Smack it on good and quick and thick.
The tendency with acrylic house paint is to stretch it out and apply it too thinly. MISTAKE! It needs to be applied thickly, as does most all other acrylic (house) paints. It is not designed to go as far as you can make it go with either a brush or roller. It needs a minimum wet thickness. A 3 mil. wet film is a typical architectural specification. That's about the thickness of five pages of paper. You're a reader of paper. See for yourself.
I miss oil-based paints. They flow tissue-paper thin like no tomorrow -- a real treat from using the heavy stringy crud of some acrylics today. And the incidental buzz was bonus. Two beers after work and you were toast. Thank God was with me that I eventually gave up alkyd paint altogether and settled on the lesser evil in life. Dieborzya naz drovya hereslookingatyookid.
Forget about precision when using acrylics. They don't flow as well as alkyds or oil-based paints. So smack it on there and forget the initial mess.
It is unusual for acrylics to sag and run, so you may appreciate just how thick this top stroke was that it reared an ugly head.
Since it's my own place, I take liberties. Were this a paid job, the customer would be apt to freak if they weren't familiar with my reputation for good work.
Yet this is the best and fastest way to do window sash with acrylics, in spite of it looking like an amateurish horror.
This is usually about the time the customer comes in and says "you got some paint on the glass there".
I have several responses to this, namely:
"Where do you mean?"
"You notice everything!"
"Oh... you wanted a good job!?"
Crucial to painting any window, whether old or new, is to achieve a good painted seal between the sash and the glass. A paint film will always want to fail first where the paint film leaves off.
Oldtimer instructions for the window finisher were to paint 1/16th inch onto the glass. With oil/ alkyd paints, it was a breeze. With today's acrylics, it's a nuisance to try and do so.
In spite of that, experience and force of habit still leads me to cut a neat line, even though it isn't necessary when using acrylics.
Look at that line -- perfectly straight in spite of being overkill-wide.
To cleanup the glass, make use of a guard of convenient width. This protects the new finish and allows for a sharp line. The guard used here is a flexible six-inch putty knife.
Keep the guard angle consistent as you work and slave away.
Before you do a cleanup scrape on the glasswork, give it a good all-round sweeping squirt with any proprietary-brand glass cleaner. Wetting the glass and paint edges softens the paint film and minimizes scratches during cleanup.
While both household ammonia and gas-line anti-freeze will dissolve acrylics, using a proprietary glass cleanser is easier on your major organs. Using a guard also protects adjacent surfaces from inadvertent damage during clean-up.
Score the paint-line first, at an angle (lesser - toward glass) than what you will be scraping. This will leave your scraped line slick and sharp rather than frayed.
Are you one of those who like to mask off the glass before painting? Sunlight quickly dries out masking tape, and after a few days, it won't strip off neatly. Use the above method and spray the tape to soften. You will need to let it work for a few minutes, but it will come off slick by spraying and scraping as above. You should still score a straight line at the glass edge beforehand.
Note that any slivers of overpainted tape left on the glass will eventually deteriorate and affect topcoat adhesion. It is best for paint to directly meet glass.
Old meets new:
See that 1/16th inch on the exterior side? Outside putty and inside painting were meant to meet inconspicuously.
But... that was then.
Acrylics will push right off glass if softened up first with a window cleaner (weak ammonia or alcohol solution) ...
Notice how I locked the first joint in my first finger. It's a zen thing, which I learned about while repairing a motorcycle.
Amazing what a little paint can do.
An edge or two yet to be cleaned up.
A drawback with acrylics -- doors and windows can be prone to stick. Ask your paint dealer what's best for your application.
Keep sash windows up where you want them with this simple tip.