Refractory Cement Menards.

[e.downs]

I am going to be building a large pizza oven with about 48 inch diameter on the inside. I am wanting to cast this thing or form it so I do not have to buy/lay brick. Can I use refractory cement over a form? I plan on insulating with mineral wool over that refractory cement and then coming back over the insulation with something (what should that something be?). I am looking at this product at Menards Akonaź Medium-Duty Refractory Mortar. I was going to make my own but I could not find any fire clay in my area. Can I use perlite to "stretch" this cement and make it go further? Thanks!

[Gulf]

E. Downs,

Welcome to the forum. I found a MSDS for the Akona Medium-Duty Refractory mortar. It lists the following ingredients:

Portland Cement ......................................20-40%
Calcium aluminate cement ......................0-55%
Silica Sand (as quartz) .............................60-75%
Lime .................................................. ...........0-7%
Calcium carbonate .......................................0-4%
Polymeric binder ..........................................0-4% *

*Specific chemical identities and concentrations withheld as trade secret. They are available upon request to health professionals, employees and their designated representatives in accord with 29CFR1910.1200(i).

Here is a Google search of Forno Bravo using the key words "david s casting forno bravo"

It will bring up many cast built threads where david s (our forum expert on casting) has given advice to similar questions.

I hope this helps.

[e.downs]

Thank you for the reply. I am not sure I understand those percentages. They are wide and varying 0-55%? I hope he may be able to chime in on this because I am having a hard time finding fire clay to make my own. But I think I would rather spend the extra money and buy a nice dense cement.

[david s]

I am going to be building a large pizza oven with about 48 inch diameter on the inside. I am wanting to cast this thing or form it so I do not have to buy/lay brick. Can I use refractory cement over a form? I plan on insulating with mineral wool over that refractory cement and then coming back over the insulation with something (what should that something be?). I am looking at this product at Menards Akonaź Medium-Duty Refractory Mortar. I was going to make my own but I could not find any fire clay in my area. Can I use perlite to "stretch" this cement and make it go further? Thanks!

Refractory cement is a component of refractory mortar or refractory concrete, generally known as refractory castable.a proprietary refractory mortar is not designed for casting, but as a mortar between bricks. If you want to make your own refractory castable you can do that, it's cheaper, but make sure you use a proven recipe. There are many cast projects on this forum, I suggest you do a search on "cast ovens".
Most builders do a vermicrete layer over the insulating blanket and a hard stucco layer over that or build an enclosure.
Do not add perlite to the inner layer facing the fire because it makes it insulating and weaker You want a strong, dense inner dome.

[e.downs]

I am looking at this castable now. Would you be able to tell me how many bags I might need? Not sure how much a 55lb bag yields. Looking at going 4" thick thanks! KS-4 PLUS 55# BAGS Great for Pizza Ovens

KS-4 is a 2550°F conventional (CaO>2%) Description: Dense, Strong, General-Purpose Castable Refractory for Temperatures up to 2550°F Features: • Good strength. Uses: Pizza Ovens, Wood fired bread ovens, • Complete furnace linings. • Pouring special shapes. • Ideal general-purpose fireclay castable. Chemical Analysis: Approximate (Calcined Basis) Silica (SiO2) 42.6% Alumina (Al2O3) 44.9% Iron Oxide (Fe2O3) 2.3% Titania (TiO2) 2.3% Lime (CaO) 6.7% Magnesia (MgO) 0.3% Alkalies (Na2O+K2O) 0.9% Physical Data (Typical) Poured Maximum Service Temperature 2550°F (1400°C) Material Required 122 lb/ft3 (1.96 g/cm3)

[david s]

Volume of a sphere is 4/3 pi r3
calculate the volume using outer radius ie 26" and subtract the volume of the sphere using inner radius ie 24"
halve the answer because it's a hemisphere.
convert answer to litres so you can use the density (1.96 g/cm3) to calculate the total weight.
The amount not needed for the oven door is approx equal to that required for casting the entry.

[e.downs]

42" Diameter internal so 50" outer diameter if I am doing 4" thick walls. I got 38,792 cubic inches and 65,449 cubic inches respectively. Subtract those and I got 26,657 and diving that in half I get 13,328 Cubic inches. Converting that to Litres I get 218? I am wondering roughly how many 55lb bags of refractory cement mix I will need to buy. Thanks again!

[david s]

1.96 gm/cm3 is the same as kg/ litre. So as V= m/d then 218= m/1.96
m= 427.8
if each bag weighs 55 lbs (25 kgs) so 427.8/25= 17.08

Every bag I have weighs 24 kgs not 25. Data says quantity may vary + or - 5%, funny how it's consistently 5% less every time.
So get 20 bags.

[e.downs]

Thank you for the reply! I have another question. I am wanting to use mineral wool or its called rock wool insulation. It is substantially cheaper than a ceramic fiber board but I am afraid it will give and sink in over time. This is for under the floor to insulate the floor. Is there a way I could set this in the cement under the oven somehow? Maybe sink in in the cement and then cement over top of it and then lay my fire brick over that? Just looking for a cheaper alternative than CFB because well its cheaper and I have this rock wool insulation available to me locally. Thanks! I also plan on insulating the top of the oven with this as well. Thanks

[david s]

I've used Rockwool blanket on a couple of ovens, but won't use it again. Although it's cheaper it is not as firm as ceramic blanket, making it harder to work over with a vermicrete layer. It also is very water absorbant. For both these reasons it is not a good choice for an under floor insulation. Because it compresses so much you would have to place something firmer like insulating firebrick stilts under the firebrick floor and fill in between the stilts with the Rockwool blanket anyhow. If you want to do the underfloor cheaper try 5:1 vermicrete at 4" thick and save the Rockwool blanket for over the dome.

Rockwool blanket does not cut as well as ceramic blanket either.

[e.downs]

Okay thank you I will give the vermicrete a go. Do you have a particular mix you use? Just regular quickcrete cement would be fine for the vermicrete underneath the fire brick? Ill only use the rock wool for the dome.

[david s]

10 parts medium grade vermiculite
1 part Portland cement
Mix together dry, then add 3 parts water
Mix well. Don't use a mixer, it gets all clogged up. Better to use a barrow.
i usually use a 50/50 mix of perlite and vermiculite as it makes a better workable mix than either of them alone (but this is not necessary with a fairly rich mix)
i also throw in around 0.2 parts powdered clay to make it more workable, but again not really necessary.

Because this stuff is wet on placement you need to let it set and best to leave it uncovered in the sun and wind to dy for quite a while or you will end up with trapped moisture which is hard to eliminate under the floor by firing. Read my experiment about drying a vermicrete slab attached.