We've had 3-4 estimates for exterior painting, but I have decided to do it myself. All the estimates specified (after prep work) applying one coat of oil-based primer and one coat of latex paint.

Why would they use oil-based primer under latex paint? I assume the existing paint is oil-based, so they need an oil-based primer to get the latex topcoat to stick. Does that sound like a correct assumption?

Also, on a related note, I was going to buy an electric pressure washer to clean the house. It's cheaper than renting a gas-powered model. The electric models seem to max-out at about 1,500 psi. Is that enough to clean painted surfaces? I don't really want all the power of a gas model, or the fuss.

Thanks very much!

If the house is already painted you don't need to prime it again, just any bare wood after you power wash. If oil based was used before you can use latex over it. That electric power washer should be fine, your just cleaning off any dirt. Scrap any loose paint that doesn't come up from power washing.

Depending on the condition of the old paint,, LATEX WILL NOT stick to oil based paints. Plain and Simple. A latex based primer, then a latex finish coat. Sanding the old paint is a good idea if it is oilbased. It is a lot of work. But if done properly, it will last 15 or 20 years.

You can put latex over oil but not the other way around. Latex will stick to oil so I'm confues where this conflicting info is coming from. Degloss the surface and you won't need to prime, do this with sand paper or chemically. 1500psi is a little on the small side but it will wash a house, don't expect to remove loose paint with 1500 psi. Like Amricca says you'll need to scrape the bare spots and loose paint. If you have time to read more try this. Exterior FAQ: Latex Paints Over Oil-Based (Paint Quality Institute)