From a reader:
I have a basement floor that is 20 years old. it has never been
painted. it has developed some cracks. during spring rains you can
see some moisture coming through the cracks.
It also has some oil on it from storing a lawn mower.
How do I repair the cracks?
How do I prepair for painting?
what type paint would be recommended?
Is priming required?
Does anyone have advice for him?
Unfortunately, he needs to call a professional; that type of damage to the slab suggests, at least potentially, similar damage to the foundation. There are some cement sealing products he could use - I used one on my driveway to good effect - but the risk to his foundation is too high for a do-it-yourself quick fix to be appropriate in this situation.
Once the damage has been assessed and repaired, the best paint to use would be garage floor paint/sealer; it is designed for cement surfaces, and repels moisture. Having used it myself, I can say that it's very easy to paint a floor with a roller as long as the surface is clean and smooth.