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Jami McBride
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Okay, so I've been thinking about what bothers me with Green Roofs, and it's the membrane.  Now before anyone tells me why the rubber/plastic is okay or good, I don't want to talk about membranes.  Let's assume membranes were unobtainable.....

I was wondering why someone using vermiculite in a water proof mix (cement) couldn't cover their plywood in a thin layer reinforced with chicken-wire, and thereby seal it for applying the rest of the green-roof materials.  Say about 1" thick or so.

I would think this would be cheaper, and it should be light enough not to cause new issues.

Any one have thoughts on how long something like this would last?  As long as a membrane?

How about run-off, would such cement add unhealthy toxins to the water coming off?
And if so, would there be a 'mix' green enough for the plants and run-off?

Any other thoughts.....

~Jami
 
paul wheaton
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first, I think you want to skip the chicken wire and use something that might work better for you - but is kinda like chicken wire for what you are thinking.  I think your mind is travelling toward ferrocement.    I know that there is a slight toxicity from the cement, but my impression is that it is really small (although I would really like to understand it better). 

second:  as for membrane (I know you banned it, but you also allowed for other thoughts) - consider a layer of polyethylene (black plastic sheeting - visqueen) surrounded on each side by a half inch of newspaper.  Would that be cheaper and more eco?

 
Jami McBride
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Yes & Yes - I like that idea.... but will it last?

Thatch roof = 50 years
Green roof = 30-50 years with membrane
How long would this version last?

This could work, so how would you know when the system was starting to breakdown before serious damage was done? 

Could a lime cob plus vermiculite be made for a membrane substitute?  Still wondering....
 
Joel Hollingsworth
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The concrete will begin to admit water once (and where) it begins to crack.

It might be worthwhile to have a tile roof of sorts: seams in the concrete that allow it to move a little, caulked with silicone and/or overlapped enough to shed water.

Toxicity: This will vary a lot based on what the concrete is made from.  Fly ash is in a lot of concrete mixes, and has some small heavy metal & radionuclide toxicity, both of which are almost completely mitigated by the concrete itself.  It's possible to make extremely clean concrete; recipes elsewhere show how to formulate it.  The main thing that leaches out is calcium, which you could formulate your roof growing medium to tolerate.

Under the heading of rocket stoves, water glass (sodium silicate...potassium silicate works too) came up as a surface treatment for masonry.  I'd recommend using that here.  Here's how it works:

NaSiO3 + CaCO3 --> NaCO3 + CaSiO3

(water glass + agricultural lime --> washing soda + calcium silicate)

The calcium silicate is much less soluble in water (especially at low pH) than the calcium carbonate, and also takes up more volume.  As water glass seeps into the pores of mortar or masonry, the reaction swells them shut; the surface is also rendered acid-resistant.

If the concrete can't dissolve, it can't leach toxins into soil.  Nothing's perfect, but waterproofing this way would help quite a bit.  On a related note, it may be worth leaving an attic crawlspace from which to refresh the waterproofing treatment every so often.

Re: ferrocement, a dense mesh of bamboo can substitute for steel.  I think the exchange is something like four times the cross section to hold a similar load in tension.  Changing out reinforcement might even save more weight than changing out aggregate, depending how "ferro" your cement is.  The bamboo should also be treated with water glass before mortar/concrete is applied.

Could a lime cob plus vermiculite be made for a membrane substitute?
 

Well, it is the lime in masonry that water glass reacts with, so it could be sealed.  I don't think this thin layer would stand up to roots & the house settling, unfortunately.

How impermeable can gley be made?  Does anyone here have experience with it?  It's listed in the Permaculture Designer's Manual as a pond liner option.  You'd have to be sure to keep oxygen away from it, and protect your house from the odor, but I like the local sourcing/biodegradability.
 
Jami McBride
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"water glass" as a sealant that's good to know.

it may be worth leaving an attic crawlspace from which to refresh the waterproofing treatment every so often.


I was picturing laying this mortar/cement down to cover the wood and then continue with all the usual layers for a green roof.  As far as I can tell I wouldn't have access to it once it was covered with all the layers.  So I'm not following you here.

