Shellac over BLO immediatly - what happens?

[jonathan snyder]

Hi, folks,

I just saw something about waiting for BLO to cure before applying shellac. Why is that an issue, and what happens if you shellac after the BLO has been absorbed but before it fully cures?

Thanks
Jonathan

[Steve Schoene]

Jeff Jewitt speaks of doing this, so I don't doubt that it works. One caveat is that the BLO is applied very sparingly, just to pop the grain, not flooded on and wiped off as you would do in starting to use it as a finish. Personally, I wait for the BLO to cure overnight (which isn't fully cured) before applying shellac, whether it is necessary or not.

[Jim Becker]

Jewitt's article is in the October 2006 issue of Fine Woodworking on page 52. Steve is correct that the BLO is applied in a quick, thin layer to pop the grain and further function as a lubricant for padding on the shellac. Please note he uses a "waxy" shellac as well as paste wax...this is not a method to use under a polyurethane-based varnish top coat. It IS the finish.

I tried a modified form of this process when I finished my tiger maple candle stand not long ago, at least for the legs/spindle, with great results. On the top, I allowed the oil to cure for a few days before applying de-waxed shellac as I knew I had to top coat with USL for kid-friendly "durablity"...

[Jerry Olexa]

I read that article and it was stressed that it be a thin coating. I personally would be very hesitant to do that, I like to Flood on the BLO and after a wipe off ,let it season (dry) for as much as a week. Just my opinion. I'm usually topcating w shellac and feel they are not compatible unless BLO is dry . My 2 cents

[Derek Foster]

I have just been using that method on my Ash Coffee table. It works and looks great! The BLO is supposed to be used sparingly though. JJ even says to use a scrubby pad after application to help soak up some of the oil.

I have had no troubles with this method. It is very fast too.

[John Kain]

I've read that article as well.

I don't see why a thick or thin BLO coat should matter. His purpose for using a thin coat was for speed of drying. However, Shellac is porous and should allow for good oil drying over time if you aren't worried about time factors.

[George Tokarev]

Apples and oranges. One cures by oxidation, the other hardens by evaporation of the solvent. Some people use a mix of BLO and shellac as a friction polish, 1/3 BLO 1/3 shellac (1# cut) and 1/3 mineral spirits. If you use the shellac, it retards the cure of the BLO by masking away some oxygen.

Aside from the amber color added by the BLO, it does the same as any other finish, diminishes the light scatter. That's what makes the contrast higher, which we call "popping the grain." You can see this in the difference in depth of the look when the oil is fluid, lying on the surface, and when it's sunk in and cured.

Since oil and water (or alcohol) mix poorly, it also slows the uptake of the shellac into the wood, which is why a cured surface will build faster. If using a mix as a friction polish you're really heating the oil in deeper, promoting cross-link curing with heat, and evaporating the solvent more rapidly as well. That's why rag marks show so quickly in a poorly applied friction polish versus a French polish, where the "coats" of shellac are many and thinner.

[John Kain]

Apples and oranges. One cures by oxidation, the other hardens by evaporation of the solvent. Some people use a mix of BLO and shellac as a friction polish, 1/3 BLO 1/3 shellac (1# cut) and 1/3 mineral spirits. If you use the shellac, it retards the cure of the BLO by masking away some oxygen.

Aside from the amber color added by the BLO, it does the same as any other finish, diminishes the light scatter. That's what makes the contrast higher, which we call "popping the grain." You can see this in the difference in depth of the look when the oil is fluid, lying on the surface, and when it's sunk in and cured.

Since oil and water (or alcohol) mix poorly, it also slows the uptake of the shellac into the wood, which is why a cured surface will build faster. If using a mix as a friction polish you're really heating the oil in deeper, promoting cross-link curing with heat, and evaporating the solvent more rapidly as well. That's why rag marks show so quickly in a poorly applied friction polish versus a French polish, where the "coats" of shellac are many and thinner.

Great post, thanx for the info!

[Jerry Olexa]

Apples and oranges. One cures by oxidation, the other hardens by evaporation of the solvent. Some people use a mix of BLO and shellac as a friction polish, 1/3 BLO 1/3 shellac (1# cut) and 1/3 mineral spirits. If you use the shellac, it retards the cure of the BLO by masking away some oxygen.

Aside from the amber color added by the BLO, it does the same as any other finish, diminishes the light scatter. That's what makes the contrast higher, which we call "popping the grain." You can see this in the difference in depth of the look when the oil is fluid, lying on the surface, and when it's sunk in and cured.

Since oil and water (or alcohol) mix poorly, it also slows the uptake of the shellac into the wood, which is why a cured surface will build faster. If using a mix as a friction polish you're really heating the oil in deeper, promoting cross-link curing with heat, and evaporating the solvent more rapidly as well. That's why rag marks show so quickly in a poorly applied friction polish versus a French polish, where the "coats" of shellac are many and thinner.

George: Excellent post. Thanks for the insight...

[Matt P]

I thought shellac was used as a sealer.. and therefore is non-porous?


I've read that article as well.

I don't see why a thick or thin BLO coat should matter. His purpose for using a thin coat was for speed of drying. However, Shellac is porous and should allow for good oil drying over time if you aren't worried about time factors.

[Jim Becker]

Matt...the "definitions" are quite confusing. Shellac is an excellent barrier coat/sealer and is also a great moisture barrier. (Moisture...NOT water...there is a difference) Like nearly all finishes, it's also porous...which flies in the face of the previous. While it will retard oxidation/curing of the oil under it, it will not stop the process. But as previously stated, working with minimal oil is important. Further, BLO is fine, but never try this with real Tung Oil...