Pdx 42" update

[Macrinehart]

Did some more playing around today with the advice on diagonal floor, but took a variation and built a V-pattern with the vertex aligned between the oven dome and landing. I also did a more thorough evaluation of bricks using a carpenter's square to check all the bricks from my prior effort.

Couple of thoughts out of this exercise. First, I rejected about half of the bricks due to various quality issues that would be irrelevant for the dome but possibly contribute to problems with the floor. Mostly these rejections were based on angles not being square. I figure minor variations in thickness can be compensated for by using the v-notched sand/fireclay bed under the floor. But that will not necessarily compensate for bricks being out of square, especially with the herringbone pattern.

The second thing is that while I did get tighter lines with my quality bricks, the layout was still not "perfect". I decided that modeling this on the template was not going to guarantee the same results on the real thing. Bottom line, it was a good practice exercise, but every time I do this, even if using identical bricks in the same configuration, it is going to come out a little different. I am glad to hear from MarkJerling that minuscule gaps will fill in with ash. With that in mind, I put away my toys for the weekend.

[MarkJerling]

Hi gang - Here's the latest from Portland! So today we put what is hopefully the last of the freezing weather behind us, although we are in for more rain over the next week. Nevertheless, we had a beautiful sunny morning today so I jumped on the opportunity to check out the hearth and make some progress on the build!

first stop, cleared out the tent and space heater, and then took a peak at my hearth to see how it's doing. It looks like a concrete hearth, no surprise there! The loose sandy material on top is about 1-2 mm thick, not a huge deal in my humble opinion. But I'm giving it another week under the plastic before I remove the forms. (That will be 2 weeks total). Weather will be highs in mid 50s (F) and lows in mid 40s with rain showers for the entire time.

Not satisfied to look at the hearth and will a week to pass in an instant, I decided to pull out the full size floor template, pick through firebrick that arrived last week layout the floor. The next couple shots show the formation of my herringbone pattern, which I realized is quite a puzzle, especially if the pattern starts to get out of alignment. I was expecting the bricks would have some variation in quality. What I didn't expect was for bricks to not be square or plumb. Yet there was some of that so I ended up doing a lot of sorting to build the best floor possible.

I was thinking of building a very large hand sanding disk to go over the floor once it's set in it's final arrangement but I think that could possibly have some unintended side effects, such as expanding gaps for bricks that are not perfectly plumb. Welcome feedback on that idea from the pros!

As for the trial run, I've attached pictures here and am interested to hear if this setup is good enough, or if any of the gaps are unacceptable. Also welcome any tips on how to maintain tight fitting herringbone pattern, as I can see that any small imperfection on one side becomes an unacceptable problem as I continue to layout the floor. Thanks in advance for everyone who's following along and offering tips!

Having done both herringbone and inside the walls, I have to say I like your floor. Is it necessary to go herringbone? Probably not. Does it look good? Absolutely yes. Does it work well, absolutely yes!
Herringbone pattern works well because it limits uncontrolled movement which is why it's used for driveways.

You need not worry about any miniscule gaps as they'll soon fill with ash.

[NCMan]

You can use your wet saw to make the curved buts by slicing small "chord" cuts and smoothing by feathering along edged of wet saw blade. You also have the option of placing the dome on top of the floor which means you do not need to be as precise on the cuts and can make them "proud". The only reason to cut inside is the potential of removing a replacing a brick. That said I have only seen one or two ovens that actually needed to replace a brick. If I were to do again, I would place dome on floor and save my time and labor resources else where.

I agree. There are probably just as many ovens out there that sit on top of the floor as those sitting around it. I also don't put much credence in the whole "you may have to replace a brick sometime" theory. Not only is it extremely rare to have to do that, I can't imagine how hard that would be to do. To me, it's just not worth the hassle of all that. The only thing I'd mention in addition, is that you want to be sure to leave some of the floor brick sitting "proud" (like Russ says) and to preferably not have your dome walls sitting too close to the edge of the floor bricks. It's also not good to have too much sitting proud, as it absorbs heat and gets wasted if too much is left sitting outside the dome. I leave about an inch or so outside the dome walls and be sure it's properly supported, as it is holding up the weight of the dome. I'm not sure if it's been discussed here in your thread, but it's best to not mortar down the first course (bed joint), but do mortar in between them (head joint) of your first course/chain. This allows some movement to occur, as is needed, IMO.

[UtahBeehiver]

You can use your wet saw to make the curved buts by slicing small "chord" cuts and smoothing by feathering along edged of wet saw blade. You also have the option of placing the dome on top of the floor which means you do not need to be as precise on the cuts and can make them "proud". The only reason to cut inside is the potential of removing a replacing a brick. That said I have only seen one or two ovens that actually needed to replace a brick. If I were to do again, I would place dome on floor and save my time and labor resources else where.

