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Which application produces the best results, with respect to mold prevention:

  • An all-in-one paint with primer
  • Apply plain primer, then regular paint

Is using either process better for mold and mildew prevention? I haven't tried it yet, and will be waiting until spring.

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    I don't think of primer as being for mold prevention, so I'm not sure what question you're trying to ask. And yes, requests for comments on specific brands are less likely to get good answers than questions about principles and techniques. – keshlam Nov 14 '15 at 16:20
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This is a bit of a broad question. Better at what? On what surfaces?

Paint/primer combos are just high build paints with good hiding abilities.

If you're painting over a new drywall one coat of paint and primer doesn't seem to give good results. You can use the first coat of paint/primer as the primer coat but why use a $30 per gallon paint/primer as the primer coat when a $10/gal PVA primer (or more savings in 5 gallon buckets) has been doing that job reliably for years.

Painting over bare wood? Most good latex primers won't seal the wood to prevent tannins from knots bleeding through so I wouldn't count on a latex based paint/primer to do much better. There are specific primers that work well in these situations.

If you're concerned about inhibiting mold you should first look to correct that conditions that are favorable to mold growth. Up until recently paints could only inhibit the growth of mold on their surface but now there's a mold killing primer made by Zinsser who I believe was the first company that was addressing mold/mildew concerns in their paints and additive products. Personally I would use traditional means of killing mold first and possibly use that primer for some extra piece of mind.

Going over oil based paint with latex or a high gloss sheen with flat? These are applications where you should get better performance with a primer that works well for those applications.

Paint/primer products work well for going over already painted surfaces where you just want to change the color of an interior surface. The high build will make covering the old color more effective and you could possibly get away with just one coat. I personally always like to do two coats though.

Primer is not a single product. There are many different types of primers suited for different situations. If you want the best results choose the right primer for your specific application. In some cases the primer will be cheaper than an extra coat of paint/primer, in others the primer may be the same cost or more expensive but will give you better results for that specific application.

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The only sure way to identify a high quality paint is to read the label. Specifically look at the contents or ingredients. It should state a percentage of "binders" or "resins". The more the better. Another easy to tell sign of a good paint is by how long the manufacturer guarantees it to last for. The types of paints advertised as "one coat" or "paint and prime" are relatively new to the paint scene. They contain a heavier amount of pigments and resins and are priced accordingly. They can be a true time saver when compared to the 2 coat process of applying primer and than a finish coat. But remember unless you are drastically changing the wall color any good paint will cover in one coat. For mold prevention most supply stores will have an additive (ask for a mildewcide) in a small packet that prevents mold growth on the paint.

  • Might be a US thing; I haven't seen a single European product specify the amount of binder or resin. They do specify the percentage of solids and amount of VOCs, and most also have the product density stated. – Fizz Sep 22 '17 at 18:09
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Most high quality paints have a bio-inhibiting additive in there already, and putting in aftermarket additives is discouraged by many paint manufacturers (and often voids the warranty). You will have the best results if you:

  1. Properly prepare the surface.
  2. Use a high quality paint: look for percentage of "total solids"- higher is better (this is pigment and resins) vs. percentage of solvents- lower is better (for latex paint we are talking about water). Glossy paints will generally work better against mold and mildew.
  3. Use high quality applicators.

Nobody has enough experience with the paint/primer combination products to give you a good opinion on durability and longevity vs. normal primer then paint technique. I personally do not use it, I can't tell you why, I guess I just think it's a gimmick and don't trust it yet.

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