All Replies on Which is best topcoat -Enamel or Shellac to protect from chainsaw oil & premix

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View Woodstock's profile

Which is best topcoat -Enamel or Shellac to protect from chainsaw oil & premix

by Woodstock
posted 02-02-2018 02:07 AM

9 replies so far

View Carloz's profile


1147 posts in 1436 days

#1 posted 02-02-2018 03:10 AM

Put some polyurethane on top. Shellac is too fragile for your box.

View Woodstock's profile


258 posts in 4133 days

#2 posted 02-02-2018 08:26 AM

Hi Carloz,

Good point.

So I guess I should change my question to:

“What is a better topcoat over plywood? Polyurethane or enamel to protect from chainsaw bar oil & premix fuel drips that will bound to happen over the life of the box?”

-- I'm not old. Just "well seasoned".

View HorizontalMike's profile


7892 posts in 3759 days

#3 posted 02-02-2018 11:32 AM


-- HorizontalMike -- "Woodpeckers understand..."

View CaptainKlutz's profile


3576 posts in 2339 days

#4 posted 02-02-2018 12:52 PM

Best top coat for oil & gas protection?

Can share some limited experience, Have built many “tote” and field boxes for R/C racing that had to suffer oil, gas, alcohol, nitro-methane, and water exposure?

“Splash” Oil protection is not too hard to achieve, but protection from low viscosity solvents is tough. Especially with environmentally friendly “lead free” fuel blends that can be 10% alcohol without your knowledge. Some R/C fuels are 95% alcohol, so shellac is useless. Setting box on the ground brings moisture issues.

First challenge is joinery and glue selection. Standard wood glue softens quickly exposed to gas/alcohol/oil. Epoxy glue joints lasted as long as box lasted. Most were 1/4”-3/8” thick wood using box joint construction with dividers in grooves. Light weight versions were 3/32” thick butt glued. Made a couple heavy duty boxes with pinned/sliding dovetail joinery without glue that solved the glue issues completely.

One difficult part of protection challenge is created by construction material. Plywood has exposed glue joints on end faces, and if the glue becomes exposed to gas; there will be softening and delamination of wood layers. So you are at mercy of glue selection by your plywood supplier. Can seal or protect inside joints (Automotive silicone RTV, urethane sealer, or epoxy) to increase protection from delam. But outside end exposures will be hard to protect. Use of tight grain solid wood (walnut, maple, or exotics) for box construction allowed to “soak” a finish into end grain to provide consistent level of protection and avoid failures of gas/alcohol getting under the plywood layers.

Plywood boxes held up best coated with engine enamel (rattle can works, need several coats, sand between to fill pores and seal well). Clear Poly or spar varnish finishes work ok if can accept minor edge delam of plywood when set on damp ground for extended periods, or add secondary protection.

Fancy hardwood (walnut, maple, oak) boxes I made that were coated with conventional poly or spar varnish blends needed localized finishing repair occasionally to fix damage from oil permeation, with biggest challenge being inside seams would trap liquids. 2-part poly coated boxes (2K automotive clear coat) worked best for clear finish as they never really had any swelling/staining issues (unless they were abused and raw wood became exposed continuously to gas, alcohol, or water).

FWIW – Found a reduction in finish damage problems from damp ground contact (on grass) or gravel dents from asphalt surfaces by bonding a 1/8” thick sheet of plastic (Polycarbonate, polyethylene) to box bottom with urethane glue. :)

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View Sark's profile


316 posts in 1205 days

#5 posted 02-02-2018 05:42 PM

Hey Captain Klutz, that was really great and useful information. Thanks

View bigblockyeti's profile


6716 posts in 2566 days

#6 posted 02-02-2018 06:03 PM

I would take chainsaw premix and bar oil and mix them together to make the finish. When something gets spilled it will be only adding to what’s already there.

-- "Lack of effort will result in failure with amazing predictability" - Me

View Woodstock's profile


258 posts in 4133 days

#7 posted 02-02-2018 11:47 PM

Thanks Captain Klutz. Your post was really excellent. And a blast from the past from 4.5 decades ago? I forgot about my 1/2A control line racing days before R/C. God was I ever THAT young? I was an expert on “re-kitting” planes that I flew. And I did make a couple of scrap CDx ply tote boxes. Well stained with caster oil & nitro racing fuels from Cox.

I’ve already built my current chainsaw tote-box out of ply & started to shoot finishes. I currently have Rustolium’s Professional grade Safety Yellow rattle-can enamel on it. Just waiting for a week to fully cure & probably will top it as you suggested from the auto paint enamel type of finish as a fuel resistant satin clear topcoat.

Next time (if there is a next time) I will look into band-sawing up some solid kiln dried wood such as red oak planking from the big box store to make thinner boards to make a tote out of instead of ply. Probably would be cheaper that Baltic birch ply too. And epoxy instead of Tightbond III.


-- I'm not old. Just "well seasoned".

View CaptainKlutz's profile


3576 posts in 2339 days

#8 posted 02-05-2018 08:47 PM

“well seasoned” lol guess that is me too…

Deep down – R/C model construction is nothing more than overly engineered wood working?

Suppose background is worth telling:
Participated in various R/C hobby for 20+ years. I flew everything, liked pattern planes most, and spent much time 0.40 size pylon racing re-kitting planes. Especially liked large scale and pattern/pylon flying.
IMHO – nothing better than that screaming sound from alcohol feed weed eater motor running a few thousand above max rated RPM only 50 feet in front of you to make you feel alive. ZOOOOOOOMMM….. :)
But when your $1000+ investment is “re-kitted” due “dumb thumb” incident, it would make for really bad day.

Never did I imagine that when I made a “simple” walnut/maple field box (box joint construction = sort of customized machinist chest) for the pits and matching field box for flight line; that others would start asking me to make them a custom “toy” box.

Someone mentioned mixing premix with finish:
One of my friends decided to use BLO/Beeswax blend on figured maple wood box. It worked pretty well, providing you were willing to sand out scuff/stain marks and refinish wood occasionally. Same BLO treatment did not stop plywood de-lamination issues due being used outdoors, but did protect from gas/oil. :)


-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

View DrDirt's profile


4614 posts in 4587 days

#9 posted 02-06-2018 08:51 PM

+1 on epoxy – - but understand it will eventually fail as a finish (as will all others)... and nothing will stick to that “50:1 oil” stain in the future.

I similarly have done some ‘rekitting’ in the day – - that is why I like epoxy – - treat the box just like the firewall of an RC plane.

-- “The two most important days in your life are the day you are born and the day you find out why.” Mark Twain

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