first you have to wipe the area down with a lint free rag and something like denatured alcohol to remove dust, dirt, grease, and whatever else is on the tile and grout. Even then paint can and will seep under the tape unless you paint carefully.
I’ve painted professionally for a few years and I found the best way was to use a properly filled 2″ sash brush and a steady hand.
“Properly filled” is with paint only on the last inch or so of the brush at the bristles. A sash brush’s angled head gives you better control and makes it easier, at least for me, to carry a straight line.
Start near one corner and set the brush down just a hair above the grout and draw the brush in a long smooth steady motion in one direction. Use almost no pressure on the brush, allow the paint to just flow off of the brush. Lift the brush before you reach an uncomfortable position. Go back and very lightly touch the half empty brush to the paint and change the brush angle so the bristles just touch the top of the grout and softly and smoothly draw the brush over the fresh paint to catch that hair’s breath of unpainted wall.
The whole process of painting shouldn’t involve work. It is supposed to be a smooth, easy, non-pressured process. Pressing too hard, flairing the bristles, and putting too much paint on the brush are common rookie mistakes.
I’ve used a 4″ sash brush to trim out an entire apartment and never had the paint any more than an inch or so up the bristles. Yes, you have to dip the brush every three feet or so, but it doesn’t drip, doesn’t splatter, it doesn’t run, and you can draw a perfectly straight line for many yards with a little practice.
The whole thing is to make it smooth and easy. If it feels like work then you are putting too much effort into it.
.