I don't think this thin layer would stand up to roots & the house settling, unfortunately.


The roots should be far enough away just as in a traditional design.  But settling could be a problem I hadn't thought of.  I was hoping the reinforcement would hold it together. 

This is what I've found on gley so far:
Aquaculturists at the New Alchemy Institute in East Falmouth, Massachusetts, report success with experiments using a traditional sealing method borrowed from Russia. They create a “gley” by cutting grass and other green vegetation, packing it six to eight inches thick in the pond basin, then trampling it by foot. The gley sits for two weeks and rots, but it doesn’t decompose because it becomes anaerobic. The gley forms a gel and after two weeks the pond is filled. A gley lining will hold water for a couple of years or more.

Sometimes concrete or ferroconcrete (concrete with wire reinforcement) is used to patch pond leaks.  I’ve also heard suggestions that both diatomaceous earth and ashes can be used to seal pond soil, but I’ve seen no proof.


Tile is a good idea, but like thatch and slate it takes much more skill than I can muster for DIY.  The thought of plastic for a shed or such isn't so bad, but what about a large barn.... or other large project.  I would like something adorable, doable and would last.

Okay - hold on to your hats.... what about a rubber paint (Liquid Rubber Waterproofing) I've probably hit the toxic mother load!  One could paint their wood base with rubber sealant and then add a course of sand for cushion, and then the gravel layer.  I wonder.... would rubber from a rubber tree work?


 
Joel Hollingsworth
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Jami McBride wrote:I was picturing laying this mortar/cement down to cover the wood and then continue with all the usual layers for a green roof.  As far as I can tell I wouldn't have access to it once it was covered with all the layers.  So I'm not following you here.


That was also my understanding of your idea. I was recommending that this should be avoided, because if the concrete cracks or the waterproofing is otherwise breached, it would be a major undertaking to apply sealant.  If the waterproofing needs to be refreshed every five years or so, I guess it would be possible to scrape all the vegetation off and re-plant...

As to the "tile" recommendation, my thought was to simply mold the concrete in sections.  Sidewalks are made this way, for example.  Sorry to phrase that in a confusing way.

 
paul wheaton
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I think that the polyethylene as a roof material has not been fully tested.  mike oehler has a sample that now has 35 years on it and still going strong.  Mike says that it should last hundreds of years.  I would think that the stuff with the newspapers would last longer still.

 
Jami McBride
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Thanks guys ~ This has really inspired and encouraged me. 

I'm glad there are options out side of membrane (and hiring professionals) as I really love green roofs ♥
 
Kathleen Sanderson
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If you live where there are lots of paper birch trees, and if you need to clear some of said birch trees for garden area and so on, the birch bark can be recycled as a roof membrane.  There are old sod-roofed cabins in Alaska and Siberia that are fifty or more years old with that type of roof.  Birch bark kept damp just about lasts forever.  I suppose it might need to be stripped off and replaced once in a lifetime or so, but for anyone in the far North with access to plenty of birch bark, it's probably the best bet.  There may be other long-lasting barks in other areas, too.

Kathleen
 
Cristian Lavaque
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Kathleen, I've been wondering this same thing some time ago, so I'm glad you brought it up.

What I had thought I'd try when I actually get to build one, was trying a corrugated roof under the ferrocement. This way, it'd have a space that would separate the roof from the cement and moisture wouldn't accumulate there. That way, even if roots got through the ferrocement, they wouldn't go further. And the corrugated roof would also prevent it from making progress and adds an extra insulation from the living roof that could permeate the ferrocement. I hope that didn't confuse you...

I attached an image to better show the idea. There's the green, the earth, ferrocement, corrugated, wood.


greenroof.gif
[Thumbnail for greenroof.gif]
 
                              
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Cristian Lavaque wrote:
Kathleen, I've been wondering this same thing some time ago, so I'm glad you brought it up.

What I had thought I'd try when I actually get to build one, was trying a corrugated roof under the ferrocement. This way, it'd have a space that would separate the roof from the cement and moisture wouldn't accumulate there. That way, even if roots got through the ferrocement, they wouldn't go further. And the corrugated roof would also prevent it from making progress and adds an extra insulation from the living roof that could permeate the ferrocement. I hope that didn't confuse you...

