[Steve Neul]

Hello,

As a wedding present, I built an oak bar top that sits on top of a wine barrel. It's meant to be an outdoor table, at least during the summer. Unfortunately, after just a couple days in the hot sun, the top finish has failed:

View attachment 464165

Here are the finishing steps, from the last step applied going down to the wood:

Spar varnish (Varathane, exterior rated, oil based) - 3 layers
Epoxy - West Systems - 2 layers
Shellac - 2 layers
Oak wood

What appears to have happened is that the varnish developed large bubbles, from a ~half inch to several inches in size and completely delaminated from the epoxy:
View attachment 464166

Furthermore, the places where these bubbles formed appear to have a "crinkled" finish underneath, presumable in the epoxy itself:
View attachment 464168

I'd like to understand where I went wrong with this approach and, more importantly, how I can put some type of finish(es) on this that can truly stand up to any weather (rain, hot sun, etc.)

Thank you!
Bryan

Hard to say what went wrong. It might have been put in the sun too soon. The epoxy should have been applied to bare wood without the shellac. Shellac takes a month to fully cure and the alcohol vapors underneath the epoxy could have lifted it. Alcohol is one of the chemicals recommended to someone wanting to strip dried epoxy. All of these could have contributed to the failure of the epoxy.

It really might be easier to start over rather than trying to take the epoxy off. Epoxy doesn't strip easily. If I were going to strip it I would probably take a belt sander with a coarse belt and grind it off. You would have to move the sander around a lot or it would cost a fortune in belts before you got it off. Then because the belt sander sometimes makes dents in the wood thoroughly sand it with an orbital.

Once you get it to raw wood use only the spar varnish to go back with and keep the sun off of it for a month. There are many different grades of spar varnish, the best is Epifanes and the worst is Helmsman. You have to ask yourself how long do you want the finish to last before you refinish again. I would also recommend putting a cover over the table when not in use, that would extend the duty life of the finish.

 

[Steve Neul]

Thank you, Steve. I understand and agree with everything you say. Couple things special to my situation:

1) I used shellac as a sealer for the wood so that wedding guests could all sign their names and add best wishes to the table. Then a 2nd sprayed-on coat of shellac sealed the signatures enough for me to add the coats of epoxy on top of those and not disturb the permanent marker notes.

2) Because of 1), I'm not really in a position where I can strip back to bare wood.

Finally, I'll add that I thought the "spar varnish over epoxy" was the best finish for outdoor furniture, the reasons given that epoxy will waterproof the wood and prevent seasonal expansion and contraction due to humidity changes, and then the spar varnish will protect the epoxy from UV damage. And since the wood won't expand and contract as much, the epoxy is thereby protecting the varnish from cracking. Clearly whatever I thought was wrong, but I wanted to at least offer up an explanation as to what I did.

Given my complex situation, I'm open to all suggestions on how to best make this table weatherproof.

Bryan

I'm surprised the alcohol in the shellac didn't screw up the permanent marker notes. Ink is often thinned with alcohol.

You are going to need to take the epoxy off somehow. You might find a rigid putty knife and pry the loose epoxy off and sand the rest. Hard to do but you might sand the remaining epoxy off down to the shellac layer without taking the marker off. The epoxy is shot and there is no finish that would help it at this point. Maybe you could take close pictures of the permanent markers in case they get damaged with the sanding. You could use the pictures to make touch ups.

 

[Steve Neul]

Would it be too much to get everyone that signed the table to sign it again? That would be the most permanent fix to start over. I think trying to fix it would be a never ending job.

 

[Steve Neul]

Thank you, everyone, for the thoughtful and helpful responses. At this point I am tending to agree with the popular opinion that the hot temperatures forced the alcohol (from the shellac) out and that in turn sabotaged the epoxy from underneath. A stupid mistake on my part.

At this point I have all the old epoxy and varnish removed (very tedious) and am in the process of repairing all the signatures as best I can (again, very tedious). Then I'm going to put several coats of Epifanes over the top of that. I still need to play around with some test pieces to ensure that the varnish doesn't smear the permanent markers as I apply it.

Again, thank you to all that weighed in!!!

Cheers,
Bryan

Generally as a rule of thumb it's best to use only one finish when you finish something, especially an exterior finish. Still having the shellac on there even though it's completely dry will weaken the finish so I would cover it with something insulated when the table isn't used. You might cut a piece of styrofoam and use on the table under a table cover.

 

[Steve Neul]

Thanks, Steve. I agree that the mismash of finishes on this project isn't ideal. FWIW, I did set the table out into the hot sun for several days. I'm hoping that all the alcohol from the shellac is now long gone. I guess we'll see. Covering when not actually using is going to be the new rule.

Cheers,
Bryan

It's more than the alcohol, even though the shellac is dry now there will still be adhesion issues. As best as you can you need to sand that shellac before applying the epifanes. It needs the scratches for the varnish to adhere.

The shellac you used, was it standard shellac or was it a de-waxed shellac? Shellac contains a natural wax which adds to your problem. If it was standard shellac you should put a coat of Zinsser Sealcoat over that and let it dry a few days before proceeding with the finish. It would also give you something to scuff sand.

 

[Steve Neul]

It was dewaxed shellac, Zinsser Sealcoat, to be exact. I get what you're saying about adhesion, but now I'm a bit paranoid about adding shellac again, when I believe that was the root of my issues...

I'm down to bare wood in most spots, and I'll pay particular attention to any remaining shiny spots before I apply the first coat of varnish.

Thanks again,
Bryan

If it was sealcoat then don't put any more shellac on it. Just scuff sand it and put the Epifanes on it. Once you put a coat or two of the Epifanes then you can do more sanding to level the finish.