The Stovebolt Site Forums The Shop Area Paint and Body Shop Pinholes in Primer

Please make sure you have the right temperature reducer as well as hardener. It is made in low temp, medium temp and high temp (some makers will call this slow dry). Right now you want the slowest drying thinner and hardener they make. If your reducer is drying as you spray (and it will if you have the cool temp or quick dry type), you'll get lots of pinholes. Try to spray only in the morning when it is cool and humidity is higher. It might sound odd but your reducer can be partially dry before it hits the surface and if the surface is warm to hot (as it can be this time of year) it will cause the reducer to dry faster and the hardener to react faster and this creates air pockets. At least it does for me. The fact it is not happening where you have body filler tells me this is acting as an insulator of sorts keeping the surface area there cooler. Good luck!

Edit...if U-Pol doesn't make temperature-sensitive thinner you can add about 10% extra when you mix the primer. Just watch how you spray so it doesn't run...you might have to adjust your gun for this. Extra thinner will reduce the build-up aspect, however for primer to dry solid and without bubbles or air pockets, the thinner has to keep everything bound together and let it dry correctly. First a film coat will form on top, then the primer will bond/attach to what is beneath it and then the middle will start to harden as the thinner evaporates slowly through the film coat. Heat and air passing over it will accelerate drying. In the case of catalyzed primer the catalyst will produce a small amount of heat as it reacts, also. Not the same type of heat as fiberglass resin or epoxy but the reaction is about the same from what I've been told.