Wednesday, November 12, 2008

Rumford Fireplace (part XVI... final?!)

Designing a house is difficult. Four years ago when I began, I knew virtually nothing about fireplace design. I made accommodations for the fireplace within the timberframe and foundation, but I neglected to include provisions for the fireplace hearth. Ideally, if I could have known everything back then, I would have poured a cantilevered concrete ledge to support the hearth. As it were, I simply framed the house as if the hearth did not exist.

It would not be safe to build a hearth on wood, so I had to perform some reconstructive surgery on the house. I began by cutting out the plywood sub-floor, and the 2x4 and 3x3 that ran beneath that portion of the subfloor. Then I kerfed and chiseled the 6x8 timberframe floor joist that lay beneath that. I did this so that no portion of my concrete hearth structure would be supported by wood within 12 inches of the actual firebox. (Although I consider these measures to be very safe for my own house, this may not meet code in other regions of the country.)

I built concrete forms using aluminum extrusions and hardi-panel cement board. By using fireproof materials, I could leave the forms in place after the concrete cured. Into the forms, I placed reinforcing steel bars and drilled holes into the existing concrete so that the rebar (not the forms) could support the hearth slab on its longest side once the concrete cured. I mixed the quickrete in 5 gallon pales and added two extra shovels of portland cement to each bucket for extra strength. The kids had fun putting graffiti into the concrete... too bad all of that got covered up!

After the concrete setup, my wife and I had a crazy idea... one of those ideas that takes a one day project and turns it into a one week project. "Why not put some kind of pattern into the flagstone hearth?" I sketched a few ideas... Gothic arches in the grout lines, a Rising Sun pattern (the hearth faces east), and an oak leaf motif. We settled on the oak leaf. My wife cut out a piece of cardboard the size of the hearth and I sketched a pattern on it that satisfied both of us. To avoid creating a dust bowl in the house, I took the cardboard pattern outside and cut the stones in the back yard using a gas chop saw and an angle grinder. It took two days to cut the stones, but that included a trip back to the creek to search for more blue silt stones of a uniform color.

I mortared the flagstones down to the concrete hearth using generous amounts of thinset where necessary to level the thinner stones. Then I smeared dark gray grout into the joints, and followed up quickly with a wet sponge and progressively cleaner buckets of rinse water. We were out of "grout easy" so I tried to clean the grout off quickly before it had a chance to stain the flagstones. I used masking tape on the finished ash floor to avoid staining it with grout. As usual, our four year old wanted to help, so she grabbed the shop vac and vacuumed up the bits of dried grout on the floor.

The hearth stones haven't been sealed yet, but that hasn't kept me from starting fires in the fireplace. Here's a picture of the final, if not somewhat dirty, hearth design with a fire in the firebox. Yes that's a timber cut-off in the fireplace -- I have a few of those laying around.

Incidentally, the Rumford fireplace works fabulously. I have never seen an open fireplace that works this well, although I'll readily admit that fireplace inserts give off much more net heat. The fireplace draws wonderfully and lets no smoke into the house, even when the flue is cold and the fire is smoky. The only fault I can find is that it draws so well that it's clearly sucking lots of air out of the house. Although I neglected the hearth in the plans four years ago, I did include a cold-air make-up supply beneath the firebox. When I get that plumbed to the outside, the fireplace will be able to fuel the fire with outside air instead of warm inside air and I think that will contribute to the net heat output of the Rumford. For now, it burns a beautiful flame and radiates warmth!

The preceding post in this Rumford fireplace series can be found here.


Anonymous Anonymous said...

I think you are building a masterpiece of a home. You should think about publishing your blog into a book.

November 12, 2008 at 8:38 PM  
Blogger Whit said...

Nice fireplace! The house I live in now is a timber frame, and I love it, but it has no radiant heat source of any kind, and I miss that. You'll love that fireplace.

November 14, 2008 at 2:26 PM  
Anonymous Anonymous said...

Hi Thomas, things are moving ahead for you, this is good. It's always an adventure following your progress.

Can I ask you what size rumford and oven you selected ? If you had to do it again would you go larger or smaller ?

I'm trying to decide what would work for my house. I've been thinking 36" rumford with 24" oven.


November 21, 2008 at 2:11 PM  
Blogger oldmilwaukee said...


I went with a 48" Rumford and 36" pizza oven. My friend has two 30" Rumfords (or are they 36?) and they work great at that size too. I think it would depend on the size of the room. Superior Clay web site has recommendations based on room size somewhere on their web site.

