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My sprayed polyurethane finish looks bad!

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Forum topic by Twisted Family Crafts posted 06-19-2012 07:17 PM 5945 views 0 times favorited 10 replies Add to Favorites Watch
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Twisted Family Crafts

4 posts in 925 days


06-19-2012 07:17 PM

Topic tags/keywords: question tip trick cedar spray gun finishing arts and crafts

I am using Minwax Helmsman Spar Urethane thinned with 30% mineral spirits and spraying it on cedar with an air detail sprayer. When it dries it has speckles in it and is rough almost like it has sand in it. We are blowing everything off and using tack cloth on it and sanding with 220 before spraying and sanding with 320 after the 3rd coat and before the final coat. The same thing happened when I tried to brush it on with the thinned poly. I brushed it with out being thinned and it looks better but has brush strokes in it and more runs because I could not control it. Is there any other urethane that will spray better? It does not need to be exterior. We use about a gallon a month. Spray cans are too expensive for the amount we use.

Is there a special way to treat cedar before coating it?

Here is a link to the things we are making https://www.facebook.com/TwistedFamilyCraftsOK

-- Twisted Family Crafts https://www.facebook.com/TwistedFamilyCraftsOK


10 replies so far

View Tennessee's profile

Tennessee

1447 posts in 1179 days


#1 posted 06-19-2012 07:24 PM

I took a quick look at the photos on your Facebook page, nice stuff, by the way.
Aromatic cedar? You know it will absorb greatly on tighter areas and lay on top in other areas. I would guess the sandy feeling is wood fibers raising off the surface. I think you should stop thinning it with mineral spirits, it is slowing it down too much and allowing the wood to react more.
Have any complaints about using lacquer for a faster dry?

-- Paul, Tennessee, http://www.tsunamiguitars.com

View PurpLev's profile

PurpLev

8476 posts in 2313 days


#2 posted 06-19-2012 07:27 PM

are you spraying indoor in a clean environment with no debris/contaminants in the air?

if so, you might be experiencing orange-peel effect. your coats might not be heavy enough, and/or your finish might be atomized too soon. try spraying a heavier coat.

Also, what made you decide on 30% delusion percentage? are you testing for viscosity or is this just a random number you went for (finish might be too thin)

-- ㊍ When in doubt - There is no doubt - Go the safer route.

View gfadvm's profile

gfadvm

10974 posts in 1355 days


#3 posted 06-20-2012 02:17 AM

I have sprayed a lot of Spar Urethane successfully without diluting it at all. I also usually lay it on pretty heavy and wipe any runs while they are still wet. Anything seems to raise the grain on cedar but after a couple of sandings it usually stays smooth.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View ajosephg's profile

ajosephg

1854 posts in 2226 days


#4 posted 06-20-2012 08:42 AM

IMO the first coat is always rough, brushing or spraying. Lightly sand between coats and the second and following coats will get smoother and smoother.

-- Joe

View lunn's profile

lunn

206 posts in 974 days


#5 posted 06-20-2012 11:39 AM

I spray everything i build, cedar included. I always use 2 coats of sand & seal (2nd coat while tacky) and sand when dry. As for thinning i figure how much i’ll need and thin to almost as thin as water to where it streams/drips off the stiring stick. Air pressure abt. 35-40 psi. Lighting is also important so you can see the flow being applied (high and lows) Spray a thin coat of finish and when it gets tackey apply a second thin coat. Let dry, sand, finish coat. If you spray it on to dry (not enough to flow/level) it will feel like sandpaper.

-- What started as a hobbie is now a full time JOB!

View doninvegas's profile

doninvegas

332 posts in 1572 days


#6 posted 06-20-2012 11:35 PM

I spray Spar on all of my Cedar Adirondack furniture and the first coat I thin about 10% to 15% with mineral spirits and it is a little rough. I sand to 220 and spray full strength. It comes out smooth as babies behind. Customers love it.

-- "Courage is being scared to death -- but saddling up anyway."

View Twisted Family Crafts's profile

Twisted Family Crafts

4 posts in 925 days


#7 posted 06-28-2012 11:30 AM

Can anyone suggest a cheaper and easier to spray interior polyurethane to use on Cedar?

-- Twisted Family Crafts https://www.facebook.com/TwistedFamilyCraftsOK

View Loren's profile

Loren

7618 posts in 2313 days


#8 posted 06-28-2012 04:19 PM

I would seal with shellac and then varnish over that.

You should get a book on finishing if you are committed to
spraying. There’s a lot to it.

-- http://lawoodworking.com

View guitchess's profile

guitchess

82 posts in 2374 days


#9 posted 07-20-2012 01:34 PM

This seems to be an older post but I thought I would give my .02 anyway.


At first glance, it sounds like your air system is to blame. Either too much air pressure, improper gun settings, or both. It could have also been contaminated air; water, oil, etc. coming from the compressor.


However, as I continued reading I noticed that you had the same issue when trying to brush the thinned mix but not as much with unthinned. Which leads me to believe that there is a compatibility/contamination issue with your thinner.


THere is also the posible issue of temp/humidity/location. Even though varnish dries slowly, when spraying with an air system, it is possible for some flash over. Especially, if it is very hot or if you are spraying in direct sunlight.


I have always achieved better results with an airless sprayer when shooting varnish/poly.

View Knothead62's profile

Knothead62

2364 posts in 1626 days


#10 posted 07-21-2012 10:42 AM

Orange peel effect can be caused by the nozzle being too close or too much air pressure. Have seen it in appliance enamel finishes.

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