42" Pompeii construction in Adelaide

[P3 Stoaker]

Also, meant to ask, doesn't seem to be much around home when searching for fire clay. Might be called something different here in Aus? Has anyone found any and what was it called?
Can anyone tell me what it's made from, and the rough ratio's? I'm concerned I'll be told something is fire clay but it may be something all-together different?? If I know what's in it I can check it's the right stuff.
Regards

[UtahBeehiver]

I am not quite sure I follow, Second sentence say dome "On Top" firebrick, which a fine. Then second paragraph talked about first course on CaSi or do you mean floor brick. Bottom line, The horizontal joint between the floor and the first course is NOT mortared, the vertical joints are. This is done so the dome and the floor expand and contract more independently and reduce potential cracking issues. No sand/fire clay need since floor appears level,

Fire clay sometimes call "brickies clay", it is powdered clay. Can also be found at pottery stores as well.

[P3 Stoaker]

Thanks Russell, apologies for confusion, I meant to say floor bricks rather than Casil.
I'm laying first dome course on the floor bricks as a header, it's a tapered half brick though and I suppose my main question was whether it's lifted at the back so as to start the 'dome curve'. As you say just lay it flat on the floor brick and mortar the side vertical joints. I guess that means as the second course is risen at the back to align with the IT it will have a sizeable gap to fill with mortar?? As you say mortar is your friend.
Regards

[UtahBeehiver]

Tight inner joints is what you are after, backfill the sides and back with mortar. I am a little surprise that you say the second course has a sizable horizontal gap, what do you consider sizable? You never see the back side one all said and done.

[P3 Stoaker]

I'm with you Russell, in that mortar is your friend, or in my case will be. I am just getting ready to lay the first course. I'm happy with, and many thanks for all the advice, but just to explain where the comment came from, in regards to the sizeable second course joint, When laying the first course flat on the floor bricks it obviously doesn't commence the dome curve. I assume this means the second course has a larger gap at the outside where it meets the first because the second course, if aligned correctly with the IT tool will take up the gap for the first and second courses, in comparison to the case if the first was laid in true alignment with the IT, and had appropriate gaps at the rear.
Hope that makes sense, either way I'm laying the first course flat on the floor bricks and I will be using a little fire clay for the rear quarter as its a little lower, I plan to start laying at the highest point and keep it level from there. I'm just in the middle of modifying the IT tool with a fork bolt at the bottom to better align with true floor level.
Kind Regards

[UtahBeehiver]

As you lay the dome bricks, any corrections such as width, or less perfect bricks place towards the front half of the dome with the best work and brick faces on the back half of the dome, you can only see the back half when the dome is complete and fired up. Also watch to make sure you stagger the vertical joints from course to course, looking on the outside joints of the dome does mean the inside joints are the same.

[GreenViews]

Greg, If you see my build, I did that very thing. I placed my first course (actually did half solder even) flat on ground, then over compensated with angle of my second course (which for me was also half soldier). That worked out very well for me! I found that adjusting as I went with my template worked very well and I didn't sweat it when one course or another ended up slightly off... I just adjusted the next as I went.... for the last few courses, I stopped using my template at all. The ending became obvious p.s. our ships in life usually never fully sail, the journey just changes course or direction. You got this.

[P3 Stoaker]

G'day All,
Thanks Russell / Tom appreciate the feedback.
Pretty much set to lay the first course but its pissing down rain all weekend so I might start next week as looking a lot better.
I'm using 12" square floor bricks and 2 of the cut edge pieces are a little lower which will cause the dome brick to tilt back out of reasonable alignment ( dome on floor). So I thought I'll get some fire clay, start at the highest point without the fire clay and move around the dome, using the fire clay to keep things level. I'm not a person to fuss too much but I do figure the better the first course is the less work later.
When purchasing the fire clay the salesman knew it was for a pizza oven but no detail. He advised me it wouldn't set and would wash away with rain or water. Whilst it shouldn't get wet and I don't plan on hosing it, I do wonder about its weight bearing strength? I know the advice is 50/50 fire clay and sand but I can't imagine sand increasing it's strength. So I'm now wondering if there is a difference in the product here in Australia compared to USA, I know other products are significantly different to the point I'm cautious and like to avoid a disaster.
I might mix some up and do a test.
Regards

[UtahBeehiver]

IMHO, you will be fine by using a peanut butter consistency slurry of 50/50 fireclay. The difference between the cuts and factory edges cannot be extreme, what are we talking, 1/16 or 1/8"? There is plenty of compressive strength in the slurry and merely acts as a spacer. These ovens are not precise tolerance, you can work yourself into "paralysis by analysis" pretty easy.

