Here’s a question for the experts out there. Does anybody spray in a Polyurethane clear coat into their mold prior to gel coat and later infusion or lay-up? I’m getting a really good finish on my parts straight out of the mold, but then if I want to spray with PU I have to let it dry and go back and sand then polish to remove the orange peel. Sanding Sucks!!!
Cheers,
Jer
Interestingly enough Lotus cars spray paint onto mould surface prior to laying up car body, so would think what you have in mind would probably work fine.
I made the mistake some time ago of spraying polyurethane paint into a mold and then infusing with epoxy, it doesnt work. Stupid me if i`d thought about it it would have been obvious. You can paint plugs with polyurethane paint and get a good release, waxed of course. I demolded it and the polyurethane was left in the mold well most of it lol.
I have sprayed parts with poyurethane and know what you mean re the orange peel it doesn`t flow out like conventional auto paints. I now use 2k paint and boy is that good gear, paint, wet sand with 2000 grit and machine buff and polish on the same day.
Baz
I cant see how anyone is spraying auto paint into a mold and it working…
The wax is the paints worst natural enemy. Ive not gotten all the wax residue off a part right out of the mold and had severe fish eye problems.
I now wipe all my parts down with DENATURED ALCOHOL right out of the mold to get rid of any wax residue.
Heres an abstract of an SAE paper detailing the Lotus production method: http://www.sae.org/technical/papers/910441
I dunno classic…Im not gonna take a sentence like “paint in mold process” and use it literally.
For all I know that means they shoot gelcoat into the mold via paint gun and then send in the machines to lay it up and infuse or however that they get it done.
There are several problems with a real PAINT IN MOLD PROCESS.
One being that there is little to zero probability of making a perfect panel that doesnt need to be trimmed and finished to get auto paint and polishing.
The second being that there is no way I can think of to shoot paint at a polished metal mold (like they say they are using…nickle I believe) and not have the paint running, sagging or any other number of blemishes.
What I gather out of that is that they shoot a surface coat and then use the ??VARI??? or whatever the acronym is. I can see them using the right colors to get the paint done faster and with less coats but I really cant believe that they are shooting paint into a mold and then pulling out perfect parts.
Suggest you take a close look at a recent Lotus…seems to me the process works pretty well!
Just because they say paint doesn’t mean they use typical bc/cc coatings like we’re used to. Perhaps it’s like powdercoat or a proprietary process.
What’s 2K paint?
Sorry jj i thought you used the same terminology over there, it`s 2 pack auto paint, in this case the clear and hardener.
Baz
We do use the same terminology. Usually only painters refer to 2 component paints as 2k; not the composite guys. 
I see one ever three to four days at our local “COSTCO” bulk grocery store.
Looking at it means nothing to me. The end result doesnt prove the claim.
I want to see them shoot automotive paint into a mold and layup on top of that…till then I think its mis interpreted.
They dont use automotive paint…this isnt likely to work at all!
I seem to remember the process they do use is outlined in the Forbes Aird composites book…think they use polyurethane paint of some sort.
Perhaps one of the major advantages of painting the cars in this way is the fact that this method is less costly, and obviously makes any repairs to body panels easier to do than if it was a gel-coat finish.
Ill have to take a look in the one I have. I think that there are three books of that specification.
Im still really unaware how anyone making parts has zero trimming to do after demoulding. I wish I knew that much about it.
In any case as a personaly case…I kind of like gelcoat…its easily repaired under paint and it gives a good surface to bite into.
Here in the states a few companies making motorcycle bodywork use white gelcoat as the surface coat. Most people hate them for the weight (non related of course) but I always encourage “street” riders to use it so you dont have massive weave shrink appearing in your paint.
I see enough race bikes and street bikes with composite bodywork that isnt gelcoated and the paint jobs always look like piss.
Thanks for all the feedback everybody. I mainly use PU clear due to its UV resistance. So does the UV break down and discolor the gel coat, resin or fabric (carbon)? If it’s just the resin or fabric, then could you spray in the PU clear after you’ve sprayed the gel coat in the mold?
Thanks again everybody!
If you’re going to use gelcoat, you can just use marine clear gelcoat. It already has UV inhibitors in it. Many of us use urethane clearcoat for better aesthetics in addition to UV protection.
I had tried spraying in paint onto a mold before (semi Perm. released) and it would just fish eye and look like crap. Even after making the part the paint stayed on it but looked ugly. Nothing ventured, nothing gained…
We had pretty good results from a water base PUR clear coat from a seller on eBay in the classroom, but you really had to use alot and spray it on until it looked like it (flat panel clip boards) was cover in milk!
Hey guys,
What brand of two-pack PU are you all using for your clear coat? I went down to the local auto body shop. They have it, but you have to wait 24 hours to sand and then another 24 hours to polish. Supposedly to let it de-gas… If I could find a brand that I could sand and polish within a couple hours I’d be a happy camper!
Cheers!
If you use medium solid products, and are able to speed up the curing process with infra red lamps maybe, you will bw able to sand quicker.
2K clear won’t stand up to the heat generated during infusion anyhow. Most you can heat that stuff up to is 160 unless it is fully cured ( 3 weeks ).
2K urethane clear can be reduced with a urethane grade reducer ( not urethane basecoat or primer reducer though). The maximum you can reduce it is 10%… usually most painters go 5% if they need to reduce it.
How to set the gravity feed HVLP gun: ( use a 1.4-1.5 tip size for clear coats)
Open the paint knob FULL OPEN, then turn it in half a turn.
With a diaphram air regulator AT the GUN set it with trigger pulled to 40-50psi. Trigger must be pulled in.
Set the fan pattern/width knob to how you desire fan width.
Your set, now more orange peel will happen. The clear should now flow out and lay nice and flat. Hold gun 8-9 inches away from part while spraying. Use a paint filter/strainer when mixing the clear components into the cup. Use a simple $20-60 inline filter after the compressor. Set your compressor pressure regulator to 80psi… you should have one at the gun AND at the compressor for best results 
If you’re still getting orange peel, turn the air pressure at the gun up 5psi. 50 is the max. If still getting orange peel it’s because the gun is a piece of junk.
Spray Away!