I have read a lot of opinions online about the hardness of different finishes, but I cannot find any authoritative numbers for hardness ratings for the different types of finishes in the lacquer and poly families. Specifically, I'm looking for comparative numbers for:

  • Nitro lacquer
  • Acrylic lacquer
  • pre-cat acrylic lacquer
  • post-cat acrylic lacquer
  • water-based poly
  • oil-based poly

I have found this information in many different forms online, but the table does not differentiate pre-cat and post-cat lacquer, nor is the catalyzed lacquer listed as nitro or acrylic. The lacquer was also tested after 24h, even though it doesn't reach full hardness for up to 7 days (from experience, there is a huge difference between 24h old lacquer and 7d old lacquer). I have found one or two posts by woodworkers about their preferred finish, but they cannot be used for comparison as their base material, technique, and testing process differ.

My specific use case is 5-7 HVLP sprayed coats over Eastern White Pine, rubbed out with 500-grit to 4000-grit sanding pads followed by Menzerna SF3500. My first project was a computer desk using Target Coatings EM-6000 acrylic lacquer with CL-1000 crosslinker. I'm satisfied with the hardness for this use, but would like to better understand alternatives for future projects without having to spend the hundreds of dollars and countless hours testing them all.

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    Unfortunately you do really need to know the numbers for specific products and not a class if you want to be sure. One of the best examples is oil-based polyurethanes, they can and do vary widely in properties and hardness will be one of the variables. If you hadn't linked to it in your Question I would have pointed you to a pencil test, as this is the easiest and most straightforward way of testing a finish for most users. – Graphus Jul 19 '17 at 21:42
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    Incidentally you're quite right to be critical of the inclusion of a 24-hours-dry finish in the results! That's simply not long enough for anything to harden up fully. Similar to the very poorly done glue comparison posted by Matthias Wandel that gets linked to still many years down the line, what's even more frustrating is that in the intervening period further testing hasn't been done to provide an updated, and much more reliable, table of results — shellac's poor showing in that test is a cause of much eyebrow raising among its regular users I can tell you! – Graphus Jul 19 '17 at 21:47
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    @Graphus I had the same thought about variations between manufacturers, but available information is so limited that I would happily take anything that anyone could tell me. The pencil test makes sense, but one person could see a mark where another one doesn't, so all coatings need to be tested by the same person for the test results to have any real relational meaning. – Nicholas Jul 20 '17 at 21:13
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    Hardness and fracture toughness are different things. Likewise, measuring hard on soft is likely to confound some variables. Is the OP concerned more about the ability of the resistance of the coating to scratching, indenting, being worn through, or something else? Does coating thickness matter? These are important considerations because, for example, if you're concerned about the ability of the coating to resist being worn through, a thick layer of softer material might be better than a harder but more brittle material that can only be applied very thin. – aaron Jul 23 '17 at 14:47
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    Meanwhile if you want to just resist showing any scratches at all, you'd go with the hardest coating you could get, and apply it thinly to prevent cracking. – aaron Jul 23 '17 at 14:47

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