[Macrinehart]

Thanks for these tips, will give the diagonal a try.

UtahBeehiver, your picture raise another question I've been wondering about - cutting rounded edges for the boarder of the floor, as well as the intersections between the interior dome wall and the opening arch?

I've seen videos of folks using an angle grinder to cut these curves, plus a stone chisel and hammer for finishing, but I keep imagining the spinning grinder wheel getting bound in the curved cut and exploding into flying bits of shrapnel.

Is that how people are actually doing those cuts? Any safety protocol aside from the standard precautions (gloves, face shield, mask)?

[UtahBeehiver]

Agree with NC you do not need to do a herringbone, a diagonal will work just as well. The purpose of either is to minimize points of contact where a peel may catch when sliding across the floor.

[NCMan]

The herringbone pattern is not really needed, if it gives you too much trouble. Yet another myth, IMO. All you really need to do is set them at a diagonal pattern to the opening. It accomplishes the same thing. As for setting the bricks, I like to use a mix of sand and fireclay to set them. mixed dry, no water. Use a notched trowel, such as one used for tile work. Usually only takes a small amount of it under the bricks. I tap them in place w/a rubber mallet to level them up. Do your best to get them all flat on top and as tight as you can. Be sure to get all loose material off the slab beforehand. Best of luck!!

[Macrinehart]

Hi gang - Here's the latest from Portland! So today we put what is hopefully the last of the freezing weather behind us, although we are in for more rain over the next week. Nevertheless, we had a beautiful sunny morning today so I jumped on the opportunity to check out the hearth and make some progress on the build!

first stop, cleared out the tent and space heater, and then took a peak at my hearth to see how it's doing. It looks like a concrete hearth, no surprise there! The loose sandy material on top is about 1-2 mm thick, not a huge deal in my humble opinion. But I'm giving it another week under the plastic before I remove the forms. (That will be 2 weeks total). Weather will be highs in mid 50s (F) and lows in mid 40s with rain showers for the entire time.



Not satisfied to look at the hearth and will a week to pass in an instant, I decided to pull out the full size floor template, pick through firebrick that arrived last week layout the floor. The next couple shots show the formation of my herringbone pattern, which I realized is quite a puzzle, especially if the pattern starts to get out of alignment. I was expecting the bricks would have some variation in quality. What I didn't expect was for bricks to not be square or plumb. Yet there was some of that so I ended up doing a lot of sorting to build the best floor possible.

I was thinking of building a very large hand sanding disk to go over the floor once it's set in it's final arrangement but I think that could possibly have some unintended side effects, such as expanding gaps for bricks that are not perfectly plumb. Welcome feedback on that idea from the pros!

As for the trial run, I've attached pictures here and am interested to hear if this setup is good enough, or if any of the gaps are unacceptable. Also welcome any tips on how to maintain tight fitting herringbone pattern, as I can see that any small imperfection on one side becomes an unacceptable problem as I continue to layout the floor. Thanks in advance for everyone who's following along and offering tips!

[NCMan]

I’ve been reading the concrete drying discussion with interest. We poured the footings for the block walls for the basement of our family home when I was in middle school. Once set, they were covered with old towels and blankets. It was summer vacation, and it was my job to keep those coverings wet all the time. I can’t recall the duration, but it was over a week. That was 50 yrs ago and my parents still live there. Not a crack to be found in those walls. Of course, I was just doing as I was told because kids didn’t ask questions back then. Now I know the why.

Bottom line: keep the existing moisture in as long as you can.

[Giovanni Rossi]

I’ve been reading the concrete drying discussion with interest. We poured the footings for the block walls for the basement of our family home when I was in middle school. Once set, they were covered with old towels and blankets. It was summer vacation, and it was my job to keep those coverings wet all the time. I can’t recall the duration, but it was over a week. That was 50 yrs ago and my parents still live there. Not a crack to be found in those walls. Of course, I was just doing as I was told because kids didn’t ask questions back then. Now I know the why.

[Macrinehart]

I am glad to see the discussion on best methods for cutting concrete. I stopped wetting my slab after NC's comments, but also concerned about freezing per Mark's comments so kept the space heater going under the hearth since we are experiencing freezing Temps 3 nights this week. Also setup the canopy again and used large tarps to build a tent structure all around for protection from rain, wind (thankfully not much to report) and temp variation. I just checked today and my temp in the tent with space heater going is 60F (15.5C). Outside it's 47F and raining.

