Pdx 42" update

[Macrinehart]

Haven't been able to work on the oven for the past couple days but I've been thinking about cutting those arch bricks where they intersect the dome and wondering about the process for marking the lines I need to cut. This is probably a challenge that's been solve 1,000 times but I've had trouble visulizing how to mark the plane I need to cut through the back of the brick.

I think I have the approach. Borrowing this picture from JRPizza, I'm visualizing the radial line as a laser line aimed from outside the dome to intersect with my arch brick at the point where the back of the brick intersects the dome and also centers on the pivot point of my IT. If I get all this lined up correctly I should be able to use the cross pattern on my laser level to mark the plane of this cut on the surface of the brick as shown in this 2D view. The only other thought I had is that my cross sight should, as close as possible, be tangetial to the opening arch where it intersects the oven dome to mark the correct line on the brick.

Of course, this has to be done on each side of the brick to mark the correct plane. My thought there is to just use the laser to mark the line on the top face, while using the cut edge of each brick to mark the opposite face.

Hopefully this ramble makes sense. I welcome other thoughts if this approach is over complicating things

[Macrinehart]

Back at it this weekend, with sunny, windy and cold weather in Portland, just a few degrees above freezing! But with long underwear, hat and waterproof gloves there were no problems operating the wet saw! Still going through the blades, though...I bought 2 new continuous rim diamond blades from HF and used one completely just to nearly finish cutting the wedge bricks for the opening arch. I wonder if my bricks are extra hard, or if I'm doing something wrong. But I've decided not to worry too much about it.

I have a question on the inside of the opening arch before I continue. Notice on the photo below I've drawn a pencil line marking the 21" radius from the center of my oven, and that line is about 1/8" above the bottom edge of my keystone brick. Does that represent a problem? Is my opening arch too far forward?

As far as next steps are concerned, my next step is to cut the backs of the opening arch bricks according to illustrations provided by mongota & JRPizza around post 132 in my build thread.

[Macrinehart]

I've been reading up on this and it may be that I am being too agressive on my cutting and overheating the blade.

[JRPizza]

I just went with the HF blades. Think I went through two of them for my 39" oven. It was back when you could get 20% off coupons any time you needed them

[Macrinehart]

Hello fellow builders! Today's question is wet saw diamond blade selection - namely, is there a recommended brand that balanced blade longevity and price?

I am back working on my project after a long pause, and today am focused on cutting bricks for the opening arch. After working for a few hours I am back on hold again as my 10" continuous rim diamond blade purchased at Harbor Freight is worn out. That's the second blade (first was lightly used) so at my present rate I estimate maybe 10+ blades to finish my 42" oven. At $40/each, its ok, but would I be better off buying a higher quality blade?

Appreciate the advice!

[UtahBeehiver]

As long as you are aware of what happens by having the pivot point off the elevation of the floor. If you use as is, the dome will be higher at the apex by the distance the pivot point is off the floor elevation. This config will make a tapered inner arch interface not mate very well . If you make sure the IT is adjusted to meet the internal radius consistently (IE 36" ID oven = 18" radius) on each course, then you probably get away with the current IT setup. Don't let impatientness cloud your work. Once the bricks go down it is difficult to correct.

[Macrinehart]

Hi guys -

Managed to break away from work early today to picup materials for my home brew. Thanks for the tips!

UtahBeehiver - I was reading your guidance on the IT for Michele Enrico and realized I could face a similar issue due to the design of my IT which uses the magnetic door stop for a pivot point. Based on another design I saw on the forum.

So I have a couple thoughts on how to proceed. First, I could do nothing and just adjust the length on the IT with eav course. .ight have to cut my IT down a bit but it's no trouble as the rod is coper pipe, which is pretty easy to work with. The threaded extender is pretty long so lots of flexibility.

Other option is to pull the center floor brick, which I plan to do in the end anyway, and then cut the plywood based down to brick dimensions and set it on the CalCil directly so that the pivot point is closer to floor level.

