Sometimes we see only spot failure.
Unfortunately, oil base paint never stops hardening.
This is especially problematic on older coating systems that have been hardening to the point of eventual failure. Much of the paint that is currently intact, will eventually
release. When we encounter a situation like this, we have two options. We can scrape the currently loose and peeling paint, and repair failed areas, and repeat this cycle every few years until the old hard underlying coating peels, or we can consider total coating removal. If lead is present in previous coatings, we need to consider chemical stripping as to not create a health hazard during coating removal and sanding.
For spot repair and repaint, we scrape off as much failed paint as possible, then sand with a dust-free palm sander (using 60 or 80 grit abrasive ) to blend in the bare areas. Final sand the remaining coating with 80 grit to leave a good profile for the coating. Prepare and prime the bare areas and recoat with an Acrylic Floor Enamel. Be aware that coating not removed now will continue to fail over time as any remaining old coating will always continue to harden.
The second option involves total coating removal. There are several biodegradable strippers available. We also final sand the entire floor to remove any wood fiber damaged by trapped moisture, or the stripping process.
We have found very few good-performing floor paints for exterior wood floors. If you absolutely want a solid painted finish, you could consider an acrylic solid stain like Enduradeck from California Coatings, or a solvent-based product like Sikkens Rubbol DEK, which is a flexible, breathable oil based wood floor coating (not a paint). It looks like paint, but performs like a stain--no film to peel.
Each of your coatings options
has distinct advantages and disadvantages depending
on your specific requirements and whether you are
recoating bare wood, or remaining paint. If you choose
not to strip the entire porch, You will need to sand
the remaining coating so the new coating will adhere
to it. Solid color stains are for uncoated wood only,
so unless you get to completely bare wood, you should
consider an acrylic floor paint , priming bare wood
and existing paint with 2 different specialized primers.