Need advice for plug surface finishing

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#1

I’m in need of some advice regarding plug surface finishing.

I wanting to make a set of molds off my motorcycle bodywork.

My original plan was to touch everything up and paint and 2k clear it all. I was going to use frekote semi perm system for releasing off the plug and get a nice mold right off the bat. So far I touched up the bodywork, primed and sprayed basecoat and clear coat. The clear coat needed to be resanded due to surface imperfections because I used a cheap gun that was very difficult to dial in. Right now the bodywork has 2K clear sanded to 400.

My dilemma…

Should I forget about laying the second layer of clear coat and go with a PVA for release

OR

SHould I lay down the clear and go with the semiperm for release?

I’m wondering which would be less work and give the best gloss surface?

Will the PVA fill/hide the 400 grit sanding scratches?

I’m worried about getting orange peel in the clear and also fibers/dust settling in the PVA. If I spray the PVA it will be in the garage, but if I spray the clear it will be in a professional booth so there should be very little if any dust etc…

Thanks.

#2

Go for a PU clear coat, if you spray normal 2k you probably end with a messed up mold.

Sand down to 800 or 1000 and then spray clear coat and polish the clear coat. Don’t try to safe time on your plug and mold. Invest time to get it perfect and it safes you a lot of time with the end products.

#3

I’ve had issues with my parts not releasing from the mould due to buffing off semi-perm like a wax instead of leaving a layer on the surface… which has resulted in me making a lot of plugs and moulds recently!

My brother and I have been spraying with 2K paint (not clear), then wet flatting with 1200, 1500, 2000 and then compounding, and I think it’s a really reliable way of making the plug. We have perfect surface finish, which means any defects can be easily seen and repaired, and our moulds have come out really nicely.

I’d recommend this, since repairing gelcoat or adjusting the mould (especially concave like mudguards etc) where you have funny highlights etc is a right pain, and if you don’t sort these issues it will ruin the overall effect of your bodywork.

Michiel, I’m aware that some ‘2k’ paint from a can doesn’t always end up being compatible with resins, but from a gun what issues may be encountered?

#4

Wet sand 1500 and polish your pattern top coat.

Frekote sealer, Frekote release and then also wax. Don’t buff anything, apply as instructed in data sheets.

Apply your mould gelcoat and layup.

No PVA needed.

#5

Pva rarely spray perfectly… I would not rely on it.

#6

I only ever use PVA for plugs, Frekote is a right prick. Fantastic for making carbon parts, but too much slip for making moulds. Pre-release and fish-eyeing are no fun at all. Also I always break my moulds in by rubbing them back with 1200 then polishing, so getting the pva perfect isn’t an issue. That said, I can actually spray the PVA to give a near perfect surface finish. Takes 15 minutes of flatting back and polishing after.

Sure beats having to redo a mould because the plug slipped out while it was curing. No risk of a paint stick either.

#7

thanks for all the suggestions!

Any tips for spraying pva? tip size/hvlp or conventional/PSI?

If the goal is to use semi perm on the final mould then what sort of buffing compound might one use that will not interfere with the semi perm sealer/release (frekote in my case)?

#8

Do you use poly gelcoats or epoxy brush on gel coats on your semi-perm’d plugs?
Any issues with the gel/surface coats balling up on the semiperm surface?

#9

The large moulds I made recently were a polyester tooling gel applied with a pressure pot (which I hate using). Small moulds are done with a gravity gun.

No problems with the semi perm as long as it is waxed over too. The wax helps the gel coat grip the pattern better and you still have the security/release of using the semi perm systems.

If your mould/pattern shape has any corners and surfaces that may typically shrink and release (pre release) then these may do so with just semi perm alone.

#10

I spray PVA with a HVLP gun, normally using a 1.2mm tip. Have used used a 0.8mm tip on smaller parts and a 1.8mm tip on occasion as well. PVA has excellent self levelling properties but runs easily, so I normally do the first 2-3 coats as a mist coat, then spray 3-4 full wet passes. Treat it exactly as you would a paint and it will turn out well with a bit of practice. Even if you get a run, let it dry and make your mould, then it only takes 5 minutes to rub the run out using 400 and another 5 minutes to polish it back up to a gloss.

#11

Thanks,

I tried spraying PVA and it seemed like the gun was spraying bubbles into the pva on the part I was laying it down on…

I just got a real fancy Iwata LPH400 but I would be hesitant to spray anything remotely water based from it, do you use high quality guns to spray the pva or do you get good results from cheap ones?

#12

Nah I just use cheap $30 ones for PVA, only use my expensive gun for spraying Duratec coatings.

The air bubbles come from spraying too heavy a coat. You need to spray it thinner and in more coats, otherwise it bubbles. Also if it is particularly hot where you are, don’t spray it in direct sunlight. I’ve found the heat can make the air bubbles a lot worse.