![]() Where as using calcium carbonate rehydrated solution there is no chemial curing, and the bond is weak, powdery and easily cracks, chips and crumbles. When drying into calcium carbonate it creates cure into the hard shape that it is molded into. When it is kept wet it stays in that form but in contact with oxygen it reacts and turns into calcium carbonate (also called limestone but chemically different). Also the product contains limestone in the form of hydrated calcium (calcium hydroxide). ![]() Rehydrating set PVA mentioned in previous comments is problematic +1. My understanding from a basic chemical point of view is: no, even if it looks similar it will be a different product without the strength or bonding qualities of the original. While not exactly your case, it should demonstrate how the curing reaction in joint compound is not simple drying, and can be broken by deviation from the proper conditions. This case study (now paywalled, see version) examines a case where the drywall contractors thinned excessively new drywall compound and got a similar result. You will essentially have drywall compound where a significant portion of the binder has already "dried", so when your rehydrated compound dries again, it won't bind as well as it should.Īs a result, you will get poor adhesion to the wall, and likewise paint will not adhere well. Even if you get all the lumps out, at a microscopic level you will still have a lot of polymerized PVA and other products of the reaction. Getting it wet then somewhat reverses this reaction, but not completely. PVA is water soluble, but by the time it has dried, the polymerization reaction that makes it work as a glue has already happened. For reference, see the USG Sheetrock all-purpose joint compound MSDS, which lists "vinyl alcohol polymer" as an ingredient. ![]() The reason is in the binder, the stuff that makes it harden and stick to the wall. While you can rehydrate mud, the rehydrated stuff you make will not perform acceptably. ![]()
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