Walthamstow Pompeii 36"

[conroyt2000]

hi,
have been building my oven for a few months now, although haven't been able to do anything too productive over winter.....
see link sdrv.ms/1fQPGFb
link
the cuts are starting to get a bit more complicated now and have been doing with an angle grinder only. I was thinking in investing an abrasive cut off saw which would allow me a bit more accuracy, especially on the longer cuts - has anyone used one for fire bricks?
plan to have either a blockwork structure with pitched roof or build outer dome in reclaimed bricks...

have quite a few 'lessons learnt' which will write down shortly!

any tips, advice etc would be greatly appreciated.

cheers

toby

[matthewcove]

Hi Toby,

A saw designed for bricks with a diamond abrasive blade in it will have no problems with fire bricks, but the only problem is the price. The ones I found were very expensive and not really designed for angles cuts. I have heard of epople putting an abrasive blade in a cheep mitre saw, but the arbour diameter is usually different, so they have had to have some kind of center adapter made. I'm not sure I would recommend putting the wrong blade in a wood saw, you would have to be sure the rpm was correct for starters

Matthew

[conroyt2000]

Thanks Matthew. Was thinking of something like the link below
www.tool-net.co.uk/p-347941/clarke-cco14.html?gclid=CISzhe7VjbwCFfHItAodpU4Aog
Guess it will be dusty but no worse than angle grinders.
With a second look at the Pompeii build in the guide it looks like a cut off saw there, not wet cut.
Have managed to get hold of two 355mm diamond blades for free too
Cheers

[matthewcove]

the inside of that guard could get very clogged up with fire clay dust, if the bricks are damp at all you may have to remove and clean the guard often, but as this is just an angle grinder on a stand, I dont see why it would not work.

edit - on second look, the max cut capacity stated would mean a standard fire brick wont fit in it

Matthew

[cannyfradock]

Hello Toby.....welcome to the forum.

One point to add straight away......you shouldn't be having any problem with dust as the fire-bricks should be soaked in water before cutting. This will make them a lot easier to cut and prolong the life of your blade.

Looking at the disc cutter you are looking at...it states it will cut through up to 8" so you should have enough depth? Other members have managed to buy a pivitol clamp for holding a 9" angle grinder. I'm not sure where members have bought these from but it's a cheaper option, although the cutting depth would then be reduced to about 3 1/2" for a 9" angle grinder.( www.amazon.co.uk/gp/product/B001CBXWHY/ref=s9_simh_gw_p60_d0_i1?pf_rd_m=A3P5ROKL5A1OLE&pf_rd_s=center-4&pf_rd_r=03642WB2MGY1Z057QFZ1&pf_rd_t=101&pf_rd_p=455344027&pf_rd_i=468294 ) Your other option if you want precise cut bricks....or "trapazoid cuts" is to hire a clipper or similar table top masonry cutting machine. These are not cheap to hire so to make it pay you would have to do all your cuts in 1 day.

If it's this guide.. plus.google.com/photos/105964699085980237524/albums/5839914686309680209?banner=pwa ...you looked at, I notice he's using an angle grinder stand with some fancy block wedges to hold the bricks when cutting. When this guy (Charlie Farly) joined the (old) forum he asked questions then said...ah well. I'll just have to learn as I go on.....then surprised us all.

Terry

[bookemdanno]

Evolution powertools also do a version of these.
They also do a direct replacement dry cut diamond blade for their cut off saws too.
I have a diamond blade for my 255mm Rage sliding compound mitre saw, which goes through bricks like they're butter.
I have not used it on firebrick though.

Check out Ebay for second handers!

[conroyt2000]

thanks all for your responses....
I have got two sizes of firebricks, with the largest 230 x 114 x 76mm which appears to be ok for the cut off saw, well until I / if I angle the brick I guess?!

couple more questions:
rather than cut every brick, on the latest ring I have been cutting both sides of every other brick rather than every brick, are there any problems with doing this, perhaps further in the build.

when do most start using a exercise ball etc / when does gravity become too great whilst mortar setting.

finally, I read in a thread recently that following firings it is the lime in the mortar which acts as the glue and that the cement become redundant, is this correct; my understanding was traditionally lime was added to improve curing and workability of mortar however I wasn't aware of it being beneficial under heat - anyone know technical details?

thanks again for your help, hoping to have working for mid May for a party so pressure is on!

[cannyfradock]

Toby

The higher you go up the larger the perps (perpendicular joints) will get. By cutting every other one you have made it easier for yourself. If you've managed to get a cutter it would be better and easier for you to cut each brick.....especially after the arch/dome transition. I however only bolster my bricks in half and go from 3" bricks down to 1" bricks the higher I go up finishing off with a mix of 1/4 cut bricks before laying the final cap stone. This build I done for my boss will give you a better idea what I've said.... ukwoodfiredovenforum.proboards.com/thread/677/terrys-2nd-build-robs-oven 

Your method of cutting each brick is far superior to my hack, slap method as I end up with massive beds and perps the higher I build. This brings me on to your mortar question. As my method leaves large area's between the bricks, I use the "homebrew" mortar of sand, cement, hydrated lime and powdered fire-clay at a ratio of 6:1:1:1. The lime is used in any mortar that needs to breath.....or move under heat. The powdered fire-clay will allow the mortar to reach a high temp. without movement. The cement is the curing agent.....hardens after a day, but doesn't start curing until 7 days....

