Shellac under Polyurethane

[Jeff]

Conventional wisdom says poly should only be applied over a 100% dewaxed shellac seal coat in order to prevent adhesion problems. Well, how about this semi-scientific report using poly over non-dewaxed shellac?

http://thewoodwhisperer.com/shellac-under-polyurethane/

No apparent adhesion problems, but it is oil based poly (compatible with waxed shellac?), not water-borne poly. Maybe that's a key point in this case. :dontknow:

An interesting answer to the statements "You can't do that" or "don't do that". :thumbs_do

Any similar experiences out there? Maybe Howard Acheson also will provide some guidance to us.

 

[Dragon]

Waxed or de-waxed shellac huh? Well, I bought a can of Zinsser Seal Coat de-waxed shellac from one of the BORG's a couple weeks ago to use on some well spalted Maple as a sealer and stabilizer. When I went to sand it down, it gummed up my paper like nobody's business.:BangHead: Don't know if I did something wrong or not but I used it right out of the can, no thinning, etc. It dried nicely but doesn't sand well at all. As for using poly over it, that "was" going to be my plan but after reading this thread, I'm not so sure about that. :dontknow:

Anybody got any hints, tips, ideas, whatever, I'd sure welcome some advice here.

 

[Jeff]

David,

That's odd. The Zinsser SealCoat is a 2# cut out of the can. They claim a 3 year shelf-life before it goes south. The date of manufacture is on the top of the can.

Assuming that it wasn't a real thick coat and had dried sufficiently then it should've sanded okay. I've read that the "stearated" papers are less prone to gumming up, but I have no first hand experience with them. However, the finer grits of plain stuff (150-180) from the BORGs does tend to gum up when sanded too vigorously without very frequent dust removal.

 

[Dragon]

Jeff, thanks for the info. No date on mine but there is a Lot. code of S 02239. Guess I could email them as to what date that references. I may have applied the stuff too heavy. I haven't used shellac since high school when I made a toy box for my pet dinosaur. Might oughta read up on the stuff a bit as I do like the end result I got after many hours of sanding. Again, thanks for the info.:icon_thum

 

[Bill Clemmons]

Waxed or de-waxed shellac huh? Well, I bought a can of Zinsser Seal Coat de-waxed shellac from one of the BORG's a couple weeks ago to use on some well spalted Maple as a sealer and stabilizer. When I went to sand it down, it gummed up my paper like nobody's business.:BangHead: Don't know if I did something wrong or not but I used it right out of the can, no thinning, etc. It dried nicely but doesn't sand well at all. As for using poly over it, that "was" going to be my plan but after reading this thread, I'm not so sure about that. :dontknow:

Anybody got any hints, tips, ideas, whatever, I'd sure welcome some advice here.

As Jeff mentioned, the SealCoat is a 2# cut in the can. When I use it as a sealer / washcoat I always cut it to 1#. It goes on easy, dries quick, and I've never had a problem sanding. I use 320 grit just to knock off the high spots.

Bill

 

[Jeff]

Jeff, thanks for the info. No date on mine but there is a Lot. code of S 02239. Guess I could email them as to what date that references. I may have applied the stuff too heavy. I haven't used shellac since high school when I made a toy box for my pet dinosaur. Might oughta read up on the stuff a bit as I do like the end result I got after many hours of sanding. Again, thanks for the info.:icon_thum

Maybe you got a can of older stuff (before they started putting the date of manufacture on the can)?
If the "lac acid" esterification process has begun then it'll be tacky/sticky and sure won't sand well. I've probably had 3 quart cans of SealCoat over the last 3 years and they've all had a "Date of Manuf." on the can lid. I can't find a Lot # on my current can. :icon_scra

There's a "Contact Us" tab at the bottom of the Rust-Oleum link.

http://www.rustoleum.com/

 

[danmart77]

Jeff
I saw your write up about Zinseer Seal Coat and sanding gum up. I have a can on the bench that's dated(8 months old). I also have a bag of dewaxed flakes. So I mixed it up a fresh batch and applied the canned stuff to one side of the walnut board and the flake mix to the other. I'm going to wait a day before I sand with 320grit then give you some feedback.

In the past I have found the Seal Coat to be pretty good but it just never seems to dry as quickly as the mix from flakes and more importantly it just isn't as clear as the stuff you mix and filter. No comparison when it comes to clarity in the jar. Zinseer has to add something to the mix to get it to sit on a shelf and continue to be good after 3 years. The stuff I usually mix is not useable after about 12 months. I don't use it after 6 months. The stuff is so cheap it just doesn't make sense to have a question about the adhesion or the dry time.

