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A rammed-earth architect and myself have had the idea of building rammed-earth water tanks that would be coated with ceramic glaze on the inside, as an alternative to a cement / concrete tanks, for remote areas of Nepal, where transporting cement would be logistically unsound.

We have yet to experiment and see the cost effectiveness of our idea.

As for now, I would like to know what type of glaze I could use to coat the inside of the tank and how I could fire it?

Is there a recommended low-temperature glaze?

Can it be fired cheaply? (For instance I was thinking of filling the tank with saw-dust and feeding oxygen / air through a ventilation pipe so temperature would soar).

I am merely speculating here, but it seems like a valid idea.

Would you have some suggestions regarding glazing?

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While this question is interesting, I'm not sure it's on topic for this site. We deal with do-it-yourself home improvement, so it's hard to see how this question would fit into that scope. –  Tester101 Feb 1 '13 at 13:04
    
I want to do it myself in my own garden and I want to help other, remote householders to do it themselves too. If working I would like to propose this solution on our website, aiming at home improvement towards self-sufficiency. openbiotecture.wordpress.com –  Benjamin Feb 1 '13 at 13:08
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3 Answers 3

Glaze is essentially glass that is formulated to bond with the supporting clay body such that it's physical properties such as coefficient of expansion are similar. Since your "clay" body is unfired earth of varying composition, even if you were to succeed in applying it, it will quickly crack and spall off.

You also will never get the consistent temperature control required for a homogeneous glass surface. A good part will be either over or under fired and not water proof. Also, pure glass fires at very high temperatures. To produce glaze that fires at lower temperatures, a flux must be added. Traditionally, low fire fluxes have been various lead compounds, which have been proven unsafe for food and water contact. I believe alternate food safe fluxes have been developed, but their functional temperature range is very restricted, so may not work for the application that you envision.

I commend your out of the box thinking, but this idea is just not practical. Keep the ideas coming though, you're bound to hit a good one eventually!

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Thanks for the feedback. I'll inquire further for an alternative to glaze. (I've seen brick temples that have a kind of glaze on the outside, which seems to be applied after construction. I am trying to find out how this is done.) –  Benjamin Feb 2 '13 at 3:54
    
I'm not familiar with Nepalese temple construction, but in general, bricks are frequently fired to a "low" (ceramic) temperature, and applying glaze to one side is not uncommon. These would be the sort of glazes fluxed with lead :( But you did mention after construction, whereas this is strictly before construction. So go ahead and check it out, you never know. –  bcworkz Feb 2 '13 at 20:42
    
Hello, I found out that glazing on temples was applied to bricks prior to construction. Firing post construction should be possible according to late Nader Khalili, but there is no technical details on the firing. However I found I could glaze with rosin. I made some tests melting resin from local saal trees and applied them to a ceramic shard, which is now waterproofed. We'll try this on rammed earth now and see if it is a success. –  Benjamin Feb 24 '13 at 9:51
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As bcworkz pointed glazing may be too difficult on the scale of a water tank, I looked into using rosin as a glazing.

I made some tests melting resin from local sāl trees and applied them to a ceramic shard, which is now waterproofed. We'll try this on rammed earth now and see if it is a success. (Answer to be updated).

NB: the resin might not be from sāl proper, but it is sold under this name on the market.

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An interesting idea! I have some reservations about this application, but I wish you the best of luck and look forward to your report of the results. –  bcworkz Feb 26 '13 at 23:44
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I find your idea interesting. I recommend the book Ceramic Architecture by Nader Khalili. Khalili was able to fire whole adobe structures utilizing a gravity fed kerosene burner. I believe he experimented in using glazes on the adobe bricks. Another path might be to use materials that would be used to waterproof swimming pools. Would it be possible to include, during the rammed earth process, a way to securely attach strings or wires in the rammed earth? If so, then you could use hardware cloth tied to the strings and white cement to waterproof. Or alternately, you could utilize white cement in the rammed earth mixture to waterproof the entirety of the rammed earth.

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