When good protection is required, I use Defthane polyurethane in brush and aerosol spray. All other competitors have aerosol cans that say,”If unable to re-caot within “X” hours, you should wait 72 hours before applying another coat.” This sure doesn’t sound very user friendly. This is why I use Defthane and am happy with the results. I can re-coat anytime the previous layer is dry.
Why do ya suppose competitors poly differs? I recently read the same warning on some water based ploy.
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Don, for some types of finishes there is a window where you can apply a second coat so it will chemically bond with the underlying coat to create a single thicker layer of finish. If you miss that window, you should wait until the film has sufficiently hardened to layer the next coat. Applying a second coat before the prior coat can sufficiently cure or bond, can create an under-layer that can ultimately affect the finish and durability. Under normal circumstances - temperature and humidity - 3 days for poly is sufficient time to cure before applying successive coats or to level the surface.
Edited 12/5/2005 11:39 am by DougF
It's hard to say without knowing the chemical differences between the Defthane and the competitors you mention. But, usually the recoat window is about the curing process of the initial coat of finish/paint. Essentially what happens when you recoat in the timeframe that they say not to is that the succeeding coat of finish will (or can) react or otherwise interfere with the curing process of the first coat, causing it to wrinkle or lift because it messes with the chemical cross-linking process of the first coat of finish. And that's invariably a very bad thing because you usually have to either strip off the finish and start over or you have to let it completely cure out and then sand it all back down and hope that you got all of the wrinkled layer off. Usually only solid color paints are good candidates for the second option.
The trade-off between the polyurethanes that have a recoat window and those that don't is probably about how durable the resulting finish will be. To achieve the more user-friendliness of the Defthane I suspect that they gave up a bit of durability when they formulated it in their labs.
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