Lately, I have gone back to Buttonlacs(dark stuff) with some wax. After dissolving the flakes the sediment goes to the bottom and I pour off the dark clear portion. I have used this method for 25 years with every imaginable varnish over it and I have touched up the varnish with a top coat of buttonlac(yes over or under) with no negative results. Its just so easy to use.

Will get back on the sanding test results

dan

 

[Dragon]

Looking forward to the update on your testing. Looks like I may have to start "making" my own shellac.

 

[shopsmithtom]

I have used poly (oil based, not water) over regular (waxed) shellac without any problems but you must sand/scuff to give it a good physical bond. If you don't need the amber tone, the Zinsser's sanding sealer is dewaxed so that's even better. From my experience, all shellacs seem to gum up sandpaper more than other stuff.

 

[michaelgarner]

Ya I watched that too. But he used only one coat so basically he made a conditioner for that maple piece. If he really wanted to see if there would be problems then do four or five coats then throw poly over it and let the project set for a year and see what the seasons do to it. I'm all for debunking urban myths woodworking or not. But I feel that he didn't give a good representation on how Shellac is normally applied on a project. (which is multiple coats building depth)

 

[danmart77]

I guess this is a test results reply and a little extra. Maybe more than a little to add to the discussion.

From my earlier post I was comparing the Zinseer Seal Coat and some flake mixed shellac. The shellac I am mixing is a blonde dewaxed type. I mixed it to a 2lb cut to make the initial test equal in my simple way.

Questions:
1. Does the shellac have an adverse effect on the adhesion of the poly?
2. Is there a difference in the seal coat and the flakes?
3. Is the convenience of the ready mix worth the doubt/wonder about the age of the shellac?
4. Is there a price difference? Are you saving money with one over the other?

1. Does shellac have a negative effect under poly? NO. Why not err on the side of caution and use the dewaxed stuff like Seal Coat or dewaxed flakes. Skip the Amber/Orange shellac you don't need it. If you like the warm glow of Amber shellac with wax in it - just take your blonde shellac and add a little alcohol soluable dye to it. Same results and you don't have to buy 2 types. Cheaper. No wax to consider. Additionally, as another person mentioned- scuff the shellac lightly to increase the tack of the poly.

2. Is there a difference in the SC and flakes? Yes. Once you mix your own flakes you will immediately see the difference in clarity. The SC is cloudy from additives and the flakes after being dissolved are clear as glass. Which one do you want? Cloudy or clear. Yes its true that the SC does dry with a nice clear film -- how clear? Have you campared the two? I have. Sorry it wasn't significant enough to sway me one way or the other -- so that one is a draw.

3. Is the age of the shellac a concern? You bet on this one. Here's where the pitch for flakes can be strong. You mix up any amount you need at the time you are using it. The flakes I buy are such a good quality that I can grind them to a powder like form, pour them in a jar with denatured alcohol and the mix will be ready in 3 hours. If I am thinking ahead I skip the grind and put them in the jar over-night and they are ready in the morning. The shellac is good for about 6 months but... I might add it is not as good at 6 months as it is the first week of the mix. How do I come to that conclusion? Mostly sanding and drying experience. Something like this test.

Test Finding 27-28 Sept:
Shellac Flakes when sanded came off the board onto the 400 paper in dry powder. Seal Coat gummed up the dry sand paper. Yes the mix is easier and the results were clear on that test. I might add, both films were applied with a rag and both films were 2lb cuts. Is this important for me? No. I never sand shellac for results with dry paper. When I sand dry shellac I always lubricate the surface with a mix of mineral spirits and mineral oil in a small squeeze bottle. I shoot the stuff on the shellaced surface and sand with 400/600 paper to level or repair shellac defects. The paper doesn't clog unless it is bad shellac. After sanding, wipe down with mineral spirits, let it dry and you are ready to apply another coat of shellac. Repeat until you have the surface you desire.
So far I can't make a case for the SC.

4. Are you saving money by purchasing SC or flakes? I don't think so. Here's my thoughts:
You pay about 10-12 bucks for the quart can of seal coat. A gallon is 40-48.00
Flakes are 20-22 for a pound and the denatured alcohol is 15-16.00/gallon. So one is 48.00 for a gallon and the other is 38.00/gal. Big Deal.

Edit: the flakes are more expensive. I forgot: at the end of the flake mix you have a 1lb cut gallon not a 2lb cut like the cans of shellac. So the flakes will cost more. Hopefully you won't have to toss the unused stuff.

My 2 cents:
If you have some SC go ahead and use it up.. its good stuff. Next time try some flakes. I think most guys I have worked with that see me using the flake mix are encouraged to try it for their work. I don't know anybody who has gone back to the can.
Source: http://shellacfinishes.com/

Hope this stirs up some thoughts. I inserted this as a reply and not a new subject so it would be buried in a thread for those interested in the shellac finish.

