# thinned urethane



## TomCT2 (May 16, 2014)

semi-odd-ball approach for finishing here . . . 
I don't want gloss; I don't want a noticeable "layer"
I want something similar to ye' olde oil finish.

why?....
I'm doing racks / holders / brackets / jigs / and-the-like 
for essentially "shop use"

the purpose is to create a non-existing "seal coat" on pine / poplar / oak / maple (scrap) woods to minimize any distortions due to humidity over seasons and age.

my "oh sheet" moment:
made up a jig for cheek cutting on the table saw.
unfinished it worked like a dream; smooth glide and resistance.
then (boo-hiss-mybad) I applied Minwax urethane neat from the can.
I thence spent hours fitzing and fussing and sanding to return the jig to its original dimensions and "gosh I luv the glide" state.

subsequently have thinned the Minwax urethane with generic paint thinner - using a metal quart container for the diluted mix. the contents of the diluted can - which has 50% (or more) empty/air head space, have the nasty habit of skinning over, clumping, generally getting nasty and unusable. 

in order to get the "desired" finish, I apply the thinned urethane, wait roughly 20 minutes, then wipe it off with a rag. this wipes off any "standing" urethane from the harder grain spots and leaves a "no visible sealant" appearance. wiping off "neat" viscosity urethane is a total loser. it is a sticky gummy goopy mess.

I have also used acetone to thin the urethane. mixed results.

so: 
what is the collective experience with thinning (oil based) urethane?
given the "full range" of solvents available in any Home Depot.... 
anything that makes for a "stable" solvent? - i.e. put urethane in clean can, add solvent, stir/shake/wait/whatever - and not have a jelled mess after after 1-2 days.....

Minwax declines to provide any answers - any solution is apparently going to be an open secret between those who have experimented . . . .

and maybe there isn't a solution . . .


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## Centx (Feb 22, 2016)

I thin just about all the oil based urethane's I use with equal parts poly, boiled linseed oil, and mineral spirits. It will clump and gel but only if the coating is too thick or if it runs or pools anywhere. I usually do use a spray lacquer for added protection afterwards as I thin in this way for the look.


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## Hammer1 (Aug 1, 2010)

Polyurethane is just a synthetic resin, it can be in waterborne or oil based products, MinWax makes both. The oil based can be thinned with paint thinner (mineral spirits). It's not recommended, however. There are very few solids in MinWax, thinning just makes an already thin product even thinner. Why don't you try some MinWax Antique Oil? Matte appearance, wipe on, wipe off.


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## epicfail48 (Mar 27, 2014)

Oil based poly thins out alright with mineral spirits, i actually go with a 50/50 mix of the 2 to make a wipe-on varnish and use it exactly like youre describing. Its also pretty stable in storage, or as stable as polyurethane ever is. 

The waterborne stuff isnt supposed to be thinned very much, so far as i know. I know a lot of them say you can thin with water, but not to go past 10%


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## TomCT2 (May 16, 2014)

ah. thanks for the input. I guess I'm not as crazy as I thought.

I don't have any specific objection to the mineral spirits dilute of oil based polyurethane - was just wondering if anyone had discovered a "more better" diluent. I keep a qt can of "neat" and "diluted" - I reckon I'll just have to deal with the skin / clump / jell as it happens.


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## TomCT2 (May 16, 2014)

continuing with this experiment....

NOTE these solvents are extremely flammable and easily go BOOM
extreme caution as to flame & spark & ventilation is an absolute must!

alcohol does not work well
acetone works, but turned the (stored) urethane to jello -
MEK is working and not jellying -

but the MEK seems a bit trickier to work with. although acetone is faster at evaporation 'by its lonesome' the MEK appears in practice to evaporate quicker. on raw wood / first coat it just about dries while you're holding the piece . . . attention to brush strokes / runs / sloppy application required!

on the spraying, anyone tried an airbrush type device for small projects?


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## mako1 (Jan 25, 2014)

I just use paste wax on all my shop stuff.Keeps them all nice and slick and keeps moisture out. If you feel you need some kind of topcoat why not just use shellac.You can thin it as much as you want with alcohol and no issues.Then wax over it.


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## Tony B (Jul 30, 2008)

There is something called a Flattening Agent. It is a pasty stuff that I add to my pre cat lacquer. Depending on how much you want to go from gloss all the way to a dead flat finish. The dead flat will not only look like an oil finish, but it will also feel like an oil finish with the protection of lacquer..I'm sure u can get the same stuff for urethane. Call tech support for the finishing product u are using and they can probably tell u where to get it.ý


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## jorma (Feb 24, 2016)

1. Flattening paste. It's been around as long as anything but "Gloss" finishes have been around. I only use it if the desired sheen is not available for some reason.
2. Not sure of the wisdom (or reason) for using anything hotter than Naphtha in an oil-base finish.
good luck


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## TomCT2 (May 16, 2014)

why ... using anything hotter than Naphtha in an oil-base finish.

because when the question was asked, naphtha did not appear in the community knowledge base.
have you tried it with urethanes?

absent known solutions to a thinner urethane coating (short of spraying) I opted to go experiment. 
my chemistry is not so hot, but it appears some solvents react with urethane (some / many / all / ? - how many different formulations are on the market....) inside a closed/sealed container turning them into sludge/jelly.


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