I do not have plastic directly over the slab, but I could add that. The tend structure seems to be retaining humidity. My inspection today I can see there are areas of the slab that have firmed up on the surface, but others other like they have a thin sandy layer on top of solid surface. I plan on leaving in the forms for 2 weeks. Possibly longer if I'm not ready to move on by then.

I did get a measure water to concrete ratio as well, and found that I couldn't work with the ratio of 2 liters/60 lb bag. After some experimentation I landed on the ratio of 3.5 liters/60 lb bag. My method was add 4 liters to the mixer, then a 60 lb bag. Then mix about 5 minutes before adding 3 liters and another 60 lb bag. My observation was that if I did <4 liters on the first bag the concrete would cake to the bottom of the mixer and I'd end up with wet concrete spinning around on top of 2 inches for cake-like material. A few times I scraped that material off with a shovel, but found that process was too slow and also just left me needing to add more water to get a workable texture.



Forgive the mess - I finished this tent at dark on Sunday and rushed inside. Actually covering a muddy area with those concrete bags so I don't track a mess all through the house.

[david s]

So we hit a low of 32 last night but with the space heater going and build covered it was very comfortable warm when I check this AM. I fixed up my tenting rush job from last night and gave the hearth slab a drink with the sprinkler set on shower.



There is an ever so slight slope to the front. I notice that water pools up on the slab but over a few minutes it gradually drains off the front. This is not unexpected. When I checked my level the last time the bubble was between the lines but touching one side indicating this slope. I decided further tweeking of the stand wasn't necessary.

Yesterday I tried to put a bull nose edge on after taking that picture, but mostly just made a mess that I'm sure will have to touch up when the forms come off.

We are currently having a heat wave here and reading your report of an overnight minimum of 32 made me laugh. Our overnight minimum was 30 two nights ago. But that was Celcius not Fahrenheit. 30 C is 85F and when accompanied with extreme humidity is quite uncomfortable. Needless to say we have our aircons running 24/7, Mixing heavy materials in a barrow in the middle (or ar any time) of the day in these conditions is not much fun.

[NCMan]

I heartily agree with you NC. For years I have preferred to refer to them as drying fires rather than curing fires. Calling them curing fires is confusing. As there is no chemical action taking place when driving off the free water in concrete at the temperatures to which we fire. Regarding damp curing, we do precast concrete and after demoulding cover the casting in wet hessian and seal it up in a plastic bag for at least a week. As you say, it is the constant retaining of moisture that’s important rather than a wet/dry environment.

Yes, David. I am glad to find someone w/similar real world experience to help explain this. There is just so much misinformation out there, that sometimes it takes someone to speak up.

[david s]

I heartily agree with you NC. For years I have preferred to refer to them as drying fires rather than curing fires. Calling them curing fires is confusing. As there is no chemical action taking place when driving off the free water in concrete at the temperatures to which we fire. Regarding damp curing, we do precast concrete and after demoulding cover the casting in wet hessian and seal it up in a plastic bag for at least a week. As you say, it is the constant retaining of moisture that’s important rather than a wet/dry environment.

[NCMan]

I have to stress again the importance of keeping the existing moisture in concrete/cement, as opposed to continually spraying it. It's the wetting/drying process that causes weakening of the surface. Ideally, a slab should be covered w/a plastic membrane or a cure/seal product to retain existing moisture, not adding water later, off and on. I also have worked in the construction field for over 45 years (now retired). I've worked on many large projects where the engineers were literally standing over you, telling you exactly what is allowed (and part of the job Specs) and what is not. Never once in all that time, would even one of them allow wetting of concrete. I get what people are trying to do, by retaining the moisture, though. When I poured my slabs for my oven, firstly, I added as little water as possible, but enough to be able to work it. Secondly, when done placing it and it had set enough, I covered it w/plastic. Next, I was sure to keep it from drying too fast, so I placed cardboard over the plastic to keep the sun out. I also left my forms on for as long as was possible. I left it that way for over a week. The slabs stayed "green" for a very long time, as they were allowed to cure as they should. Ideally, I'd say the absolute best way to cure a slab is to flood it w/water (once it is able to be) and keep it that way, fully immersed, but that is not feasible in most cases. On a somewhat related note, this is why when people call it "curing" an oven when starting a fire, it is the absolute exact opposite of actual curing. No one ever cures any cement product by starting a fire to dry it out. Calling it a "drying fire" is more accurate, but it is in no way "curing". Not by any stretch of the imagination. It's what I call another "internet myth". There is no curing going on w/a fire. None.

https://www.cement.org/learn/concret...n-construction