So I am working at my uncles fiberglass factory now and getting more hands on experience. We seem to go back and forth on how things should be done and how they shouldnt. I dont know his level of actual knowledge but he has worked with fiberglass for almost 30 yrs. We have a plug that we are wanting to rework to make new molds for a customer of ours. It just has a few waves and dips here and there. I said I could do body work and have them done in no time. (I have a degree in autobody work) I then said that it would be sprayed with an epoxy or urethane primer, wet sanded and buffed and call it good. Hes saying that it cant be done this way. Whos correct? I have thought I have often heard of people doing this with no problems. Hes wanting to try and sand just the high spots with 1200 grit and call it good on the plug. I said this would be to fine of paper to get the waves out and that it would just create more problems just sanding one spot only. He hired me for my knowledge in both composites and painting, but never listens to my advice on anything and its starting to annoy me. 

Depending a little bit on what the plug is made from, I would say that You're right ... Do it properly ... 1200 grit will not remove very much material, so will probably not remove all the "wavyness" or uneven spots.
Skimping on the plug makes for more work on the mould, and/or more work on the finished product ...

Knowing what the plug is for, and what it is made from will give you better feedback from this forum ... 

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

Thanks Dravis. The plugs here are made out of fiberglass off an original steel door. The plug is made from a chop gun and PE resin I believe. With coremat and wooden bracing. They are semi old and have scratches and some very small chips in the tooling gelcoat. They are for the door for the rear portion of a utility truck. Since I'm doing this with my phone it was just easier to copy a link than upload a picture. The top pic in this link is the actual side and doors we make. You can see a more square door, then a longer rectangular door. I hope this helps?!

They will be polyester for sure, if they are old..  What type of materials will you use for making the moulds from these old plugs?   This may well determine what materials to use for repairing the plugs to a good surface.

I would not skimp on this part of preparing for a new production run (even if it is only a short run of doors) Make the moulds from good materials, like the EC Unimould system (Vinyl ester based I think, to reduce shrink)

Repair the plugs using epoxy or good polyester filler such as the EC "pattern coat" stuff ..  leaving cracks and surface blemishes on the plug. just makes for more work on (in  . ) the mould..

Properly made moulds will stay good for many releases, saving money and hassle ..  Just my $ 0,10  ...

 

"Sapere Aude"... Dare to KNOW!

The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...

103% of all people do not understand statistics...

Do not adjust our mind, theres a fault in reality :-)

That's my thoughts exactly and where we keeping going around. I say fix these plugs properly and don't worry about doin the work in the mold. I'd rather buff and sand a convex part than try to get in the corners on a concave part if that makes sense. I'm just racking my brain around his thoughts on why to not fix this or fix that.  Most of out stuff is chopp gunned with PE still. They had a bad experience with epoxy products and swear all epoxy is junk. He's very old school and stuck in his ways. I'm really the only person with a passion for composites that works here so I keep reading this forum and learning and other sources to improve and stay up with trends and products. He's about to retire and looking to sell the company. I'm interested but would change a lot of how things are done.