Filling joints in hearth slab?

[mikku]

Re: Filling joints in hearth slab?

The beam of light from my IR thermometer.

OK, a comedian this morning. My IR shows wildly varying temperatures, dome one temperature, floor another but hotter, sometimes pegs the meter that max's at 550C, then I point it at my hand it reads the same...I sometime think I'm hot but that is sizzling and in both instances a crock! Old farts cannot be hot!

I threw flour onto the hearth brick and it flamed while hitting the firebrick--a place where they mill flour must be a very dangerous place because of the chance of such an explosive fire. The places where the flour hits just makes a black spot and later difficult to get off or blackens the first pizza crusts! If not flour??? What?

I'm back to my old lazy habit of not searching previous posts...must be the newbie blood or just plain summer heat lazy!

[mrchipster]

Re: Filling joints in hearth slab?

OK, a comedian this morning. My IR shows wildly varying temperatures, dome one temperature, floor another but hotter, sometimes pegs the meter that max's at 550C, then I point it at my hand it reads the same...I sometime think I'm hot but that is sizzling and in both instances a crock! Old farts cannot be hot!

I threw flour onto the hearth brick and it flamed while hitting the firebrick--a place where they mill flour must be a very dangerous place because of the chance of such an explosive fire. The places where the flour hits just makes a black spot and later difficult to get off or blackens the first pizza crusts! If not flour??? What?

I'm back to my old lazy habit of not searching previous posts...must be the newbie blood or just plain summer heat lazy!

Sounds like you need a new ir gun.

[david s]

Re: Filling joints in hearth slab?

Cast a little semolina on to the centre of the oven floor. If it turns black in 2 secs the floor is too hot. 3 secs, just right, 4 secs, not hot enough.

[mikku]

Re: Filling joints in hearth slab?

Thanks again Davids,
Seems like you never tire of answering the same stupid questions from newbies and not so new newbies.

Now I need to figure out what semolina is! And where to find it!

[RichC]

Re: Filling joints in hearth slab?

Guys, can anyone direct me towards whats considered a 'good set of instructions' for installation of any modular oven? I cant imagine they differ much but Id just like to compare some from a different manufacturer.

Thanks

Richard

[david s]

Re: Filling joints in hearth slab?

Guys, can anyone direct me towards whats considered a 'good set of instructions' for installation of any modular oven? I cant imagine they differ much but Id just like to compare some from a different manufacturer.

Thanks

Richard

Every manufacturers design will vary eg dome on top of floor or floor inside dome. Dome casting in one pice or dome in multiple pieces. Cast floor or separate fire bricks. Foil or no foil. Blanket or vermiculite etc. etc.
If you buy a kit it should come with comprehensive instructions, if not look for another.

[mikku]

Re: Filling joints in hearth slab?

So what do you if you build your own modular oven? Make up your own instructions?

You follow the advice of some of the contributors who just told you all that you need to know. You can build modular either on top of your hearth tiles OR with the tiles inside the oven that do not actually touch the surfaces of the modular dome pieces.

In both cases, the hearth tiles are set loose--not bonded to anything. They are laid on top of either a pericrete insulation base or in your case the thermal mat. In your case, there should be no need for additional leveling. If set on top of pericrete; some additional leveling may be required to get a smooth working surface--but nothing that will bond any of the pieces.

If you are setting the modular pieces on top of the prepared hearth tile base, then put some newspaper on top of the hearth base (or paper baking sheet); then set-up your modular dome. The newspaper or baking paper guarantee that no mortar will come in contact between the dome and the base. You want this to be a slip joint! Then continue with your assembly. The mortar that was provided is probably a trowel grade refractory cement that can be generously slathered over the joints of the modular units..no need to place it anywhere else on the dome pieces. It will crack anyway when heat starts working on the completed dome. It is meant to fill any larger voids that have occurred due to poor alignment or poor manufacture. Do not mortar anywhere else! You always want these two surfaces to be free to move independently.

If you are building with the dome surrounding the hearth pieces, it might be a good idea to cover the hearth with paper and possibly use tape to keep the paper flat. Whatever you use will eventually burn away anyway. The paper can extend beyond the base where the modular pieces are to be set. If you are setting on pericrete or insulating mat same applies. You do not want any mortar used to assemble the pieces to come in contact with the hearth. Make sure that no mortar falls into whatever crack you have between the hearth and dome. If it does get in there, remove as much as you can while you still have access. You want to maintain the separation. Then same as above, slather your seams and you are golden.

My oven is modular; formed and cast myself; sets on top of the oven hearth. I anchored my entire dome to my structural base with the pericrete insulation only. So far--so good, but mine is only a three piece modular and fired only maybe 20 times.

