Poppameth:
You said: "Saying that there is no difference in interior or exterior latex primers is very misleading. There are several differences. Use what is made for the application at hand. All the primers on my shelves use different resins between the interior and exterior versions."
When I read your response, I figured "Where is there any room for any difference?" Every latex is elastic enough to stretch and shrink with wood, and you don't need to add UV blockers and mildewcides to a primer because it'll be covered with paint anyway. So, where could any difference lie? Clue: Poppameth said it was in the resins somewhere.
(For those who want to know why a "low-VOC" primer or paint would require a different resin than a regular VOC primer or paint, see the PS at the bottom of this post.)
So, I did a Google search for "Interior latex primer" and "Exterior latex primer" and I found two web sites that, to my mind at least, explain the difference, and also indicate that there is very little difference at all.
Take a look at this one:
http://www.benjaminmoore.com/bmpsweb/portals/bmps.portal?_nfpb=true&_windowLabel=contentrenderer_1_10&contentrenderer_1_10_actionOverride=%2Fbm%2Fcms%2FproductSearch%2FgetProductDetails&contentrenderer_1_10NodeUUID=%2FBEA+Repository%2F36008&_pageLabel=fc_productsspecs
It's an "interior" latex primer that is low odor because it has low VOC's. That is, the reason they recommend it for use indoors is because of it's low odor.
And take a look at this one:
http://wallsalive.com/pdf/specs/Spec C3000.pdf
which is an "exterior" latex primer that has 124 grams/liter of VOC's in it.
That is, I expect the difference you speak of is that latex primers that specify that they are "interior latex primers" will be low odor whereas primers that specify that they are "exterior latex primers" won't be of the low VOC, low odor variety, and using them outdoors isn't a problem because the odor won't be noticed as it would indoors.
But, from what I can see, either can be used indoors or out. That don't mean I'm seeing everything tho. And so I can't be 100 percent certain that the only difference between interior and exterior latex primers is the olafactory one.
My understanding is that you own/manage a paint store. Can you check with your suppliers or manufacturer's sales reps to find out what exactly the difference is between "interior" and "exterior" latex primers?
We all learn from each other in these forums and maybe this will be my turn.
The following is just for people who don't understand why the solvents used in primers and paints have to be matched to the resins in the primer and paint.
PS: Why do we need a difference in the resins if it's a low-VOC primer?
Latex paints form films by a process called "coalescence". Latex paint consists of a slurry of tiny hard clear plastic particles (called resins) and coloured pigment particles suspended in solution of water and a water soluble solvent called a "coalescing agent". When the paint is applied to the walls, the water evaporates first, resulting in the plastic resins being surrounded by the coalescing solvent at an ever increasing concentration. Those solvents soften the plastic particles enough to make them both stick to each other and pull on each other (due to surface tension and capillary effects) so that those plastic resins form a soft continuous film of plastic. Then, the coalescing solvents evaporate from the paint film, creating that "newly painted smell" in the room.
It is these coalescing solvents that are the primary source of "VOC"s in latex primers and paints. (The glycerine they add to the latex paint when tinting it and the propylene glycol they add to it as an antifreeze so the paint won't freeze as readily also add to the VOC's that evaporate from the paint film, too, but the quantities of these in the paint are less than coalescing solvents.) So, if you have to make a low-VOC paint to meet government regulations, you either have to use a different resin that will coalesce at a lower coalescing solvent concentration, or you have to use a coalescing solvent that will react chemically with the paint and therefore actually become part of the paint film rather than evaporate into the air.
Follow up:
After posting the above, I thought to myself: why not do a Google search for "exterior latex primer" AND "low odor". My thinking was, if the only difference is the odor of the solvents as they evaporate from the drying primer, I should have NO hits because no one would make a low odor primer and call it an exterior primer, right?
That would tell me whether the difference is entirely in the odor or not.
Anyhow, I came across this web site:
http://www.cloverdalepaint.com/info/pdf_tds_ar/10-0125.pdf
Which talks about their "Horizon Exterior Latex Primer" as follows:
Intended Uses:
Horizon Exterior Latex Primer is ideally suited for use wherever paint odor is a problem such as schools, hospitals, nursing homes, offices and other smell-sensitive areas. This primer has been designed for use with HORIZON topcoats providing a complete low odor and environmentally friendly system. Suitable for
brush, roller or spray application on exterior and interior substrates.
Which is confusing because this Cloverdale Paint Company seems to be saying that the important difference between this primer and others is it's low odor, and specifies that it is therefore well suited for INTERIOR applications such as schools and hospitals where odor may be a problem for some sensitive people.
That is, they're calling it an "exterior latex primer", but they're recommending it for interior use because of it's low odor.
My web search so far seems to suggest that the only difference is the odor.
Benjamin Moore says this about it's ECO SPEC Interior Latex Primer Sealer 231:
General Description
A low odor, low VOC, 100% acrylic interior latex primer sealer with spatter resistant properties.
Ideally suited for commercial, facility management, and residential applications. ECO SPEC
® Interior Latex Primer Sealer (231) does not have the odor of conventional primers which contain ingredients known as Volatile Organic Compounds (VOCs). Always use ECO SPEC® Interior Latex Primer Sealer (231) as a first coat when a low odor, VOC free primer/finish system is required.
Still, I'd be curious to find out what the paint company sales reps say is the difference.