![]() ![]() Lime plasters, however, can excel outdoors under most weather conditions, and with certain additives to ensure they have a long useful life. Gypsum plasters are interior plasters, typically not meant for exterior use because they do not do well with repeated exposure to water. It typically didn’t require horsehair to strengthen it either like lime plasters do. Unlike lime plaster, gypsum cures fast (only a few days) and sets even faster, which is why we make casts for broken limbs with the stuff. Most gypsum plaster came from Paris, and so the name stuck. It got the nickname because in the 1700s, Paris was built on top of some of the largest natural gypsum deposits in the world at the time. Gypsum – You’ve probably heard of Plaster of Paris? Well, that is gypsum plaster.Lime plaster also takes an extremely long time to fully cure, sometimes taking as long as a year before walls could be painted or wallpapered. Lime also needed the addition of fibers like horsehair to help strengthen the wall. ![]() Lime plaster is a rather laborious process of mixing water and lime and waiting for the lime to “slake” before it can be added to the sand for application. Up until this time, it was cheaper to acquire than the expensive gypsum plasters. Lime – Prior to the early 1900s, lime was the primary binder in any plaster.Plasterĭepending on what kind of plaster you have, you will have one of two different binders, lime or gypsum. My purpose is to help homeowners get their feet wet on the topic. Plaster, stucco, render, etc have been around for millennia with so many variables and formulas that a 1000 page book couldn’t cover everything. I’m going to preface this post for all you plasterers out there by saying that this is a purposely oversimplified explanation of the topic. The binder is what holds everything together and cures into the rock hard consistency that we all know and love/hate. Both need water in order to mix everything together and activate the curing process. Both are made with an aggregate of some kind, usually sand of various sizes and textures. Like I just mentioned, the ingredients are what make the difference in these two similar building materials. Today’s post might be a little more “building geek” than “hands on preservation”, but I think that understanding how and why your old house is the way it is makes you not only a wiser human, but a better homeowner. Plaster and stucco can both be applied much the same way, with the same textures and thicknesses, but the main ingredients in each are what make them different animals. Their differences are not readily apparent to the naked eye. While they are similar in a lot of ways, they are different enough that understanding when and where to use them, especially in renovations, is imperative. A lot of folks confuse plaster and stucco in old houses. ![]()
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