128 – Shellac Under Polyurethane


Voiceover:The Wood Whisperer
is brought to you by Powermatic, the gold standard since 1921 and by Rockler Woodworking and Hardware, create with confidence. Marc:This is a can of
Bulls Eye Amber Shellac. It says right on the back here, not recommended for use as a sealer under polyurethane. Am I the only one who when
told not to do something, pretty much does exactly the opposite? (lively music) I don’t do this stuff just because I have a rebellious streak. I want to know why. Maybe it’s the scientist in me, I just can’t take someone’s
word for something, I need to try it out for myself. If you’ve been in the world
of finishing for awhile, you’ve heard that said that you can’t put wax Shellac
under a polyurethane finish. I’m sure it comes down to the wax content providing adhesion issues
for the polyurethane but why specifically polyurethane? There are other varnishes out
there made with other resins. Will those bind just fine? Is it something with the
urethane resin molecules that don’t bind to Shellac
that has wax in it? That’s kind of the
question I want to answer. I want to use a few test boards using dewaxed Shellac as one test. Waxed Shellac is another and then just pure
polyurethane on the surface as a third test. Now, just as a little disclaimer, this is not really a true test. I’m only doing three boards. I just want to see if I develop
any adhesion issues at all using the wax Shellac. Let’s talk a little bit more about the Shellac products themselves. The most common brand
that I see in the stores is Zinsser Bulls Eye and it’s important to know the differences between the products
that they have available. Typically you’ll see two varieties of the regular Bulls Eye Shellac. One would be amber and the other will probably be labeled
either blonde or clear. Basically it just means it’s not going to bring
a whole lot of color to the wood when you apply it. Now this is the waxed version. It’s a three pound cut,
so it’s relatively thick and it’s good for
building coats of finish. The dewaxed product is
their Bulls Eye SealCoat. This stuff is only sold
in clear, there’s no amber or any other colors for this one. It’s just clear but it still will bring a little bit of ambering to the wood. Make sure you’re aware of that. This is sold in a two pound cut. It’s a little bit more dilute which means it’s more ideal
for sealing applications. At first coat, you generally
want to be pretty thin so it can soak in, dry quickly and then you could sand it and start applying your top coats. These are the two products I see the most. Now if you go to woodworking
stores or shop online, you’ll find Shellac flakes. Typically these are just dewaxed flakes that you mix with a certain
amount of denatured alcohol. Alcohol is the thing that
dissolves Shellac basically and you can make whatever
mixture you want. You can make three pound
cut, two pound cut, down to one and half pound cut sometimes just for spit-coats of
Shellac they call them. The primary thing that
you’re going to find people using this stuff for is blotch control. It’s for stopping especially something like cherry for instance
may have pockets of grain that absorbs more finish so it gets a little bit spotty and dark. Other woods like pine, certain
soft woods are like that. Cherry and maple, soft
maple, there’s a lot of woods that just don’t take finish very evenly. It’s important to apply a sealer first and then apply your top coats and that helps the stain
and your clear top coats look better on the surface. That’s why we’re going to use this stuff. Incidentally complete side note but I want to make sure
I throw out a little, a shout out for Charles Neil stuff. If you are looking for
some blotch control, Charles Neil recently came out with his pre-color conditioner. It’s a water based product and it works great for stopping blotching. You want to check that out. The polyurethane I’m using is Minwax fast-drying polyurethane. It’s just clear gloss, nothing special. It’s just the cheapest stuff I could find. Now before I apply any finish, I need to make sure we’re doing a sort of apples to apples experiment here. Remember I mentioned that the seal coat is at a two pound cut. That’s a little bit more
dilute than what we have in the amber Shellac which is three pounds so we need to make that dilution. Diluting Shellac is
actually kind of difficult because we’re talking
about the dilution itself is a volume of liquid mixed
with a certain weight of solids. Coming up with the dilution
can be pretty complicated and in fact that’s why
we develop the calculator in the WoodShop Widget and that’s exactly what I use to come up with this dilution. Let’s dilute a little bit of this stuff, I don’t need that much. Using the calculator, I told
