Wildstyle

I'm just at the stage of making my first mold, it will be a mold taken from an existing fiberglass cowling. I've researched a fair bit across the net. Question is, what is the best type of paint to use if I paint the mold before laying in the glass cloth? acrylic, lacquer?? how long should I wait from spraying the paint in the mold to laying in the cloth, and is there any reason why painting the mold won't work with a standard "non-vacuum bagged" layup, as opposed to vacuum bagging.
Thanks Anthony

sensei

I know this is really not what you asked but unless you are willing to spend the money and time to perfect your paint application process with whatever paint you wind up using, along with insuring your layup process is void free under the finish while not using vacuum is also perfected; you may just want to consider laying up your part, prime, and finish in the old school way.

Bob

ByLoudDesign

If you have a good smooth surface in your mold then a good waxing is all you need. If the surface is bad then repair it with epoxy and fillers, polish it to your desired smoothness and wax it. If you wish to have your part a specific color, you can use a colored gel coat, AFTER waxing.

Timthetoolman1

My Feedback: (6)

Painting the mold with regular layup and no vacuum will work but be sure not to have any void spaces under it from bubbles which is really hard to keep bubbles out in a wet layup.

I would use some thickened epoxy (thicken with microballoons or silica is even better) and brush it in the cowl after your paint has flashed off but before it's cured. Let the surface coat of thickened epoxy setup a bit so it's still tacky but does not leave any brush stokes if you run a brush across it. Then layup your fiberglass and the surface coat should keep any air bubbles from showing through the paint. The thickened epoxy will be thick enough not to run but not so thick it clumps up. Like warm creamy peanut butter. You just need a thin coat.

For paint on nitro models I'd only use Klasskote and use their primer. For gas I've seen just about anything including Behr house paint. If it's going to get a lot of use I'd still go with Klasskote on the gas planes. I have a big gas plane that has house paint but I don't use it that much. With KK paint you will wait about 4-12 hours before you start your surface coat of thickened epoxy so it has time to cure enough so it isn't damaged when you brush in the surface coat of epoxy. You could do it a little sooner depending on temperature and humidity...just press on it and see if it leaves a thumb print. If it does, give it a bit more time. I don't paint in the mold so from what I've seen with painting with KK this should work but I'm not going to say that any paint will bond properly with uncured epoxy.

I'm not a big fan of painting in the mold because if there's a seam you have to sand it down and repaint anyway. Even if you just prime the mold I would worry that the release agents will get in the primer and the paint won't stick. I still don't know why guys do it because it seems like it's more work in the end. Unless they just like seeing that pretty part come out of the mold. If your mold is perfect you can get a nicely blended multi-color paint scheme but you ruin it if there is a seem in the mold that has to be sanded and repainted.

I've seen guys use rattle can primer and they prime the mold and let it cure, sometimes for days, and their paint and primer is always peeling off. It may be the quality of the product they are using, or the dissimilar materials like polyester and epoxy, I don't know.

Good luck and post some pictures.

Tim

sensei

In 2002 or 2003 my aerospace composites company was granted a contract for the manufacturing of tooling, detail components and assembly of 50 all composite UAV airframes, these vehicles were completely in mold painted in olive drab green. There was a learning curve in mold finishing process to get the performance needed to satisfy the requirements of the contract, and that was utilizing vacuum and high temp pre-pregs with the exception of one wet layup in mold painted part, but still with the use of vacuum. So unless you are going into production, keep it simple.

Bob

MTK

From experience with same, do the following particularly if the lay-up uses epoxy laminating resin (any of them):

Wax the mold as if you were doing a non paint lay-up. Don't skimp on the wax layers.I really like Part All wax
Seal the wax with sprayed PVA. A couple med-lite coats are perfect and make sure you allow enough drying time. An hour is great. DONOTomit this step
Spray your paint or primer. I really like Klass Kote epoxy paints and their primer is terrific but extremely aggressive on its adhesion. If sprayed directly on the waxed surface, it will stick and you will ruin your mold. Polyurethane paints, heck, dope even, are all fine. Allow them enough cure time; DONOT lay-up epoxy and glass on wet paint
Do your layup. Vacuum is not required
Wait the appropriate amount of time for epoxy to settle down. If curing at room conditions a minimum of 24 hours is better unless you used an extremely slow hardener.
The part will come out of the mold easily. Peel one edge by hand and use an air gun to pop the rest of it off. Wash the PVA off with warm water....VOILA!!!

