Just wondering if anyone has had problems putting shellac over a wipe on poly? The reason i ask is im finishing up a laser engraved plaque ive made out of solid cherry and just put on a thin coat of wipe on poly. I stupidly forgot about the rather intense smell it has and im gifting it to someone who is sensitive to this sort of thing. I have a little dewaxed shellac left over from a previous project which i thought about using just to cover up the smell a bit. Think that will give me problems?
I’ve never tried, but I suspect shellac will not adhere or bind well, and will flake or peel as it dries & shrinks on top of the poly. Just an educated guess, so try it out on a discreet area if you can.
I would think the smell would dissipate with time. How about a scented furniture polish? Lemon or pine may be preferrable to burnt poly??
If it was just one coat of poly likely the shellac would work. The oil based poly and shellac aclohol base are compatible so you can only try.
When I build boxes that are closed I use lemon flavored was on the inside for the very reason you mentioned about the smell. Poly takes about a month to fully cure and if enclosed inside a box you get the unpleasant odor every time you open the box.
You could finish with poly and let it cure and then apply some paste wax to help eliminate the smell. In the future you can use water based polyurethane. Just use the water based sealer, sand because it raises the grain, and then apply the water based polycrylic. The water based does not have a lingering odor. Since you already put oil poly the water based would likely not work but you could try. Just try the sealer first and if it does not stick you can sand it off.
No guarantees here but shellac is noted for its ability to go on just about anything. It’s used to seal knotty wood to keep the sap from affecting subsequent painting.
I used to be a luthier in the days before all these great water-based products. One of the early finishing steps was pore filling which was done with an oil-based paste filler. Following that I (we, since this was common for many luthiers) would apply light wash coats of shellac before nitrocellulose lacquer.
Both with guitar making and my recent endeavors to replicate Stickley finishes on my furniture making, I’ve use shellac as an undercoat before applying oil based stains to prevent too much saturation into the wood such that the pores are contrasted.
All that said, I have not used shellac in combination with polyurethane. But one thing to consider is that if it’s still smelly when you shellac it it means the poly is still outgassing which could lead to problems if gasses accumulate under the shellac.
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Shellac can go UNDER poly, but not on top. Schlack soaks into the wood to some degree and even second and third coats of will bond with the previous. Top coats like varnish, poly, ect, form a shield over and while they can bond to each other with additional coats, shellac will not bond well at all. it will dry, and appear to cure, but it will not bond enough to make for any long term usage.
Sand off the poly; apply a coat or many coats of shellac and then put a finish topcoat of your choice on the project.
Learned the hard way…too many times.
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Dewaxed Shellac can be used on top of poly. Sand the poly though, not off but slightly to create a microscratchy surface.
Waxed shellac will never adhere to Poly.
The shellac is bristle at the end, and sensitive to alcohol, a wet glass of Whisky will leave a print. Therefore I strongly recommend to wait for 2 weeks, the poly does not smell forever. But the shellac always stays extremly sensitive to scratches and booze.
The days where shellac was used as a top finish are long gone for a good reason.
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Thanks for everyones input. I decided to just keep going with a few coats of the wipe on poly and ill just let it air out for a while outside. I do really like shellac but even in ideal situations i struggle a little getting a nice result let alone less then optimal conditions like this. I dont know why but ive tried shellac from the can and making it from flakes but its always like it starts drying to quickly or something when applying and the finish ends up all streaky and uneven looking.
I would hit it with a light sanding with 220 grit.
yep, shellac is tricky. Always when I walk through our local Hyde Collection I need 15-20 minutes just to look at a chair made by Thomas Chippendale. What a carpenter! He -and his collegues- were happy to have shellac, and what did they make out of it! Not even sand paper was invented yet, the did all with shark skin. How much knowledge is lost in time.
Shellac is cut with mineral spirts and if you thin it down about 50% for the final two coats, I usually apply a total of 4, it smooths out nicely. Just a trick to help I hope.
Sorry, I meant to add that I use a foam brush, wide one, and drag across the finish in a final pass from one end to the other without stopping and keeping the brush at as low an angle as possible.
Usually flaked shellac is cut with aclohol. I dont know about mineral spirits. I know the Zinsser Universal Sanding Sealer (dewaxed shellac) is made with aclohol. I use that all the time as a sealer. The dewaxed shellac is a good sealer for both oil and water based top coats.
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