I can't help but respond to this series of posts, even though I have very little that's useful to contribute. I worked for US Gypsum 36 years ago, and had some familiarity with the process and the practices of the time. Of course, at the time, wallboard compound was loaded with a magical ingredient called asbestos, as was the air on the rail car loading dock where 100,000 pound carloads of asbestos bags would be unloaded. Being a 100-year-old building with closely spaced columns, inevitably a forklift operator would clip a column as he rounded a corner, breaking every bag on the corner he clipped, and leaving a trail of asbestos that stretched on the length of the warehouse. Of course, today they can't use asbestos. But I digress... When gypsum is calcined, at temperatures considerably lower than those used in lime burning, water of crystallization is being driven off, turning the rock into a powder. When mixed with water, it is that same water of crystallization that is changing the structure of the gypsum, making it hard again. This is accompanied by a slight expansion. Gypsum is good for fireproofing because it has the capacity to absorb energy from a fire by driving off the water of crystallization again. Consider your house to be an impromptu calciner. I have vague recollections of the formulations for wallboard and joint compound, and am fairly certain that at least in the wallboard formulas there was some sugar. The gypsum slurry used for making wallboard was actually two different formulas - one for the edge of the board and one for the center. If I remember correctly, the edge formula was the one with the sugar, which was purported to improve the ability to nail into the wallboard without having it shatter. There may be some cellulosic thickeners in joint compound today, which are biodegradable. The ethylene glycol is undoubtedly there for the same reasons you would have used it in your car, at one time. Somebody leaves the pail outside when it's cold, there's less chance the stuff gets frozen. As for MSDS, not every ingredient is always reported. Hazardous ingredients must always be reported but gypsum would not necessarily be considered a hazardous material. I remember being told, all those years ago, that breathing gypsum dust was good for you. Then I got pneumonia. Then I quit. Edison Coatings, Inc. Michael P. Edison President 3 Northwest Drive Plainville, CT 06062 Phone: (860) 747-2220 or (800)341-6621 Fax: (860)747-2280 Internet: www.edisoncoatings.com www.rosendalecement.net E-Mail: [log in to unmask] ---------- Original Message ----------- > But it's definitely a gut job to remove the gypsum blocks, which > surely have absorbed a lot of moisture. > > Yeah, like, why is this, scientifically? Why would wetting/drying (or > is it just wetting?) destroy the bond of all the little teeny tiny > particles? And how did they stick together to begin with? > > c > > -- > > >From what I have read, gypsum materials expand during setting, primarily > because the dihydrate crystals push against each other as they form. So > if the block got wet, it will expand and weaken and probably needs to > be replaced. > > Let me know if we can help! > > Eric Hammarberg, Assoc. AIA > > Actually the mold grows on the sheetrock paper facing (food source), > not the gypsum > > Eric Hammarberg, Assoc. AIA > > > As you suggest, the paper is usually what > > usually supports the mold, put it appears there must be an > > additive in the compound that did too. > > High fructose corn syrup? It's in everything else (including the space > between my ears, which makes me sweet but dangerous sometimes). > > _______________________________________________________ > Dan Becker, Exec. Dir. "The workman ought often to > > Its my understanding that Gypsum based products are not more or less > likely to grow mold then other chemically neutral surfaces, but that > while lime plaster has a high pH level is actively discourages mold > growth. Gypsum from what i can tell seems to be pretty close to > neutral, and when it gets wet it holds moisture... all mold needs is > moisture and a neutral environment. A quick Google astral projection > seems to indicate several manufacturers saying that without the paper > that Gypsum does not grow mold... unless you get it wet. > > Could just be some dirt. Whatever those little microbes will eat, like > a hound-dog eatin' his own poop and my 3 year old daughter eatin' dust- > bunnies from under the radiator. > > Eric Hammarberg, Assoc. AIA > When we were in the Holy Cross neighborhood after Katrina I did an > assessment of a house which was about to be gutted. Fortunately we > saved that one, but it did have a peculiar condition on the bedroom walls. > They > appeared to be lime based plaster like the rest of the house (and most > of > the unremuddled properties there) but they were exhibiting mold growth > at > the waterline. My trusty pocket knife revealed that a gypsum veneer > (probably Lowes drywall compound) had been applied to the plaster > surface > and the mold was in the veneer. As you suggest, the paper is usually > what > usually supports the mold, put it appears there must be an additive in > the > compound that did too. > > Rudy > > Well just going by free information on the internet... they don't make > it easy to find out whats even in Gypsum Paste besides Gypsum. I > wonder if its a "proprietary" thing by manufacturer, or if my surfing > skills are insufficient. Anyone know whats in this stuff? > > > Here's a link to an MSDS for Certainteed's ProRoc, see the "Hazardous > Ingredients" on the third page and other places: > > http://www.bpb-na.com/canada/pdf_ProRoc/Safety_Data_Sheet/1- > 06_readymix_ compounds_SDS_EN.pdf > > It's mostly limestone, mica, and kaoline clay. No high fructose corn > syrup but it does have some ethylene glycol (don't let your cat or > rabbit get into it). > > > According to Susan M. Escherich's article on Gypsum Block and Tile in > Twentieth Century Building Materials (a great resource), gypsum block > loses compressive strength when saturated, but can regain it if it is > allowed to dry out. > > We can expect to find gypsum block on interiors as fireproofing for > structural steel and as partition walls (as stated in earlier posts). > > Generally, gypsum (as in Plaster of Paris) is not considered stable > for exterior applications-- it degrades when wet (it is essentially > water soluble) and produces soluble gypsum salts. > > -Mary > > > Marked absence of Gypsum in that MSDS... Ethylene Glycol is kind of > neat stuff... i wonder why they put a small amount of it in the > product? I wonder if its a binding agent? seems from its description > it could be sticky. > -- **Please remember to trim posts, as requested in the Terms of Service** To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: <http://listserv.icors.org/archives/bullamanka-pinheads.html>