There are probably other techniques that are as successful. But I've re-discovered this method the hard way

Wildstyle

Thanks for the replies. for my first attempt or five, I'll stick with just a non-painted layup. If or when I do try painting the mold I'll be only using one color to start with at least.
I've done a bit of glassing over the years and made plenty of "lost foam" wheel pants. I've recently put together a vac pump system with a refrigeration compressor, and brought all of the necessary molding products (PVA, part all wax, tooling gel, chop mat, peel ply.. ). very first attempt I'll most likely not vac bag the cowl.

I'll stick up some photos when I get that far in the process, and share the steps. I'm sure there are plenty of others wanting to start out mold making and glass layups.

Timthetoolman1

My Feedback: (6)

Matt brought up a good point, the one thing that will ruin the layup is not using PVA and make sure it is dry before you layup your part. Be careful if you're trimming the glass on the edges if you trim the edges when it's green.

As far as the paint, I know you said you weren't going to use it but if you do at some point the KK paint is not wet at the 4 hour mark. You can handle it at this point without leaving prints in the paint. The majority of the paint kicks of in 24 hours and additional layers may have adhesion issues without sanding. With a few more days it will reach final hardness.

If you get a chance watch these videos http://www.youtube.com/watch?v=FCivvXA2FVU I have the guys watch this series of videos first before they come over to lay up their first time during our build nights.

Tim

sensei

The truth is a properly sealed and released tool surface will yield a much better surface for a finish application then anything you can achieve with a waxed and PVA coated surface, in fact utilizing PVA on any high temp tooling for pre preg application is literally an impossibility, so we only use it as an interface between our master models and lay up blocks, we never use it for production components. Boat manufacturer's have polished tooling surfaces to mirror a finish, then sealed, and waxed their tooling followed by gel coat and FRP applications without the use of PVA for decades, they do this for one reason, it yields a class A finish allowing them to move the product manufacturing to the sales department in less time. I do agree that that if you dabble in or do not possess a full understanding of composites then PVA can be an insurance policy from sticking things together, at least in the room temp to near room temp world.

Bob

SCALECRAFT

My Feedback: (13)

All good advise. If you use a silicone base mold release, your paint may fish eye. Test a small section with all your components once you decide to paint in the mold.

Back in the day, we used partall wax and PVA along with Duplicolor auto body paints and primers. We did the paint in the mold because it was a quick/cheap way to create a skin layer that was flawless. Plus you couldn't see the lay up. Today we have a better method.

As mentioned, PVA in the mold will yield a less shiny finish. The finish can be lightly buffed with a car wax to shine, but is the extra step that was mentioned in the Boat example.

steve

MTK

Sprayed PVA dries to a shiny surface usually. The result is also excellent, shiny. If PVA is sprayed thick the surface may not flow out right and the result won't be quite as nice as it could be

If the mold is glass smooth and shiny, and the PVA is the same, the end result will be the same. One man's experience

Timthetoolman1

My Feedback: (6)

Bobs right. Frekote is used in those molds in my experience, but we may be muddying the water for Anthony talking about production work, plus the storage of the prepreg, the tooling, and autoclave system to cure it are way beyond what he is wanting to do. I've only seen aluminum molds made and that was with mills and lathes but Bob hit the nail on the head, the tooling is a lot more expensive but the results from prepreg are beautiful and you can get the same finish every time.
I haven't seen how they do boats, just the SAE competition race cars, but I'd like to see the boat layup.

Steve, what were you making and how did the Duplicolor hold up? I've used Duplicolor a couple times but it's adhesion when using nitro was poor. Don't get me wrong, I'd use it in some cases.

