Forno Bravo Forum: The Wood-Fired Oven Community

Forno Bravo Forum: The Wood-Fired Oven Community (
-   Getting Started (
-   -   Portland and Perlite (

jschadt 09-02-2008 06:21 AM

Portland and Perlite
To all,

HELP! I just spent the weekend pouring the oven base and insulating layer. The base went well and the rebar gave it a lot of strength. The Portland and Perlite layer is what I am worried about. I use Perlite, not Vermiculite. We mixed it in the 5:1 Ratio, five parts Perlite and one part Portland, by volume. We got it to the consistency of oatmeal. We screeded it off and it looked OK but did not trowel well. Problem is when it dried I could crush some of the screeded materials with my hand! This concerns me as to the strength of the mix.

I confess I was so concerned I took some Portland and sand and troweled on a skim coat while it was still somewhat wet. I have been standing on the top after two days cure and doing the initial layout but it is still worrying me that something is not right. I think it would be better to admit it and do it over than lose the oven later. Remember I live in Iowa! Cold Winters!

Any thoughts?? Hopefully it is OK and this is all normal, but like I say better to know now than when the dome is on top!

Thanks in advance for your help!

PIZZAMANMIKE 09-02-2008 08:12 AM

Re: Portland and Perlite
My guess is you should be OK, it will compact a little,not much. A mix of that type has no strenth like concrete and will crumble, It would be a little stronger if you added some sand and fire clay to the mix.

jschadt 09-02-2008 12:38 PM

Re: Portland and Perlite
Today I actually thought I should have put a structural concrete border around the whole thing, like I did for the front. Maybe I am overthinking??

PIZZAMANMIKE 09-02-2008 12:52 PM

Re: Portland and Perlite
That would help lock in your floor, you should be able to do that when you finish up the dome exterior.

jschadt 09-02-2008 05:12 PM

Re: Portland and Perlite
Thanks PizzaMan Mike. I am a bit more relaxed after talking to you. I also talked to some of my concrete buddies and they also use portland and a sponge to "dress up" their pours after they remove the forms. They don't know much about Perlite, but what the heck.

I think I will have my wife put some heels on and do a dance on top of the base. If it holds up we will go ahead and put in the firebricks. (No, she is not heavy!)

I think my bigger problem is being in construction I just proceed thinking everything will be great, and problems like these are quite a surprise to me!

Dutchoven 09-02-2008 05:18 PM

Re: Portland and Perlite
Neither perlcrete or vermicrete trowel at can just kind of tamp will get harder with time as the perlite holds the moisture and will keep it green for quite a while...when mine was fully dry I could wlak on it no problem but it feels like cork...the edges will always be a bit crumbly...have no fear it will be fine

PIZZAMANMIKE 09-02-2008 06:44 PM

Re: Portland and Perlite
jschadt, I would keep you wife off the deck in her high heels, as you will be asking us how to add a brass pole. Ha Ha
keep us posted

atdabch 09-02-2008 07:02 PM

Re: Portland and Perlite
should be ok...slab will get harder at curing completes

RTflorida 09-02-2008 09:59 PM

Re: Portland and Perlite
Like everything else involving portland cement, perlcrete or vermicrete need time to cure. I know you want to move forward, but give it a week to set up...Dutch is spot on with his assessment - cork-like, crumbly around the edges, and it seems to stay "green" longer than one would expect. In the end, it has good compression strength.....even when set firm, your wife is going to get stuck wearing heals; but I do like the brass pole idea (maybe in my next oven)


nissanneill 09-02-2008 10:03 PM

Re: Portland and Perlite
Speaking of a brass pole in the centre of the proposed oven, might be more interesting and profitable than cooking pizza. You might even be able to sell tickets, charge $5 for a stubby of beer and reap the rewards.
Build an oven later with the profits.


All times are GMT -7. The time now is 12:56 AM.

Powered by vBulletin® Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Search Engine Friendly URLs by vBSEO 3.6.0
2006/10 Forno Bravo, LLC