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four2knapp 02-02-2014 10:39 AM

Clear coat over old shellac
 
I am working in a 1920s house with some original woodwork with it's original shellac finish. The homeowner put minwax oil stain over all and it looks kind of dull. It needs a clearcoat. Most of it is vertical surfaces...trim & doors. There are just 2 horizontal surfaces. Some areas <10% have alligatoring. On the 2 horizontal areas I was planning to use shellac then a poly.

Should I use more shellac?
Shellac then a poly?
or Poly? Oil or waterbased?

The stain is very dark so I am hesitant to use a water based

ToolSeeker 02-02-2014 11:04 AM

Zinzer makes a product called Clear Coat You use this over existing finish and it makes it compatible with other clear finishes. If I remember correctly shellac and poly are not compatible but I could be wrong on this. I really don't care for the water based finish. I guess I should say Clear Coat is a de-waxed shellac.

Gymschu 02-02-2014 11:57 AM

Toolseeker, I can't remember the compatibility issues either and I don't do a lot of clear finishes anymore. My guess is that I wouldn't put poly over top of shellac since shellac has a waxiness to it like sanding sealer. To be really safe, I would never put a clear over a clear unless it was the same product. This is an odd situation though with oil stain put over top of shellac. We need the expertise of Ric Knows Paint.

ToolSeeker 02-02-2014 12:06 PM

Yes he should be aquatinted with Clear Coat also. Curious to know if i'm close to correct. Kinda nice to have a back-up when your not sure.

four2knapp 02-02-2014 12:26 PM

Thanks for the quick replies. I will try a small area of shellac tomorrow. I the library they were 2 panels of fixed shelving removed and replaced with a newer sheet of oak plywood that was only stained. I put 2 coats of (zinser) amber shellac. It turned out beautifully and matched the sheen of the original parts.

four2knapp 02-02-2014 02:05 PM

1 Attachment(s)
Pic of the library- before. The wood in here is lighter than elsewhere.

ric knows paint 02-03-2014 10:08 PM

Quote:

Originally Posted by four2knapp (Post 1300539)
I am working in a 1920s house with some original woodwork with it's original shellac finish. The homeowner put minwax oil stain over all and it looks kind of dull. It needs a clearcoat. Most of it is vertical surfaces...trim & doors. There are just 2 horizontal surfaces. Some areas <10% have alligatoring. On the 2 horizontal areas I was planning to use shellac then a poly.

Should I use more shellac?
Shellac then a poly?
or Poly? Oil or waterbased?

The stain is very dark so I am hesitant to use a water based

Hiya 42knapp,

Just out of curiosity, how do you know the original finish is shellac? ...and a homeowner put a Minwax oil stain?...or oil finish over the "shellac"?

Shellac is a wonderful coating. Like all finishes, it has it's distinct advantages and disadvantages, but overall it is a very durable, hard finish - great for bookshelves, furniture, etc...Not so good tables and bar tops that could have standing water or even incidental exposure to spilled alcohol, though.

I don't understand the Minwax oil stain (or finish) over shellac though. That really wouldn't work all that well. If you decide to use shellac again, one of it's advantages is it can be applied over most existing finishes without damage...so, going over what's there wouldn't necessarily be a problem. I would not, however, put a poly over the shellac (existing or new). Toolseeker and Gymschu mentioned that in their posts and they were both dead-on.

Polys are decent enough coatings and provide plenty of protection in most residential exposures. Just as with shellac, they have their own unique advantages and disadvantages. One of the major disadvantages is they don't always play well with existing coatings - shellac and sanding sealers are 2 types of applications that shellacs sometimes have problems with. With shellac this issue is the naturally occurring wax that is present within the film and can wreak havoc in the poly's ability to both adhere and cure properly...with more common sanding sealers, it's the chemical soaps that are added to allow for sealers to sand easily that, again, interferes with a poly's ability to adhere and cure properly.

Personally, if I was doing this and knew the original finish to be shellac, I'd wipe the surface clean with mineral spirits to remove any waxes or un-cured oils that may have found their way to the surface of this woodwork over the years - then lightly sand with a fine paper. Use a tack cloth to remove any sanding dust. Unfortunately the areas that have alligatored are going to have to be sanded smooth - probably start with a medium grade paper (or sanding sponge) and followed with fine then ex fine...just enough to remove the texture and have a nice, slightly profiled surface for finishing. Again, remove all sanding dust with tack rags.

