prepping old wood for painting newb questions

poppameth

I believe Tom Koby is the guy you generally want to talk to at Richards. If he doesn't know an answer he'll find a chemist that does.

Nestor_Kelebay

Thanks, Poppameth.

I phoned Tom today and he referred me to Al Guzman who's the head chemist at Richard's Paints.

Al told me that they do make separate indoor and outdoor primers, but that they make over 200 different formulations and to tell me specifics on any of their products he'd have to know what the product numbers were. He says one of the differences between interior and exterior latex primers is that the outdoor primers they make will all have mildewcides added to them because the primer may not be topcoated right away. He said that if the primer gets left unpainted, then the mildewcide in the primer will prevent mildew from growing on it. He also told me that they may also use a 100% acrylic binder in some of their exterior primers for exactly the same reason; so that it'll stand up better to UV light from the Sun if it's not top coated with paint.

When I asked if another difference could be whether or not they're low odor, he said that could be another difference too. He said he'd have to know the product number before he could discuss specific differences.

I was surprised that they used mildewcide in their primer and that they'd use a 100& acrylic binder IN CASE the primer wasn't painted.

I didn't want to say this to Richard's Paint, but it seems to me that if they're charging more for their exterior latex primer because it has mildewcide and a more UV resistant binder in it (just in case the primer is left unpainted), then 99 percent of the time the extra money spent by the customer is wasted. That's because 99 percent of the time, the primer IS top coated with paint right away. Once there's a coat of paint on top of the primer, it's the paint that has to deal with the UV rays from the Sun and the mildew spores in the air.

If you could get me the product numbers for the interior and exterior latex primers, I wouldn't mind asking Tom Guzman if someone is planning on painting over Richard's exterior latex primer right away, whether they would still be better off buying their exterior latex primer or saving some money and just using Richard's interior latex primer on the outside of their house.

I think that's a darn valid question considering that they're telling me that they make their exterior primer with mildewcide and a more UV resistant binder IN CASE the primer isn't painted over. (?)

afabco

Once again, thanks to all. The oil <-> alkyd link was what I was missing.

now for the weekend activities....heh.

enjoy!

poppameth

I stock Richards primers almost exclusively because they are very comparable to Zinsser and cost me far LESS than most other primers I can buy. For example, Richards 7-44 100% Acrylic is an indoor/outdoor very much like 1-2-3 (which also has a mildewcide) except that it's a dead flat primer instead of having a sheen, and I retail it at $26.95 / gal. which around here is very good unless you go to Lowes for Zinsser.

Lets see:
7-11 is an interior latex primer/sealer/undercoater
7-22 is an int/ext alkyd enamel primer/sealer/undercoater (fast dry)
7-33 is an int/ext alkyd enamel stain killer (fast dry)
7-55 is a synthetic odorless alkyd stainkiller (fast dry)
Those are the main ones I carry right now.
On their distributer list:
6-210 is an Int/Ext Modified Acrylic House Primer
SR-933 is their long oil Alkyd house primer

Edit: Full product list http://richardspaint.com/allproducts.cfm

That's all I've got on my list other than industrial products. I know they make far more than that though. They private label a lot of things that they'll sell me on request if I need it.

I've been trying to get a hold of my Pratt & Lambert rep but he's a pain to deal with. Here is the list of their primers. http://prattandlambert.com/products/...mers/interior/

Nestor_Kelebay

Poppameth:

That explanation by Al Guzman that they use mildewcide and a more UV resistant binder in their exterior primers IN CASE the customer doesn't paint over the primer didn't make any sense to me because it would mean that the 99% of the people buying Richard's exterior latex primer and painting over it are wasting money on the extra mildew and UV resistance in the primer. I thought I would get a better (or at least more plausible explanation) from Pratt & Lambert.

I phoned Ryan Kearney at technical support for Pratt & Lambert for the US at 1-800-289-7728. I asked him what the difference was between P&L Suprime Interior Latex Wall Primer and their Suprime Exterior Latex Wood Primer.

He says the only difference is that the exterior latex wood primer has more mildewcide in it. He says that dormant mildew spores are more common outdoors, and by painting over bare wood outdoors, there's a good chance that those mildew spores will become active and start to grow, with the result that the mildew could grow under the primer. Having more mildewcide in the primer ensures that the mildew spores are killed before they grow.

Ryan told me that without this mildewcide, mildew spores would feed on the latex primer, and would be visible under a top coat of latex paint.

With utmost respect, I would disagree with Ryan in regard to the last statement. Mildew spores, just like everything else, need both food AND WATER to survive. Aside from the question of whether or not a latex primer would be a food source for mildew, it seems to me that if there wasn't sufficient moisture in the wood for the mildew to grow before priming, the little bit of moisture that comes from the primer isn't going to last long enough to sustain any mildew growth for long.

That is, once the water evaporates from the primer and subsequent coat of paint, where does the water come from to support the continued growth of mildew if there was insufficient water to support the growth of mildew on the bare wood.

Anyhow, according to P&L technical support, there is no difference in binder used between interior and exterior latex primers, the only difference is that there's more mildewcide added to the exterior latex primer.

My feeling is that Richard's exterior primer has more mildewcide in it for the same reason, and Al Guzman may not have been aware of that reason, and believed it was there in case the primer wasn't painted. But, I think it's fair to say that any difference between interior and exterior latex primers revolves around the amount of mildewcide in the primer.

I also asked about the Supreme Interior Deeptone Primer, and that one is just where they don't fill the can up as much to allow room in the can for plenty of colorant for making tinted primers.

I can't say I'm happy with P&L explanation either. Mildew needs water to grow, and there's no reason to believe that the mildew would continue to grow under the primer once the primer and paint are dry. If anything, the mildew would have less water available to it under a coat of primer and paint than it would have previously had when the wood was exposed to the weather. If the previous amount wasn't sufficient to support growth, I have difficulty understanding how growth could occur after priming and painting.

Anyhow, that's what I found out. I guess it's up to everyone in here to decide whether it's worth it to use an "interior" primer indoors and an "exterior" primer outdoors, or just keep a can of "interior/exterior" primer for use both indoors or outdoors. But, no everyone knows where the differences lay.