varnish over shellac OK?

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azra boo
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varnish over shellac OK?

Post by azra boo »

CONFUSED! I recently purchased a new cherry door for the front door of my home. After researching your site I opted for the following approach:

One finish that's often recommended starts with a light coat of oil, then a coat or two of shellac (choose a grade that gives you a color you like), and then use 2-3 coats of varnish over the shellac to make the finish more durable. This finish has become VERY popular since it came out in Jeff Jewitt's book "Great Wood Finishes

I have completed sanding, light oil, and 3 coats of shellac and it looks great. I sat down yesterday to apply the varnish, and in the fine print on the Varnish can it says, "do not apply varnish over shellac or laquer." Should I ignore the advise of the manufacturer? Perhaps I bought the wrong varnish? What do you advise? The door will be exterior so it definately needs a strong waterproof seal over the shellac.

The varnish I purchased is Cabot Semi-Gloss Spar Varnish.
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Post by stirdawg »

I am not an expert by any means but I always adhere to when a manf. says not to apply over a certain substrate. Perhaps a vinyl sealer and then the conversion varnish.
AsonnyA
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Post by AsonnyA »

Cabot did some testing and found there were some adhesion issues, when applied over shellac, even when the shellac was sanded to allow for gripping. Seems the chemistry was not compatible, in some way. To be safe, they recommend not applying over shellac.

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Post by atmoore »

Varnish will not adhere to Shellac, what you need to do is put on a coat of Zinsser sealcoat 100% de-waxed Shellac. Varnish and Poly can only be use over Shellac that has had the wax removed. Jeff Jewitts book should have made this distinction. Maybe you missed it. Zinsser also makes regular shellac so make sure you buy the can that says Sealcoat on the front with 100% de-waxed shellac printed just below the label. One coat should be all you will need.
azra boo
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Post by azra boo »

Thanks for your inputs. I struggled a bit with rough patches on my first coat of shellac so I ended up with between 2 and 3 coats of it on the door. If I now add a coat of Zinsser sealcoat shellac as you recommend, and then 2 coats of Varnish, do you think this will all be getting too thick and I may lose the cherry luster? Although I am not thrilled about stripping it all back to bare wood, would that be a better strategy at this point, in your opinion?
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Post by atmoore »

I don't think the extra coats will take away the luster of the cherry wood but you are the best judge of how it looks. I would continue finishing the door with 1 coat of sealcoat and 2 of varnish. If at that point you feel the tone of the wood is not to your liking then you can strip it and start over. But if it the wood looks find then you have avoided the task of stripping it back to bare wood. If you do decide to strip it back, then I would advise you put 1 coat of sealcoat then 3 coats of varnish. Good luck
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Bob Boardman
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Post by Bob Boardman »

OK Guys here are some facts. Varnsh will adhere to shellac - period!! In fact everything adheres to shellac.

Shellac is an alcohol based finish. Alcohol mixes with waterbased finishes (think scotch & water) as well as oil based finishes. The problem is that what is today called "varnish", is actually a finish with a lot of plasticizers in it, making it basically "poly". Up until Zinnsser came out with Sealcoat there was some issues with some finishers using regular shellac. I never had this problem myself, but there was enough of an issue that people started de-waxing their shellac, until Sealcoat came out.

The reason mfgr's don't want you to use shellac has nothing to do with adherence of the finish - it's because they want you to use more of their product. Instead of using a diluted coat of poly or varnish, as a sealer, people were using shellac. Hence the bogus warnings.
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Post by AsonnyA »

Thanks Bob. We need updating, from time to time.

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azra boo
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Post by azra boo »

Thanks Bob. Great to hear such good common-sense straight from the "horse's mouth"! I appreciate your guidance very much. One final question for you: you say ... instead of using a diluted coat of poly or varnish as a sealer ... and again the manufacturer warns: Do not thin. My understanding is that, following the concept I took from this web site that cited the Jeff Jewitt book, I am not diluting or thinning this varnish, I plan to use 2 coats full strength. Correct? Thanks again.
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Bob Boardman
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Post by Bob Boardman »

For final costs you're fine. Again, mfgr's want you to use more of their product which is a large part of the reason they say don't thin.
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Post by atmoore »

Bob, I'm a little perplexed, both Michael Dresdner and Bob Flexner (well respected authors in the refinishing business) recommend that you do not put varnish over shallac as they do not bond well together. That you use only shellac that has been de-waxed. That's where I got my information and one of the rules I've adhered to over the years.
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Bob Boardman
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Post by Bob Boardman »

I'm agreeing with both Bob and Michael, my comment was:
"Up until Zinnsser came out with Sealcoat there was some issues with some finishers using regular shellac. I never had this problem myself, but there was enough of an issue that people started de-waxing their shellac, until Sealcoat came out."
Sealcoat is a dewaxed shellac.
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Re: varnish over shellac OK?

Post by Bobcatz55 »

I would like to add a question to this forum. I have a similar project with mahogany doors and I’m getting ready to stain it with an oil based stain (Old Masters or General Finishes) but it’s too cold at night to varnish it. I may have to wait till spring time. Would it be wise to use shellac to seal it temporarily to prevent water marks/penetration until I can varnish? My varnish is Proluxe Cetol Door & Window.
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Re: varnish over shellac OK?

Post by Bob Boardman »

Shellac isn’t a great exterior finish. You could stain it now - even though temp isn’t ideal. Because you’re using oil base stain the oil will offer some (not a lot, but some) protection. When dry, you could apply a coat of a wipe on oil finish. This would hold until spring
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