Filler Hardener vs Sanding

[jcclark]

Any one on here notice a relationship between how much hardener is
used and how easy or hard the filler is to sand.
I've been comparing ratios and it seems to me that if I use less hardener
in my fillers and putties that it's easier to sand.
Of course it's longer to set up too.
But if it makes it easier to sand, I'll wait a little longer.
Anyone else notice this?

 

[crashtech]

I try not to deviate too much, since one time I went too low and had to scrape the filler off of a '63 Impala door. We do tend to under-harden a bit on a regular basis, I know this because we end up with extra hardener on the shelf, and I have to date them to make sure we use the oldest ones first. This happens mostly in the summertime, when putting it the full 2% results in extremely short work times.

 

[DATEC]

If you do deviate between your coats each coat will tighten up at a different rate and will show up later sometimes after you get the job done and a day or two later you can see issues. Seems to really show up on layers of Polyester putty more so then regular putty. The last coat would be best to kick off completely before sanding to minimize any shrinking before prime and paint.

It's really best to mix it normal and catch it at the correct time and it will sand easy. That would be just after it doesn't feel sticky (gums paper and rolls off) and isn't completely hardened.