Painting - Mildew problem

9 years ago I had my house painted. He used oil based paint. three years ago I noticed mildew. In 2007 I Jomax and let it stand longer than they suggested. I rinsed the composite wood and applied exterior Kilz and two coats of oil based glidden paint. The mildew is back. One store tells me I have to sand all paint off and start over. Another tells me a oil based primer over the oil based paint will allow a latex paint to adher just fine. Who is right? Any of you pro's have another suggestion?

Thanks

Welcome to the forums!

I doubt the mildew is really a paint problem but more of a climate problem. When moisture stays on a surface for any period of time coupled with heat = mildew. It is true that latex paint is a little less prone to mildew than oil base.

On interiors it is common practice to use a solvent based primer over oil enamel to allow the switch to latex enamel. Generally exterior latex can be applied over weathered exterior oil paint. I'm not overly fond of priming over sound oil and switching to latex.

I'd recomend just washing your siding for the time being. I've always used a bleach/water solution for removing mildew - it's cheap and effective although products like jomax are a little more diy friendly. What I do is wet the siding down, spray on the bleachwater [never more than 50% bleach!] let it set but not dry and then rinse off. A pressure washer makes the job easier but you can use just a water hose w/nozzle.

I used to have a place outside of orlando and the north side of my home needed washing 2x a year. When I repainted, I added extra mildewcide to the paint which helped a lot - but I still needed to wash that side every 12-15 months.

btw - I doubt you needed to use a primer, definetely not 2 coats and there are much better exterior oil base primers than kilz.

Thanks Mark. I'll take that into consideration. I even thought to let the clorox and rinse dry 2-3 days before doing anything. Just concerned about painting over the old based paint. Valspar has a latex paint with mildewed and don't recall the name but antoher other than Kilz has an oil based primer. You're right. Definitely cheaper. BTW, all the houses in this subdivision have siding of some sort and I've only seen one of hundreds of houses that has this problem. I do appreciate your insight.

Nothing is gained by letting the bleach mixture dry on the house. Unless rinsed well it can cause adhesion problems. I'd continue to clean the house as needed and when the current paint starts to look peaked, I'd wash it again but add TSP to the mix. Once dry you should be able to repaint with latex [no primer] If you run into any glossy areas, they should be sanded a little.