I am currently working the final leg of a desk project. This is the lid that I have NOT FRENCH POLISHED. The shellac is applied with a cotton rag dipped in shellac and applied like a brush. There are 4 coats at present - each sanded with 600 paper between coats. I will need to apply many more 1lb cuts till I get the surface I want.

So long
dan
danmart77

View image in gallery​

 

[Joe Scharle]

Good write-up, Dan. First a comment: I'd quit right there on your desk, 'cause I hate finishing and it looks great to me :tinysmile_tongue_t:.
But I have to ask,"Can you really see a difference with a lot more coats?".
And why not just use laquer if you want a deep clear coat?
Thanks for sharing,
Joe

 

[danmart77]

Reply to Joe's questions:
Can you see a difference in many more coats? Not really but.... I use the shellac to final fill the grain pock marks. Between coats you can polish/sand down and use the next shellac coat to level. Done multiple times, you get the final finish you want.

Lacquer or shellac? I have used lacquer but I have been using shellac for 30 years or more. I can make shellac do things I can not make the lacquer do. Now I have an "artist's box" full of dyes and colors. By using shellac I can continue to tone and color the film and match the wood in my shellac/dye mix. I like to French Polish but decided this time to go a different route. Choice.

The piece that I am building is from the 1760-1790 time era. To the best of my knowledge, there was no FP going on in Penn. at that time or for that matter anywhere else in the colonies. I am not a dead purist on a rampage, if I was I would be using Seedlac or one of the "dirtier" lacs like they did in the past. No, I'm using a purified shellac mix for my convenience here in the 21st century.

Lacquer: to date I have not been skilled enough to take the cold look out of lacquer that I see. I have not seen too many pieces built with a lacquer finish that I can not spot. There have been a few beautiful pieces done in lacquer and touched up that watered my eyes but I don't know how to do it and the guys that did the work started out explaining how they set up their spray guns. I like spray guns, I have painted lots of cars and airplanes but when I am in the woodshop I don't want anything to do with that skill set.

I don't feel stuck in a hole with my finishing methods but I am at a point where I am trying to expand my "spirit varnish" vocabulary.

Spirit Varnish(shellac) to date:
Recently, I am adding some copal/B-72 to my shellac mix to harden the finish. Far as I can tell its working. I am also fooling with other resins and gums but its a slow process and like carving it takes patience and commitment to get to the top. So... that's a little background and not a sales pitch.

 

[Bill Clemmons]

On the subject of shellac, the latest issue of Fine Woodworking came today and there's a pretty good article on p.48. It's mostly about the production process in India, but also some other discussion that is relative to this thread. Just FYI.

Bill

 

[Dragon]

WOW Dan. Lots of information and advice there. You've swayed me to use a lot more shellac in my finishing processes. Mucho thanks for you investment of time, talent, and expertise here, not only in your woodcraft but your writing skills as well.:notworthy:

 

[woodlaker2]

+1 on the FWW article. Read it last night and it offers ome great insights into the making of shellac and the different types/grades.

 

[Marlin]

On Dans numbers per price of mixing your own shellac vs SealCoat.

I thought SC was a 2 pound mix? So the price would be much higher then mixing your own? One of the reasons I bought SC was its premixed and good for someone with limited exp with Shellac. So I may mix my one one day but I always had SC because of its price point.

Right now I use it for washing before I stain/dye so color is not a real issue for me.

 

[danmart77]

Marlin when I did the math more closely, I found the Seal Coat at 44.00 for gallon to be lower than 20.00 for the flakes and 15 for the gallon of DNA(35) which gives you a gallon of 1lb cut.

The SC comes in a 2lb cut so you could have 2 gallons of 1lb cut for 44.00 and the flakes would be 20 x2 40.00 and 15 for the DNA for a 55.00 2lb cut gallon.

SC is cheaper.

The flakes allow you to have FRESH clear shellac that dries better IMO than the SC.


Convenience and choice.

Hope this is a little bit more clear.

dan

 

[Howard Acheson]

As far as I know, Zinsser is the exclusive importer of all the shellac flakes sold in the US. They are also the sole manufacturer of liquid shellac in the US. Zinsser sells shellac flakes in bulk to packagers who break it down into smaller quantitiy packages that get resold by retailers.

 

[danmart77]

Howard I would be curious where you found that piece of information or maybe if you could post a little more information. It sure is a surprise to me. I've never heard that before.

A few years back, I bought slabbed shellac in these block pieces. They were like Hershey candy bars. They were imported by an artist supply company in NYC.

Maybe this is like the hide glue business? There is only one producer of glue in the entire US but commercial suppliers use imported glue.

Interesting stuff
dan