[Strawbale] Carbide lime

[Derek Roff]

I've worked with carbide lime a few times.  The lime experts that I 
worked with said they thought it was a pretty good material, as limes 
go.  The carbide lime was stored in ponds at the acetylene plant, and 
so it was harvested as a slurry, although in one case, the pond had 
dried up, and the lime was in lumps and powder.

Since the intended product is acetylene gas, pollutants in the lime 
slurry are not a concern to the manufacturer.  We found small, hard, 
black grains, which someone guessed would be silicon carbide, and 
whitish lumps of various sizes.  We ended up screening the slurry 
through window screen, which was a slow and tedious process.  The lime 
putty had a slight yellowish color.  After the plaster dried, it looked 
white, but was not as brilliantly white as the bagged, hydrated lime 
(type N and type S) that I have worked with.

The lime slurry smelled strongly of acetylene.  I presume that a very 
tiny amount of the carbide was still present, slowly reacting with the 
water, and producing small amounts of acetylene gas.  Breathing 
acetylene, even in low concentrations, makes me sick to my stomach. 
Some other people had similar reactions, but many did not.  The odor 
disappeared within a few days (maybe quicker) after the plaster was 
applied to the walls.

Acetylene is heavier than air, and can therefore accumulate in enclosed 
spaces.  I don't know if the acetylene released while transporting, 
storing or using carbide lime has the potential to create a hazardous 
situation for the owner-builder in any normal circumstances.  Perhaps 
Murray could comment.  If I were using it indoors, I would certainly 
leave windows and doors open.

derelict


> Acetylene (C2H2) production from calcium carbide (CaC2) is achieved by
> reacting the carbide with water [CaC2 + H20 = C2H2 + CaO], but the
> CaO will immediately and violently (exothermic) react with the water
> to produce 'hydrated' lime {Ca(OH)2}  [CaO + H2O = Ca(OH)2]. As I
> mentioned in another communication, the hydrated lime reacts very
> very slowly with the CO2 in the air unless the hydrated lime is
> continuously maintained wet. I suspect that the reaction is still
> very slow, but I am not sure about that case.

Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm.edu