TEMPERATURE VS DRY TIME
Temperature certainly does affect the dry time of both stains and f inishes. An important step in the drying process is the ev aporation of the solvents from these liquids. Only after the solv ents evaporate can the liquid lay down and start to f orm a f ilm. The higher the temperatures the f aster the solvents ev aporateâ€¦think pot of water on a hot stov e, only a lot more f lam- mable. So if the temperature is lower than normal, the solv ents ev aporate more slowly and it takes longer than normal to dry.
A nifty little rule of thumb is that the dry time changes by a factor of 2 f or every 12 degree change in temperature. Said an- other way, dropping your temperature 12 degrees will double your dry time; increasing your temperature by 12 degrees will cut your dry time in half.
As an example: if y our dry time is normally 20 minutes at 77 degrees, then it will be about 40 minutes at 65 degrees, 80 min- utes at 53 degrees, and 160 minutes at 41 degrees. Lower than this is a good temperature f or beer, not f inish. Conv ersely if y ou increase the temperature from 77 degrees to 89 degrees y our dry time will drop f rom 20 minutes to about 10 minutes.
As long as we are talking temperature there are two other issues that should be pointed out.
As the temperature drops the viscosity of the f inish material increases. If sprayed in this state the f inish doesnâ€™t flow out as well and will often dev elop orange peel. The normal reaction to this is to add more solv ent to the finish to lower the viscosity, which brings us right back to the temperature â€“ evaporation thing. More solv entâ€¦more dry time.
The f inal temperature related issue applies only if y ou are using any type of cataly zed finish (pre or post cat). As the solv ent in these types of finishes evaporates the catalyst starts a chain reaction that cross links the resin molecules in the finish. Think of the resin molecules as strands of spaghetti. Cross linking is like welding all of the strands together to form one big strand. It is the welding, or cross linking of all of the resin molecules that gives these f inishes their enhanced wear, water and chemical resistance. Once sprayed the object must stay at a temperature of at least 68 degrees for a minimum of 6 hours in order f or the catalyst to complete this chain reaction. At lower than 68 degrees the film will dry but it will lose many of the per- f ormance characteristics that you paid good money f or and that the client expects.