Surface bonding with epoxy
Greetings.
This question is too long. Sorry. Blame it on brain dumps.
I’ve grown up with farming where many times you don’t have what you need, and have to make do. And later in life, I found out I am Autistic, which explains why it is hard to find engineering positions (I have an M.Eng. in materials science and engineering).
I first grew interested in the materials aspects of building science with Hurricane Katrina. And the earthquake in Haiti made me look at things yet again. I live in NW Alberta, Canada, far away from the US Gulf Coast and Haiti. I have visited a few Caribbean islands in the past. Post Katrina, it bothered me that residents regarded houses as disposable. But, if you live outside the cities, you are lucky if you get good concrete, which certainly lends a lot to the idea that houses are disposable. And this is where I first heard of dry stacked concrete block construction, and surface bonding. Which is a method amenable to vounteer construction.
Haiti came along. They have nothing. Importing anything to rebuild is a drain on the economy. Haiti has the raw materials to make aluminum bronzes, which in many applications are equivalent to steel or stainless steel. Haiti used to have trees, but it has a lot of bagasse now. You can make carbon fibre fabric from wood tar, presumably you can do the same from bagasse tar. You can make epoxy from wood tar, and again presumably bagasse tar would work as well. Concrete block is their preferred method of construction.
So, one could envisage making buildings by dry stacked concrete block, and then apply carbon fibre/epoxy surface bonding to it.
And pretty much anything/epoxy is a stronger surface bonding agent than the surface bonding mortar which is commercial.
I’ve got a bee in my bonnet about trying to get a volunteer built structure which isn’t a house. Yes, a person could probably do it withsurface bonding mortar. But I am stuck on “what if”. Epoxy/anything for surface bonding is a moisture barrier. To surface bond any block structure (concrete or other) with epoxy/anything, has 2 vapour barriers on either side of the wall. And they are likely strong barriers.
And this goes against building rules. I am beating myself up to think of some way, to make the one epoxy/anything surface water permeable., on one side, or to find some way to exhaust water from the wall.
The best I have so far (theoretical), is to coat the core of the lowest block with a hydrophobic material (silane?), and then cut into the foundation a narrow groove into which a person lays a wick, to draw water out of the wall as it develops. Maybe a person puts a cage at the bottom to actually make an air gap, but I think just having hydrophobic surfaces is enough.
What is an ugly solution, is to have high heat transfer pipes come from the roof into the top of the cores of the wall. And paint them black. At the top of the pipe, is nominally a ball. If there is excess pressure (nominally from water), the ball gets lifted up to exhaust water. To work well, you want really spherical balls, and nearly perfect mating surfaces.
The silane idea looks more practical to me, but neither seems really practical. Any other ideas?
Totally unrelated. None of the image upload formats allowed are vector (like SVG). For things like line drawings, SVG can be much smaller (especially if compressed) than other formats).
Wonderful blog!
Gord
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Replies
Forgetting things, sorry.
To use epoxy/anything in the tropics isn'the problem I am thinking of. If a person was to carry the very volunteer friendly dry stack concrete block into more arctic climates, we run into the two vapour barrier problem. Which I have been spending too much time trying to find a way to remove water from that inter-barrior region.
Gordon,
A few (somewhat random) reactions:
1. I applaud your interest in helping find building solutions for Haiti.
2. As a veteran of two stints volunteering for earthquake-relief construction projects (my experiences were in Armenia), I am wary of high-tech speculative construction schemes for Third World countries. My mantra: keep it simple, and use local materials as much as possible. (I know that you hope to use local materials, but I strongly suspect that there is no factory in Haiti that makes bagasse-based epoxy -- yet.)
3. Concrete blocks are not damaged by moisture, so your concern that surface-bonding cement has to be vapor-permeable is misplaced.
If employers won't consder you because you have autism, it is easy to spend too much time studying things.
I have often found myself bootstrapping, building tools to build tools, or guessing other useages for things, as I have never had a budget to work with. And this includes working at a research nuclear reactor and doing GPS/GIS applications in farming.
Everybody keeps beating at the two vapour barriers is evil, I just assumed. Thank you. I expect then, for a concrete block wall there is actually an optimal amount of water which should be between the 2 vapour barriers, to maximize the thermal mass of the wall.
Organic chemists are truly outstanding people. Back when I was working with pharmaceutical chemists, I happened across a tremendously expensive compound. On one side of a benzene ring was something that required an oxidation reaction, and opposite it was something that required a reduction reaction. But today I found out that while most epoxies are water barriers, it is possible to make an epoxy that is an insignificant water barrier, and still has high adhesion to concrete.
I am going to guess your comment about "high tech" refers to surface bonding. Scandanavia has a long history of making wood tar by partial combustion of wood. The fuel, is all the low molecular weight stuff in wood (like formaldehyde). But at the end they got their wood tar, and a bunch of charcoal. Haiti has gotten used to using charcoal for household cooking. But if a person used solar instead of combustion to make the "wood tar", one could also recover the light molecular weight organics, and still be left with charcoal for people to cook with.
One of the trees being planted to attempt to re-forest Haiti is I believe Red River Gum. This is a one of many Eucalypt trees that has a nickname of "widow maker", as they spontaneously drop limbs. It is a fast growing tree. Dropping limbs is probably useful in the context of charcoal supply, just going through a developing forest should allow one to collect wood. Using solar destructive distillation instead of partial combustion allows access to the low molecular weight organics.
I don't think there are epoxy plants (or glass fibre or carbon fibre) in Haiti, but perhaps there should be. It would give them more possibilities for high strength materials, that doesn't require imports. (Which is why I think someone should investigate using aluminum bronze for rebar, because they can make aluminum bronze, but not steel.)
Thanks for the input (possibly to continue?), and have a good New Years!