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I like to thin my polyurethane finish with mineral spirits as an alternative to buying a wipe on poly - but when I started to look at several of the easily available options for Clear Gloss, like Varathane or Minwax or Arm-r-seal, their MDS sheets show a huge range of total solvents, in each product, like they cant (or wont) tell what’s in each can.

Here’s Minwax Gloss Poly which I think of as a “full strength” (and seems thicker than Arm r seal, for instance):

Ingredient name % by weight

Light Aliphatic Hydrocarbon ≥50 - ≤75 (other ingredients listed are each less than 1%, no listing of polyurethane or resin or anything.) So, 50-75% solvent - quite a range there!

Here’s ArmRSeal which I think is more a wipe-on poly, fairly thin out of the can:

Chemical Name (3 separate listings with different CAS#s called mineral spirits)

Mineral spirits 20-40%; Mineral spirits 10-20%; Mineral spirits 5-10%; Nonane 5-10%; Oil modified urethane resin 10-35%; Resin 0-25%.

https://www.woodturnerscatalog.com/docs/MSDS_Arm_R-Seal.pdf

(Nice they give at least a mention of resins, but again, ridiculous ranges! 40-80% solvents, 0-25% resin etc)

Varathane Gloss showed similar large ranges.

Why don’t these companies a)know or b)have to put better estimates of total solvents? I’m a newbie but have read enough online at least, to have absorbed that finishing products are mostly unregulated, buyer-beware, no way to find out what is in them (eg Danish Oil). Is there any way to know which is more concentrated, except by how thick it pours out of the can? Frustrating!

Anybody with the inside track, on this?

Cheers! Steve

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  • Hi, welcome to StackExchange. You need to be aware that data sheets are sometimes written deliberately to obscure the actual formulation, while fulfilling the legal requirements. Also there's coverage for variations, if for example sometimes during production the MS percentage does go up to 75 during a batch they're covered..... although how that could double unintentionally I can't get my head around!
    – Graphus
    Dec 5 '20 at 5:50
  • "Is there any way to know which is more concentrated, except by how thick it pours out of the can?" Yes, empirically. While you can sort of go by product viscosity be aware that this can be altered by additives (as in "gel stain", which despite its name is actually thickened varnish") so the only real test is in how fast products build a finish.
    – Graphus
    Dec 5 '20 at 5:51
  • Honestly, this might be a better question for Chemistry. They'd probably be in a better position to explain how the chemistry can work correctly with such a wide variety in formulation.
    – FreeMan
    Dec 9 '20 at 17:22

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