[P3 Stoaker]

G'day All,
Thanks again Russell, and I must say I had a good laugh at your comment, paralysis by analysis, I know it got me !!
I have had some progress, a little slow with competing time consuming requirements. First course down this morning and preparing to lay the second, photo's later tonight.
One thing I've discovered is the inner arch template prevents access to that mortar line to tidy it up/finish it, the long inner line along the inner joint of the inner arch, and will be the same for outer arch I guess.
What did you all do about this? Did you simply tidy that mortar joint later when the template was removed?
Regards

[P3 Stoaker]

G'day All,
I've run into a bit of an issue with the inner arch which is causing a few headaches. In addition to the question above in the last post I have also discovered the inner edge of the arch bricks are kicking out and therefore look stepped. To be honest I'm not not all that fussy but I will try to get things looking reasonable, and the misalignment looks worst than the photo shows. In photo no 1 you can see how the lower edge of the next brick kicks out in relation to the brick below. Any thoughts on why or how to fix would be appreciated. I don't really want to continue as the stepping may get worse ?
Few other photo's of progress.
Kind Regards

[JRPizza]

P3, I'm a big fan of laying out the arch flat on the ground to make sure you know how it is going to look. If it is not too late I'd encourage you to do similar to the pic I attached. If you do this you can probably come up with a better way to space the bricks and index them to your form. At the very least you need to make the center line of the brick tangent to your form, which the lower bricks don't appear to be. This also requires your form to be a nice smooth circle.
As far as mortar goes, I had the same problem and all I can say is try to butter up enough mortar that you can see the joint being filled and the mortar squeezing out as uniform as possible - you have visibility on the lower rows. Then try to do same on upper rows. I had to go back and do some grinding and filling after I pulled my form.

[P3 Stoaker]

Thanks JRPizza. Initially I was going with a lower inner arch and I did dry lay which worked perfectly. I then thought safest to stick closer to the 60 odd % ratio and raised the arch, using a new form for which I didn't do a dry lay. I've just now removed the form and tried a dry lay which has the same problem. One issue I previously looked at was the inner arch height (radius) needs to be taller than the radius of the arch width, according to all the guidance. I assume everyone works through this, did anyone have the same considerations? So the arch height is 315mm (12 inch and 13/32) and the radius of the width is 240mm (9 inch and 29/64). So what I did which may be the problem was to essentially start the arch radius around 3/4 the way up that first brick which was layed on the oven floor.
Another possible problem may be the bricks I'm using. I've worked out the required gaps along the inner and outer to be around 3.25mm (1/8") and 24 mm (15/16"). The bricks are already somewhat tapered but it seems that opening the back up to 24mm causes the inner edges to be mis-aligned and yes that lower brick is not tangent to the form, but seemingly cannot be when the back is set to the required gap.
The only thing I can think of so far is to reduce the outer edge gaps thereby improving the inner alignment which will most likely require a wedge at the top. A little disappointing given bot too much of the brickwork is ever seen and the arches definitely are seen !!
Any thoughts/comments on how to solve this will be greatly appreciated.
Kind Regards

[UtahBeehiver]

I agree with JR that prelaying out the full arch is you best bet. I also believe the issue starts with the first arch brick, the face is not perpendicular to the center of the arch but rather tipped up too much. Mark the center point on the face of the brick this should be the contact point on the form, not the edges of the brick.

[P3 Stoaker]

Thanks Russell. Certainly makes sense what you are saying, but achieving it, or importantly why I'm not is the question. The first brick is square and not tapered, 75mm (2 61/64") thick and the bricks above that I'm planning to use are tapered, with the same size at the back, or outside of the arch and reducing to 65mm (2 9/16") on the inner face. As detailed above I positioned that lower brick and started the arc above the floor. For info, given all the advice is that the radius of the arch width along the bottom, across the arch is shorter than the height required what is the common way to combat that ? ( some measurements in posts above). What I did was to start the arc at the top of that first brick which meant the radius width and height worked, but as described the height was lifted by the lowest brick thickness which is why its a square brick.
So currently working through, do I cut it all out, or continue where I'll likely have a wedge at the top as a result of not opening the gaps at the back to the required 24mm.
I'm going to run into the same issues with the outer arch so understanding this will be important sooner or later, might as well be now. Many thanks for your ongoing assistance.
Kind Regards