Last year, I built my first piece of outdoor live-edge furniture: What are the potential issues with this bench design? and What should be done to treat decorative wood for outdoor use?.

I expected there would be problems, and that's fine; making mistakes over and over is how we learn and grow. Often I expect to throw away my first couple attempts at something new and replace it with better once I've perfected my skills. However, I would like to 'save' this particular piece as it has meaning to me.

This bench was sanded down to 220 grit, then coated with 10 layers of Target Coatings EM-9300 exterior polycarbonate urethane applied with an HPLV sprayer. I then sanded this down lightly with 500 grit and rubbed it out for a mirror smooth finish. The bench was placed outside in April of last year and weathered the summer just fine. However, upon inspecting it this year after the winter, I'm seeing what appears to be water damage in some areas:

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My guess is that the cold weather caused contraction and expansion which cracked the coating. I also probably shouldn't have tried leaving the bark on (or is that phloem or cambium?). What is the proper way to address this now, and prevent a recurrence next winter? Or is the most time and cost efficient option to take my lessons learned and create a new piece from scratch to replace this one?

  • The closing two paragraphs, above Fasteners, in my previous Answer seem veryrelevant here. Anyway, obviously this seems to have indicated that the finish you used is not up to this application (especially after 10 coats). – Graphus Jun 4 '20 at 15:11

The material you selected for the top coat is only water-resistant,i.e., not water-proof nor for use for continuous exposed in an area exposed to the weather year round. In your initial questions that you provided links to; correct answers were provided for "water proof" finishes for exposures to weather year round.

You could refinished the damage area, and recoat the entire bench with a weather proof finish.

Section below added to answer OP's question in comment.

Your finish was more for UV protection and it can be difficult to read between the lines, Your finish is for vertical applications, not standing water. The EM9300 product description reads

...that require a hard yet flexible coating in high UV exposure environments. EM9300 contains UV reflectors for a finish that is resistant to sun exposure that can cause graying or fading. EM9300 water based exterior urethane offers excellent water resistance during vertical water exposures.

In the comments of your original post, comments were provided that the choice of the Target product as a top coat may not be right one.

Another mistake is that you might have over-sanded or did not apply enough thickness to the layers of finish. It's hard to believe that 10 layers of finish allow water to penetrate that fast.

Above is a short answer to show where you went wrong, I need time to review the other Answers and recommendations in the other link, but the selection should contains something like, "Marine varnish, spar; weather-proof", not weather-resistant"

The Target brand might have worked if applied in proper thickness, and covering the bench in the winter, etc.

This is a link to top outdoor finishes. #5 on the list is stated to be highly rated for its water resistance and exposure to extreme weather. "Waterproof" as a description may no longer be used because of legal concerns. No more waterproof watches, only water resistance, LOL

  • Could you please expand on this? The original question answer suggested an exterior or marine polyurethane. I used an exterior polyurethane, that a rep from Target said was designed for year-round outdoor use. I thought all polyurethanes created a water-proof coat. Understanding what I did wrong in choosing my previous finish will help me understand how to avoid the mistake in choosing a new one. Thanks. – Nicholas Jun 2 '20 at 18:35

I think your best bet is to flood the edges with a thin epoxy. Since you're using a glossy film finish this won't really impact the look too much.

  • I assume I would need to sand the area down, first, to unblemished wood? – Nicholas Jun 2 '20 at 18:35
  • If your objective is to just shore up the cracks that have already formed I don't see that as strictly necessary. If you want to fully seal/stabilize the piece then yes, you probably should sand it down first. – SaSSafraS1232 Jun 2 '20 at 21:44

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