tag:blogger.com,1999:blog-11904671.post6433250832646147894..comments2023-08-25T03:21:41.842-07:00Comments on The Petch House: Plaster Pictures, As PromisedGreghttp://www.blogger.com/profile/02807710209656158413noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-11904671.post-77073905269632517902008-07-09T08:44:00.000-07:002008-07-09T08:44:00.000-07:00ok, I know this is a blast from the past post - bu...ok, I know this is a blast from the past post - but in case you hadn't picked up this info already I thought I'd pass it on....<BR/><BR/>Gypsum plaster goes "off" as it gets older. When its off it behaves like you describe - it sets way too quick. The reason this happens (as I understand it) is that moisture from the air gets into the unused plaster and the reaction that hardens the plaster partially starts.<BR/><BR/>Professionals in the UK get around this by keeping their supply in air tight plastic barrels. They will Also throw out old plaster and replace with new. I used to keep an eye on the manufacture date printed on the bag (do they even do that here?) and pick the newer lots, not those from the top / front of the pallets.<BR/><BR/>HTHmickmaguirehttps://www.blogger.com/profile/08461835355315823105noreply@blogger.comtag:blogger.com,1999:blog-11904671.post-39190506336911650142007-04-24T05:13:00.000-07:002007-04-24T05:13:00.000-07:00I guess I should start logging into blogger and po...I guess I should start logging into blogger and posting under my real name... you probably know me as Texas Ranger from the oldhouseweb boards.<BR/>I am indeed located in Europe and of course, products vary greatly.<BR/><BR/>As I said, my perlite plaster was NOT gypsum based but cement/lime based and since it was pre-mixed I can't tell the mix ratio - might be pretty bad, lots of perlite to keep the price down. That stuff I used for the basement walls IS fairly soft.<BR/><BR/>If you want I'll try to look up recipes for slaking lime. I think you have to leave it for months and it's a pretty ugly job. My dad recalls when a cousin of his built a new home in 1964 the threw lime into the unfinished open cesspool and added water. It got hot and started bubbling and splashing wildly.<BR/><BR/>However, maybe I'm just confusing things once again... might just be mixing the lime with water and let it rest for some time.<BR/><BR/>German Wikipedia helped a lot... slaked lime is the powder you buy at the hardware store. Slaking is the process I described above, the stuff with the cesspool. Not something you'd want to do yourself... Hydrate lime is the same stuff, and I guess mason's lime too.<BR/><BR/>For good plaster lime putty is created by letting slaked lime soak in water for... now grab a seat and hold onto your desk or chair... 20 years! The older the better. I vaguely remember typical times of several months.<BR/>So, if you manage to buy lime putty that would be perfect, otherwise you're in for some soak time...Ragnarhttps://www.blogger.com/profile/06087234298605439486noreply@blogger.comtag:blogger.com,1999:blog-11904671.post-43564050375424472562007-04-23T12:28:00.000-07:002007-04-23T12:28:00.000-07:00"The surface can be scratched with the finger nail..."The surface can be scratched with the finger nails."<BR/><BR/>This is another one of those things I've read, but which doesn't really apply in real life. If you can scratch the stuff I put up yesterday with you fingernail, then you have finger nails made of steel. The Plaster ceiling medallions I've purchased can be scratched with a nail. From what I've been told, those are made out of Plaster of Paris. They are bright white and have an almost chalky feel to them. I am not putting pure Plaster of Paris on my walls.<BR/><BR/>"Gypsum plaster is pretty rare stuff here"<BR/><BR/>Where is "Here"? Are you over in the UK, if so, then what you are saying makes sense. When I first started looking in to plaster I got a lot of information at Period Properties UK. The problem is, the information does not relate well here in the US. Products are different. Things that are easy to get in the UK aren't available here.<BR/><BR/>This is the umpt-teeth time I've been told to "just go buy slaked lime", and I've yet to be able to find it. Everybody uses different terms: Masons Lime, Slaked Lime, Hydrate Lime, Lime Putty, etc, etc, etc. Trying figure out which is the right – and best – stuff to use for historically accurate lime plaster is very hard, and a bit frustrating.Greghttps://www.blogger.com/profile/02807710209656158413noreply@blogger.comtag:blogger.com,1999:blog-11904671.post-4420142359086974382007-04-23T00:04:00.000-07:002007-04-23T00:04:00.000-07:00I commonly use pure gypsum for patch work and fast...I commonly use pure gypsum for patch work and fastening stuff in masonry walls (pure gypsum sets in 5-10 minutes, some kinds even in like 2 minutes, to install an electrical box in a masonry wall you just smear some gypsum in the hole, push in the box and hold it until the gypsum hardens). I mostly use the same brand since the hsop where I buy only stocks that one, and the curing time varied greatly. Some bags got rock hard within 2 minutes, others were useable for almost 10 minutes.<BR/><BR/>Perlite plaster (though cement and lime based) is advertised as "thermo plaster" here since the perlite somewhat acts as thermal insulation. I once used it and the main differences seem to be: the bags are much easier to carry around and once the stuff is cured it's lighter too. On the other hand, why would you need that? Once it's on the wall the difference doesn't really matter any more... besides, thermo plaster doesn't really get hard. The surface can be scratched with the finger nails.<BR/><BR/>I don't really see any reason to use that stuff, depending on the application I either use pre-mixed bagged lime-cement plaster or mix my own lime plaster.<BR/><BR/>You can both mix plaster from dry bagged lime or slaked lime and I noticed a big difference. The dry variety is just like sand mixed with water and doesn't get extremely hard. The slaked lime plaster is really sticky and nice to use, it can be troweled perfectly smooth and gets ROCK hard.<BR/><BR/>Gypsum plaster is pretty rare stuff here, lime plaster is simply cheaper and easier to use (stays soft in the bucket for several hours). I think in old houses gypsum plaster (if at all) was used only for ceilings because gypsum needs to stay perfectly dry (and especially single story brick houses were never completely dry at the bottom). It seems that ceiling plaster didn't contain any sand since it's smooth as glass.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-11904671.post-10384903857429754412007-04-22T14:45:00.000-07:002007-04-22T14:45:00.000-07:00hott!hott!Anonymousnoreply@blogger.com