it that I’ve got a quarter cup because it’s the smallest line on here. I’ve got a quarter cup
of a three pound cut and if you don’t see any episodes of the Wood Whisperer for a while, it’s probably because Nicole killed me for using her Pyrex measuring cup which by the way is not
going back in the kitchen. This is dedicated to the shop now, which means I’ll be going
to buy a new one later on. Now a quarter cup is of
course .25 in a decimal form and the calculator said in order to get these to a two pound cut, I need to add .11. That’s a little bit less
than half of .25, right? Half of .25 would be next line up on here would be basically an eighth of a cup. I’m going to go just
under an eighth of a cup. It doesn’t have to be absolutely perfect, just get it pretty close. Stir it up real well and I think that would be close enough. Since I’m going to use the same brush for both of the Shellac mixtures I’m going to start with the dewaxed and then take my brush to try to get as much
of the dewaxed Shellac out of the brush as possible but then use that in the waxed solution. If you go the other way, it kind of messes up the
experiment a little bit here. This first coat is
going to absorb readily. The raw wood is going to be very thirsty and of course using a
sharpie to label this piece probably wasn’t the best idea because it’s going to run but no big deal. Now for the waxed Shellac. You notice an immediate
difference in the color, that amber color that it brings to it when you use amber Shellac
is really, really nice. It’s like watercolors when you get that alcohol over the ink. Ignore the slight blue cast to my finish. Nothing to see here. The third one gets nothing but the poly. I’m not being too careful here
with my brushing technique. I’m just trying to get a nice even layer. Now I waited a couple of
hours to let the Shellac dry and give my polyurethane
coat on this piece a little time to dry. With my temperatures
it’s really all it takes is a couple hours. Shellac dries very quickly. The Shellac was probably
dry within a half hour, 45 minutes but I just gave it some extra time. Just going to remove the dust here with a just lightly dampen paper towel. Now each board is going to receive another coat of polyurethane, well the first coat for the Shellac boards and the second coat for the poly board. (lively music) You might be wondering why I only put on that one light coat of Shellac onto each of those Shellac boards. The reason is that’s exactly
how I would use Shellac. There may be an issue here where if you have a
significant coat of Shellac and then you try to put
poly on top of that. Maybe that’s where the problems occur. Bottom line is I don’t
care about that situation because I can’t think of any time that I’m going to have a
really thick layer of Shellac and I’m just going to pile a layer of poly right on top of it. Anytime I use the Shellac, it’s going to be as a sealer coat, a very light coat into the raw wood and then I’m going to come back with a poly on top of that
as my primary top coat. That’s really what I want to know because half of the time
that’s the questions that you guys are asking me is if I use Shellac as a sealer, will I have a problem with polyurethane. Hopefully that’s the answer
that we’ll get from this. (lively music) With just one coat of poly, we have a significant gloss build on here. That’s really one of the advantages of using a Shellac under coat is the fact that that first coat of poly looks pretty intense. I mean you could look at this board which has two coats of poly and it’s pretty much the same thing. The good thing about using the Shellac is that it dries so quickly. With one coat after one
day, we have the same build that it might have
taken us two days to get because we did two coats
of poly on this piece. Either way, I’m going to
give it a light sanding with 400 grit by hand and give it one more
coat on all three pieces. I think two brushed on
coats is pretty realistic and pretty close to what I
usually would do on a project. Let’s get started with some sanding here. I’m just going with 400 grit here. Here we go with one final coat. (lively music) All right that looks pretty good so the only thing to do now is wait, I want to give it three
or four days to cure. You can give it a little
bit longer if you want to but I think after three or four days we should have a pretty good idea of whether or not we’re going
to have any adhesion issues. (lively music) Now it’s actually been well over a week, I got caught up in a
couple different projects and I wasn’t able to get
back to this until now but about two days ago I decided I wanted to
come up with a couple ways to actually test the finish and see if we could somehow
