A brand name for a setting joint compound. Has gypsum crystals that make it set like plaster, and bonding agent that makes it stick like joint .
durabond
Spackle is the registered trademark of the Muralo Company located in Bayonne, New Jersey. It is a hard smooth white patching paste to match the finish of a painted wall. Durabond is soft rough gray joint compound designed to match sheetrock wallboard. If Durabond is used to repair a painted wall, it will result in a patch that will show thru the paint. Use the correct product for the proper job.
Regular mud for first application and 'lite' for the next ones.
Be certain that the surface dew / moisture has completely evaporated before applying.
The thin set you should use over plywood is called Durabond. Durabond is a water-based coating that dries to a hard, durable finish. It can be applied directly to new or old drywall and will not cause any harm if it comes in contact with insulation.