Alexseal finish primer

[margitchris]

Something is not right. I sprayed a coat of white Alexseal Finish Primer on my deck about a month ago. I sprayed it over gray finish primer. Last night I started sanding with 320 grit and the primer doesn't sand; it loads up the sandpaper in little cakes. Another anomaly is that the primer is glossy. Experimentally, I just wiped it with some wipe own solvent and the primer showed no tendency to soften. The paint surface holds up to making tape equally well. I sprayed and sanded gray primer on the topsides and everything was normal. The only thing I can think is that the primer was too old. I've had it (unopened) for about two years.
I suppose I could try wet sanding. As it is now, though, the surface has no teeth and I don't want to put topcoat on it until I resolve this problem.
Thoughts?

[Tim]

Something is definitely not right. The finish primer gets harder over time, to the point of becoming extremely difficult to sand, but it will not clog sandpaper at this point--rather it would just resist sanding altogether. Also, I wouldn't call the finish primer "glossy" ever; when freshly spray-applied and unsanded, it's perhaps satin rather than truly flat, but never anything I'd call "glossy".

Clogging of sandpaper suggests that your primer has cured soft and improperly, which points to some product error--whether age of the product or improper mixing.

Alexseal suggests that maximum shelf life is 2 years for most of their products (new and unopened). Perhaps this is your problem, but just as likely is a mixing error. Did you do the mixing ratio correctly? Alexseal made a change in the primer in the past year or so: the old primer, which may be what you had given its stated age, was a 2:1 mix (base:converter), while the current (442) primer is a 1:1 mix ratio. Is is possible you did this incorrectly?

Any chance that you mixed incompatible primer products--say, old-style base with new-style converter?

I'm not saying you did it incorrectly, but rather that the symptoms you describe tend to point to an improper mix ratio or related problem. If not, then I am not sure what the issue could be. In any event, I would not trust the primer as currently applied.

[margitchris]

As always, Tim, I appreciate your time and expertise in answering. It turns out that despite my great care in matching Alexseal products I did use "old style" finish primer with "new style" converter. The reason I didn't use the "old style" converter is it looked suspicious when I opened the can ( again, two years old in an unopened can ) and mixing a small test batch revealed that it did not harden or even dry. The very idea that there might be competing generations of Alexseal products never crossed my mind.
I'll refrain from expressing further emotions and concentrate on deciding how to proceed.
Chris Miller
Searafer 31 yawl