Terraced enclosure

[kebwi]

Here's a really crazy design. I have, from the beginning, wondered if I could cover the thing in dirt and let moss, grass, and other weak-rooted (nondamaging) plants grow on it. I especially like the idea of terraces, as shown.

There are two major issues: preventing dirt, water, and roots from damaging the structure and building such a self-supporting structure in the first place.

On the first issue, I would put down several layers of heavy plastic and only make the dirt an inch or two deep so only small plants could grow in it. I would also provide good drainage off the sides, and maybe even slope the terraces a little so they run off the outer edge.

On the second issue however, I am less certain. This is basically a corbeled arch, which is notoriously weak. I would need to build annuli (flat rings) of rebar-enforced concrete.

The question is, do you think these concrete annuli can be built in such a way that they will support the load of the upper terraces (and a few inches of dirt)? How thick should the terraces be?

In addition, how the heck would I do it? If I form and pour an annular terrace in place, I won't be able to get the plywood out from under it! Could I make the concrete form out of that hardi-backer stuff (is this just sheet rock?) and then just leave it in place under the poured concrete? Could such a material be cut to this kind of shape?

On a related note, could I simply build the terraces out of hardi-backer (perhaps several layers) and not bother to pour concrete terraces at all? On major problem with that approach is there won't be any metal (rebar) to support it.

There must be a way to build this structure. It doesn't have to support much weight after all (just itself).

Is this totally crazy?

[nissanneill]

Re: Terraced enclosure

Hi kebwi
I don't see a problem at all provided that you have adhered to the proper shape and proportions of the Pompeii and insulated then sealed it carefully. This would be critical to ensure that no moisture will get into your oven and no heat get out to steam your plants/grass/moss etc.
I would get some chicken wire or fine weld mesh, fold it over once and then 'put a halo over your oven' and then ferro cement it in place. This is then repeated at the next level and so on until you have the dome 'terraced'

Neill

[kebwi]

Re: Terraced enclosure

I think I understand your idea. One thing I want to clarify though. Are you suggesting that the ferro structure ultimately rest against the oven such that *if* it sank even the small amount it would immediately become load-bearing upon the oven?...are you are suggesting that the ferro structure be free standing from its lowest-outerest footprint against the hearth?

I don't want it to rest against the oven for two reasons:

1. There will be about 3" of "fluff" insulation and I want additional loose vermiculite between that and the outer shell.
2. The fluff insulation layer will obviously not be load-bearing. Any significant pressure will compact it down onto the dome, thus not bearing a load anyway while simultaneously reducing the insulation thickness.

But ultimately I like the idea of a ferro structure. I had imagined some things like that (for other designs) but didn't know the lingo for it. Thanks for the head's up on that.

Do you have a recommendation on the kind of cement or the basic recipe for cement to use in ferro construction?

[Tscarborough]

Re: Terraced enclosure

That would be a great place for the herb garden.

[Archena]

Re: Terraced enclosure

I think it's a neat idea but would probably be better as a free standing structure surround. You can add insulation in the void between the two. Use stringers to tie the rings together and to support each terrace. As long as everything is connected firmly it should eliminate the problem of stressing the arch and would probably support the terraces much better.

I agree with Tscar (who needs a shorter, easier to spell user name) - it would be wonderful for herbs (non-invasive, naturally)! Actually, if your climate will support it thyme would make a good ground cover and you could use annuals which wouldn't endanger the structure. Basil, sage, dill, - I'm getting hungry!

[kebwi]

Re: Terraced enclosure

Help me understand your idea Archena. Are you suggesting a skeletal framework *above* the above, from which terraces are suspended, like a suspension bridge?

[stonejohn]

Re: Terraced enclosure

Hi All, I will Only speak to the issue of moisture into the oven and surrounding masonry. I worked for a builder of water features, ponds, fountains, and pool type structures. Any time we had loss, leaking of water from the structures themselves we would use a product called " Pond Armor" It was a two part epoxy coating, worked very well. It would make sense to me if it keeped the water in the fountain it should keep the water out of the oven. I'm also making the assumtion the areas to seal are the outer shell of the wfo, are insulated and do not get hot. i just googled it, It still around.
John

[kebwi]

Re: Terraced enclosure

Yes, thanks. I am quite concerned about the aquatic and botanical threats my idea poses. Aquatic, as you said, in the form of seepage from my dirt, and also from Seattle's weather in general, which had strongly warded me off any "stucco"-style (of which this design counts, i.e., no true roof). Botanical in that I am worried about stronger plants breaking the outer shell with their roots...but I guess plants don't generally break pots that are too large for them, so perhaps that concern is unwarranted. For both reasons, water and root, I would put down a layer of plastic under the dirt.