Good luck with your build- and listen to people like Davids, MrChipster, Stonecutter, Tscarborough, Faith in Virginia, Laurenteus, Brickie in Oz and others too many to mention. they have their s--t together, all in one bag and know their stuff!

[RichC]

Re: Filling joints in hearth slab?

They are laid on top of either a pericrete insulation base or in your case the thermal mat. In your case, there should be no need for additional leveling. If set on top of pericrete; some additional leveling may be required to get a smooth working surface--but nothing that will bond any of the pieces.

Thanks Mikku, mines going in on top of vermicrete insulation which should be quite level. I think I might need to add a little more as I want a reasonable slope from the cooking surface down to the outer edge of the finished external countertop. At the moment I'd say its a few mm to low, I probably need to add about 5mm to the vermicrete underhearth insulation.
I think I have all the info I need now to proceed, thanks to the contributors here!

[mikku]

Re: Filling joints in hearth slab?

If you have your pericrete level at this point, don't screw around with trying to get a 5mm slope to anything. What is the idea of the slope in the first place? Once your oven dome is complete, you can adjust the height of the outer counters to match your hearth brick not vice versa.

but these are only my "opinion" on this particular subject. Wiser people may have other things to say on the subject. I would look at the effort involved first and what you expect to get in improvement. If there is only slight improvement leave it like it is and call it "Good"! then go on with the next step.

You will run into a lot of situations where you need to make a decision. Like any decisions in life, think it over but use your instinct as a guide. Usually human nature is pretty smart! Then just go for it! But remember--whatever decision you make is "yours and yours alone" for us who give advice--it is really cheap. Accept it knowing the cost of it!

[RichC]

Re: Filling joints in hearth slab?

Put down my hearth slab sections today. The sections arent very well manufactured and dont sit very well together. See images below, although the pics arent that good. Theres gaps of around 5mm in places. I was tempted to 'rework' the edges with an angle grinder but afraid I'd do more damage. Is it OK to leave these gaps as theyll fill with ash over time? The joining edges arent straight.
Also, the surface of the base slabs isnt very level again down to poor manufacture. I can see there will be some air gaps under the tiles in places. Also, to avoid lips where the sections butt up against each other ive packed them up slightly in some areas. I was wondering, should I put down a thin layer of sand or even a thin layer of pure vermiculite(no cement) under the slabs to avoid any air gaps between the insulation under hearth and the hearth slab?

Thanks

Richard

[mikku]

Re: Filling joints in hearth slab?

Looks like things are going fine.

If you want to use sand or vermiculite under the hearth pieces, I'd think either would work fine.

As long as the greatest majority of the slab hearth pieces are making contact with your vericrete base, you should be fine. If you had access to a cup sanding wheel the kind with diamond imbedded in the surface, you could cut the top surface to get it really smooth. I guess even a belt sander would cut enough to get a satisfactory surface.

These pieces are your cooking surface so nothing else is placed on top of them, therefore non-load bearing. Little gaps are fine and allow for each to expand when exposed to wood burning temperatures.

I like the job you did on your vericrete base--looks pretty professional to me!
But I've only done one and it is not 100% yet--But it bakes and makes good pizza already!

Keep the pictures coming.

[RichC]

Re: Filling joints in hearth slab?

Thanks for the compliment Mikku, im tempted to just leave it and continue with the rest of the build because its sitting OK right now.

[mikku]

Re: Filling joints in hearth slab?

See--there you go! intuition is leading your way.

You are probably 100% correct!

But if you wanted to easily adjust the surface for smoothness, now is the time when there are no other obstructions to deal with. But maybe better leave well enough alone and go with your gut reaction!

[RichC]

Re: Filling joints in hearth slab?

So I ended up using dry vermiculite under the hearth slabs to bed them down as they were moving due to uneven undersides when the dome pieces were placed on them. There's some very big gaps in the upper dome sections probably 30mm in places but the supplier told me to fill them with the refractory cement he gave me. They don't sit together very well, not sure how much that matters. If I trusted myself I'd probably 'reshape' them with an angle grinder but I need to get the dome insulation done in the next week or so.

[mrchipster]

Re: Filling joints in hearth slab?

When I look at your photos I see that the tops are out of alignment as well as the sides. If you shim up the bottom of the dome pieces can you get a better match for the vertical seams?

I think if you shimmed up the bottom with firebrick shims and made your larger gap at the floor, filing that gap with your castable, first placing a piece of card stock down so as not to bond the dome to the floor. I think it might be more durable than having those large vertical seams.

It is unfortunate that the castings are so far off.

Another thought, have you played with the order of the pieces to possibly get a better fit between sections, and or is it possible that the orientation of the pieces is off, such that you have laid a side at the bottom or something?

Another question, are the floor pieces level to one another?