Epoxy Layup: Paint in the Mold

After writing this for another thread I thought it might be interesting for others as well:
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I've done this a lot on small parts-rc sailboat hulls to 6': wax with partall#2 and POUR not spray PVA in the mold. If done right in a clean room(with a clean recovery receptacle) the PVA will come out wih no imperfections and a gloss the equal of any wax.The part should be poured nearly vertically and left that way until the PVA sets. I tried using "High Temp" wax with no partall but because of the trace silicones it fisheyed-I'm fairly sure a good wax with no silicones would work as well.I then spray a Rober(Italian) primer or Imron into the mold(depending on whether or not the flange has to be finished); after about 30 minutes the hull layup can be completed(epoxy only) and the boat pops out with a first class paint job(or ready for one) weighing 65% less than gelcoat. I believe most polyurethanes that are catalyzed will work; epoxy paint will not work.
I even tried using Krylon(older formulation) and it worked perfecly!
Should work on larger parts. If you're going to spray primer in the mold you can spray the PVA-just takes a little 600 to get it ready for paint after the part is pulled. But if the flange doesn't require finishing spraying the Imron works like a charm as long as you lay up before 1.5 hours more or less. If you wait too long the epoxy and paint don't bond well.

 

Doug,

I've had pretty good luck spraying Proline fast cure epoxy primer into molds waxed with TR hi-temp wax. Once sanded it gives a nice surface to paint. (yes indeed, I've had some harrowing experiences with other wax/primer combinations) What I don't like about PVA is that it can release a little too easily, like when I pull the peelply off to bond in coring.

Yoke.

 

Hi temp

Interesting Yoke. I called Hi Temp and they said
their stuff had only "trace" amounts of silicones but it was enough to make Krylon and ,once, Imron fisheye. So I experimented with PVA which works real well in my application.
The other problem with wax was the tendency of the wax to transfer to the part-with PVA that problem doesn't exist.
How did you deal with the wax problem before painting? Is that primer catalyzed ?

 

Just use a Epoxy Gelcoat SP systems has a good one .and brush it in end of story. No pin holes ,Sandable You have a 3 hour wait and a 3 day lamination window ..

 

Like Yoke, we are spraying epoxy primer into the mould, but we're using Frecote 770n semi-permanent release - we then infuse Sicomin 8100 epoxy resin with excellent results. Sure it needs 'post finishing', but that can be with a zillion two-pack paint colours and finishes.

I rejected epoxy gelcoat because, as far as I could find out, it's either light-fast OR durable. Also, the very limited range of colours didn't suit the way I want the ROCAT to look.

Christopher
www.rocat.co.uk

 

HUH ?? Colours there are none !! I use the clear so I can check the laminate for bubbles/inclusions and provide a sanding base! What is so confusing?

 

paint in the mold

The system I discussed: spraying paint in the mold--- is an exceptionally light finish that requires no finish work when the part is pulled. No gel coat could touch it for weight-especially one that was brushed in. I think if you use a paint like Rober and spray Imron first you could spray the Rober primer on the Imron and have a finshed job with the added advantage of a primer for future repairs.I 'm not 100% sure that would work but the two together would still be lighter than gel coat...
---------Christopher, the Rocat is simply outstanding- you should start a topic about it under "Boat Design"...

 

You are talking about tiny little bitty projects I was spraying Linear PU paint in molds 20 years ago but did not like the results I.e.: the profile and durability question on a bottom of a trailered launched retrieved boat! As for weight my 11X 3 Meter offshore Cat weighed 488 with fuel tanks ready for power (two time WC BTW) Brushing GC is no different than varnish. Too thick Quickly change the Brush along with the brusher!!

 

War Whoop ... your cats and ours are VERY different animals!

So you are epoxy gelcoating, then painting on top? I can see the advantage of an initial clear surface on a big boat, but that would be one process too many for us, apart from the added weight.

"What is so confusing?" ... who said they were confused?

Christopher
www.rocat.co.uk

 

It is just I can not take a chance at todays speeds and demand for the more Mirror like fairing ..Oop's that was 488 Kgs Infusion behind the core is working blind I have not had any problems yet but the piece of mind from being able to do a Inspection is WELL worth the extra effort

 

Doug ... thanks for those encouraging words.

The reason spraying the primer in the mould is going to work for us is that the boats will be 'made to order', with the customer being able to choose the colour and finish. Producing the hulls in a primered state will give us much more flexibility, as production rate will not then be determined by colour choice.

Christopher
www.rocat.co.uk

 

... as I said, different animals ... my boat's good for about 10mph, and each 5m hull weighs just 8.5kg!

Christopher
www.rocat.co.uk