Here's something I've wondered about. When painting the interior portion of a window sash, is there any reason *not* to use an exterior primer/paint? I've actually tried this on less noticeable sections of a couple of windows, thinking the results may not be as good as with an interior paint. However, I really can't tell a difference between the sections where I used an interior versus exterior product. The only reason I ask is it's slightly more convenient for me to use the same product when painting an entire sash, inside and out.
It has a different chemical compostion make up than the interior paint.Which I have heard that can make your interior paint fail in time,how long is unsure to me.If you are doing this then use a exterior paint to go along with this.What this will do is make sure you have the paint that goes with the primer you are using. I wouldn't recomend doing your whole windows like this for the ext. paint has a little less sheen to it.I tell you what though your window sashes will be pretty durable. Again use ext paint with ext primer or your paint may let loose. I have seen actually quite a few home owners do or ask the same thing,to save time,open the window and hit the sides top and bottom. You will be ok.