Forno Bravo Forum: The Wood-Fired Oven Community

Forno Bravo Forum: The Wood-Fired Oven Community (
-   Pompeii Oven Construction (
-   -   Perlite Concrete on free form igloo (

martywatts 12-21-2009 10:33 PM

Perlite Concrete on free form igloo
Has anyone used lime in the perlite concrete to make it stickier. I am have a time getting it thick enough on the near vertical surfaces?

tfasz 12-22-2009 08:50 AM

Re: Perlite Concrete on free form igloo
What kind of perlite/cement ratio are you using? Is it too wet (or too dry) maybe? What kind of structure are you putting it around - some chicken wire or other reinforcement?

I've only setup my base insulation layer with perlite/cement, but I know that my first attempt would have been too dry and crumbly to stand up vertically. This weekend I did an additional layer on top and felt like I got the water content right.

The only other suggestion I've heard is to start at the bottom and work your way up.

martywatts 12-22-2009 11:00 AM

Re: Perlite Concrete on free form igloo
2 Attachment(s)
My mix is 5 perlite to 1 portland cement. It is placed on expanded metal lathe which I have covering 1 to 2 inches of mineral wool. I have been working from the bottom up and eventually I think I can be successful. I was just wondering if a little lime in the mix would make it stick together better?

david s 12-22-2009 12:49 PM

Re: Perlite Concrete on free form igloo
Some lime might help, but make sure you use rubber gloves. I think a 5:1 is way too rich. You are adding much more weight in cement than perlite which will make you mixture denser and a poorer insulator. I use 10:1 and add 3 litres of water for every 10 litres of vermiculite (perlite probably the same) The mixture will seem too dry and crumbly when you apply it but it hardens up ok and is left with lots of air spaces between the grains, which is what you want. This layer does not need to be strong, merely enough to hold it together so you can apply your outer shell over it. Let it dry well, cure then do the outer shell.

Neil2 12-24-2009 11:25 AM

Re: Perlite Concrete on free form igloo
I wouldn't use the lime. Use a 10:1 or 12:1 mix. You have to play around with the water ratio. You may find it easier to do in several courses, going up 6 inches or so and letting it set for 3 or 4 hours before placing the remained.

JoeyVelderrain 01-15-2010 11:00 AM

Re: Perlite Concrete on free form igloo
I started at the bottom of the soldier wall and went all the way around and then by the time I got to the end I went back to my starting point which was slightly firmer now and began with another six inch or so "row" and went all the way around...I continued to do this until I reached the top of the dome. It stuck fine to the original dome. Didn't use any lath or chicken wire.

martywatts 01-16-2010 08:51 PM

Re: Perlite Concrete on free form igloo
Thanks to good advice from other posters, I leaned up my mix and put it on as dry as I could. By starting at the bottom as you suggested I was able to the perlite mix to stay long enough to set. I applied in several sessions.

The chimney has been my last project. It runs over the oven and up the back. I decided to do it all of clay tiles rather than have a metal middle piece. I tied into an existing chimney. I had some tricky miters to cut and a reduction from 13 1/2 to 8 1/2. I got it all together tonight at lit a paper fire. It drew perfectly.

JoeyVelderrain 01-16-2010 09:25 PM

Re: Perlite Concrete on free form igloo
the chimney sounds interesting. like to see some pictures of it.

martywatts 01-18-2010 09:04 AM

Re: Perlite Concrete on free form igloo
2 Attachment(s)
Here are a few pictures of the chimney. It seems to draw flawlessly which was a big concern of mine since the oven is in our kitchen. I have a little fitting and mortaring to do before its completed, but there is no sign of leakage even with the loose fitting tiles and a very smoky fire. Is anyone aware of a product I could use similar to fiberglass mesh tape to wrap the joints with in addition to the fire-clay. I am guessing that after time the fire-clay will crack and drop out of the horizontal joints. With some mesh the clay would at least be held in place.

I plan on covering the whole chimney and oven with adobe after I have test fired for a while and after my stock of adobe thaws out (April). I will be building an armature out of expanded lathe to allow an air space for expansion around the flue tiles.

JoeyVelderrain 01-18-2010 01:00 PM

Re: Perlite Concrete on free form igloo
Man! I am liking that oven! that is a saweet chimney!

All times are GMT -7. The time now is 03:47 AM.

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