[Paintguy]

Steering things back on course, if I may

I'd totally agree with the trapped solvents explanations, for any of the reasons given.

To illustrate, here's a little story:

We tend to prime all our repairs together, at the end of the day, to save wastage. When I was doing it, we hardly ever suffered shrinkage problems. Now the boss has begun to let our young lad do the priming, we are having regular problems (same product used).

He thinks that if he bombs 3 thick coats of 2k primer on the big repairs, with minimal flash times, he can go home early (and it'll 'hide' his poor filler work). The problem starts the day after. Upon hitting the primer with a DA, you can smell the solvents bursting out! I've even had it so bad, that the primer has popped right through the base and clear during baking!

Besides re-educating him, which is difficult as he is the boss's son, I've found one way around it is to block or DA the primer down early in the day, and leave it to sit as long as possible before final sanding. This seems to give the solvents time to escape, after 'breaking the surface', and shrinkage problems have been reduced.


Clearly, as stated above, the better way would be to take more time applying the primer, and allow plenty of flash time between coats, but maybe my method of 'breaking the surface' could help a little also.

Andy.

[jcclark]

That makes perfect sense to me.
Like Barry pointed out in another thread, that works good for buffing clear
too, after you sand it allow it to sit a few hours and it'll also buff better.
anytime you sand a surface you open it up to dry more.

[MARTINSR]

An example is in my gun set up "Basics":

As an example of the use of a 1.3 tip I did a test once that proved the point well. I shot two panels of metal with a med solids urethane primer. One was shot with a 1.3 super high atomizing top of the line topcoat gun. The other was shot with a 1.5 (or a 1.7 I can’t remember) “hoser” primer gun. Three coats were applied and after a full cure (the one shot with the larger gun took MUCH longer to flash and cure by the way) the film thickness was measured. The one shot with the 1.3 tip was 2 tenths of a MIL thicker! The larger gun laid out the marble sized droplets full of solvent and when the solvent flashed the film shrank.


Now, the 1.3 tip may be too small for some products so check the tech sheet. The facts of the findings won't change.

Brian

[MARTINSR]

Originally Posted by jcclark

Well obviously we have a different definition of boast.

I think where the miscommunication is that "boasting" can still be based in fact and not pushing the product.

If the product can safely be recoated in 5 minutes by the manufacturers own testing, then "Boasting" it can do that isn't an issue to me.

I think what you are thinking is that they would "push" the boast to sell product by saying it is faster than it really is. Now, that would be wrong.

Certainly, that happens from time to time. we all over sold ourselves on our first date.

But, really, really, the manufacturer with millions of dollars in products, with hundreds of millions of dollars on the line in warrantees isn't going to push that envelope. They want things to WORK, to NEVER be a problem, that is the goal.

Brian

[crashtech]

I can't say I have the answer here, but I tend to follow some procedures that help ensure a job will have no visible problems from shrinkage. First of all, never feather filler up onto non-factory paint unless you KNOW it was all catalyzed and well cured. Second, never feather filler up over your paint featheredge unless it has been nicely feathered back with at least 150 grit, preferably 220. Third, make sure the featheredges are in 320 grit before priming. Fourth, let that primer flash off! Don't stand there and look at it, go do something else between coats, and set a timer if you tend to lose track of time. Fifth, don't apply thick coats. Just go one coat extra if needed. Now, I'm sure a guy could follow all these steps and still get shrinkage, but that would be rare, IMHO.