I have a question about Shellac.
I have never used Shellac before but I am contemplating using it for a consul table I’m building out of soft maple. I would like to finish the table with one application of Danish Oil (Tried & True) followed by 4-5 applications of Varnish Oil (50% Tried & True – 50% Spar Varnish).
Will it be beneficial to apply a shellac to the parts in advance of these finishes. I prefer to to finish to various table parts i.e. stretcher, aprons, legs & table top prior to gluing the aprons to the legs (protecting against finishing the tenons and shoulders of the legs of course). Or is the shellac unnecessary?
I appreciate shellac is a sealer so given that, does shellac prevent oil finishes from penetrating the wood if applied after the shellac and can the two finishes be used in conjunction with each other?
Thank you in advance for any advice.
Replies
Shellac is a sealer/top coat.
It forms a barrier that other finishes can adhere to. Using an oil or other penetrating finish AFTER shellac is just a waste, it will not penetrate.
Unnecessary. T&T is a good raw wood finish and the FWW archives offer good info on this finish. Maybe others can chime in on the discoloration effect of a varnish on maple.
I think you would be asking for trouble using an oil finish over shellac, as indicated above. The shellac seals the wood and prevents penetration, so the oil finish would sit on top. Generally, people use a surface film finish over shellac. One of shellac's major virtues is it is compatible with most other finishes; it is used as a barrier between two finishes that are incompatible with each other, for example an oil based stain and a water based top coat (or a lacquer thinner based top coat that would dissolve the stain.)
I typically apply at least one coat of finish (my favorite being Waterlox Original) to as much of the piece as possible before glue up. It makes the glue squeeze out easier to remove, and I don't have as much trouble sanding and finishing into those pesky inside corners. I also use a lot of blue tape, both to protect glue surfaces when I apply the finish, and to catch squeeze out. Removing it and the excess glue is easier than removing glue with a chisel.
This is interesting to me, as I have used Waterlox Original on top of shellac (usually garnet, sometimes in multiple layers) with good results. I'm pretty ignorant of finishing techniques but tried this owing to its suggestion in Pekovich's Why and How book. Be interested to hear what you think.
Waterlox is sort or an oil finish, but really its a varnish -- an oil mixed with a polyurethane resins. So, typically the first coat or two of Waterlox soak into the wood fibers (like an Boiled Linseed or pure Tung Oil would), and then as it dries the resin starts building to a film finish. Subsequent coats are really about building the film. Applying Waterlox over shellac is similar...you're getting the polyurethane film but not those first oil/penetrating coats. I personally like Waterlox a lot, especially on projects where T&T linseed oil doesn't have enough protection...it has much of the warm penetrating oil finish qualities and offers some of the film finish protection without looking or feeling too plastic-y.
You are correct that Waterlox Original is really a varnish, now called by FWW a wiping varnish. However, I don't believe it contains any polyurethane resins. The info from them says it contains bakelite resins, which is an older varnish ingredient. One of WO's nice features is that it can be recoated later, which polyurethane can't ever be (after it polymerizes.) Nothing (even more poly) sticks to cured poly. Repairing poly is removing all of it and starting over. Whereas, repairing Waterlox is cleaning, sanding if necessary, and recoating. The cleaning can be difficult if lots of wax has been applied, as it will need to be completely removed.
thanks, jharveyb and mattk41; I've learned something!
Varnishes are made by heating oils (linseed, soy, tung, or other) with resins (poly or other). So you can call a varnish "oil-based" without it having any of the properties of a pure oil finish. Marketing can be misleading in the finish business.
Yes, it's a varnish, highly thinned. It has less than 2% linseed oil.
Thank you all for sharing your knowledge, experience and advice. Your comments have been informative and helpful. I will not be using shellac this time, only the Tried & True finishes.
JHarveyB thank you for your feedback on pre-finishing parts prior to assembly (1 coat) and the use of blue tape. Great idea.
Your assistance is much appreciated.
All the best
one last question - could I apply shellac over top of several coats of Tried & True original wood finish as a final coat/application to seal the finish and help make it more water resistant? Or is an application of a furniture wax a better idea?
Shellac is not very water resistant. I wouldn't put it on top.
The lack of water resistance is perhaps the biggest drawback to shellac in my mind. I would not use it as a top coat for that use.
Neither shellac nor furniture wax is very good for the final finish of a table. The wax will form white spots when it gets wet (tho they disappear fairly well with another application of wax.) Shellac is especially vulnerable to alcohol, since that is its solvent, and it never polymerizes like varnishes and oils do.
My understanding is that Tried and True takes a long time to polymerize; this is chemically dependent on oxygen. If you do cover it up, make sure you wait long enough for it to finish hardening.
When I finish table tops, I try to avoid needing wax. I use Waterlox Original (a wiping varnish), and smooth the next to last coat with 400 wet or dry lubricated with mineral spirits and then 0000 steel wool also lubricated. Then I apply a very thin coat with a very used men's handkerchief wrapped around a cotton ball (like a "rubber" used for French polishing) that dries quickly enough that it doesn't trap dust. The handkerchief gives off no lint, and has an extremely high thread count, so it leaves no texture to the finish like coarser fabric does, important since the coat will dry so quickly it might not level well. All the last coat has to do is fill in the minute, hazy scratches from the steel wool. Until I figured this out, I used wax to fill in the haze, which was not a good solution for a table. A coat this light may not fill in the scratches left from the 400 grit; the steel wool further refines the surface. Lastly, make sure you remove all the steel wool particles; steel, wood, and water can get ugly quickly if the water/steel combo gets through the finish.
The idea of finishing as much as possible before gluing was learned from a FWW article many years ago. Sometimes it can feel like it takes forever to get ready to glue up, but when you do, you're almost done.
Thank you all for your comments and kind advice. JHarveyB your experience and explanations are valuable and very much appreciated.
All the best
“[Deleted]”
From the T&T FAQs:
26. Can I use Tried & True over shellac/polyurethane/wood fillers/wax-based finishes
Shellacs – Tried & True products are compatible with shellac used as sanding sealer. Do not mix them together, generally Shellac is used as a pore filler, sanded down, and then Tried & True over top for the finishing coat.
This forum post is now archived. Commenting has been disabled