DIY Touch Up Wall Paint
Touch-ups on walls and ceilings painted long ago can sometimes create a more unsightly finish than the old paint itself. To avoid this, it's important to use the original paint, and only the original paint, for retouching existing finishes.
It's also important to realize that any white will not match any white. There are hundreds of shades of white paint available from dozens of manufacturers using completely different formulas, making it impossible that any of these colors will match each other. And what about different finishes like semi-gloss, eggshell, high-gloss, oil-based paints, etc. Can these finishes be retouched successfully? Unfortunately, as a general rule, only flat paint can be retouched without "flashing" in the finish.
What is Flashing?
Flashing is a term used by professionals to describe the obvious difference in a finish that will occur when retouching old or shiny paints. Flashing is most obvious when viewing a surface from the side. Look down a wall while standing at one corner of a room, you will see all the little imperfections in the surface as light is reflected off of it. Any difference in the overall finish of the wall is called flashing.
What Causes Flashing
Flashing will almost always occur when using anything other than original paint for touchup. It will also occur when you try to touchup a shiny finish, as the sheen of the new paint fails to blend with the old. Finish flashing will also develop when a shiny finish is applied over bare wall repair patches without priming with a flat paint first. To avoid this, joint compound and spackle must always be primed using a flat, before semi-gloss, eggshell or oil-based paint is used over wall repairs.
If you suspect that the irregular appearance of your walls is caused by failure to prime mud patches before applying a shiny finish, re-coat the spots with flat paint, let it dry, and then touch up the shiny finish to cure the problem.
Always use the original paint from the original can to minimize the chance of flashing. Trying to touch-up your wall or ceiling using anything other than the original can will most often cause flashing.
When you have a flashing problem with your touch-up job, the best solution is to do a whole wall from one break to another. This Paint from Break to Break method will diminish the noticeable difference in the new finish when the color isn't exactly right.
A break in a wall is usually at the corner, but can also occur when trim molding stretches from floor to ceiling, or some other feature of the room blocks off a section of wall. When a wall is broken into isolated sections like this, it can be repainted with a closely matching color and the minor difference will not be noticeable in the overall appearance of the room. Wall corners work well as break points because the two surfaces reflect light differently, making it hard to see small variations.
Choosing Paint for Touching Up
If possible, always use the original paint, that is the can leftover from the original job. If the original paint is not available and it is a stock color (a premixed color made at the factory, not mixed at the store) then a new can of the same color will most often work as well as long as the paint isn't dirty from smoke or some other contact.
While stock colors are pretty safe, custom mixed colors will usually not match the original paint. The problem is the accuracy with which the color is mixed at your local store. Different people on different mixing machines, or even operating the same machine, will use slightly different amounts of tint. All it takes is a tiny change in the amount of tint to change the color enough so it shows on the old finish. Even computerized machines can produce enough of a difference in the mixed color to cause a mismatch. If you must get a new batch, check the new color for matching before you proceed with touching up.
Make sure your paint is mixed well before putting it on your walls. Shake the can for several minutes or stir vigorously just before using it. Apply the new coating using a brush on small areas and a roller on larger spaces. Check to be sure the new paint is blending well with the original finish before doing the whole job.
Do a small area first and wait for it to dry completely, use a hairdryer to speed drying if you're pressed for time. When it is completely dry, examine the finish while looking down the wall, if you can easily see the spot where you applied the new paint, then your touch-up job probably won't look very good. If you look at the wall face on and you don't really notice the difference, then you can choose if it will do for your purposes. If you find the finish unacceptable, use the "break to break" method described above to fix the problem.
Shiny finishes can be the most difficult to touch up. This includes eggshell, semi-gloss and high-gloss, as well as all oil and alkyd-based finishes. Even flat oil and alkyd will flash if you try to touch up in the middle of a wall or ceiling. For all these finishes use the "break to break" method to freshen the finish. Original paint or not, the only way to avoid a flashing problem is to do a whole wall.
Trim should be treated in the same way as shiny finishes, painting from one break point to another. Break points for trim are the points where two separate pieces of molding come together such as at the corners on door and window casings. Also where one pieces of molding is laid over another, the joint between the two makes a good break point. The edges of an individual piece of molding can also form a break point where the plane of the wood surface changes.
To touch up on a door casing, for example, do all along one side from the floor, to where it meets the header. Don't do the narrow edge of the casing where it meets the wall, just do the face. The touch-up will not be noticeable because the edge is seen at a different angle than the face and so it reflects light differently. And as long as the new paint is fairly close to the original color and sheen, it will be hard to see the difference between the side and header molding pieces when it dries.
Dealing with Stains
Touching up the paint is one thing, but stains present another problem. Some stains will bleed through the new coating if they aren't sealed first. Water, ink, cigarette smoke and grease stains will all ruin your touchup job. To avoid this problem, use a sealer to block these stains before applying any finish paint. It may be necessary to do from one break to another when treating stains like this. See Repair Tips for Stains and Repair Water Stains for more about dealing with this problem.
Shellac-based sealers and oil-based sealers like Kilz® dry very quickly (about half an hour) and will block almost any stain with the exception of tannin from redwood trim. Redwood is not commonly found in new homes but historic building will often have redwood trim that has been painted. When tannin from redwood bleeds through the finish, use a water-based sealer like Kilz2® to block the stain and then touch up as described above.