I'm thinking I'll just use option 1 as I'm impatient to get on with the project, unless someone see's a crisis looming.

BTW - with the magnetic door stop the base is mounted to spin, which allows for the horizontal rotation, while vertical rotation is accomplished on the magnetic rails in the pivot point. My welder friend made the bracket for me. The rest is done with standard plumbimg materials plus the threaded rod, nuts and wing nuts. The pivot end of the IT has a transition fitting that is perfectly sized to fit a 1.25" wooden dowel (discovered that through trial and error around at the Home Depot). The dowel is glued in, and then I used that as the base for the rod side of the door stopper.

[UtahBeehiver]

HC Muddox is a west coast producer of fire or brickies clay or call a brick/mason supply house. Fairly cheap but you have to search around for it.

[Gulf]

Some products labeled as “paver sand” have polymer additives that may not be suitable for refractory mortar.

[david s]

I think any sand should be suitable, but a graded sand (ie a mix of different grain sizes is preferable, but if it contains grains that are large and problematic for thin mortar joints, then these should be sieved out.
For the Portland cement use General Purpose cement.
For the clay, any should be suitable, but it needs to be powdered so it will mix in evenly with the other dry ingredients before adding water. Avoid Bentonite clay because its extremely small particle size leads to excessive shrinkage. The cheapest should be Bricklayers Clay from builders supplies.
For the lime, use hydrated or hydraulic lime, not agricultural lime.

[Macrinehart]

Thanks David! I like having the detail to understand the reasoning! So 3:1:1:1 it is! Regarding my other question, are there material spec guidelines for the home brew? Am I good using my paver sand, or do I need to find some specialized ingredients? Cheers!

[david s]

Hey there pro builders, I have a friend who happens to be a ceramic arts specializing in wood fired ceramics and kiln building for wood fired ceramics. He offers a different opinion on the formulation of mortar. His ratio is 1:1 sand and fire clay. Also he advises having a couple different screen sizes in the sand, half 40, half 70. The reasons, no chemicals, longer dry time, easier to work with and he's also considering deconstruction and reusability of materials in the long range plan. I guess, also, if your an unskilled laborer like me, it may be easier to undo errors in the build process and fix them. (Not that I'm likely to make any mistakes of course, since I have the measure 20 times, cut once and take a coffee break work philosophy).

So I've read a lot of posts about the recommended 3:1:1:1 home brew formula, and the advice to work in small batches and get comfortable with dry times, which are faster. I wonder if anyone will take up a discussion on the whys of the recommended home brew vs. my friend's advice. (He didn't have a strong opinion, just a preference for not using cement and lime).

I recall he also talked about the inevitability of shrinking and expanding, and may have felt his approach was preferable in accounting for that movement. But he also expressed that he was not overly concerned with small voids or cracks. His main concern on that front was water penetration, not heat loss. He talked about having more care with cracks on the exterior stucco wall.

So, any takers in extolling the merits of one formula vs. The other? Or maybe just linking to some thread that already addresses this?

One other question I had - what material specs are recommended for the homebrew ingredients? My friend say use a 35 screen fireclay, and mix of 40 screen and 70 screen sand. I haven found many recommendations on specs for home brew. And I happen to have an extra bag of paver sand (no additives)...can I use that?

That's a lot, sorry for the ramble and looking forward to the discussion!

Cheers!

Mac

The requirements for a mortar to be used in a kiln are very different to those of an oven. Sand, especially in the presence of certain fluxes will melt at around 900C. Most kiln interiors will well exceed this temperature. For this reason grog (ground firebrick) rather than sand is a preferable material for kilns fired to stoneware temperatures. A mix of grain size enhances strength just as we use aggregate in concrete. The large spaces between the larger aggregate get filled with large grains of sand, the spaces between those get filled with finer sand and the spaces between them get filled with the cement paste. For mortar the same applies, but you don't want any large grains which could interfere with seating the brick units. The finer the sand the more workable will be the mortar.