Tim

wyowindworks

I really like using an IMC (in mold coating), PITM (paint in the mold), or what your want to call it. If the mold surface is excellent and the seaming edges of the molds are tight then the labor savings is significant. You can also typically get lighter parts as there is no need for primers or fillers. The bond of the paint to the layup, as long as the system is compatible, is also excellent. As others have said, if the mold is poor and layup has voids then painting the mold is a waste of time.

A few thoughts:
There are lots of paints that can work. Rattle cans, lacquers, acrylics, 2K urethane, and epoxy based paints can all work. Unfortunately, not all paints and resins will play nice together. Some combinations will leave a tacky finish that never hardens properly. The exact same paint with a different resin can cure hard as rock. Some resins will cause in mold clear-coats to turn hazy. Testing is helpful. My favorite resin that is compatible with every paint that I have ever used is MGS L285.

Klass Kote has release issues with many waxes and is touch and go with Frekote. Wax and PVA does work though. It works with just about any paint out there.

The waiting time between the painting time and layup can vary. If you are using epoxy layup resin then you can often wait for days before doing the layup and still get an excellent bond. I've often forced cured 2K urethane with an IR lamp in 20 minutes and then moved right on to the layup. Doing the layup too soon can cause curing issues with the paint and or resin. Again testing is helpful.

You cannot count on the paint to block any reactivity between the mold surface and layup resin. If you have a reactivity issues (sticking) then the paint will usually not solve the problem. Some mold surface and layup resin combinations will stick with only wax. Some will stick with semi-permanents like Frekote as well. Paint in the mold will not fix the problem. PVA will fix the issue. I personally don't like using PVA for in mold coatings because it's one more thing Ihave to spray into the mold. It's also never as good as my mold surface is and rounds out the seaming corning. Wax can work with some combinations but not all. I prefer to find mold surface, release system, and layup resin combinations that play nice together. Frekote is my personal preference for using IMCs.

Spraying paints onto high slip releases like Frekote takes practice. Shooting a flowing coat straight off will cause fish-eyes. You need to shoot a light mist coat, let it flash off, and then proceed with a heavier coat. If you like wax release then Dolphin wax is a great wax to paint on as it typically eliminate the fish-eye problem. 2K urethane can be tricky. A hotbox or IR lamp can be really helpful to force cure the mist coat before applying the heavier coats.

Backing the paints with primer is unnecessary for proper bonding. This is one of the the great things about using an IMC.

Seaming processes are typically better if they are done wet (co-cured) rather than processes that require green trimming, joggle tools, or cured laminates. The IMC can be very prone to pre-releasing from the mold surface. You then get resin creep between the mold and the paint. For this reason vacuum bagging can be problematic since the seaming is typically done after the resin has cured. It is possible to vacuum bag a closed mold but bladder molding is easier (my preferred method). Doing bulkheads with bladders is a bit tricky but totally possible and worth it. The layup gets compacted and seamed all in one shot.

Vacuum bagging is not necessary. In fact, it can cause more problems if you don't know what you are doing.

I'd recommend doing a few layups without paint to learn how to do layups before trying in mold paints.

sensei

This is why I stated what I did in post #2, as you can see from all these posts there are many different opinions based on each ones own experience of what thay may or may not have. Eventually you will form your own opinion on how to get it done from the road of hard knocks of your own trials and errors. Just have fun along the way...

Bob

daven

My Feedback: (1)

I would not use Klass Kote in the mold, I have had problems with it sticking (yes, with wax and PVA). Use automotive paint or primer, I'd suggest priming the mold for your first go around, the primer helps with pinholes dramatically.

sensei

Sealing your plastic or metal tool surfaces with something like FMS (Frekote Mold Sealer) prior to release coating them aids a great deal in any type of sticking issues. tool surfaces are far more porous than most realize.


Bob

Foxman

I just wax the mold a couple of times and then spray paint the mould before laying up in whatever color I want the finished part to be in.
I can even lay up the resin before the paint has hardened fully and it still never sticks.
I live in Thailand and we can buy some 2 pack polyurethane paint that goes off very quickly. Plus it's always over 30 degrees c or 90 F which helps I suppose.
I never use PVA or any other release agent, just the wax.
The finished part just pops out.