Painting over old exterior lead paint - prep?
I need advice re preparing and painting *over* old exterior lead paint. A portion of my house is wood siding with 1 or 2 layers of modern latex paint (Sears Weatherbeater, circa 1975) over old white paint that, per home test kit, contains lead. The latex paint is peeling in some areas to expose the white. The white paint still seems to be adhering well, with just one or two patches of small peels.
What would be the appropriate way to prepare this surface for painting? I donít need or want to take off the leaded paint except in the peeling patches; I just want to take off the loose latex paint on the surface of the leaded stuff, as well as ensure that the surface of the latex paint thatís still holding is clean so the new paint will adhere.
This section of wall starts over the garage doors and runs up to the second-floor eaves. I have not definitely decided to do the job myself, but having painted all the one-story areas myself, Iím at least considering it.
1) Would it be safe to use a power-washer for this purpose?
2) Would I be able to get sufficient force with a rented power washer to knock the peeling paint off from the ground?
3) Should I prime the exposed lead paint, and is an oil-based primer best? Given that any exposed lead paint is exposed *because* the top coat peeled, I'm inclined to prime those patches to try to improve the adhesion for the new paint. I'm further inclined to use oil-based primer because I think it's tougher than latex, but is that true?
4) I think I should prime the rest of the siding with latex primer, for color reasons as well as to ensure good adhesion, because I'm changing the color from avocado to light blue, but is that actually necessary? I'm planning to use two coats of color paint regardless of whether or not I prime, but if priming really isn't necessary it'll be a very big savings.
Re: Painting over old exterior lead paint - prep?
I have always been an advocate of a thorough, vigorous powerwash. However, be aware that too vigourous can damage the wood. Also, you apparently have bad adhesion in some areas of the later coat of paint to the original coat. You risk aggravating this bond with too vigorous powerwashing, however, if the bond is so poor, it would probably eventually let go anyhow.
I doubt that washing from the ground with a zero tipped, high power powerwasher would give you good results. If you are going to paint the upper portions of your house yourself, you are going to have to figure out how to get up close to the surfaces anyway.
Bad adhesion peeling is usually caused by: going over too slick a substrate, going over dirty siding, or going over too much oxidation from the old paint, especially if it was oil paint. The vigorous powerwash will take care of old dirt or oxidation. A good primer will help with the slick substrate.
Personally, I would probably just prime the whole house with a good acrylic primer tinted toward the finsih color. I would follow with a complete coat of acrylic housepaint. If you have peeling to bare wood, you might want to spot prime these areas before the general priming.
I feel two finish coats is unnessary if the primer has been tinted toward the finish coat and you have effectively blanked out the old color. It depends somewhat on how light and clear the blue is. A dull, grayish blue will have much better coverage than a bright, clear blue. Buy a sample gallon of the finish color before you buy enough for two coats. Make a sample over the tinted primer. It will be readily obvious if it is covering or not.