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I have a problem on a fresh soft cedar wood project, scratching easy with Varathane-Premium-Diamond Wood Finish-Water Based-Interior-Satin. Steel wool & vinegar stain dryed for 24 hours. Shop temp 15-18 DegC (59-65 DegF)(witin spec).

1st Coat- Light sand to knock out raised grain (220grt), Varathane coat applied with brissel brush, let set overnight.

2nd Coat- light sand with fine grit sand pad (330grt) (nice powder from sanding), wipe clean damp cloth & let dry, diluted Varathane with 20% water (maybe where I went wrong but people do this all the time & stirred it well just before use), (10CC Water/40CC Varathane), applied with brissel brush and smoothed with foam brush immediatly, let set over night.

3rd coat- Light sand (330grt), good powder, wiped down & dry, same diluted 20% water/80% Varathane solution. Dried in good shop temp for 3 days, then shop temp dropped to about 10degC (50degF) for 2 weeks to cure.

Problem- After the two weeks my finger nail scratched the surface super easy! I can't sand down too much or the stain will be effected. I usually use gloss and not in Varathane brand (i.e., Min Wax Poly) and never had this problem before. I am thinking to switch type of finish with different brand and mabye not satin. This bench needs to be durable & I intend many more coats. I see this issue popping up with the Varathane Satin finish but everyone blames the applicator. Maybe there is something wrong with Varathane or dilting was my downfall. My sample stains and coats were done in same temps of shop with non-diluted Varathane-Fast Drying-Professional-Clear Finish-Water based and I just tested it and it's scratching pretty easy too, but not quite as easy. I don't want to mess this up as the wood it was built from is the last wood from my late father's property.

Maybe it's only scratching easy because it is a softwood and I need to just keep going with coats undiluted.

Cedar_Varathane_Diamomd_Satin_Scratch

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    Hi, welcome to StackExchange. Thanks for the great detail here, we don't get that enough! For future reference, when composing a Question try to aim for just one ? please. Although you can include some rhetorical questions as well as the actual query the Q is about, you shouldn't actually ask multiple separate things that could each require their own Answer, especially if you definitely want them answered. It's perfectly OK to ask multiple Qs about various aspects of any single project, as long as a search has not provided a solution, or finds a prior Q&A on the topic (no duplicates allowed).
    – Graphus
    Commented Feb 18 at 7:17
  • Now about the scratching problem. As mentioned in an Answer I wrote only yesterday (!), the main thing might be that a finish cannot be assumed to be as hard and tough as it's going to get (exhibiting its full potential in terms of scratch resistance, among other things) until after full curing. The other contributing factor could well be the dilution but that's hard to know; but for waterbased finishes in general dilution is simply not necessary — and often not advised by the manufacturers usually — and 20% water may be way too much as well. Unrelated, 'deep scratch potential' is [contd]
    – Graphus
    Commented Feb 18 at 7:22
  • ...always a matter of how soft the wood is underneath. As American cedars are so soft it is important to be realistic about how ding resistant anything made from them is going to be (no matter the finish used). However, a good finish does harden the surface and prevent superficial scratching, up to the level the finish provides whatever that is. And the scratching that you've photographed does seem to be basically 'in' the finish rather than going through it to involve the wood deforming if that makes sense, although it's hard to be sure from a photo even one as clear as this one.
    – Graphus
    Commented Feb 18 at 7:28
  • Your edit should get approved, but you couldn't edit it because you tried from a different browser/device. Please log into either of your two accounts, register it, then request that your two accounts be merged so you can edit your own posts in the future without them having to go through the review queue.
    – FreeMan
    Commented Feb 18 at 23:06

1 Answer 1

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I think fundamentally this is going to be unanswerable because we aren't there to examine it in the flesh, look at some variables including how soft the unfinished wood is, and perhaps most critically to run some comparisons.

In terms of possible causes I'll repeat and expand upon the stuff from my Comments above.

Curing?
The main thing might be that the finish hasn't fully cured yet (although my personal bet would be that that is not the only factor).

No finish can be assumed to be as hard and tough as it's going to get — exhibiting its full potential in terms of scratch resistance, among other properties — until after full curing. Waiting two weeks certainly isn't nothing, but it could still be slightly too short a wait.

Dilution?
The other contributing factor could well be the dilution, although that's impossible to say1. However for waterbased finishes in general dilution is simply not necessary — they're plenty watery and exhibit good brushing properties straight from the container. And dilution is often not advised by the manufacturers; where it is, 5% up to a max of 10% would not be unusual2. 20% water could be way too much and undermine how the finish performs.

Other variables
Temperature and relative humidity are the big two in terms of how finishes first dry and then cure.

Most of us don't work in the textbook conditions mentioned in the manufacturer's guidelines unfortunately, but any deviation downwards in temperature and/or upwards in humidity can have a pronounced effect, slowing drying or curing significantly3.

10°C/50°F is well below the ideal drying temp for waterbased finishes in general — a full 11°C/20°F below the usually mentioned ideal conditions.

Bottom line, test first
This is unfortunately a prime example of why it's important to always, always, test a new finishing routine and doubly so if using a new-to-you finish (no matter how well rated, even by trusted authorities).

Some people even go one step further and consider every new tin of finish, even an old favourite, an unknown and test it before committing to a project piece. This is sound practice, because batch variations and possible mistakes in formulation are not unheard of.


1 Some finishes that aren't supposed to be diluted do actually perform quite well when diluted, but other superficially similar finishes don't. So it's impossible to know in advance and why testing should be done if one wants to dilute for any reason.

2 Such as High Performance from General Finishes, "Thin as desired with distilled water; start with 5%, adding up to 10% by volume" [my emphasis]. Follow this link for more details.

3 This is especially important with waterbased finishes which might have only one shot to dry properly. On the other hand oil-based finishes will continue to cure no matter what.

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