Pond Armor, noted. Thanks.

[kebwi]

Re: Terraced enclosure

How about this idea, assuming you guys are following this thread. I had been hoping to fill loose vermiculite inside a walled cavity, much like a house enclosure, but what if I simply mold the terraces out of vermicrete? To get nice sharp edges I could basically form each terrace with plywood and fill it like pouring normal concrete (I might use large 2" concrete blocks for the vertical walls of the terrace).

Would that be a much easier way to achieve my intended result than various enclosure ideas (concrete-wall-and-floor or a ferrocement)?

Related questions: If this structure must support the weight of perhaps four to six inches of dirt, should I use a stronger vermicrete mix than is often used for domes to make it stronger? 5:1 to 12:1 seems to be the FB range. FBers often go stronger at the hearth to support the weight of the oven and weaker over the dome for maximum insulation. Should I go a littler stronger (sacrificing insulation for strength) if the structure will have half a foot of dirt, or is that so inconsequential a weight that the 10:1 to 12:1 mixes would be sufficient?

Thanks again.

[jmhepworth]

Re: Terraced enclosure

I believe you will need a 100% certain moisture barrier between the oven insulation and the dirt. While I didn't use vermicucrete, my understanding of it is that it will likely absorb moisture if there isn't a moisture barrier around it. I like your idea to make the terraces. But I would figure out how to do it by building an enclosure that is impervious to water and put the terraces on top of that.

[kebwi]

Re: Terraced enclosure

Hmmm, good point of concern jmhep. I had been thinking that a copious layer of surface bonding cement, following by several layers of plastic (weighted down by the dirt) might be sufficient, but perhaps I need other factors as well. Pool Armor was mentioned earlier in this thread. Having not worked with surface bonding cement yet, I'm not sure what its properties are in terms of water absorption.

P.S., I never had any intention of trusting the vermicrete layer to be even the remotest bit water-tight. Remember, my original design was loose vermiculite fill, so, I had been planning on a waterproof shell from the outset.

Thanks.

[Archena]

Re: Terraced enclosure

Help me understand your idea Archena. Are you suggesting a skeletal framework *above* the above, from which terraces are suspended, like a suspension bridge?

No, but I think I know where the confusion comes from - I hadn't thought about what 'stringer' would sound like since my Daddy taught me that stuff as a kid (not that I was actually building things - I was just the really curious kid pestering him with questions).

This is a stringer:


What I'm suggesting is basically a circular staircase that surrounds but does not touch the oven. You can build it out of wood then seal all or part with concrete or build steel containers - whatever. Wood stringers can be bought pre-made at most any home improvement store (the image is from Amazon) or you can make them to whatever size you like since the rise won't matter as much.

Hmm, come to think of it, that would be a pretty cool planter surround for a deck or patio. I may steal the idea if you don't mind?

[kebwi]

Re: Terraced enclosure

Go for it.

[kebwi]

Re: Terraced enclosure

I'll keep this question in this thread since it arised from my various enclosure designs, but it is somewhat of a tangent to the original subject of the thread:

I am trying to determine what I will *lose* by molding the terraces out of vermicrete instead of building an enclosure shell and filling it with vermiculite. In either case, I would apply an outer coating of some sort of stucco (surface bonding cement being the most likely candidate), along with perhaps other surfaces to increase water resistance. That's not my point here though.

What I really want to know is the comparative insulation value (R value?!) of loose vermiculite vs. the common ratios of vermicrete, 5:1 to 12:1, although I admit that for an upper enclosure I would probably do something between 8:1 and 12:1.

Does anyone know how much better loose vermiculite is vs. 8:1 or 12:1 vermicrete? Obviously for a given thickness, that goes without saying.

Thanks.

[Tscarborough]

Re: Terraced enclosure

I have seen that information on this forum...somewhere.

But, there is no way that vermicucrete at anything more than 1-2-3 (P-S-V) ratio could be used for anything structural in a vertical plane.