Anyone have experience with using a shellac washcoat under pre cat lacquer? If this will work it’s easier for me to do it this way instead of having to first spray a thinned down coat of lacquer. I wanted to use a washcoat to deal with the blotching that might happen in maple. Thanks for your help.
Discussion Forum
Get It All!
UNLIMITED Membership is like taking a master class in woodworking for less than $10 a month.
Start Your Free TrialCategories
Discussion Forum
Digital Plans Library
Member exclusive! – Plans for everyone – from beginners to experts – right at your fingertips.
Highlights
-
Shape Your Skills
when you sign up for our emails
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. -
Shop Talk Live Podcast -
Our favorite articles and videos -
E-Learning Courses from Fine Woodworking
-
-
Replies
No this will not work. Not meant to be meme, just that I have been there before.
This is two part over one part finish. The two part will soften the exiting finish and keep the new finish from drying properly. A sticky gooey mess, alligatoring if dries, bad thing will happen.
You can do one part over two part.
Do what it says on the can and it will do what it says on the can.
Use the approach sanding sealer recommend my the manufacturer would be best practice.
I've used precat lacquer over shellac with no issues. I recently asked at Mohawk about it and he said it was fine.
What is the concern about blotching? Are you staining?
Last line below:
Products will not be held liable for
finish failure resulting from mixing products or systems.
Mohawk Product Data Sheet
Finishing Products, Inc.
CLASSIC INSTRUMENT LACQUER
M610-140 (GLOSS)
Directions: Surface should be clean, dry, and finish sanded with a wood moisture content of 6% maximum.
Apply over natural wood or that which has been stained, preferably with Mohawk M520 stains. Following the
instructions for the use of M520 stains. Seal the surface using Mohawk Vinyl Sealer M610-170 as per
instructions. Should a sunburst or other appearance be desired as edge shading apply such color coats after the
sealer coat.
All build coats of the instrument lacquer are to be applied without reduction, suggest 4-5 coats. Air dry time
between coats should be 1 hour minimum. After the final full coat allow the lacquer to air dry 1-2 days. After
this period wet sand surface smooth using #400 wet paper and mineral spirits. Rag clean surface and air dry for
1 hour. Follow with a final coat of lacquer applied by spray and reduced equal volume with Mohawk Lacquer
Reducer M650-010. Air dry finish 2-3 days and wet sand with mineral spirits and 400, 500, and finally 600 wet or
dry paper. Air dry 1 day or longer and finish with a final rubbing using Poly-Buf M890-003 compound. The finish
can be machine buffed and then waxed using a good quality paste wax.
Clean up with M650-010 Lacquer Reducer.
Note: Total dry film should not exceed 4 mils. All products should be stirred properly before being used and also
continuously agitated while in use to insure product consistency from start to finish. Filtering at every opportunity
is suggested. The system should be pretested on the wood to be finished under application conditions. Mixing
with other products or finish systems is not recommended. Mohawk Finishing Products will not be held liable for
finish failure resulting from mixing products or systems.
Where does it say you can't use over shellac?
I'm telling you the Mohawk guy said it's ok.
I guess you have to prove it to yourself.
Sorry I didn't mean to get up in your face.
Just a difference of opinion.
I once called a manufacturer to speak with them about accelerating or slowing the drying time of their finished with Japan dryers etc…
Man on the other end of the phone said just a moment, Joe is retiring and I’ll let him explain. Then Joe asked me if I was a chemical engineer, I said no, but I knew a little bit about finishes. Then he ask me if I could calculate a Gibbs available energy equation to se if my system was a exothermic or endothermic reaction. Of course I said no
Then he said.
If you do what my instructions, say on the side of the can, it will do what I say on the side on the can.
He was working with empirical data.
I was working with a free floating rational.
Paint drying is an exothermic reaction.
Gibbs Equation ΔG = ΔH − T × ΔS
ΔG must be negative. When ΔH=+ve or endothermic then to make ΔG=−ve, temperature should be high so that the term TΔS. becomes greater than the term ΔH and ΔH−TΔS becomes less than zero. Given that ΔG=ΔH−TΔS, how is the spontaneity of an endothermic reaction to change with decreasing T?
You forgot ΔP , it will not dry at the same rate at sea level or in the Himalaya due to the differences in air pressure.
Thank for proving my point I am not a Chemical Engineer but I do dabble in alchemy.
Here are a couple of tools that will help your finish.
A viscosity cup: is an instrument used to determine a fluid's thickness and flow resistance.
Paint thickness comb gauge:
A device that will measure the thickness of wet finish.
Best practice would to keep a log of the temp, Humidity, viscosity, thickness, of wet coat, and your Mood for the next three days for each application.
Use dewaxed shellac and you should be fine.. However, unless you are 100% sure of the combination, always make a complete finish sample before proceeding.
+1. I spray the lacquer that doesn't need additives though. Post Cat, no cat, whatever its called. The combo really brings out the color and chatoyance in the wood much better than straight lacquer.
Yes you can use pre or post cat right out of the can but if you want to dial it in you can use a Viscosity cup. It is an instrument used to determine a fluid's thickness and flow resistance. The manufacturer recommendation for the finish I was using was 26 to 28 seconds #2 Zahn and added thinner no more than 7% to a equivalent of a Weight Solids: 34% + or -1%.
The viscosity of your wet finish should match the Spray Tip Sizes. Best practice would be to use the manufacturer recommendations.
I have no real recommendations but a Interesting search would be "Steinway lacquer solution".