember but it was mixed with sand. Let harden, then sand the bejezzus out of it to make it roll as best you could. For large throats it was done in 2 pieces so they were manageable.

Not a real precise answer but as I say i didn't have first hand knowledge.

JBM, I've done "modified" rumfords, basically because they were small and if they had the proper ratios there would have been no room for wood (only about 8" deep if I remember). With a real Rumford throat and still relatively shallow firebox, (I think i increased to 12" deep) the homeowners later told me they had to open windows in the middle of winter cause it got so warm in the room. The chimney was located inside the house however.
 
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