Clean - Dull - Dry
The unversal rule of surface preparation. The second term "dull" is the subject of this article.
All paints, and latex paints in particular have a hard time adhering to glossy surfaces. The problem with glossy surfaces is that the new paint needs some "tooth" of surface profile to grip to in order to adhere properly.
The question often arises "how dull does dull need to be?" This is a good question. Actually, a lot depends on the type of paint is on the surface to be painted, and what type and quality of the paint you will be using.
Before I begin, you need to familiarize yourself with the issues concerning lead paint. If your house was built prior to 1978, do not sand to degloss painted surfaces in your home, as their may be lead in the paint or an underlying paint film. Instead, clean the surface and use a glossy surface primer. See Glossy Surface Primers.
How dull is dull?
There is some ambiguity and subjectiveness to the term "dull" High gloss, gloss, and semi-gloss are definitely not dull. Is low-luster dull enough for recoating? Maybe, but maybe not. I have seen paint fail when applied over "satin" sheen paint. A lot has to do with the quality of paint you are using and the type of paint you are recoating.
General Rules:
If the old paint was oil sheen paint (eggshell, satin, semi-gloss, or gloss) you should degloss AND prime to convert to latex.
If you are changing from sheen down to flat you should degloss AND prime to convert to flat (otherwise you may get a crackle finish).
If you are changing from varnish to paint, you should degloss AND prime to convert to paint.
The higher the gloss, the more carefull you need to be. Often, the best way to tackle semi-gloss and gloss is to degloss and prime.
Deglossing
There are a number of ways to degloss a surface for paint. Let's examine three common methods are: 1) Sanding 2) Chemically deglossing 3) Scouring (while cleaning).
Sanding (read the above caution concerning lead paint)
Sanding is simple, but it is hard to do a thorough job on a large area like a whole room - ceiling and walls. Sanding is great for small areas like wood trim. Sanding will re-surface (and thus expose a fresh, clean surface) a substrate which is good paint prepartion. Pole sanding is the method used for walls and ceilings. You can use a orbital sander attached to a HEPA vacuum too. Trim is easily sanded with a sanding sponge. You don't need to use several grades of sandpaper to degloss, use a fine grit like 220 and that will do.
Strengths
- works with all paints / varnishes
- no harsh chemicals to work with
- cheap
Weaknesses
- hard to do a thorough job on large surfaces
- textured surfaces can't be done very well
- creates dust
- can be hard work sometimes
Recommendation:
I sand semi-gloss or gloss walls/ceilings, prior to using a bonding primer. Because I know sanding large areas is tough to do a thorough job, I follow up with a bonding primer. I sand latex satins / eggshells (without priming) walls/ceilings when recoating with a sheen paint. If recoating with a flat, I convert over with a oil based or shellac primer.
Please read lead paint warning if your house was built before 1978,
You are not going to go wrong if you degloss it is the safe and sure thing to do. I for one, sand as a rule sand satins and eggshells before repainting.
Surface preparation also must factor in the previous paint type as well as the type (and quality) of paint you are going to be using. Also, you need to factor in how clean (of dirty) the paint is, has it been wiped down with cleaners and other contaminants over the years.
Deglossing
How to Prepare Glossy Surfaces for Paint
part 1
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