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I think I screwed up... Spar Urethane on an outdoor table

25852 Views 33 Replies 22 Participants Last post by  Jockstrap
hello all, I think I might have screwed up. Working on an outdoor table for my covered deck. The top is a lovely and hard to come by (at least in my neck of the woods) 35" wide double live edge slab of dawn redwood. After flattening the slab and sanding I am up to 4 coats of Minwax spar urethane, recommended from a good friend of the family who has been running a high end cabinet and furniture business for 40 years (also a sawyer and where I got the 10' long slab for FREE!). He has made several tables and outdoor bar tops out of the same stock and swears by the minwax finish. The intended location of the table is fully covered, 18'x13' deck so it should have no more that 2-3 hours of sunlight per day.

I should have done my research but after looking for some in-between coats advise on the forum I am seeing nothing but horror stories form this product. Is there anything I can do now, short of sanding it all off and getting some proper spar varnish? My thought was, is it possible to sand and finish the last coat of spar that I have on there now and switch to the proper marine stuff? Would that protect the urethane and hopefully prevent the splitting and peeling, or will it happen anyway?

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I don't think so. I would strip it all off and start over. Anything you put on top of it will be dependent on the substrate finish.
A cursory search for Minwax spar urethane on these pages didn't show the horror stories you're talking about. What were the problems reported ? Were the application procedures the same as yours and for usage in the same conditions ?
I have used Minwax spar urethane in the past and have had no issues. What issues are you expecting since your photo shows none.
Thanks Fred, that is largely what I suspected but you can always hope for a miracle cure!

Yonak, i found most of the issues under the finishing forum, I searched Spar urethane in the toolbar. Most were similar stories although the worst of them seemed to be one or two coats that were in direct, all day sunlight. Looks like after a season or two the urethane discolors, flakes, and peels.

The advise I got was 6-8 thick coats, wet sanding in between with 400 grit paper.

I think my solution is going to be sticking with what I have on there now and making it an indoor table, I have two more smaller slabs that would be perfect as end tables so I think I will just make a set and replace the cheap tables I have in the living room.
I've had the Minwax Spar Varnish flake after two years outdoors, went with Epifanies Spar Varnish (Jamestown Distributors) and it is still fine after five years.

Any surface film type finish will fail outdoors eventually. The key is flexibility (hence the 'spar' formula) and the UV protection.

Penetrating oil finishes do well (Penofin for example) if regularly re-applied.

You can sand the old stuff away and apply something else or just leave it be and see what happens. I'd refinish at the first hints of failure however, that slab is beauteous!
The problems related on the internet could be caused by improper application, Minwax would be out of business if they produced sub-standard products.

The main mistake I have seen is applying too few coats. To endure outdoor exposure, one needs a thick film. I would keep the 4 coats already applied and continue with a better quality Spar varnish such as Epiphane or one of the Interlux products available from marine supply stores. Apply as thick a coat as possible, to the edge of having runs and sand between well dried coats with 220 grit. Whipe with mineral spirits as a final wash between coats and put no less than 8 coats total, adding a fresh coat every season.

45 years of boating experience varnishing teak and mahogany.
I'll somewhat disagree with your assessment. Anything with urethane resins in it is going to fail outdoors, they just don't work well in that application. All of the quality true marine varnishes are based on a different resin, usually alkyd. I am humbled by your experience, but I'd bet it was always working with the good finishes….not the crap like Helmsman.
If it's for use under a covered deck then it's only semi outdoors and since there isn't actually a problem I think you'd be foolish to sand it off and start over. Also the internet has a horror story for everything. If you make every decision based on internet advice, every decision you make will be wrong according to someone.
Thanks guys,
Risk M I agree that the internet is full of the bad, people don't get as excited over a product that does what it says it does.
I wouldn't do anything until, when and if it fails.
I'm with Bondo - it aint broke [yet], so don't fix it.

For reference, one of the big differences between interior and exterior, U.V. protection aside, is the amount of oil used in the product. More oil means less durability, but more flexibility. More flexibility means more tolerance of dimensional shifts in the wood.

One thing you can do to crank of the life is, make sure EVERY surface is sealed. If you haven't already, think about applying highly thinned oil based poly to the underside. Initially, thin as much as fifty percent. As long as the wood takes the thinned finish, keep adding. It may soak for an hour and be ready for more. Then two hours…........

A big piece of, essentially, plastic wood cannot gain or lose moisture, so will not expand and contract as its counterpart. This could add years to the longevity of your work. It did to the one I did and which sat in front of a fire place for decades.
Sunlight exposure (not water) has always caused MinWax Spar Urethane to crack and peel in ALL outdoor projects I have used it on. I like/use this finish a lot (just not where it will be exposed to direct sunlight).
I forgot an important detail to my post, above:

You can add flex to cheap surface coats, like Varithane or MinWax, by adding more hardening oil. You might have to experiment, but you could play with trying, for example, twenty-five percent more oil. If needed, you could also add thinner, as needed.

Again, more flex will allow the finish to hold up better to dimensional shifts due to gain and loss of moisture.

Keep in mind, even the best finish can be knocked off the wood if moisture can get behind it.
That looks gorgeous. Use it like it is and recoat down the road if it fails. You could always put a screen of some type hanging from the edge of the overhang so the sun doesn't beat on it.
So my end solution was to keep the spar urethane and make this an indoor table. I didnt seal the bottom of the table because this was not kiln dried wood and I wanted it to be able to breathe, or more accurately, I wanted somewhere for the trapped moisture to go other than through the finish.

I suffered for a long time trying to get the final coat completed. I ended up dry sanding with 220 paper, polishing with 00 steel wool, then sanding with 1200 grit and mineral oil, then finally polishing with silicone free automotive polis
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hing compound. I had two "final coats" as I learned an important lesson about letting the last coat cure before trying to polish it…

Finished pictures below
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I used this on a walnut table that is on my covered porch. It gets very little rain and no direct sun and it appears to look as it did the very first day which is over 5 years ago. I also sprayed two coats on outdoor chairs that are in direct contact with the elements. It has not held up well. I am actually disassembling the chairs to sand and refinish. Most likely I did not put enough coats on the chairs. If you are under cover it should be fine. Just watch and re apply at the first signs of wear.
Table update.

After a few weeks in the house, the crack that runs the length of the top (through those big knots in the picture above) widened significantly; maybe 1/4". So I took the top off and back out to the shop. I had to belt sand the middle of the table down to get both sides of the crack flat again then put four butterflies in. I should have done it to begin with and I think I knew that then but I had already spent too much time on this project and was getting anxious to get it finished. A lesson well learned I guess.

I made the butterflies out of cherry, I'm hoping after they age they will compliment the reds and browns nicely. I had to pour in quite a bit of epoxy to refill the crack and will get to work sanding and smoothing that later this week
I covered the butterflies in painters tape just to keep the epoxy out of the grain. I will have to end up stripping the spar urethane finish down all the way and restarting. I think I will go with a standard poly finish this go-round since I've decided to keep this as an indoor table.
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