Lip on dome bricks using a tramell

[TEDFB]

I wanted to start building the dome, so on a small dry test I found that on the first brick after the "soldiers "the brick squared off well, but if I square the second brick it leaves a lip on the top of the first brick.
Any ideas
I also layed the floor with a sand clay mix 50 /50 and I found that there are a few bricks that are not solid, (loose)
Would appreciate any input

[Giovanni Rossi]

I'll jump in since no one else has yet. Pictures would help. If you set your trammel so the inside of the dome is at the bottom of the soldier and you used a true soldier (i.e. 9" high), it stands to reason that the next course would line up inside of the top of the soldiers. You'll need to adjust the length of your trammel now that the soldiers are in place.

Also important is the position of the shaft of the trammel. Do a search for IT or indispensable tool and you'll find a lot of good info from the experienced builders who have made their own tools. You'll see that it's important to have the pivot point at the center of the floor as close as possible to the final floor height. AND, the center of the trammel shaft must line up in the middle of the dome bricks to achieve a hemispherical dome.

If your reason for starting with a soldier course is to make a flatter, Neapolitan style oven, I believe your going to need a different trammel set up or make it an adjustable tool, but I'll let others with more experience weigh in on that as well as your floor brick question.

[TEDFB]

Hi Giovanni
I have got my Email and web sites cross wired hope this works

[TEDFB]

Hi Giovanni,
Did you have any take on me building on my floor that has a few loose bricks, as the dome just rests on the floor
Best regards

[TEDFB]

Mmmm the questions are building up..
How long after soaking the dome bricks can I start building with them, and then how long can I build with them before I need to soak them again.
Hope I am not being too much of a pain

[david s]

The bricks should be moist rather than wet. Avoid water sitting on the surface of the brick. In order to get a good bond the brick needs to suck some water from the mortar. A totally soaked brick, especially with a further film of water on its surface will not allow this, so just totally soak the brick then give it a few minutes to dry a little.

[rsandler]

Back on the trammel question, you need the pivot point of the trammel to be centered vertically on each brick. From your picture, it appear that the pivot point is in line with the top of each brick, leading to the substantial ledges in the picture. Lots of ways to get that offset; here's a picture of the one I built for my second oven. My bricks were 2.5" thick, so the bit of angle iron that the top of the brick sits against was 1.25" above the pivot on the castor.

[TEDFB]

Hey guys
I am really grateful for advise and help, I am going to get stuck into this lot today and will give you an update on the progress,
Have a great day

[Giovanni Rossi]

Sorry Ted, I've been away. rsandler already gave you good direction and clarified my earlier comment: "AND, the center of the trammel shaft must line up in the middle of the dome bricks to achieve a hemispherical dome."
The guys who have built proper ITs (trammels) are very clear that you need to be able to visualize a straight line from the pivot point at the floor through the shaft to the mid point of the inside face of each brick, both vertically and horizontally. Otherwise, each course will be out of alignment with the last.

As far as your floor under the dome, I'm not the best source of info as my floor tiles were mortared in place. I'm not quite sure what you mean by "loose". But, from what I've read on this forum, as long as you've used enough dry sand/clay mixture to be able to get your bricks level and seated well (not rocking) under where your dome rests you should be fine. I've seen some builders recommend using a 3/8" - 1/2" notched trowel to apply a proper amount of the bedding. The weight of the dome will help to hold the bricks in place.

I'll add to david s 's comment about how wet to make the bricks. I had good success with soaking my bricks for at least 15 minutes. When I was ready to lay the next group, I would lightly dry them and rest them in place on the dome. This allowed some water from those bricks to drain and dampen the bricks underneath. This keeps the bricks already in place from pulling too much water too quickly from the mortar.

[mongota]

You want the "L" (green line) that cradles the brick to cover more of the inside face of the brick so that your trammel arm (red line) is centered on the face of the brick.

[TEDFB]

Mmmm, ok if I look at what you guys said and see the green line explanation it should be common sense, obviously that evaded me for a while , any way I modified my trammel and all looks good.
I have layed my soldiers /sailors but because of 104 degrees F I lost my enthusiasm for a couple of days.
Really struggling to cut my spacers for between the bricks with only a hand held angle grinder, but never the less it is coming slowly.
Have a great day, I have been greatly helped by your advice, THANKS

[rsandler]

Won't help with the weather, but as far as spacers, depending on your design, you can use a 12" clamp (I used the squeeze action kind, I think maybe called a clutch clamp) to clamp the brick into the L shaped part of the trammel. Leave it there for a bit so the mortar can stiffen, then no spacers needed. On my tool, pictured above, the clamp sits against the back (outside face) of the brick and the smaller wood block.

[TEDFB]

Hi rsandler
I was under the impression that the spacers were there to prevent cracking if the cement is too thick.
I don't suppose adding a bit of fine sand to the refractory cement would be a good idea for that.
Also is it a good idea to keep it damp for a day or so to allow for the curing?

[rsandler]

I was assuming you were using the Portland cement-based homebrew mortar made of sand, cement, lime and fireclay in a 3:1:1:1 ratio. That stuff can handle a large joint--I've heard of people sticking wedges of firebrick (offcuts from tapering the dome bricks) into the joint to use less mortar and have more strength, but it's not necessary, and surely more work than it's worth if you only have an angle grinder. Neither of my ovens, built with homebrew, used spacers, and if the one I built 11 years ago ever cracked I never saw it and it never affected performance. As with any Portland cement based product, the homebrew mortar will have more strength if you can keep it damp for a week or more, though it will probably have sufficient strength to keep the dome together without doing so. I put a wet blanket on top of the dome of my second oven once I closed it up, but didn't do anything to keep the mortar in the lower courses wet as I laid them (by the time I close the dome, those lower courses had been set for weeks).

If you're using a Calcium Aluminate Cement (CAC)-based product, which typically are engineered for smaller joints, all bets are off and I don't know what to tell you :-)

[TEDFB]

What a pity I did not start off by first getting advice on the this site, as I was advised to begin with that I should stay away from home made mixtures as they tend to fail. Anyway we live and learn, I have spent the money so I will have to plod along.
Thanks again for your input