36" Build Alberta, Canada

[Vee]

Hello,

After months of lurking, I finally started my 36" build at my cottage. Since I'm only there on the weekends for the most part I used landscaping blocks to speed up the stand build. I'm about to pour the concrete for the hearth. I have 8"'s to play with for the concrete slab and perlicrete base. I was planing on 4" concrete and 4" perlicrete. Would it be better to go 3.5" concrete and 4.5"'s of perlicrete to maximize my floor insulation? Is it better to add slab strength (69"x 54") or floor insulation?

[UtahBeehiver]

5 to 1 pcrete is typical for floor insulation with 4" of pcrete roughly equal to 2" of CaSi board and is the "minimum" recommended floor thickness

[Vee]

Russell,

Thanks! Maybe I'll drop my plywood floor down a couple of inches to make room for a larger pcrete base.

[fox]

Have you stuck all the bricks together with adhesive or do you plan to cement them together ?

[Vee]

They are glued with PL600. Dome enclosure bricks will sit on top of the counter levered bricks of the hearth to provide extra stability. Here is what I was planning.




I was aiming for a floor height of 42" but could build a taller pcrete floor by 2" but that would bring me up to 44" floor height. Is that getting too high. I'm only 5'7"!

[MarkJerling]

They are glued with PL600. Dome enclosure bricks will sit on top of the counter levered bricks of the hearth to provide extra stability. Here is what I was planning.




I was aiming for a floor height of 42" but could build a taller pcrete floor by 2" but that would bring me up to 44" floor height. Is that getting too high. I'm only 5'7"!

44" to floor level is absolutely fine if you're 5'7". Mine's at 49" and I wish I made it another inch taller. I'm 6'2".

[UtahBeehiver]

A rule of thumb is elbow height plus or minus.

[NCMan]

I agree. Anywhere from elbow height to armpit height is good. I have come to like the armpit height myself, as I think the elbow is a bit low, but each user has their own comfort level. The pizza doesn't seem to mind, either way. I do get a kick out of some discussions online (not here) where some builders give out a firm number, as if that height is the final answer, totally ignoring the fact that we are all different heights, so there is no such thing as a "final answer".

[Vee]

Thanks everyone for your comments on floor height. Helped me validate that my final floor height will work for me. I have a few more questions before I pour my hearth and floor insulation:


1) When is it too hot to pour your hearth concrete? Looks like the temperature is forecasted to be 30C/86F. Would that be ok?
2) I'll be putting down 2" for FoamGlass topped by 3.5"'s of Perlcrete. How can I estimate how much volume of Perlite I will need? Does it expand? Pouring 5:1 about 54"x57"x3.5".

Thanks!

John

[david s]

I’m not sure what temperatures you are experiencing, but we live in the tropics and I find if I cast in the morning I’m in danger of getting shrink cracks if the concrete gets hot in the afternoon. So I prefer to cast in the late afternoon so by the time the concrete is setting the sun is off it and it has all night to go off slowly. I then cover it first thing in the morning.

[Vee]

I got my concrete poured and I've covered it with wet cardboard and a tarp in order to protect it from the heat. A couple of questions regarding the next step:

Do you pour 5:1 Perlcrete under the vent landing as well or stop at the inner arch bricks?
Do I need to keep the Perlcrete wet to slow down the curing as well?

My floor base will have 2" of Foamglas topped with 3.5" of 5:1. Does the Foamglas go on top of the Perlcrete or below against the concrete.

Is it a good idea to put tiles below the Foamglas to assist drainage to the drain holes?

I've done my own searching to find answers but it seems like folks use different methods and I was wondering what best practice is.

Thanks!

John

[UtahBeehiver]

You want your best insulating material closest to the fire brick floor, 0.75K for 5 to 1 pcrete is not as good as FoamGlas at 0.29K so the pcrete first then the FoamGlas then the floor. You need to check the working temp of FoamGlas, some of the newer versions have a lower temp rating.

[Vee]

Russell,

Thanks for the advice. I would have done the opposite not knowing better. Foamglas I got has a "maximum working Temp" of 900F+. I should be good putting it under the floor brick?

John

[david s]

While I agree with the principle of placing the higher quality insulation facing the floor bricks, in this case there is also an advantage of placing the foam glass on the bottom because of its resistance to water absorption. It could be more helpful to keep the far less water resistant vermicrete "high and dry", especially if it is combined with drain holes and a pathway to them in the supporting slab.
Weather conditions and whether the oven has a roof over it are other factors to be considered which may influence your decision.

[NCMan]

It is usually not a good idea to keep any cement pours (including Perlcrete and Vermicrete) wet by adding water to them after they are poured. The best practice it to keep them damp by maintaining the existing moisture in them, as opposed to adding extra water over them later. Covering your Perlcrete is a two sided sword, however. Yes, it will help it achieve strength by covering it, but it will (naturally) slow down the drying process. It's really up to you, but I have covered mine for a day or so (plastic and cardboard), then uncovered it to allow it to dry. It really should be allowed to dry as much as possible before building on it. As for using Perlcrete under the vent landing, that is optional, usually for most builders. My own opinion is to use it if you aren't incorporating any type of thermal breaks in your floor. If you do use them, it's not needed as much. Either way, you can't go wrong by using it there, in most cases. Personally, I have used thermal breaks between the floor and landing and don't use any insulation under the landing.