Blisters in lacquer finish

[douglas hyde]

I have a dining room table that has the Deft brushing lacquer on it and I've gotten blisters and hot spots in it. Some are showing up on the second coat where they didn't show up on the first coat. I've sanded the lacquer finish smooth. Now should I put sanding sealer over the whole top and start again with the lacquer or could I use another type of finish such as polyurethene?

[jerry nazard]

Doug,

What is under the lacquer?

[douglas hyde]

That's a good question. I am unsure of the original finish and I did not strip the table down to bare wood so I could preserve the color. I did lightly sand the piece and repaired a few spots which I then sprayed with shellac.

[Mike Henderson]

If they're small bubbles, it's caused by outgassing of the lacquer thinner after the surface has skinned over. You can address it a couple of ways.

1. Do thinner coats.
2. Use a retarder.
3. Make sure you're working in a cool place. Absolutely do not let any sunlight hit the surface.

I usually get it in the first coat because I put that coat on thick. I let that coat dry then sand with my ROS and 320 grit sandpaper. Then shoot thinner coats.

If it's big areas, you probably have a problem of interaction with the original finish. Strip, lightly sand, then put a coat of dewaxed shellac on before you put your final finish on.

Good luck.

Mike

[douglas hyde]

My problem is not exactly bubbles, it looks more like I've put some sort of finish stripper on it. Plus, I'm using brushing lacquer rather than the spray.

[Jim Becker]

Putting lacquer over an unknown finish is a very risky thing. The solvents in lacquer can craze the previous finish and cause all kind of disappointing problems. And since you're brushing, that means a thicker layer that takes longer to flash off...meaning more potential for dissolving the previous finish. Like Mike, I think you're going to have to strip and start over from bare wood if you want to use that type of finish.

[douglas hyde]

Thanks guys for all the help. I've got sanding sealer on the table now and I'm not having any problems with it. Do you think water based poly on top of the sanding sealer would work? I'm needing something that will dry fast.

[Jim Becker]

Um...what kind of "sanding sealer" are you using and did you put it under the lacquer? You should only use lacquer sanding sealer from the same manufacturer under lacquer. And as far as using off-the-shelf "sanding sealer" under anything else...it's a waste of money and due to the inclusion of certain ingredients, such as stearates (to make sanding easier), it makes for a soft underpinning to the top coat. Further, it may be incompatible with any water borne finish. If you want to use the locally available water borne "poly" (presumably Minwax Polycrylic), you'll want to put a barrier coat of de-waxed shellac over the "sanding sealer" to insure you don't have adhestion issues. Anything with polyurethane resins in it hates to stick even to itself without proper preparation and water bornes also have limits to what they will stick to, too.

The bottom line is that you cannot use "just any" finish over "just any" previous finish product...there are combinations that work wonderfully and others that set you back to stripping and starting over.

[douglas hyde]

Thanks Jim. The sanding sealer I used is Zinsser Bulls Eye Seal Coat Universal Sanding Sealer 100% wax free. The Minwax water based polyacrylic is the finish I was referring to that I wanted to use. I actually have two coats of that on over the sanding sealer and so far so good. My understanding is that you can use the shellac sanding sealer on any finish and top coat with any type of a finish. Is this true? Thanks in advance for all your help.

[Ed Peters]

Plus, I'm using brushing lacquer rather than the spray.

Just an aside to the "Brushing Lacquer" title on the can. That is the manufacturers dodge to be able to sell the product in a retail outlet as it is currently formulated. With the VOC content, spraying is considered "Ungreen". It is however, the same material we have been spraying for years.

Ed

[Jim Becker]

Zinsser Seal coat is absolutely a universal barrier coat. I think calling it "sanding sealer" is a pure marketing ploy, however... It's just dewaxed blond shellac. Very little sanding required. In fact, I generally hit it with 320 or 400 just to to get rid of any whiskers. I use it by the gallon under the water borne finishes I spray as well as by itself. It is indeed compatible with the Polycrylic.