I attached an image to better show the idea. There's the green, the earth, ferrocement, corrugated, wood.


I have been thinking of your idea for three years.

It seems to me that if a ferro-cement tank can be used to store water, ferro-cement should be equally able to keep water out.
Thus a steel building covered with ferro-cement might be suitable as an underground house.
I've never heard of a ferro-cement tank cracking unless it was struck with a lot of force, like a truck hitting it.
I have been looking at  steelbuilding.com
http://www.steelbuilding.com/
Their website allows you to check out any size you can imagine and the costs of steelbuildings is very low compared to conventional buildings.
 
Jami McBride
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Okay, after much more thinking about all of this and some research I have a couple more questions....

So some are suggesting the ferrocement would be used much like my original thought on using cement - got that, but this causes a problem of moisture.... (via condensation?)....when touching the plywood on the panel ?  Or are you just speaking of when it is mixed and set?

Others are thinking plastic would be enough of a water barrier, even with seems, if protected by newspaper on both sides - got that.  Maybe even add a layer of felt with it.

What about pitch and slide - anyone have the numbers on this? {edit} That's pitch of the roof and slide of the green materials 

And my big question, my secrete reason for the cement question, what about the roof-edge?
I've seen wood edges in place to hold the 'green' part.   So what kind of roof edges do you all envision for a DIY green roof?

 
Jim Argeropoulos
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rob roy talks about a clay that expands when it comes in contact with water, so it is self sealing. I can't remember exactly what clay it is.
He says it is expensive.
 
Matthew Fallon
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Silver wrote:
Rob Roy talks about a clay that expands when it comes in contact with water, so it is self sealing. I can't remember exactly what clay it is.
He says it is expensive.

"swelling clays " expand with water
bentonite clay is one of those.not sure if its the oen he's meaning
ive seen the food-grade stuff for about a dollar a pound when bought in bulk
theres also construction grade stuff though,maybe it's cheaper.
 
Jim Argeropoulos
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Bentonite is the right answer. Thanks
 
              
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I bought some chicken wire recently to mess around with ferrocement. Only issue I am going to have is it is heavily galvanized and a bit on the high side of the wire gauge.

Not an expert on this stuff, but here is what I remember from a few years of reading on and off.
Technology is over 100 years old.
Boats, watertanks, art, stair cases, pipes, repairs, fences, exterior walls, roofs, bridges (seen an artist make some), driveways, domes, houses, planters... have been made out of ferrocement.
It gets its strength from having the cement within 1/4 inch of reinforcement.
Believe the better test results are from 1/2 inch and 1/4 inch welded wire.
Galvanized metal reacts slowly with the cement and loses strength over time (chemistry?).
Lamination methods can be used to reduce or eliminate the need for rebar while reducing labor and material costs.
Read one guy used washed beach sand in his mix while others say to use a cut sand to give the cement something to grip. I am assuming the beach sand was smooth.
You can fiber reinforce your mix, just make sure you are happy with the fiber (asbestos, glass, paper... you may not be happy with for different reasons).

Water tanks last 50 plus years. Most leaks occur at the seams. Simple solutions to those when you build or drain the tank. Tanks are easy to patch, and lots of solutions for waterproofing. Pick a few and you should be set.

Even papercrete has held up well in the elements, though I wouldn't recommend it in this situation, sure you could find a way to make it work too (selecting the right wood pulp or bark )

You can apply some countertop methods if you want and polish and color the whole thing too.

If it ever needs patching, you can patch it from the inside or outside. Just add another layer or two.

