Fix a mold

General Composites Discussions Composites Talk
#1

I wanted to use my old carbon dash (not so great) as a mold for a new shiny one. the issue is that after i applied the primer and did the fist sanding, i could see all of the little pin holes that the primer didn’t fill. Now for the big question, will this be an issue in the infusion process? will wax and PVA fill the voids well enough?

Also is is there a good off the shelf primer that i can coat the molds with that comes in a spray can? I would need to polish up well. I don’t have a gun and the last time i tried to use my buddies, it clogged up and stopped working. I have access to one at the school but it can be days or weeks until i can go in and use it.

#2

You’re cutting a lot of corners and hoping to get a good result, I can assure you that won’t end well.

#3

Yeah I don’t need to cut corners nor do i intend to if the part needs work. If the infusion wont go well then i plan on trying to fill the holes somehow, as I am sure bondo wont fill those, re-spraying and going from there.

the original mold used to make the carbon part was ruined so i am trying to get the new part as close to the old one as possible.

#4

You need to surface the plug to perfection. That means sanding flat (using an appropriate epoxy or polyester mix), and re-spraying with Duratec surfacing primer.

As Hanaldo said, if you cut corners you’ll end up paying for it later. You need a perfect plug if you want a perfect part.

#5

Yeah its a mold not a plug. I will just fill the holes respray and sand up again.

#6

Sorry, I misread the post…

If you’re trying to re-surface a mold with primer you’re in for a bad time. You would be better off re-making the entire mold. That is a LOT of pinholes to repair…

#7

For an open/hand-lay mould a coating of Durabuild would suffice. Done it many times to reduce customer expense. However, with the amount of pin holing I would be inclined to make good and pull a new mould suitable for infusion. The quality of a moulding is linked directly to the tool in which it originates

#8

You can use a spot putty/glaze like Icing (USC) to fill the pinholes and weave. Then spray over with a surfacer like Duratec Surfacing Primer to make a decent mold surface. Of course, you need to sand the primer smooth and then buff. You’ll probably need to wetsand and buff (or clear) the part after you pull it out of the mold.

You don’t need a high dollar gun to shoot primer. I’ve got a Harbor Freight gravity feed spray gun that does a decent job on small parts I think it cost $50 or so and came in a kit with a jamb gun and a full sized gun. Buy some paint strainers and use MEK solvent as a thinner if you use Duratec.

Don’t catalyze more material than you can use in about ten minutes. Spray as quick as you can and then clean the gun as soon as you are done spraying.

#9

If you can get Duratec surface system, that’s the way to go. You won’t get a good result without being able to spray, so commit to that. The Duratec surface primer and high gloss topcoat are made specifically for resurfacing moulds, and they do a great job of it. Fill the holes, spray the primer, and if you need a very good surface finish then use the high gloss top coat as well. That will give you the best result you can hope for without remaking the mould.

#10

Yeah i did purchase a gun so that i could spray it and not relay on others and the spot putty worked really well in this application. I will shot it today and i am expecting the mold to be as nice as my other ones.