Regarding the clay, small amounts make a mortar more workable, however anything exceeding around 15% can make the mix a bit too sticky to work with and also introduces excessive shrinkage leading to cracks. At 573C clay undergoes the Alpha change that sinters it and makes it permanent (won't return to mud). As the temperature increases the "fired" clay becomes harder and shrinkage increases further. For a kiln this process makes a 1:1 clay sand mortar permanent, but for an oven probably only the mortar facing the fire at the crown, on the inside will achieve this temperature.

The use of lime in the mortar gives it a greater tolerance for higher temperature. Portland begins to fail north of 300C and lime 500C. If that fails the clay takes over as the cementious material.


The homebrew mortar is a highly suitable (and cheap) mortar for home ovens. The lime content actually extends working time in conjunction with calcium silicate (Portland) cement. It would not be suitable for the higher temperatures experienced in kilns. What is commonly referred to as refractory mortar is expensive and has a very short working
time because it relies on calcium aluminate cement which uses a different chemical reaction.(never mix lime with calcium aluminate cement, it acts as an accelerant.)

To seal up the door of my kiln, I use a 50/50 mix of clay and sand.
Attached are two pics of a spy hole bung made of 50/50 clay and sand that shows the shank of the bung (fired to 1120C) while the knob, exposed to ambient temperature remains unfired.

[Macrinehart]

Hey there pro builders, I have a friend who happens to be a ceramic arts specializing in wood fired ceramics and kiln building for wood fired ceramics. He offers a different opinion on the formulation of mortar. His ratio is 1:1 sand and fire clay. Also he advises having a couple different screen sizes in the sand, half 40, half 70. The reasons, no chemicals, longer dry time, easier to work with and he's also considering deconstruction and reusability of materials in the long range plan. I guess, also, if your an unskilled laborer like me, it may be easier to undo errors in the build process and fix them. (Not that I'm likely to make any mistakes of course, since I have the measure 20 times, cut once and take a coffee break work philosophy).

So I've read a lot of posts about the recommended 3:1:1:1 home brew formula, and the advice to work in small batches and get comfortable with dry times, which are faster. I wonder if anyone will take up a discussion on the whys of the recommended home brew vs. my friend's advice. (He didn't have a strong opinion, just a preference for not using cement and lime).

I recall he also talked about the inevitability of shrinking and expanding, and may have felt his approach was preferable in accounting for that movement. But he also expressed that he was not overly concerned with small voids or cracks. His main concern on that front was water penetration, not heat loss. He talked about having more care with cracks on the exterior stucco wall.

So, any takers in extolling the merits of one formula vs. The other? Or maybe just linking to some thread that already addresses this?

One other question I had - what material specs are recommended for the homebrew ingredients? My friend say use a 35 screen fireclay, and mix of 40 screen and 70 screen sand. I haven found many recommendations on specs for home brew. And I happen to have an extra bag of paver sand (no additives)...can I use that?

That's a lot, sorry for the ramble and looking forward to the discussion!

Cheers!

Mac

[Giovanni Rossi]

Welcome back Mac. I was hoping you were just taking a break from building. Looking forward to your progress updates.

[Macrinehart]

Well guy and gals, it has been a long and momentious summer filled with too many trials and tribulations to recount...but I'm back and getting ready to resume work on the oven. So, when I left off, I had laid my oven floor and cut bricks for the first course of my dome. I also have my indispensible tool built - used the magnetic door stop as the fulcrum. But I haven't decided how to secure it to the floor yet.

I made a jig for the compound angle cuts, but it's not well engineered so I'm looking into a 3D printing option to make it a little more precise and robust. And JRPizza I will take you up on your offer of help with the tapper jig you used for your opening arch. I will follow-up with the taper angle I need.

It's good to be back! I am looking forward to finishing the build this winter!