Then, I'd apply 1 or more apps of amber shellac by brush or spray (if you've never used shellac before, practice a little on spare boards to get the feel of the flow and drying of shellac - it's different than applying varnishes and polys). If the shellac is too high of a gloss, you can rub it out with oil and pumice (or rottenstone) and 400 - 600 wet-or-dry paper - or just rub dry with polishing cloth found at most independent paint stores.



Not everybody is gonna agree with me here but IMHO I think woodwork from the 1920's deserve a nicer looking finish than polys provide...

Best of luck to you and let us know what you decide - some before and after pics would be great.

P.S. to Gymschu and Toolseeker - I think the product you were describing is "Seal Coat" by Zinsser (not clear coat)...Seal Coat is a "de-waxed", 2# cut shellac and would be fine as a sealer for poly...

chrisn 02-04-2014 03:21 AM

quote"
Not everybody is gonna agree with me here but IMHO I think woodwork from the 1920's deserve a nicer looking finish than polys provide...


I do:yes:

joecaption 02-04-2014 05:24 AM

Try a test spot with a lint free cloth with some denatured alcohol to see if it will soften and level out the cracked areas.
That will clean it and save a lot of sanding.
If it works going right over the soften old stuff with new shellac will bond the two together.

ToolSeeker 02-04-2014 06:21 AM

I also agree I think that old wood work is beautiful when cared for. And you are correct on the name. Thanks Ric.

four2knapp 02-04-2014 07:45 AM

"Just out of curiosity, how do you know the original finish is shellac? ...and a homeowner put a Minwax oil stain?...or oil finish over the "shellac"?"

I am wrong about the shellac as denatured alcohol did not dissolve/soften it. Although it may have been used in that library. The new/current Homeowner wiped minwax stain over all to hide the scratches and wear. Which it did, but left things dull in spots. It has a lot of partially worn (in the finish) around door knobs etc.

On my way over there now. How does one check to see if it is a varnish finish? And can go over varnish (after prep) with another varnish?

"Not everybody is gonna agree with me here but IMHO I think woodwork from the 1920's deserve a nicer looking finish than polys provide..."

I agree!

Jmayspaint 02-04-2014 08:08 AM

If aggressive rubbing with DN alcohol does not soften the finish you can also deduce that it is not a water based clear. So it's most likely oil varnish.

Should be good to go with an oil varnish after sand and clean. Do a test piece to be sure.

Gymschu 02-04-2014 11:40 AM

Quote:

Originally Posted by four2knapp (Post 1301519)
"Just out of curiosity, how do you know the original finish is shellac? ...and a homeowner put a Minwax oil stain?...or oil finish over the "shellac"?"

Um, no offense four2knapp, but YOU gave us that information, lol. Easy to misidentify clear coats. I've been doing this stuff for 34 years and still can't tell you which clear coat is compatible with another. Varnish is exceptionally hard, but, I can't give you a litmus test to tell if it actually is varnish or not……anyone?

Here's all I could find about testing for varnish:

Varnish
How do you determine if you are dealing with a varnish finish? The quick answer is that no solvent will dissolve varnish. Various solvents can destroy it but it cannot be dissolved. For example, paint remover and lacquer thinner will both destroy it but not remove it. To test, put a bit of lacquer thinner or paint remover on a hidden piece of the surface and watch what happens. If it's varnish it will become crinkled and cracked. But when you try and brush or wipe it off, it will not come off. To fix the damage on a varnished piece will take a great deal of time. Your choices are sanding down the piece and refinishing or using a specialty solvent and refinishing the piece.

ToolSeeker 02-04-2014 07:08 PM

That is why I find the Seal Coat so good. If you don't know what a clear finish is use the seal coat and you can put almost any other clear coat over it.

kt82 03-30-2014 01:53 PM

Quote:

Originally Posted by ToolSeeker (Post 1301702)
That is why I find the Seal Coat so good. If you don't know what a clear finish is use the seal coat and you can put almost any other clear coat over it.

the info says the Clear Coat will be a stain preconditioner
when spraying how much denatured alcohol is needed to keep it from drying in the tip? I was using a 3 10


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