The thing I like about ferrocement is its strength. I couldn't see myself living in some of the structures mentioned where I currently live. High yet random water table, clay and sand, huge trees, 50 inches of rain a year, hurricanes, tornados, ground hogs, beetles, termites... I just do not see myself trusting a few feet of soil to protect a membrane. Guess we are all looking for low maintenance longevity for the least amount of effort, labor and cost. Depending on where you are changes what that is. I would trust ferrocement and know there is a lot of documentation on it. Also know people have replaced the ferro with other stuff and had excellent results. Once you understand the concepts behind the different techniques and materials, it makes mixing and matching easy (i'm hoping )

You might even be able to overbuild and put a pond on top instead of dirt. I read you can use different levels of salinity or different membranes (clear plastic?) to collect solar warmth at the bottom of the pond. Or, you could let a stream flow through the pond and cool it.

Corrugated metal underground was used for bomb shelters during WWII. Many of them lasted 50 years or so. I would think with a little bit of care, you could get the same or better.
 
              
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Questions on Water Glass

What is a good source for Water Glass?
Approximate cost?
Can you apply it anytime after the initial cure?

Also, according to wikipedia, you can add water glass to vermiculite and perlite to make a high-temperature insulation. Might be a useful application or layer in the ferrocement structure to help keep a more consistent temperature. Either way, temperature should be fairly constant, keeping expansion to a minimum. Might also be a good additive to the combustion chamber on the rocket stove mass heater. source: http://en.wikipedia.org/wiki/Water_glass#Refractory_use

Meant to mention that there may be some benefit to mixing in blood with the mix. Read it helps bind it, waterproof it, reduce cracks, and increase tolerance to freezing, changes the cure time, makes it more workable. Not sure which are true, as different places mention different facts. Guess it helps in most of them. Not sure how it changes the water mix. Appears Romans used it.
 
Jami McBride
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Only info I have on waterglass is in using it to seal a cob (earthen) floor.



11 Waterglass Earthen Floors
This technique relies on using Waterglass, either sodium or potassium silicate, as a hardening agent for mixtures of clay soil and sand.  This is a technique with which we have had much experience, but we feel that it is worthy of further testing in that the samples we have done turned out to be extremely hard and abrasion resistant.  They were every bit as hard, if not more so, than earthen floor mixes sealed with linseed oil.  Consequently, they provide another option for anyone not wishing to use an oils and solvents to harden the surface of their floor.  This approach is based on experiments conducted at the Building Research Institute – University of Kassel, Germany. 
Waterglass, is added to a mixture of clay soils and sand at the rate of 10% by volume. The sodium silicate needs to be diluted with water at a 1:1 ratio before being added to the floor mix.  Additional water is added to attain a consistency that can be applied with a trowel.  The one difficulty we have found with this method is that mixes containing sodium silicate tend to set up fairly fast and provide a limited window of opportunity to work them.  One needs to get as good a surface as possible when applying the mix as it will tend resist further troweling. 
In that sodium silicate does little to resist the absorption of water, another material is needed to seal the floor.  One option is a product called Safecoat Penetrating Water Stop manufactured by AFM of San Diego, California www.afmsafecoat.com. It is a solvent free, acrylic based, low-odor and no VOC (volatile organic compound) formula.
Sodium silicate can be easily found through suppliers of clays and other materials needed to make pottery and ceramic products.   




Good point on the roof possibly blowing off, I've never thought of that....

 
Matthew Fallon
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found a good price on water glass here, quick google.
$10/gallon.
http://shop.clay-planet.com/sodium-silicate-solution---pint-1.aspx
 
Emerson White
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could you impregnate cotton, wool or linen with a heavy wax and then encase that in clay? I'd think you've get a few years out of that. Maybe try and get your hands on a bunch of second hand denim and sow it all together. It wouldn't be easy but it would be doable with DIY skills.
 
Cristian Lavaque
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Emerson White wrote:
could you impregnate cotton, wool or linen with a heavy wax and then encase that in clay? I'd think you've get a few years out of that. Maybe try and get your hands on a bunch of second hand denim and sow it all together. It wouldn't be easy but it would be doable with DIY skills.


That's an interesting idea. I wonder how long that'd last... Linseed oil could also work, I'm guessing.
 
Emerson White
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Linseed oil actually sounds like a much much better idea. In another thread I linked to a documentary on cob building and at some point someone mentions making floors by soaking earth in linseed oil and letting it dry up. I wonder how long that would hold up as roofing ...
 
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