I would not build an oven smaller than 30" for the simple reason that you really want to keep a fire going in it while you cook. The fire gives you at least three things - better browning, infinite cook time (as long as you feed the fire), and light to see what you are cooking. One of the best things about a brick oven is that you can cook with the oven door off (open) and can therefore watch your food cook. No more wondering what is going on in there. 36" is a little bigger than we need most of the time, but 24" might be too small to keep a fire and cook food at the same time. 30" would still be a seriously useful oven.

Thanks Whit! I like the hewing (actually adzing) videos on your blog.

Anonymous: Thanks! A book is too much work! :)

November 21, 2008 at 5:40 PM  
Anonymous Anonymous said...

Dude...been following your Blog from the beginning. I think I first caught you in the Forestry Forum a ways back.
I have to say...pretty amazing stuff you guys have done. Some nice family you have goin' on : )
Hey...mind if I post your blog in a group I started. We're just a buncha misfit builders and artists and the such.
anyway...great work bro!

November 22, 2008 at 9:04 PM  
Blogger andybuildz said...

Dude...been following your Blog from the beginning. I think I first caught you in the Forestry Forum a ways back.
I have to say...pretty amazing stuff you guys have done. Some nice family you have goin' on : )
Hey...mind if I post your blog in a group I started. We're just a buncha misfit builders and artists and the such.
anyway...great work bro!

November 22, 2008 at 9:06 PM  
Anonymous A and J said...

You guys never cease to amaze me with your talents and determination. Love the design - awesome. I think your wife can hire you out when you finish this house. Great job.

November 23, 2008 at 6:12 PM  
Anonymous Brad_bb said...

This comment has been removed by a blog administrator.

December 3, 2008 at 6:02 PM  
Blogger oldmilwaukee said...

Anonymous Brad_bb said...

can't find your email(lost it) or your blog profile to PM you. The iron remover I use does not require you to add anything. It has media like a water softener (Pyrolox), that the iron sticks to, but is flushed away only with water, no salt or anything else needed. They work great. I bought the ones I've used on They use a Fleck head to backwash(same as a softener head), which is good, but there's not brine tank or anything, just a 1/2 in. ID drain hose that I run to my septic. Plumb it inline like you would a softener. Let me know if you have any questions, or about softeners. My group here at work and I studied the different systems and settled on using traditional salt for water softening. Most all of the heads today are now metered and adjustable settings to adjust to your approximate use.

*** note deleted private email ***

December 4, 2008 at 6:38 PM  
Anonymous Oak Garages said...

Hi Dude!!!!!!!!!!!!!!!!!!

Your blog is very interesting regarding timber home making. It looks very colorful and full of pictures.

January 28, 2009 at 8:05 AM  
Anonymous traditionalist said...

Great piece written here.
You should publish more or write a book
keep up the good work and spread the news on the wonders of timber framing

September 7, 2009 at 3:38 AM  
Anonymous woodmen said...

Superb fireplace, we have been following your story from the beginning and this hearth is the finishing touches to all your efforts (not to mention the copper step flashing etc)...

Good stuff, keep the pictures coming

September 7, 2009 at 3:54 AM  
Blogger swesd said...

Great design!
I usually seal the stone before it gets grouted or sometimes even before it gets set. I don't like to "get on" the grout too fast with too much water as it can cause problems like efflorescence and it's sooo much easier to clean the grout with the stone already sealed.

October 10, 2009 at 11:41 PM  
Blogger oldmilwaukee said...

swesd, you are spot on!!!

our grout now has an uneven color, even after sealing with the best sealer we could find. My wife has decided that we used too much water. In fact, she thinks we might have gone so far as to wash out the stain in the grout. At first, we though it was efflorescence, and I guess it could still be. In any case, do you have any ideas of how to help our grout have a more even color now?

And thanks for stopping by and taking the time to comment!!!!

October 11, 2009 at 9:42 AM  
Blogger oldmilwaukee said...

BTW, I haven't sealed the stones or the grout on this hearth, and it is actually quite even in color (but not very bright, since there is no sealer). The uneven grout color I'm talking about is in our kitchen, where my wife used a solvent based sealer. The kitchen looks great when it is wet, but when it dries out the grout looks splotchy. Ideas?

October 11, 2009 at 9:48 AM  
Anonymous Mike from Wood Stove Wizard said...

Beautiful! I have to say the pattern in the hearth is a stroke of genius. It really lifts the fireplace and makes it a feature of the room.

I don't know if you thought about this, but when the stove is not in use you could block the chimney off. If you didn't install a damper in advance I've heard of using a "chimney ballon". You inflate them in place within the chimney and they seal the airway. It might help stop the draft when the stove isn't in use.

I think they are reusable too.

November 29, 2010 at 6:19 PM  
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