39" Stargate Pompeii

[Amac]

Re: 39" Stargate Pompeii

Try an old window screen. If your careful you can clean it up and put it back in the window before she finds out that it is missing

Luckily we don't really need window screens here. I guess we don't get a lot of balmy evenings with tropical insects etc. zooming about, and our mosquito population is virtually non-existent. I was tempted by some kitchen utensils but thought better of it and bought a sieve (with a few different grade inserts) for a few quid instead
that brickdust looks good. Mine is all over the place though because of the grinder.

Gianni

According to tscarborough, the ideal mortar has a variety of aggregate sizes in it, much like the jar with multiple sizes of rocks, pebbles, sand, etc. This keeps the portland to a minimum, and if the aggregate is small chunks of firebrick, even better.

This stuff will work with larger joints Ok I suppose - but the smaller and variable widths I will need something finer. I guess I can make two mixes at once

thanks for the feedback - really appreciate it
Aidan

[GianniFocaccia]

Re: 39" Stargate Pompeii

According to tscarborough, the ideal mortar has a variety of aggregate sizes in it, much like the jar with multiple sizes of rocks, pebbles, sand, etc. This keeps the portland to a minimum, and if the aggregate is small chunks of firebrick, even better.

[Gulf]

Re: 39" Stargate Pompeii

Try an old window screen. If your careful you can clean it up and put it back in the window before she finds out that it is missing

Here is one way.

[Amac]

Re: 39" Stargate Pompeii

Don't throw it away, you can simply sieve out the course stuff.

Thanks David - I will try that. I also got on to the seller - they are getting back to me on Monday - maybe get another bag for free.

As I understand it, the largest particles in your mortar should be smaller than your smallest brick gaps..

Yes Chris I would agree - not the case in this clay though. Maybe with sieving as David suggested I can use it - but I feel it should be "workable" not this coarse!
Aidan

[SCChris]

Re: 39" Stargate Pompeii

As I understand it, the largest particles in your mortar should be smaller than your smallest brick gaps..


Chris

[david s]

Re: 39" Stargate Pompeii

Don't throw it away, you can simply sieve out the course stuff.

[Amac]

Re: 39" Stargate Pompeii

I ran into a small - maybe not so small - problem. When I did some testing of the mortar mix the other day I thought the mix felt "gritty" and found some largish bits of grit (brick?) had got in it. Since I mixed it on a concrete slab near where I was cutting brick I assumed I had picked it up from there but today I mixed some more and found the same problem. It was obviously not the lime, sand or cement, so I examined a trowel of the "fireclay" and it seems to have quite a lot of grit mixed through. How fine should this stuff be?

The bag in which it came was sealed although without any markings so I can't say if it was some particular grade? Now I don't trust that clay at all - see pic. Note the rather large piece separated out at the top centre which looks like a piece of brick to me.
Anybody else have a problem like this?
Aidan

[GianniFocaccia]

Re: 39" Stargate Pompeii

I thought it's main purpose was as a hardening agent

That's what I thought too. I am by no means knowledgeable on this, but it has been explained here that the role of mortar is to keep the bricks apart, not joined together. It was also explained that portland's role in mortar is to provide body/resistance (guaging) for proper alignment when squeezing a brick into place.

Portland cement does bind all of the mortar ingredients together, but with it's non-refractory properties, loses it integrity over time and thermal cycles. This is where the lime takes over.

I would think that Frances' dome and mortar has gotten stronger over time because of the thermal cycling. Just my thoughts.

John

[Amac]

Re: 39" Stargate Pompeii

Hi Gianni

blessed with a high level of dexterity and coupled with your layout skills and keen eye

Not too sure about that - I think you left out a smiley there! Already I feel I might have to give this another go to get it right. I am still confident though about the dome to arch integration though

Once I found out that the role of portland cement is to act as a guaging material..

I'm not sure what exactly you mean by "gauging material". I thought it's main purpose was as a hardening agent. The mix seems to work Ok. I tried to separate two brick pieces with today my hands and they held strong.

So if Frances used no portland - just sand and FC her oven should be easy to dismantle. Isn't that a kind of daub mix. It certainly should mean any cracks will be in the joints rather than the brick itself. I read her build and was impressed by the mosaic covering - but I must take another look.

I planned to start building but the rain is back Back to browsing.
Aidan

[GianniFocaccia]

Re: 39" Stargate Pompeii

Hey Aidan,

Nice looking arch! You are obviously blessed with a high level of dexterity and coupled with your layout skills and keen eye, you will no doubt have an oven to be proud of. What's nince is that as you fit each brick (arch and dome) together, you will know intimately what minor tweaks to make and can build a truly custom oven. I know it takes time, but hell - you only gotta do it once I say.

FWIW, I bought a continuous rim 4" masonry blade for my angle grinder thinking it would give me a smoother cut. Not so.

Gianni - I read somewhere that you added more lime and clay and less portland for a more sticky mix. would it change the ratios or how precise were your measures?

