sawdust vs. vermiculite insulation

[pizzaholic]

hey oven, pizza, bread, building lovers. i hail from the olympic peninsula in washington.

i have taken part in building 3 cob ovens at this point, enjoyed baking in all but have been disappointed in their ability to hold heat, especially in the 475 degree range.

i have just finished building a 27 by 32 oven and recently got a lot of small wood chip/sawdust material. i was planning on doing 6 inches of insulation with the chip sawdust and clay but i am beginning to think i might be much better off with vermiculite. i insulated the hearth with vermiculite portland and layer of 3 1/2 inch bottles on their side.

the sawdust was free but im thinking i might want to just spend the extra for a better insulator. thanks.

mark

[Neil2]

Re: sawdust vs. vermiculite insulation

You could keep a book to take bets on the sawdust catching fire before rotting.

[pizzaholic]

Re: sawdust vs. vermiculite insulation

thanks for your friendly advice. just trying to keep it cheap and stay out of the hardware store.

[david s]

Re: sawdust vs. vermiculite insulation

Kiln builders often use sawdust as an insulating material. They fire to temps way higher than we do. Maybe the sawdust burns, depending how close it is to the fire source and how high the temp goes, but what does it matter if it burns anyway, the result is a void which heat does not readily pass through.

[pizzaholic]

Re: sawdust vs. vermiculite insulation

yeah, thats ultimately what you want. a friend recommended using straw which will do the same thing but provide more airspace, mix easier with the clay slip and be faster to apply.

[dmun]

Re: sawdust vs. vermiculite insulation

Insulating firebrick voids are made with sawdust, but they are fired to a high enough temperature to completely burn the sawdust to create holes in the brick. Any plan which leaves the sawdust in contact with hot masonry is doomed to fail, imo.

[Neil2]

Re: sawdust vs. vermiculite insulation

"thanks for your friendly advice. just trying to keep it cheap and stay out of the hardware store."

Vermiculite (or perlite) is not that expensive. Check with local plant nurseries.

[splatgirl]

Re: sawdust vs. vermiculite insulation

on another thread someone mentioned McMaster-Carr as a source for Vermiculite. I needed some recently so I ordered a bag instead of driving all over town trying to get it from a nursery. IIRC, the 4 cubic foot bag was ~$30 including shipping and was on my doorstep in three days. Hard to beat that for easy, efficient and cheap.