You are operating under a few misconceptions
One is, if it's on the internet, it must be true
Another is, if its not on the internet, it must be false
Neither is true
Nestor_Kelebay said:
If latex primer bonded better to old latex paint than new latex paint, everyone would be recommending a coat of primer before repainting, even if you're repainting the wall 10 years later with exactly the same paint. I think if you do a web search, you won't find anyone recommending that.
I truly don't care what you find doing a "web search"
I don't care what "everyone" in the DIY world is suggesting or not suggesting
(frankly, you'll never get "everyone" to agree on anything)
I'm not here to help spread any internet myths, rumors, and falsehoods, of which the web is full of...especially in the DIY painting arena
Every day I deal with people that have seen ridiculous stuff on the web, and for some reason, think it's gospel
It came from their computer I guess...it sounds smart
Or the magazine or TV show...it must be true
Few people stop to realize it's to sell ads and entertain people
Some of the "tips" or "advice" can be absolutely scary
Anyone with a search engine can find tons of opinions labeled as facts on the interweb, and spout them till they get tunnel carpel to give the appearance of real and actual hands on knowledge
I'm here to give real advice, from actual learning and real experience, as a professional in the field
Anyway....
In my experience on the web, and with real people, you will find loads of persons recommending priming before recoating
Most of the time, it's ridiculous
Most of the time, there is absolutely no reason to prime a re-paint
I agree with you, and said as much
There is no reason to use a primer on most ten year old repaints
Nestor_Kelebay said:
Can you point to any credible source on the internet that suggests it's advisable to prime over a gloss latex paint before applying a flat latex paint?
As I mentioned, I'm not here to give my search engine a workout and find, or not find, any "facts" to support my position on the interweb
As it costs money to host, absolutely everything on the internet has a sponsor, and I'm sure one could find lots of official looking stuff to support just about any position
You will, however, find countless professional coatings application technicians, coatings manufacturers, and professional coatings providers recommending primers for many reasons, in many situations
One of which is a wall coating over a semi-gloss wall in a kitchen or bath
Most quality professionals would never do anything but
We have seen what happens when you don't
That's not to say it will always fail
That's not the case
It's more a matter of stacking the deck
We don't want it to fail...we can't take a 25%...a 15%...a 5%...a 2% chance
It's our name, it's our word, it's our warranty, it's our reputation
Nestor_Kelebay said:
However, if you've already scuffed up the surface to increase the surface area, you're not going to get appreciably better adhesion by priming the old paint and then painting over the primer.
That may be true
In most cases I wouldn't prime either
But in a bathroom or kitchen, all bets are off
Nestor_Kelebay said:
Bathroom paints have mildewcides in them...etc... effectively giving you a larger reserve of mildewcide to draw upon.
If you prime over a bathroom paint before repainting with another bathroom paint, you're most likely to trap the mildewcides in the old paint behind the primer.
Uh....yeah...I'll take my chances with the "fresh" mildecides thank you
I really wouldn't worry about trapping any old mildecide behind the primer
Nestor_Kelebay said:
Take a look at this paper:
etc...
No thank you
The mildecide transfer is not the important issue
Most of the time it's not even the same paint being used, certainly not the same mix of chemicals...I can't imagine they would be compatible...I can't imagine simply assuming a quality mildecide is still functioning in the old coating...
I think you are focusing on the minutia and obfuscating the real issue
In reality, I have seen and repaired way too many failed bathroom re-paints that would have not failed had they simply gone the extra step and primed
That's why I (and most quality painters), always prime a semi-gloss bath before repainting
I hope this clears things up regarding my position and reasons for it
I'm sure the OP will decide merely to scuff and repaint