Vermicrete or Perlcrete as last layer

[mrchipster]

I am building an enclosed 42 inch corner oven. The enclosure is block with an outer brick veneer. My roof is going to be steel and I will be putting sheet metal in my corners to reduce the amount of vermiculite needed to fill the enclosure.

My dome will be covered with 2 inches of FB blanket and then filled with vermiculite or perlite.

From working with both of these materials in the past I know any air movement will cause the stuf to blow away easily.


I am thinking of putting a piece of aluminum window screen over the top of the loose vermiculite and then mixing up a batch of vermicrete 8/1 mix. And put about 1 inch of this over the top to prevent any future blowing around of the loose stuff.

Any comments or other suggestions.

Chip

[GianniFocaccia]

Re: Vermicrete or Perlcrete as last layer

Hey Chip,
I've not heard of this idea before. Won't the loose fill just stay in place once the roof is on?

This might sound like a crazy idea, but do you think it would be viable to mix up a really thin batch of portland slurry and apply it to the top of your loose fill with a garden sprayer?
John

[Tscarborough]

Re: Vermicrete or Perlcrete as last layer

I put building paper over the rafters before I put the metal roof on mine (loose perlite fill).

[mrchipster]

Re: Vermicrete or Perlcrete as last layer

Hey Chip,
I've not heard of this idea before. Won't the loose fill just stay in place once the roof is on?

This might sound like a crazy idea, but do you think it would be viable to mix up a really thin batch of portland slurry and apply it to the top of your loose fill with a garden sprayer?
John

I will be using vented metal soffit panels to let out any condensation that may build in the future so there will always be some air movement.

Not sure I want to kill my garden sprayer... It is so easy to mix up a batch of vermicrete if I decide to do it I think I would just do a batch.

I am not real excited about adding tar paper under the metal close to the oven.

[Neil2]

Re: Vermicrete or Perlcrete as last layer

If you make a weak (12:1) vermiculite/portland concrete for all of the the fill, you will not have to worry about if blowing or sifting out.

[david s]

Re: Vermicrete or Perlcrete as last layer

If you make a weak (12:1) vermiculite/portland concrete for all of the the fill, you will not have to worry about if blowing or sifting out.

That is true but then you have the problem of removing the water, of which there is plenty (about a third of the total volume of vermiculite used.
Tests show perlite to be a superior insulator to vermiculite, but when you mix cement with either (a 10:1 mix has more mass in cement than vermiculite ) there is no practical measure of difference in the two.
Chip,I think your original idea is a good one. I also like your plan of including vents.

[mrchipster]

Re: Vermicrete or Perlcrete as last layer

If you make a weak (12:1) vermiculite/portland concrete for all of the the fill, you will not have to worry about if blowing or sifting out.

The sifting problem is not an issue I have sealed all of the joints with High temp silicone and covered the outside of the metal seams with Aircraft aluminum speed tape. It does not let go even under heat stress.

I was trying to avoid the large mass of wet stuff around the oven and have just a capping layer to prevent blowing around.

I mixed up a batch of 22:1:1 perlite/portland/lime (equates to a 11/1 mix) for the area of my thermal break between the inner arch and the flue arch and it is quite weak but it does not move around and stands on its own as a vertical wall of at least 14 inches. It was supported by a piece of corrugated until it set up (about 24 hours). I was looking to give some high heat resistance with the lime should there be a high heat breach at some point in the future.

Because this proposed cap layer will be well outside the heat zone I think perlite/portland only would be a better choice i will leave out the lime because of the very long cure.

Chip

[Mike D]

Re: Vermicrete or Perlcrete as last layer

Pictures? We Love Pictures. Why do you need to reduce the amount of vermiculite in the enclosure?

Mike

[ugnsnisse]

Re: Vermicrete or Perlcrete as last layer

Anyone know why vermicrete is supposed to be OK for insulating under the floor when portland cement breaks down at those temps?

[cobblerdave]

Re: Vermicrete or Perlcrete as last layer

G'day
I have wondered the same thing too. Because these ovens are homemade there will probably never be a truly exhaustive study like you get in construction for example.
These ovens stand up and keep working so no one to my knowledge has had any reason to pull a working one apart. That would be interesting.
I suspect that in the top layer the Portland does break down. The pearlite/vermiculite is packed together during its time as a liquid cement mix. The underlying pearlite continue to hold the upper in position and the upper continue to protect the lower from the heat. This of of course pure speculation. But you have to admit it continues to work.
Regards dave

[david s]

Re: Vermicrete or Perlcrete as last layer

G'day
I have wondered the same thing too. Because these ovens are homemade there will probably never be a truly exhaustive study like you get in construction for example.
These ovens stand up and keep working so no one to my knowledge has had any reason to pull a working one apart. That would be interesting.
I suspect that in the top layer the Portland does break down. The pearlite/vermiculite is packed together during its time as a liquid cement mix. The underlying pearlite continue to hold the upper in position and the upper continue to protect the lower from the heat. This of of course pure speculation. But you have to admit it continues to work.
Regards dave

Yes this is exactly what happens. The top layer (about a millimetre) of vermicrete/perlcrete may break down if it gets hot enough, but as the temperature drops away any deeper the stuff holds together ok. When testing insulation panels made of perlcrete, vermicrete and foamcrete, I discovered that where the panel was in direct contact with the heat source (over 400 C) the surface was dusty but the rest of the panel was quite ok.

[cobblerdave]

Re: Vermicrete or Perlcrete as last layer

Thanks Dave
Your certainly our R & D department
You didn't try to see what happens with AAC sheet did you?
Regards dave

[david s]

Re: Vermicrete or Perlcrete as last layer

No, but I would expect it would be the same, AAC, or Hebel is made from Portland after all. Be careful with fibro though, I think it may explode. Next time your wife is not in the house, put a really dry lump of the Hebel on one of the electric stove hotplates turned up full and leave it for around half an hour, taking temps on the cool side every 5 mins or so. Turn off the hot plate and turn the lump over and record the hot side temp with an IR gun, it should reach over 400 C. Turn it back over again recording the temps periodically on the cooler side it drops back to ambient.

[cobblerdave]

Re: Vermicrete or Perlcrete as last layer

G'day Davids
The child bride will put up with a lot of things but after 30 yrs marriage I'm still
not gutsy enough to invading her kitchen with WFO experiments.
I'm still interested in trying this though... But I think I'll retire this one, quietly to the gas BBQ.... A mans still got to eat day to day!
Regards
Dave