# Varnish over sanding sealer?



## Pyro (Dec 16, 2017)

Hi guys,

I am a novice when it comes to real wood working so please excuse stupid questions as well as the situation I've gotten myself into here.

I've done a few interior wood projects over the last year. I usually use water based Transtint dyes and then apply a coat or two of sanding sealer before spraying with lacquer. Has turned out great so far.

I just finished building something for a friend. I put my sanding sealer on and started researching spar varnish as this is going to be an exterior project. I haven't had good luck with spar varnish holding up for more than a year so I started searching. Found what seems to be a great answer detailed here

http://www.askhlm.com/Articles/ArticleViewPage/tabid/75/ArticleId/26/Paint-On-A-Clear-Finish.aspx

So I'm on my way back from the paint store and it dawned on me: This is going outside and I'm planning on putting an oil based finish over a water based sealer. I'm pretty sure I've heard this is a bad idea because water and oil based finishes expand/contract at different rates, and a soft water based finish under a hard oil based finish is going to make the oil based finish crack and separate. Is this right?

What should I do? Can I use a water based spar varnish or even an acrylic neutral base paint as detailed in the article I linked? Any pointers are appreciated. Thanks.


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## bilyo (May 20, 2015)

I have enough experience with this to tell you that the article you linked is correct in that the paint base does dry clear; either oil base or acrylic. I cannot vouch for the exterior durability because the only project i've done is in a protected area without much direct sun/rain exposure.

I'm sure others will have more experienced opinions, but if I started with a water based sanding sealer then I think I would stick with a water based finish. Having said that, I question whether you need the sanding sealer at all; particularly if you are painting new wood and especially if the sanding sealer is not specified for exterior use. Note that in the linked article, the author did not mention using any kind of primer or sealer on his test panels. Not sure, but, I think, most sanding sealers are for interior use only.

In my one and only project using an uncolored paint base, i found that it did not self level well. When dry, it exhibited brush marks I didn't especially like. This might have been just the nature of the brand I used. However, you might want to consider using a foam roller.


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## Pyro (Dec 16, 2017)

Thanks Bilyo,

If I applied a neutral base acrylic I was thinking I'd spray it on for that very reason. I wonder if fleutrol would dry clear and help with that? Might be something I'll test in the future.

Re: interior sanding sealer, yeah, definitely a snafu on my end. Inexperience can sure make things harder. Due to the nature of the project, stripping it isn't a viable option either.

I'm betting that water based spar varnish by the same brand (minwax) will go over it just fine. I'm just hoping that if I apply enough coats, that sanding sealer won't make a problem for me down the road.

Thanks again for your advice.


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## wapakfred (Jul 29, 2011)

Your supposition about putting hard finishes on top of soft ones is correct, it's generally a bad idea. I'm less certain that the water based sealer is softer…almost all water based finishes (and their brethren) are actually acrylic finishes (some of them may have a small dollop of urethane so the manufacturer can put that magic word on the label) and they are fairly hard. As to the paint, the article you linked is excellent and the one that turned me onto untinted paint for outdoor use. I've used quite a bit of it for that purpose and always had excellent life from the finish. I'v also used some deep base tint exterior acrylic enamel with no tint. It looks milky in the can but the one I used (Olympic) dried clear and so far seems to have a long life. SW A100 exterior also dries clear and I'm sure is just as good. I an almost guarantee you that any Minwax spar will fail in the outdoors. Flexner tested their oil base spar and concluded it must have almost no UV inhibitors (though it is labeled it does) because it performed so poorly.


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## Pyro (Dec 16, 2017)

Fred, thanks for the info and for saving me from the spar. I've never had great results with spar anyways.

The sanding sealer does feel hard. What would you think about me putting exterior acrylic over this sanding sealer? I'm assuming SW A100 is a Sherwin Williams exterior? Thanks again


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## bilyo (May 20, 2015)

May Fred can answer. Will the interior (if it is) water based sanding sealer that Pyro already has applied perform OK outdoors when covered by a couple of coats of exterior acrylic paint base?


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## John Smith_inFL (Dec 15, 2017)

Pyro - probably the reason you have not had good success with Spar Varnish
is that you - - - either have the wrong type of spar varnish or Minwax Spar Urethane,
which is not a true spar varnish. it is a cheap blend with spar and urethane with very little
UV blockers and inhibitors for interior projects and floors (in my very personal opinion).
there is no "one coat and it's done" type of coating on the market outside of automotive 2-part epoxies.
for instance: look at the beautiful antique wooden boats with spotless finishes.
pure Spar Varnish has good UV protection but ALL varnishes must be touched up
or recoated every year or two. Not just one coat and expect it to last 5 years. it's just not gonna happen.
it really depends on what you want your project to look like and for how long.
there is spar varnish for $8.00 a quart and there is spar varnish for $65.00 a quart.
the higher price obviously indicates a much higher quality with more UV blockers.
bottom line is: you get what you pay for and you must maintain it properly through the years for optimum results.

here is an article I wrote last year for a boat forum I belong to about varnish and urethanes.
https://www.tinboats.net/wp-content/cache/all/varnish-vs-polyurethane//index.html

good luck in your project !! (photos of your progress would be great).

WARNING: Any rags used to apply coatings, oils, stains or solvents should be thoroughly air dried 
prior to storing or discarding in the trash.

.


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## wapakfred (Jul 29, 2011)

I have no experience with sanding sealers so can only guess…but I would think the exterior paint wold give it protection in outdoor use. It pays to remember that NO outdoor clear coating is perfect forever and will need maintenance…but i thin the maintenance window is much longer when using finishes that are made for that use (following what John said above).


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## Pyro (Dec 16, 2017)

John, thanks for the info! I usually use Man O War which I thought to be pretty decent(?). I think that perhaps my expectations are just a tad unrealistic.

Fred, my gut tells me that you're right. I did a test a few days ago and applied an oil base over a piece of wood with the sanding sealer on it. Left it outside where the sun really hits it. Although it's only been a few days, so far so good. I am thinking about going with the SW A100 though just to be safe. What do you think?

Thanks again guys.


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## bilyo (May 20, 2015)

You addressed Fred, but my 2 cents worth is that our guts are on the same wave length. I'm assuming that your friend is a good friend or you wouldn't be making something for him/her. I would be inclined to proceed with your plan to use the A-100 over the sanding sealer (remember to use the deep base). Then I would explain to your friend that this is a bit of an experiment and offer to refinish the piece if it doesn't work out well. He/she may appreciate being a part of the experiment.

Please keep us posted on how it works out.


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## wapakfred (Jul 29, 2011)

I think I'd go with the A100, remember bilyo's point about it being the deep base. the exterior should do very well for you.


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## Pyro (Dec 16, 2017)

Thanks for all the help you guys. I will report back in a year or so and give an update. Really appreciate it.


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