A real problem here. Hope you can help

i got 1 gallon of Behr1 part epoxy garage floor paint to paint a remote corner of an old unpainted concrete basement floor. of course the directions recommend one product to clean and etch, and than a primer. this is a remote corner which will not be subject to any heavy traffic, additionally i did practically clean the surface as best as practically possible. my question is if the primer is absolutely necessary or will direct application of one or two coats be ok. i know they always recommend a primer or an etcher but is it always really necessary or is this just their attempt to sell more product? thanks

We just finished our bedroom about three months ago. Now on the wall and around the ceiling I'm noticing the paint is bubbling and in some spots I see a few small cracks. This was an area where the roof originally leaked and this whole area had to be re-plastered. So, it has a history but to the best of our knowledge it was fixed. The cause of this is either one of two things: [B]1)[/B] Because we didn't prime the mudded areas underneath the paint or [B]2)[/B] We still have a leak. [B][U]Which brings me to my question:[/U][/B] What's the best way to determine if this is being caused by water damage behind the plaster and paint? My thought was to put dry sponge in the addict above the wall to see if it gets wet during the next rain. Any other thoughts?