Newbie mortar question

[skemcis]

Hi, Does anyone know where I can find firebrick mortar in the British Columbia interior? I have found Superior 3000 mortar, but it can only be used for 1/8" applications. Also have some Cercast mix, but it is pretty full of fine gravel, not something I would want to use to try and tamp into the crevices. Any help would be greatly appreciated.
I have been a background reader on this forum for a long time, and have finally gutted it up to get to the actual brick work. The hearth(s) are built on 8"*8" Spruce timbers, all sitting on 24"*24" concrete grade beams. Oven floor set in place, and awaiting the dome. Sorry no pics, spent $$ set aside for camera on brick.

[skemcis]

Re: Newbie mortar question

Ha, found one. Steel Industrial Supply in Kamloops, BC. Premix Fireclay in 25kg bags. $52.00 Cdn. Seeing as I have a 6 hr round trip to pick this up, anyone got a rough idea of how much one would use to complete a 42" high dome?

[DrakeRemoray]

Re: Newbie mortar question

For the record the HeatStop that many of us have used also says it is for thin mortar joints, but it worked fine for me.

[skemcis]

Re: Newbie mortar question

Thanks Drake. Well, I've got a 4 litre pail of it. Maybe I'll start the oven entry pillars and arch with it. Read your build blog by the way, very,very nice.
Another question, if the Pompei plans are correct, there should be no mortar showing at the inside edges of the dome. Is this doable? This is my first project with brick, and I do want to get it right.

[Neil2]

Re: Newbie mortar question

"I have found Superior 3000 mortar, but it can only be used for 1/8" applications."

This stuff works OK. For the parts that will be more than 1/8", extend the mortar mix with mortar sand mixing 1:1. The sand particles act as a "bridge" and reduce shrinkage cracks.

[skemcis]

Re: Newbie mortar question

Thanks, Neil2. Mortar sand, now does that mean I can justify using the wife's flour sieve? chuckles..... or being a little more serious, I was thinking of using window screen material in a frame, does that sound about the right size? Got lots of clean river sand here.

[Les]

Re: Newbie mortar question

Another question, if the Pompei plans are correct, there should be no mortar showing at the inside edges of the dome.

Actually, the plans have a mortar joint on the inside - it can be done without one if you spend the crazy time cutting the brick. The verdict is still out if it's the right approach because of spalling. I'll let you know in ten years

Les...

[skemcis]

Re: Newbie mortar question

Les, yeah I figured so. So here is another question. If the arc of the dome is based on the radius of the inside at floor level eg 21", a straight edge centered on the floor and reaching out to the outside of the bricks being laid, if the bricks are positioned/angled correctly the straight edge should lay flat on them, which theoretically should be true for each course. This should give me a reasonably true arc, coupled with an accurately cut keystone. Am I correct in presuming this?

[Les]

Re: Newbie mortar question

a straight edge centered on the floor and reaching out to the outside of the bricks being laid, ?

Did you mean inside? Yes, for a 42 inch dome, it's a 21 inch radius (on the inside). I cut a form that was true to ideal - you are working with brick so it will not be perfect.

Les...

[Les]

Re: Newbie mortar question

if the bricks are positioned/angled correctly the straight edge should lay flat on them, ?

I re-read your question. Do you mean if you taper every brick (inside to outside) should they lay flat? Absolutely! I advocate a dry stack - if I could do it over, I would give it a shot (but I would still be cutting brick instead of cooking).

Les...

[skemcis]

Re: Newbie mortar question

Les, yes inside radius. Sorry, just not used to explaining things very well. As far as a form, I think I will cut up an old interior door to size, slice the form horizontally and install a couple of hinges on one side and a latch on the other. That way I will be able to fold it and get it through the oven opening when done. Hey, I looked at all your photos, what a grand job, hope mine turns out half as well.

[skemcis]

Re: Newbie mortar question

I re-read your question. Do you mean if you taper every brick (inside to outside) should they lay flat? Absolutely! I advocate a dry stack - if I could do it over, I would give it a shot (but I would still be cutting brick instead of cooking)

Yes, I got the idea when originally thinking about a barrel vault oven. 42" wide inside. I dry laid all the bricks with wedges and a form. I glued a nail 21" or center at bottom of form and then used a straight edge from the nail to the outside edge of each brick to get the correct angle of arc. Turns out that the keystone when set in place tied this together very well. I pulled the form out very gently and the arch stayed together without any other friction other than the bottom edges of the bricks. No cutting. I was just experimenting.

[DrakeRemoray]

Re: Newbie mortar question

Well, I've got a 4 litre pail of it.

The word "Pail" makes me alarmed. Is this a premixed mortar? Premixed mortars are air-set and remain soluble to water....not the right thing for an outdoor oven.

Drake

[skemcis]

Re: Newbie mortar question

Yes it is premixed. Well now, am I ever in a steep learning curve. Learning to fly was easier than this project. Anyway, I have sourced some fire clay in 'bags', which should arrive in Kamloops on Thurs/Friday this week. I am wondering if you would be interested in looking at some pictures of the mock up? I think I can post them here. I am having some problems figuring out the transition between the wall and the vent area. The way I understand it is the vent and associated stuff should be thought of as separate from the dome. Given this, I suppose I could create the entire dome (without opening) then cut a door through the brick. Then add vent structure to dome. I know this is overly simplified, but I have been pulling my hair (whats left of it) trying to figure this out. Any, and I do mean any help would be greatly appreciated.

[Les]

Re: Newbie mortar question

Given this, I suppose I could create the entire dome (without opening) then cut a door through the brick..

Are you on crack? Why not build to the plans - they will get you damn close. It IS hard to visualize, but as you start going vertical you will get the feel. The upside, we are here to walk you through it. I think it's great when people push the edge, but cutting your entry is going to cause some problems - compromising mortar joints come to mind.

Les...