As fas as I know, the homebrew recipe relies on measurement by volume. This is what I used. Once I found out that the role of portland cement is to act as a guaging material and is prone to failure over repeated 500F thermal cycles, I took it upon myself to slightly modify the ratios in a very unprecise process (eye method). Given that Francis' (Switzerland) dome was built using mortar of sand and fireclay only and is still going strong after several years, I believe the ratio is not all that critical.

Hope this helps. Keep the pics coming.

John

[Amac]

Re: 39" Stargate Pompeii

Hi Aceves

I like that you decided to go with the homebrew 3:1:1:1 mortar mix. You will be glad you did. A lot of us have gone that route and we are super-happy with the ease of application of the mortar.

I tested that mortar mix on a few offcuts yesterday. I was expecting that it would be pretty solid after 24 hours - but I could still scrape it easily with a fingernail today. How long before it would be set solid enough to, for example, remove an arch form?

Gianni - I read somewhere that you added more lime and clay and less portland for a more sticky mix. would it change the ratios or how precise were your measures? I think you are maybe more precise than most.

BTW those proportions are by volume - not weight?

Only additional progress was I decided to taper the arch bricks ever so slightly. - just to test if I could manage it with the angle grinder. I just did a bit (2/5") at the inner side of each arch brick up to the height of the part you can see at the inside of the oven. Not the best cuts in the world, but I was happy enough with the results. I used the edge of the blade to grind them down. It meant I have to cut three additional additional arch bricks but it will cut down that much mortar also.

By the way anyone thinking of using an angle grinder - there is serious torque in these things - and I have had a few kickbacks and bricks flying. You must not force it - just let it's own weight do the cut - always cut straight. The slightest twist and the kickback is frightening. Having said all that it works much better than I expected, and since I borrowed it from a good neighbour - the cost so far was just two blades (maybe some pizza later). I'm still on the first blade.

Here are a few pics of the resultant arch laid out on a table. The last one shows what should be seen from the inside of the dome as well as where the dome walls attach.

[aceves]

Re: 39" Stargate Pompeii

Hi Aidan,

Glad to see that you started your own thread! Not that I was at all upset about you posting on mine, but now you have free reign on your own thread and will have documentation of your progress for generations to come!! Congrats on starting!

And you're welcome on the first 2 rows cutting idea. It actually wasn't mine, I read it somewhere on this Forum. I tell ya, there is some great advice on here!

I like that you decided to go with the homebrew 3:1:1:1 mortar mix. You will be glad you did. A lot of us have gone that route and we are super-happy with the ease of application of the mortar. Keep building and posting pics, and we'll add comments when we see fit (or when you ask for suggestions).

Aceves

[Amac]

Re: 39" Stargate Pompeii

Ok - I haven't removed that vermiculite board yet - I'm a bit reluctant I thought I might just put an edge of mortar or concrete around it to ensure stability.
I just laid out the bricks of the soldier course, the first row and a few of the arch bricks just to make sure they look Ok and so far so good. I used Aceves idea to cut the first two rows - the first row can be seen in the pic. I cut them 4 7/8 by 4 1/8 and the second row 5" by 4". It looks good, and will save mortar by narrowing the vertical joints. Great idea thanks Aceves I may try to skim the inside edge to get rid of the inverted V - maybe wait till row 2 or 3.

The IT centre is already 1.25" high so the floor covering (1/8") and a few off cuts under the IT brings the IT pivot up the required 1.5". Since the soldier course is 1.5" and the floor is 3", a straight edge across made it easy to verify.

Notice I added a temporary block to the IT angle. This is because I plan to do the arch first and to use the IT to check each brick. To fit snugly the arch angle should originate at the IT pivot centre.

Note that the Jcg31 IT design specifies that the IT angle will be offset by 1/2 a brick - which means that for the normal dome bricks the top of the brick points beyond the IT pivot, the bottom of the brick in front of the pivot and the centre of each brick at the centre. For the arch the outside slope of each brick points to the pivot - hence the additional 1.5" block (1/2 brick).

Not sure if I explained that very well but the pic may explain what I mean.

BTW - I checked with the brick manufacturers who also make the "airset" mortar and I decided after all that it wouldn't be suitable. Two reasons:
1. The recommendations on the forum (James) seem quite specific about all or most airset mixes - don't use them!
2. The manufacturers told me any joints should only be 3mm max. otherwise there would be cracking. Most of the joints will exceed 3mm in my case.

Luckily (it's expensive stuff!) the suppliers took back the three tubs (still unopened) in exchange for a gift card for the full value. I use them a lot so I should easily spend it there. Instead I got some sand, lime, cement and fireclay and will do a some testing of the 3:1:1:1 mix over the next few days if the weather holds out. We are getting the edge of a Siberian cold snap (which has killed >100 in Ukraine so far) Here temp are down to -4, -5C, the last few days which is not too bad but not good for mortar. Still the cold is preferable to the rain we were having.
Aidan

[Amac]

Re: 39" Stargate Pompeii

thanks Doug
bookmarked that one. It's high time I extended my meagre range of cooking skills. one of the kids gave me a book on WFO cooking for my birthday - I think maybe he's an optimist!
Aidan

[brickie in oz]

Re: 39" Stargate Pompeii

Dont get any with plastic bits or even silicon inserts, we have a Scanpan roaster that used to have silicon inserts in the handle.