Discriminating Bubbles

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Forum topic by MarkTheFiddler posted 06-19-2016 11:48 PM 802 views 0 times favorited 5 replies Add to Favorites Watch
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2068 posts in 2701 days

06-19-2016 11:48 PM


I’m finishing my bathroom vanity top. I used a variety of woods in 2 inch strips. No one piece reaches from one side to the other.

I used the following scrap pieces.
Peruvian walnut.
Redish mahogany.
Dark mahogany.
Zebra wood.
Curly maple.

I am applying the first coat of McClosky’s “Man O’ War” marine spar varnish clear. The final coat will be a satin finish.

The redish mahogany, Purple Heart, and zebra wood all bubbled up. The rest – nothing, nada, zip.

The zebra wood only has a few bubbles but they are the largest of all. The big one is about 3/16’s of an inch. The others have quite a few bubbles from 1/64 to 1/8 inch.

I’ll make my guess and give another detail. The 3 woods I mentioned did not drink up the first coat like the others.

The counter top has been in the garage for a few hours. I left the door open. There is a slight breeze this afternoon.

I’m guessing the breeze had something to do with the bubbles. What does your superior knowledge tell you?

-- Thanks for all the lessons!

5 replies so far

View MrUnix's profile (online now)


7482 posts in 2712 days

#1 posted 06-20-2016 12:59 AM

I’m guessing the breeze had something to do with the bubbles.

I’m guessing that the breeze had nothing to do with it… and that the wood was simply out-gassing as the varnish soaked in. I’m also guessing that you didn’t apply any type of sealer prior to application of the varnish.


-- Brad in FL - In Dog I trust... everything else is questionable

View MarkTheFiddler's profile


2068 posts in 2701 days

#2 posted 06-20-2016 02:50 AM

Thanks Brad. I didn’t seal the wood. I’ve gotten away with not sealing the wood for so long that it never dawned on me that this could happen.

It does occur to me that I have had micro bubbles before that I take care of when I scuff up the finish with 220 grit. I always thought I had introduced the bubbles when I stir the finish.

Now I know a little bit more. Thank you again.

-- Thanks for all the lessons!

View AlaskaGuy's profile


5355 posts in 2822 days

#3 posted 06-20-2016 02:55 AM

Don’t know about the bubbles.

How come you’re using an exterior varnish for an indoor application? The thing about “exterior varnishes is that exterior varnishes are actually less water and water vapor resistant than an interior varnish. Exterior varnishes UV additives and contain a higher percentage of oil to resin. The primary feature of a higher percentage oil content is that is makes the varnish more flexible and soft. These characteristics are benefits in improving the ability of the finish to maintain adhesion due to wood movement caused by frequent and large changes in humidity and heat in the outdoor environment. But, the added oil reduces the water and water vapor resistance”.

For the above reasons, a good interior varnish is better choice for a moist interior application. An exterior varnish used indoors is actually a downgrade in protection.

This is a copy and paste from Howie…...

-- Alaskan's for Global warming!

View Tabletop's profile


139 posts in 1260 days

#4 posted 06-20-2016 03:58 AM

I’m with Mr UNIX, air in the wood needs to escape as the finish penetrates. You can get by without using a sealing product. Just apply a 1st coat of the finish and then sand most of it off. Your next coat should be bubble free, at least none from displaced air in wood. Good luck and be safe.

View MarkTheFiddler's profile


2068 posts in 2701 days

#5 posted 06-20-2016 12:19 PM

Howdy AlaskaGuy and TableTop,

AG, thank you. I appreciate the information but I’m getting a little nervous about what I did.

I truly thought I was doing the right thing. That small bathroom gets super steamy when my daughter takes one of her hour long hot showers. I’m not going to take all of that expensive finish off but perhaps there’s a finish I can apply for a top coat. Any advise?

TT, I think you just sold me on the sealer for every job that doesn’t involve linseed or tounge oil. Sanding off the the first coat is wasteful of the expensive finishes. I do a lot of sanding to smooth out the first coat. That’s wasteful in so many ways. Thanks to you and Mr. Unix.

-- Thanks for all the lessons!

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