28" Pompeii

[GianniFocaccia]

Re: 28" Pompeii

Gene, you're going through exactly what I did. My mortar seemed dry and grainy and not that easy to work with. I messed with the sand/fireclay ratios in an effort to get a more pliable mortar. Things didn't improve. I inquired about this with Tom (tscarborough) and he explained about using the correct sand grain size for the size of joint you are using. He said to 'build' your mortar aggregate 'mix' using varying sand sizes in order to minimize the volume of Portland cement needed which reduces the potential for shrinking and cracking. His analogy was the jar filled with marbles, sand and water.
I was gifted 400lbs of 120 grit fine silica sand and the difference was like night and day! The mortar is smooth and buttery, not gritty, and a joy to use. Because my joints are small I elected not to add any larger-grain sand. Interestingly, up to now the dome has been largely built in cool, damp weather (no cracking) but recently the day temps have climbed into the 80's and the quicker dry times have revealed a few super-fine cracks. Try a smaller (30/60?) grain size, consider blending, and cover your latest work with a damp towel if it's warm.

[ggoose]

Re: 28" Pompeii

Great advice John - makes sense. The logic seems similar to sanded vs. non- sanded grout I think. It all depends on your joint size. The smaller grit should also allow greater workability. I think the sand in the FB is a bit course (or perhaps its just my mortaring proficiency).
Thanks,

gene

[ggoose]

Re: 28" Pompeii

Over the last several days I have been able to set a few courses of the dome and the arch columns. There is defintely a learning curve associated with the use of this refractory morter. I expected it to behave like thinset, though it behaves more like wet sand. I am going to try various types of refractory mortar on this build to see if one behaves (for a novice) any better then another. I'll post anything worth passing along. In the mean time, the weather is favoring dome building: not too hot and not too windy. My neighbors, seeing the dome rise from the hearth, are beginning to be believers and are perhaps thinking this thing could cook pizza one day, so they have been offering me beer as I work, no doubt to endear themselves to me in the event it actually all comes together .

[GianniFocaccia]

Re: 28" Pompeii

so they have been offering me beer as I work

Wow, Gene! How perfect! I can see it now: Just as you get underway your neighbors see you throw your head back in exhaustion, press the back of your hand to your forehead and mumble 'heat exhaustion!'. They run over with a cold one to see if you're all right and after a swig it two you reassure them you'll make it!

[ggoose]

Re: 28" Pompeii

I have added a course or two since my last post. I have begun my 6th (though not shown in the photos) and will need to transition to the arch with this course. The mortar is fairly dark and, even though I wipe down the bricks as I go, I will likely need to clean them again. Judging from other posts, it sounds like the solvent of choice for this is muriatic acid. I have no experience with this stuff, but that is par for the course, since I have no experience setting fire bricks either...

[Les]

Re: 28" Pompeii

the solvent of choice for this is muriatic acid. I have no experience with this stuff

Some may advise against it but I used a 50/50 mix. It will clean the mortar pretty easy. Just don't let it touch your skin, clothes, or lungs - it's nasty!

[GianniFocaccia]

Re: 28" Pompeii

Gene,

Dome's looking good! Nice control on your joints. You're not kidding - that mortar is dark. What kind is it? Have you been using a sponge on it after each brick is set?

[ggoose]

Re: 28" Pompeii

Thanks Les and John.

John, the mortar is FB50. I clean each brick after setting it. Still it leaves some rather dark haze though. No matter; it seems to bond well which is all that matters in the end. I will try the muriaric acid at 50/50 as Les suggests to see if I can get it a bit cleaner.

gene

[ggoose]

Re: 28" Pompeii

Just completed the interior arch and intersecting brick course today. I angled the inner portion of the arch bricks as I have seen others do (GianniFocaccia and Kerangi Dude come to mind) and it seemed to make the transitional brick cuts simpler. It looks like I will be completely above the arch after the next course, though I am running low on mortar, so I may not get to it until next week. It is amazing how much time it takes for me to do a single course, though I do seem to be getting the hang of it...

[GianniFocaccia]

Re: 28" Pompeii

Congrats, Gene. You've done a beautiful job engineering a graceful, easy transition. No wicked v-cuts to have to make and the outside of your dome above the arch will be clean.
One recommendation, though. You may want to fudge the horizontal joints of the next two or three courses (above the arch) up about 1/8" each. Although I was trying to be careful I didn't do this on the lower courses and ended up with a mild case of the dreaded droop. Also, cutting the bricks immediately above the arch a little taller than the rest of the course helped bring each successive course back into round.

All told your arch looks clean and strong.

John

[ggoose]

Re: 28" Pompeii

Thanks for the comments John. Funny you should speak of the "dreaded droop". I was fiddling with the next course above the arch and it kept rearing its ugly (drooping) head. I have a bit of a drop there, but only about 3/16's inch...difficult for the eye to detect, especially since I am not cleaning the outside of my dome as you are. By the way, I nominate your dome as the best example of how to build round dome out of square-ish bricks - that thing is a work of art. Too bad they don't make transparent insulation ...

gene

[gt40]

Re: 28" Pompeii

That is a beautiful oven. I really think you nailed it with the transitions on the arch.

congrats!

[ggoose]

Re: 28" Pompeii

Partially thru the 10th course now. I am just about to open my 4th bag of mortar...taking a bit more than I planned, but then I am smearing it on the outer edge which accounts for quite a bit.
I think I will need to set a form in the dome to support the final courses, as the indespensible tool becomes less efficient as the bricks are set more vertically. Hopefully I can complete the dome this weekend and begin the front of the arch and chimney by monday.
After using several bags of FB50 I have come to like it. It bonds very well - no cracks yet. It is was intitally bit of a challenge to work with for a novice like me, but once I figured out the proper water ratio, I was able to place it faster and with greater ease. My next sack of mortar is Heatstop50, just to be able to compare the two. I'll post anything of note.
Here are some progress pics...

[GianniFocaccia]

Re: 28" Pompeii

Nice work, Gene, and even nicer progress! It won't be long now before you're yelling "who wants pizza!"

[Lburou]

Re: 28" Pompeii

Nice work, Gene, and even nicer progress! It won't be long now before you're yelling "who wants pizza!"

John's right, looking good