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Mildew issue and deck paint/stain questions

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I've got a 6 year old Acadian style house (i.e. big porches) in Louisiana. It's on the original paint job but I've got a couple of issues. It was a spec house so I'm sure every expense was spared when it came to paint quality used.

I'll start with my mildew issue: The exterior is Hardy Plank siding with wood trim and columns. It's all painted white with some kind of contractor grade exterior acrylic from Sherwin-Williams. The Hardiplank looks great for about 2 years between pressure washing with almost no mildew. The wood components however look gross with mildew in 6 months. The 6x6 columns (I assume pressure treated) are particularly bad and have started to peel. They actually are about 1.5-2 years overdue for repainting. So, I'm going to have to repaint the columns and trim and I would like to not have to deal with this again for quite some time. I just finished pressure washing and bleaching over the weekend. I've seen several recommendations for Zinsser Perma-White. Would this be a good choice for going over an exterior acrylic? I'm setup for a contractor discount at Sherwinn Williams too if they'd have a better or equivalent option. Whatever I use will have to look ok next to the painted hardiplank because I don't want to have to repaint the whole house.

On the porches they were painted but I'm unsure of what type of paint. About 30% of the paint has peeled off and I need to do something about it. I'd love to do an opaque stain that will wear instead of flake off with age but I'm thinking it will look stupid unless I strip all of the paint off. Stripping the paint off would be a huge job that I'm not really willing to do. What's my best option with minimal labor here? Can I just go over it with an opaque stain or should I just repaint? This is about 3 years overdue and I definitely don't want to be repainting the porches every 3 years. I'd replace it with composite decking before I go that route.
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Hey Jeff, welcome. Mildew/algae are one of the unfortunates of exterior paint. Zinsser guarantees mildew free for five years, so for what that's worth?? Give it a shot, it can't hurt. As to the peeling, be sure that all joints in the wood are properly caulked. Technically, all wood joins should be caulked, whether they're gapped or not. What's tight today may not be tomorrow. Moisture getting into/behind the structure is the single biggest cause of paint failure. Caulking occurs after priming/first coat of stain to prevent absorption of caulk vehicle and premature failure. As to covering painted surfaces with a stain, you can. Just be sure to scrape, sand, and properly prime all surfaces. You don't need to prime if you go the stain route. Also, after you prep be sure you give ample time, couple of good drying days, for any exposed wood to dry out before recoating. A lot of people prime immediately, sealing residual moisture in which only guarantees repeat failure. If you're certain the wood is dry you're okay. Good luck.
PS Why would putting a solid stain over a solid painted surface look stupid? There's no need to strip any paint. With the proper prep, the stain will bond to the paint.
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