Hi there,
I’m looking to laser some drywall … clean, unpainted, drywall. I am actually just wanting to cut the paper on the drywall so that I have some nice clean sharp lines to cut with a knife. Cutting the actual drywall with a laser would be bad for my application as drywall has moisture in it that acts as a fire retardant, through evaporative cooling in a fire, and provides structural strength. My expectation is that a couple of passes on the Heavy Paper power setting, 20%, will do the job while keeping the drywall temperature below 100°C (except at the surface transition between the paper and the gypsum interior).
MSDS sheets for drywall are tough to find, but I’ve located:
http://www.commercialdrywall.com/files/products/liftlite-drywall.pdf from Continental Building Products in the US.
For full disclosure I must point out the following … (I know TMI) …
The major component of drywall is Gypsum which has a melting point of about 150°C and a boiling point of about 1450°C. INCHEM, the International Chemical Safety group (associated with the WHO) lists Gypsum as “Not combustible. Gives off irritating or toxic fumes (or gases) in a fire.” (see ICSC 1215 - GYPSUM (MINERAL)) I have looked around and found no further discussion of combustible by-products although my expectation, from my University chemistry daze, of the process is Gypsum (CaSO4·2H2O) when heated leading to it’s melting point, probably around 100°C begins to give off it’s water leaving behind calcium sulphate (CaSO4), i.e. plaster, to melt around 150°C. Above 1500°C (the boiling point) I would expect that the gaseous Calcium Sulphate chemically breaks down and various sulphur oxides, SOx, are produced. These are generally bad as they are chemically reactive and I further expect that they will readily combine with the moisture in the air the to produce: Calcium Hydroxide, Ca(OH)2; Hydrogen Sulphide, H2S (that rotten egg smell); Sulphuric Acid, H2SO4; and probably lots more stuff depending on what’s in the air.