I've only seen one person use an exersize ball and it went well if I can remember. I use removable forms but most use the "indispensable tool"....or central pivitol arm (never used that system myself).

[bookemdanno]

Don't think of mortar as a glue. You're not really gluing them together, but there is a binding action.
Its more like icing between two bits of cake.

Like Terry mentions, the cement provides an early set, the lime adds an element of flexibility and the fireclay an extra temperature resistance.

Its all a bit of alchemy, and i expect there has been no direct comparisons or exhaustive testing to confirm of deny whether all of the components are necessary. But elements of the mix come from hearth and chimney building, etc.
I know of Lime Kilns, Ovens and Pottery kilns built using pure lime mortars, no cement and no fireclay which run at hotter temperatures, for longer timescales and over many decades.

Stick to the 6:1:1:1 if you want a tried and tested WFO mix, and don't fancy going into uncharted territory.

As for cuts...you have a full trapezoid, four angle cut with no or little mortar at one end of the spectrum and a roughly piled bunch of bricks with handfulls of mortar slung at the gaps at the other. Both will cook a cracking pizza!

[conroyt2000]

Thanks for your comments.

I have been able to make a bit of progress recently although the wind and rain aren't helping! Link to photos at start of the thread

For the latest ring of have been cutting one side of each firebrick, this seems to make the angles etc easier to achieve without a stand/cut-off saw; I would imagine that if I want to minimise the mortar exposed in the later rings I may have to shell out for the stand or something like that

Have been using a hombrew but with less lime, definitely going to increase the ratio to normal now I understand the physics of it, hopefully this won't make mortar deteriorate too quickly later on - thanks for explaining terry/bookemdanno.

Can use the cellex forms you see in the photo to support these rings but this limits the number of bricks I can lay at a time, have taken my wife's pregnancy ball so can start using that next weekend.

Recently been away in Italy and had some great pizzas and wood fired oven food which is really spurring me on to finish! Trying not to rush now

After some thought I am planning to make a block work structure with a pitched roof on top and either render or tile/Brick slips to the sides. I will need to putting decking down in front of the oven as I didn't really think about the eventual oven floor height properly....

Finally, I came across some propane greenhouse heaters for about £20 recently which I could use to help dry the structure out, has anyone used similar?

Thanks again for any help/tips

[kipper]

hi Toby
the domes looking good. i would get a piece of plastic on the oven floor to catch some of that homebrew. it'll mean less cleaning later. and I think those formers may need to point into the middle to help keep the shape.

david

[conroyt2000]

thanks dave. I had sort of given up on cleaning the floor and planned on doing at the end but think you are probably right that I should put something down to save myself some work (and brick acid). thanks for pointer on the forms, will have to trim them down I guess so that they can all meet in middle, perhaps with a downpipe in centre as have seen in other builds - the bricks you can see held up by forms are dry-laid luckily.

cheers

[cannyfradock]

Toby

I use formers very similar to your's although they're made from thin chipboard. I find that even if the following brick doesn't rest on a former, you can hold it in place until that initial mortar "grab" takes hold. The following brick then usually sits on a former again and holds it all in place.

Unless you're an absolute genius in cutting these bricks for the dome, the outside will always look quite rough....don't worry as the homebrew will work well on these larger voids. It gets more trickier the higher you go up with the dome....I try to fill the gaps as I go...i.e...I put a heavy mortar bed on before laying a brick and either put mortar on the side of the brick I'm about to lay.....or, on the side of the brick I want to lay against. I then "squidge" the brick into place.I find this a lot easier than trying to point in the voids after.

It may be easier for the last few rings and capstone to use a propped up piece of board with a sand former to complete the dome (that's what I do)....if you do, then use coarse wet sand which you can compress and make a nice even curvature to finish off your dome. Once the capstone/keystone is laid....and all the joints and beds are full of mortar, you can remove the sand form (I do it after 1 hour, but it's best to wait perhaps 1 day) ..then you can clean the interior while the mortar is still "green" and then use a wet sponge to buff up any of the interior joints.

Great progress.....

Terry

[conroyt2000]

Finally a break in the weather and able to make some progress.
Have persevered with only cutting one side of the brick, it seems impossible to cut both into a trapezoidal shape without a stand but relatively easy to get one cut fairly accurate.
Was getting a bit frustrated after laying a couple of bricks during a weather window on Saturday as they didn't look too pretty, however once the rest of the ring was complete and the oven tidied up a bit I'm not so downbeat! I had an imagine of a perfect dome but doesn't seem quite as important compared to how in cooks, so fingers crossed!
I have noticed that the dome is going into a tear shape rather than circle, hopefully this doesn't affect strength? Have seen some really good tear shaped ovens so not too concerned if it still functions well, I imagine that this is due to the forms not being centred.
Pictures on the sky-drive link at the start of the thread

[kipper]

looking good Toby.that teardrop shape is quite normal and to be honest once the dome is complete you won't even notice.did you manage to get any heaters? I used my small gas portable bbq to help dry the dome.