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Old Jan 14, 2013, 03:30 PM
A geriatric flier
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Australia, NSW, Braidwood
Joined Nov 2008
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Paint bleeding under masking on foam.

I did a search for this particular problem because it must have been bought up before but I mustn't have used the right words. Is there a trick to prevent this bleeding under the tape. I do not spray(cannot, my spraying looks like a seagull s#$t on it from a great height) so I brush the paint.

As a side can someone tell me why covering like Monocote wrinkles when the plane is left in the sun? I would have thought it would have gone as tight as a drum.
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Old Jan 14, 2013, 09:52 PM
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Joensuu, Finland
Joined Mar 2002
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The problem with foam is that it is porous and the tape just can't reach the bottom of each and every microscopic valley. A primer layer would help, but also add weight. In any case, use the thinnest possible tape you can find and carefully rub it onto the surface. Use thickest possible paint you can manage. Begin your brush strokes on top of the tape and pull the brush away from tape edge, never towards or along the tape. First paint the edge with a colour that matches the foam (or the colour under the tape), this seals the tape edge and if it bleeds under the tape, it won't be as noticeble. After this sealing layer is dry, paint on the actual colour. If possible, don't use masking at all, but do it freehand. (I know, I can't do it either. But on camouflage patterns etc irregular shapes it really doesn't matter.) Or if you can find those brush-on masking liquids, they might also be worth of a try.
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Old Jan 14, 2013, 11:42 PM
A geriatric flier
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Australia, NSW, Braidwood
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Thanks jkettu. Brush in hand, smile on my face and an air of confidence away I go. I'm 70 yo so trying to freehand paint an edge is a bit of a challenge so masking is my best option.
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Old Jan 16, 2013, 10:37 PM
RC Adddict
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Monocote on foam ? Foam off gases when in the sun so that could be the reason .
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Old Jan 17, 2013, 04:45 PM
A geriatric flier
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Australia, NSW, Braidwood
Joined Nov 2008
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I mean Monokote on balso. I understand there is a special Monokote for foam, I think it is called Econocote. (Problem at present typing as I have just had a cataract operation. Everything is blurred.)
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Old Jan 17, 2013, 06:43 PM
Space Coast USA
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Quote:
Originally Posted by Watdazit View Post
I did a search for this particular problem because it must have been bought up before but I mustn't have used the right words. Is there a trick to prevent this bleeding under the tape. I do not spray(cannot, my spraying looks like a seagull s#$t on it from a great height) so I brush the paint.

.
Easy to fix.
After applying the tape, coat the interface of the tape and the foam with a coat of Minwax Polycrylic varnish. It is a clear thin water based acrylic based varnish which will seal the tape edges and give you a nice clean edge.
Let it dry for a day and then use your water based paint on the foam.

Try it on some scrap pieces to get an idea on how to do it.

If you are talking about that popcorn textured EPP, that's a problem which will require a primer of light weight spackle to fill those pot holes.
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Old Jan 18, 2013, 08:25 AM
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Quote:
Originally Posted by Watdazit View Post
As a side can someone tell me why covering like Monocote wrinkles when the plane is left in the sun? I would have thought it would have gone as tight as a drum.
A new Monokote covering job that shows wrinkles is an indication that, in open structure, it was not shrunk completely (even if it looks ok) and over sheeted areas it was not completely adhered to the wood surfaces. I've always found that Monokote needs to go through one seasonal change, heat, cold and moisture, before it will show you where you missed in its application.
It's extremely important to fix the wrinkles over solid wood areas as soon as they appear; if not and they become larger. You may find that re-shrinking will leave a crease from not enough area to take up the expanded film.
Covering over solid wood areas require that the surface be absolutely free of any wood dust; otherwise adhesion will be to the dust first and when the film lifts in that area there is no adhesive left to re-stick in place.
An indication for adequate heat in the application of Monokote is to see a darkening color change to give adequate shrink and adhesion.
I have 30 year old Monokote covered aircraft that retain a painted look as the film hasn't moved. Still, Considering really hot days at the field, I keep the model in the shade, or completely cover with a white bed sheet if shade isn't available.
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Old Jan 19, 2013, 03:54 PM
A geriatric flier
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Australia, NSW, Braidwood
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Thanks for the suggestions and advice.
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Old Jan 23, 2013, 04:29 PM
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In my experience, it's much harder to prevent bleeding under the tape when brush painting foam, than when spray painting. Good quality masking tape helps a lot- the items sold by Tamiya being the best in my opinion. The low tack 3M brand painters tape is good too, or even Post-it notes for small areas.

When the masking is done, paint some of the base colour, or even use clear paint, along the mask line to seal it- that way, if there is bleeding it will be invisible.

In reference to hoppy's good advice: Minwax Polycrylic is not available in Australia, but you can get some Cabot's Carbothane from your local Bunnings. It makes a good primer coat for foam. BTW, if you are painting a moulded EPO model, give it a wash with Windex to remove the surface waxiness left over from the moulding process before priming/painting.

FWIW, the Tamiya acrylic spray paints (NOT the polycarbonate paint!) do not attack EPS or EPO foam, but at $10 a can your paint job can get expensive.

Also the small jars of Tamiya water based acrylic paint, slightly thinned, spay very nicely through an airbrush or hobby grade mini spray gun (and brush paint well too), and are of course foam safe too.

Good luck

Odd
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Old Jan 23, 2013, 04:40 PM
A geriatric flier
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Australia, NSW, Braidwood
Joined Nov 2008
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Quote:
Originally Posted by wizard of odd View Post
In my experience, it's much harder to prevent bleeding under the tape when brush painting foam,............Good luck

Odd
Thanks for the advice. I had thought a water based "varnish" might be the same as the Minwax and I was going to give it a go. I have bought some tubes of an acrylic "hobby" paint from Bunnings to try. They are only $2.99 a tube and they also have a primer in a bottle for what appears to me to be the same as carpenters acrylic glue.

Something I have found over the years is not all masking tape is equal and the cheap $1 a roll is really no good for anything and quality branded tape is the way to go.
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Old Feb 22, 2013, 08:02 PM
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Second the tamiya masking tape as its extremely versatile, conforms to any shape, and is practically bleed proof.
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Old Feb 22, 2013, 10:15 PM
A geriatric flier
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Australia, NSW, Braidwood
Joined Nov 2008
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Thanks for all the advice guys. I have put the painting to one side at present whilst I recover from eye surgery. No flying, no building and no painting....bored
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