pull the finish back up. Let me show you what I did, as you could see each board has a number of things stuck to it. I tried to think of what I
had laying around the shop so we’ve got some duct tape here, we’ve got some aluminum duct tape that you might use for
putting HVAC together and we also have epoxy that was literally just
dripped on to the surface. Now I don’t know what to
expect on any of these boards. Let alone determining a
difference between them so let’s go ahead and start
pulling these things off and just see what happens. This is our polyurethane board, just poly. Let’s start by peeling up this duct tape and see if any finish comes off. I don’t see anything at all on the surface so that was pretty good. This I might need a little help with. Now the aluminum tape,
it’s pretty sticky stuff, once again no damage there. Let’s see about this epoxy, I really don’t know what to expect here, I’m just kind of trying to … Hoping that I could just pop this off. Let’s try a nice sharp chisel. That’s a little bit better. Now here’s a spot where I actually started to chisel through the wood, what I want to look at is the area where the epoxy
just peeled up off the surface. I’m going to see if I
can’t get a better result with the bevel down. Here we go, that’s what I’m looking for. The epoxy definitely
pulled the finish right up and we’re left with bare wood here. Now this is the one with dewaxed Shellac and poly on top. Okay, no damage there with the duct tape. This stuff is tricky to pull off. I don’t really see any damage there so not really worried
about the second one, just try and pop those off now. I think we’re pretty much
seeing the same behavior here as we saw with the polyurethane only board so it’s pulling the finish up regardless. All right now I would … It’s hard to say with something like this because this is obviously
very non-scientific test but if there were any
major adhesion issues you would expect that
things like this tape, very sticky tape would pull that finish up at least a little bit
or some evidence of it. I don’t really see
anything coming up here. Let’s move on to the epoxy and see if there’s any
difference in how this pop off. All right, absolutely no difference there. What does this prove? Not a whole lot, realistically this is one very poor test to just see if we could
detect the difference in the surface that was treated
with the waxy Shellac first. I didn’t detect the difference, it behaved in the exact same way as the other two finishes
using dewaxed Shellac as a sealer and no Shellac whatsoever. I didn’t see any evidence of a weaker bond between the polyurethane
and the Shellac layer so I’m not prepared to necessarily say that we’ve hands down proven anything here but I think we have sort of
built a little bit of a case for the fact that that
is somewhat of a myth that maybe in some situations
with some polyurethanes or some Shellacs on some species of wood maybe someday, somewhere, someone will have a
problem with the binding of the polyurethane but if I don’t see any issues and really if you think about daily abuse and things like that, putting
duct tape on the surface and then peeling that back off, if there was adhesion issue I really would have to
think that we would peel a layer of finish off of there. Of course there’s a time factor here, maybe this is something that would happen a year or two down the line as when you would start
to see these issues occur but I can imagine over that period of time this finish all of the
sudden just peeling off if its bound are strongly
as it seems to be right now. The point here is to just
think about these things, I mean I just saw a recent
article in fine woodworking on finishing that specifically stated not to use waxed Shellac because it will cause binding problems with polyurethane and I’m just not seeing
the evidence of it. Maybe this video in and of itself will bring out the folks
who have a lot of experience and years of experience who can say, “You know what I’ve seen that before,” and they could let us know about it. I’m not refuting this just for the sake of being argumentative. It’s just finding an answer for myself so I can tell you safely in my shop if I’ve got a can of waxed
Shellac and I need a sealer and that’s what I want to use, I’m just going to use it even if I’m going to use
polyurethane on top of it. I don’t see any reason not
to at least at this point but I always keep my mind open because you just never know. Hopefully you enjoyed my
little non-scientific, pseudoscientific experiment. These kind of things are
always fun for me to do and I hope you guys enjoy them. Thanks for watching. (mellow music)

Danny Hutson

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