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fixing of pinholes and other surface imperfections.

BlackDogIron (Automotive)
13 Dec 10 1:38
I am using West Systems Epoxy 105 with special clear hardener. I made a mold of a motorcycle chain guard and vacuum baggeda carbon part. The molded surface of the part is not SMOOTH. I tried sanding it a little and brushing more resin on to fill voids but the resin resists voids like the plague. Resin builds up fine where there is already resin but does not want to fill pits.
Any remedy?
Hojo1122 (Materials)
13 Dec 10 8:19
resin infusion
Compositepro (Chemical)
13 Dec 10 13:03
Blow-of the part after sanding with compressed air to remove dust from the pits. Wipe the surface with acetone. You are probably brushing resin over the pit and trapping air in it again. Dab with the brush so the bristles carry resin into the pit. Too much brushing will create bubbles.

Lower viscosity resin may help. This can be done by adding solvent or heating with a heat gun (hair dryer), or both. Heat will expand bubbles, particularly if solvent is present. If they pop and the resin levels your pit is gone. Acetone is usually the best solvent for epoxy, but with some formulations it may interfere with cure.

It is better to make parts without pits in the first place.
BlackDogIron (Automotive)
13 Dec 10 14:40
I agree, avoiding pits in the first place is desirable smile
Lowering the viscosity sounds good. Didn't really have this problem with poly-ester resin.

Guess I didn't use enough resin to begin with?
Compositepro (Chemical)
13 Dec 10 15:58
Your problem is more likely air bubbles trapped in the resin rather than lack of resin. Wet layup of carbon is difficult due to lack of visual feedback. Practice with your resin on glass fabric and imagine how you would do things differently if you could not see the bubbles.

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