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Old 05-13-2019, 11:48 AM
theBongolian theBongolian is offline
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finish/sealer woes


I wanted to seal a piece of MDF I was using as a work surface.

I first applied linseed oil. When that fully dried I put on a coat of oil based polyurethane. It's been TWO weeks and it still hasn't dried - extremely tacky.

Will this not cure over linseed oil? I want to seal all hardwood (""masonite") painting panels with linseed oil but don't want any surprises. I wouldn't use an oil based polyurethane since I paint with acrylics, but are there finishes that should not be used over linseed oil.

btw my current favorite painting (not panel) sealer is water-based shellac.
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Old 05-13-2019, 12:24 PM
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Dcam Dcam is offline
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Re: finish/sealer woes

I guess you haven't read Contumacious and myself commenting on the virtues of Wax free shellac (Bullseye sealcoat) or Gac 100 as terrific sealers.
Also, White pigmented shellac primers.
Sorry Bong.......never use polyurethane for your purpose.
and.....why did you first use linseed oil? Not Good!
I'm only speaking from my own experience.
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Old 05-13-2019, 02:59 PM
theBongolian theBongolian is offline
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Re: finish/sealer woes

Quote:
Originally Posted by Dcam
and.....why did you first use linseed oil? Not Good!...
.
out of ignorance. I thought linseed oil was the go-to for strengthening and sealing. I used the other stuff because it's what I had on hand. I've started using shellac as a finish on my paintings - will now use it too on the back -no?
thanks Derek

also the best way to get tacky polyurethane off?
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Old 05-13-2019, 03:27 PM
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Dcam Dcam is offline
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Re: finish/sealer woes

When you say shellac as a finish....like varnish.NO.
Only as a sealer for your board and use only wax free.
You will have to use a nasty paint stripper to get that poly off.
I would just put it aside and move on. Good luck.
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Old 05-13-2019, 08:35 PM
theBongolian theBongolian is offline
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Re: finish/sealer woes

Quote:
Originally Posted by Dcam
When you say shellac as a finish....like varnish.NO.
Is there a good reason not to use water-based shellac as a varnish for acrylic paintings?
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Old 05-13-2019, 10:39 PM
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Re: finish/sealer woes

Shellac on paintings tends to crack and darken with age.


Check out this thread: http://www.wetcanvas.com/forums/showthread.php?t=303389
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Old 05-14-2019, 01:04 AM
contumacious contumacious is offline
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Re: finish/sealer woes

The stuff in your photo is a solvent / oil based polyurethane varnish. My guess is that the MDF with the oil in it is still not fully dried and is keeping the polyurethane from curing.

Polyurethane works quite well as a finish for bare wood particularly if you apply multiple thin layers, sanding between, but it is not something you would want to paint on top of. The water based Polycrylic stuff is also used by a lot of people for a wood finish (again, not for painting on top of) but I have never tried it. I have heard of some acrylic painters using Polycrylic as a final, permanent varnish on their acrylic paintings.

https://www.thesawguy.com/polycrylic-vs-polyurethane/

https://woodworkingtoolkit.com/polyc...-polyurethane/
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