I am renovating our bathroom and have the following problems/questions.

1) current wall paint is peeling from 3-4 bubbled areas, the current color is a dark gray and the underlying wall feels like blue board. I plan to be using a Sherwin-Williams Bath semi-gloss paint. I plan to scrape and sand the bubbled areas. Do I need to remove the old paint from all the areas to be repainted or only the bubbled/peeled areas? If I don't need to remove all the old paint, can I still repaint with a lighter color and not have the dark old paint show through?

2) There is a metal pipe carrying hot water to higher floors in the bathroom with peeling paint. How do I paint metal pipes, what kind of paint would resist cracking from the temperature change and stick on metal? Should I cover the pipe with insulation foam and cover the foam with something else (paper, foil)?

3) There is a old metal radiator in the bathroom with old paint, minor amount of paint cracking off. It looks like this radiator was painted successfully before. How do I prepare the radiator metal for new paint, what kind of paint, given the same concerns for this radiator holding paint without cracking as for the heat pipe.

Thanks for your help.

 

I don't know what you mean by blue board, but I assume that it is waterproof sheet rock. First, why is the paint bubbling up? You must solve this problem first. If it is an old problem and isn't getting any worse, you can sand or scrape any loose material off, prime it, mudd it, sand and prime again and then paint. As for the metal pipes, and the radiator, I would sand them smoothe and then use an industrial enamel on them both. Insulation on the pipes would help to keep the water hot and commercial types of insulation can usually be painted also.