This question has come up a couple times recently in my work. I have
some clients who need stuff repainted that's currently painted with
semigloss paint (latex). I know you need to "scuff up" the surface in
order to get new paint to stick to it.

My question is, is it better to physically scuff the paint with
sandpaper, or to chemically etch it (someone mentioned using TSP in
another thread)? I suppose it may depend on the specific situation, right?

One thing I do know about TSP is that if you use it, you'd better make
damn sure that you remove all of it before you paint, else the paint
won't stick worth a damn.


--
"In 1964 Barry Goldwater declared: 'Elect me president, and I
will bomb the cities of Vietnam, defoliate the jungles, herd the
population into concentration camps and turn the country into a
wasteland.' But Lyndon Johnson said: 'No! No! No! Don't you dare do
that. Let ME do it.'"

- Characterization (paraphrased) of the 1964 Goldwater/Johnson
presidential race by Professor Irwin Corey, "The World's Foremost
Authority."

David Nebenzahl wrote:
This question has come up a couple times recently in my work. I have
some clients who need stuff repainted that's currently painted with
semigloss paint (latex). I know you need to "scuff up" the surface in
order to get new paint to stick to it.

My question is, is it better to physically scuff the paint with
sandpaper, or to chemically etch it (someone mentioned using TSP in
another thread)? I suppose it may depend on the specific situation, right?

One thing I do know about TSP is that if you use it, you'd better make
damn sure that you remove all of it before you paint, else the paint
won't stick worth a damn.


I've never had a problem with inside or outside
paint and I use semigloss both places.

I always wash with TSP and have never had paint
fail to stick. The key may be too use a lower
concentration of TSP than recommended. My box say
1/2 cup per gallon but my concentration is
one-forth to one half of that. Second, I rinse it
with with fresh water. I use a wash rag and ring
out most of the water, wash or rinse, and rinse
the rag with every few swipes when rinsing.

Of course, many professional painters now use the
silicate substitute for TSP because they say you
don't need to be as careful when rinsing.