Don Casey Tip #45 Sealant Shorthand What type sealant to use can be confusing. Here is the code: * Use silicone to electrically insulate dissimilar metals and to bed plastic. * Use polyurethane only to join components that will NEVER need to be disassembled. * Use polysulfide for everything else. There are exceptions, but following these three rules will avoid most wrong-choice problems.