36" Castable in the Philippines

[robi]

I am still in the process of building the stand upon which I'll build my oven, tomorrow I start the suspended slab formwork... I hope to pour the slab next week, it will be 3" reinforced slab with a few drain holes where the dome will be. An awesome guy I think his name is Ben at Melbourne firebrick made some equally awesome videos on the whole process (he doesn't mention drain holes tho... thanks Dave and the forum)... this is my first attempt at building something big like this (I was an internet security geek in my previous life, no previous experience) so his step by step videos are really helping a lot... I wish I could order one of his or any pre-cast oven kit, but congress won't approve the cost of shipping... I wish I could say thanks to him and buy him a beer and of course all of you as well for your guidance so far as you helped others which I continue to glean thoroughly.

So I found what I hope is suitable firebrick (318mm x 318mm x 63.5mm or 12.5" x 12.5" x 2.5") the seller calls it 'Shiplap Brick' and 'pizza stone' about $17 USD each, he also sells 25kg refractory cement almost $100 USD...


If this 'shiplap brick' is suitable I hope to use refractory cement to cast around it as shown in the drawings below... the black line represents the black plywood upon which I'll lay the bricks, I will place thin cardboard between the bricks and the outer perimeter of the bricks for expansion space then cover the tiles with plastic wrap so they won't stick when I pour the castable in the 4" mold, I'll screed the top which will be the flat bottom of the floor (when flipped over). Total oven floor thickness will be 4" (2.5" floor bricks plus 1.5" castable under the bricks 4" thick around the bricks) Should I chickenwire or do any reinforcement for inside this floor? Once cured this will be flipped over and placed on top of 36mm CaSil which will be on top of some deco tile sheets for drain channels. The bricks will then be placed back in the space they left when the floor was cast.



So far is this floor plan a good or bad idea? Will two 25kg sacks be enough for the floor? I also plan to cast the flue top, do I need more refractory cement? Or should I do it all with homebrew?

For the dome I will use homebrew, my problem is I can't find polypropylene fiber or Stainless needles locally... I find fiberglass GFRC strands on Aliexpress but no PP. I can probably get some PP sent from family shipped along with some documents they will be sending here soon, but the stainless probably not... How much PP do I need and are the PP fibers on amazon the right stuff or is there a better online source for ordering these fibers?

Thank you for your help and thoughts...

Take care
Rob

[david s]

Hi Rob,

you’ve thought this all out well. Be aware that a large casting, especially on a floor is more prone to cracking because of uneven heating, especially more so if the casting is thin (1.5”). It doesn’t really matter if it does crack because it’s just making its own expansion joints.If doing it that way I’d be casting it in quarters, but it might be ok in one section. Forget the ss needles, most manufacturers don’t use them, but if using homebrew you need them. About a handful for every 10 L of homebrew and mixed really well. They take a while to disperse. Castable refractory already has them added and is of a higher quality than homebrew although for the price homebrew is quite adequate and many builders have used it and found it both effective and user friendly.

[robi]

Thank you Dave for the confidence boost, also the expansion joints totally makes sense, thanks for the idea to cast the floor in quarters... I'll do it.

I was thinking to go with homebrew but getting the essential SS needles and Polyproplene fibers is harder than getting the refractory cement. Could any voice of experience share how many sacks I am going to need for the floor, the 36" dome, and the flue? I'll need to have it all shipped from Manila to my province up here in the north.

Thank you for any advice you have to offer.

Rob

[sergetania]

Forget the ss needles, most manufacturers don’t use them, but if using homebrew you need them.

I believe David meant to say that you need PP fibers but not SS needles. Sorry,David, that's what you usually recommend,right?

[robi]

So after doing a cardboard layout and after reading more posts from David S and others I have decided to go with a 27" dome... 36 is way too much when 99% of the cooking will be just for my family of 6... my mind was made up after seeing the occasional crowd can be fed as long as they share as the pizza comes out, makes sense. Thanks for that nugget of info Sir David S.

So I am ready to start the purchasing of supplies. I calculated my 343mm radius dome at 63mm thick, to be about 56 liters or .056cu meters. Which equals about 4 25kg bags of castable if I were to go that route. Please, is my math correct? I'll probably need 2 bags more for the floor & flue gallery.

I would much rather go the homebrew route, I found SS needles and PP fibers on Alibaba but I am not sure how safe that will be... any Alibaba experience from the forum??? Locally, I can get 25kg calcium hydroxide for about 12usd, 25kg powdered clay the locals use for making bricks for about 10usd. 40kg Portland is about 6usd. Of course, if I can't get the needles and fibers, I am 'brown & lumpy' outta luck. Also, the exact quantities I will need for my project are proving difficult to determine, any help???

The lowest price for refractory cement I found is called Castocrete Super at about 50usd per 25kg bag.

The journey continues...

Thank you to the contributors and maintainers of the forum for providing a wealth of knowledge.

[sergetania]

They recommend to cast not thinner than 1.5-2" with the castable I have used. Not sure why you want to make the walls 63mm thick. It could be just a waste of material but I don't know especially with homebrew. Quantity looks about right. I always forget to divide by 2 because we only build a half of the sphere
Alibaba is more popular in some countries than others. Find out what kind of experience other people in Philippines have had ordering from them. Shipping is a big part of it, especially now.

[robi]

Thanks Serge... yeah I think I am gonna need to skip the SS, I found a place advertising SS but when I placed the order they said "sorry they are not SS, but they look like they are" they gave me an option to cancel... I am not sure if it's better to have plain steel than nothing or am I asking for more problems if I use plain... I did find PP so it looks like I'll be going homebrew... just not sure right now if I should cancel the plain steel needles...

oh and I assumed that David meant PP fibers in his earlier post, thanks for at least confirming my thought... I hope David is okay and he didn't get any covid on him...