Model Boat Mayhem
Technical, Techniques, Hints, and Tips => Painting, Finishing and Care. => Topic started by: wullie/mk2 on February 01, 2012, 09:41:32 pm
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Hi guys, I have just varnished a mahogany planked deck with Polyurethane, and ended up with hundreds of pin holes. My procedure was:
1 sand down deck
2 wipe over with white spirit and dry
3 first coat 20 % thinned
4 light sanding and clean
5 second coat unthinned
6 pinholes!!!
What did I do wrong ?
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Personally I think it is not enough time between coats,I think what has happened is that the first coat hadnt dried properly and as it dried the solvents have evaporeated and bubbled thru the second coat.................I could be wrong but not often
|Dave
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Hi Dave thanks for the reply. You may be right, but it was at least a week between coats.
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Sorry just re read your Post I should have gone to specsavers lol.
Right then maybee you should have done second coat 50%,third coat 75% then gone full coat,what I think then has happened is second coat was to thick.
ALL IS NOT LOST
Wet /dry the deck with 800 grit dry thoughrely and apply a 50% coat of varnish thinners and build up thin coats
Dave
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Back to front with the coats. More coats you apply, the thiner they become, as you are applying "gloss", finish and not "material", polish.
Polyurethane is notorious for pin holes, air bubbles trapped in the coating.
You need to use a good thick pigs hair brush with a straight end. It is the flowing of the coat that traps the air bubbles so work slowly in one direction and don't overbrush, that is, continue brushing over the applied coat.
(Applying "polish" is different to painting. When painting you work back into the applied coat to eliminate brush marks. However 'Plastic' paints have virtually eliminated brush marks.)
Subsequent coats, after the base coat/layer should be thinned, and lightly sanding and cleaned off between coats.
Experiment on a little scrap, to get the technique right, as you will see the bubbles occurring, if you are not doing it right.
These days you can get equally as good a finish with other simpler produsts instead of using Polyurethanes.
Those locally can advise what is available and what they use.
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Thanks guys, will do as you have advised.
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Hi,
Now not knowing anything else other that what is allready posted -
Given the current low temperates perhaps the applied coats are to thick? Also trapping air in the allready thick varnish... perhaps thin the varnish, raise the temp & thin the coats applied.
Regards
Kim
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This can be caused by the surface not being properly dry before varnishing.
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I have just realised the OP is in Australia... I could draw many conclusions but withought photos i cant say much of any use....
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I have just realised the OP is in Australia... I could draw many conclusions but withought photos i cant say much of any use....
If it was Austria would it make a difference ?(http://i124.photobucket.com/albums/p8/DickyD_photos/Smileys/thinking1.gif)
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Actually the comments made regarding the temperature might explain my problem. My workspace is a small shelf right under the kitchen window, and it is bl**dy cold here in Austria at the moment!!!
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Terry,
Most if not all applied finishes, painting etc, have a minimum and maximum temperature range for applying such finishes.
Usually marked on the can, etc.
The temperature affects the drying of the coating either slower or faster and in some cases too hot or too cold to apply.