Thinning finishes

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Forum topic by Betsy posted 03-14-2009 06:15 PM 940 views 1 time favorited 5 replies Add to Favorites Watch
View Betsy's profile


3336 posts in 3320 days

03-14-2009 06:15 PM

Topic tags/keywords: finishes

Just a curiosity question here. When you thin a finish such as varnish or oil based paint, what do you prefer to use as a thinner – mineral spirits or naptha? I’ve used both for no particular reason. Would be interested to know what you use and why.

Thanks in advance.

-- "Our past judges our present." JFK - 1962; American Heritage Magazine

5 replies so far

View Douglas Bordner's profile

Douglas Bordner

4010 posts in 3488 days

#1 posted 03-14-2009 06:29 PM

I’ve used both. I used MS with black paint used to spray outdoor iron rod deck furniture, because the “dry out of dust” time (time it takes for the finish to be dry enough to not let particulates that fall on the finish to stick to the wet paint) didn’t matter to me especially.

While making wiping varnish, I use VM&P (varnish makers and painters) Naptha, because I wanted the thinner to flash off faster to minimize dust nibs and hasten the time between coats.

-- "Bordnerizing" perfectly good lumber for over a decade.

View Scott Bryan's profile

Scott Bryan

27251 posts in 3246 days

#2 posted 03-14-2009 07:03 PM

Betsy, like Doug I have used both but I prefer mineral spirits largely because it is what I usually have available and it is the cheapest. Another advantage, to me at least, is that is takes longer to flash. This gives the poly/varnish more time to level out and let any air bubbles escape. But the trade-off is as Doug describes.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View hObOmOnk's profile


1381 posts in 3551 days

#3 posted 03-14-2009 07:53 PM

What Douglas said:

Naptha dries a little quicker than mineral spirits.

However, when you dilute a varnish, some of the insoluble components, like flattening agents, may settle quicker than usual. This is particularly true for Satin and Matte finishes which may contain silica and clay derivatives.

You’ll want to stir from the bottom more often.

Hope this helps.

-- 温故知新

View woodnut's profile


393 posts in 3476 days

#4 posted 03-14-2009 09:35 PM

Betsy your question could not have come at a better time for me. I just purchased the earlex sprayer and have never sprayed before. I have nothing to add to your question but will follow this thread for info. Thanks for asking.

-- F.Little

View Betsy's profile


3336 posts in 3320 days

#5 posted 03-18-2009 02:59 AM

opps – I let this one slip out of mind. Thanks for your replies guys. I seem to be favoring Naptha lately. Just seems to work better for me.

-- "Our past judges our present." JFK - 1962; American Heritage Magazine

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