First Plug and Mold - Please provide any advice.
 

I am making my first plug and mold for a model I am building from plans.

I am making cowls for a twin. It is a very simple shape. Here is what I have done so far.

1) Got a big piece of foam insulation
2) Cut it up and glued it together to make a block.
3) Cut and shaped the block to form the shape of the cowl
4) Did oh so much sanding to make is smooth
5) filled in any pock marks or low spots
6) More sanding

The foam is about ready now these are the steps I am going to take

7) Sand with very find grain
8) Filler and sand some more
9) Lay on fiberglass (6 oz) and cover with 30 min Epoxy, lay on two more layers of the glass, maybe 4 layers with epoxy - let it cure
10) Sand it as smooth as possible, get rid of any high or low spots......
11) Prime with standard auto body primer
12)Paint with Gel coat (is this the right thing to do???)
13) Wax 3 - 4 layers with release wax-not sure what product to use

At this point the plug should be finished.

Questions:

Am I missing any key things?
Can I make a one part mold or should I do a two part mold?
Is there a better / faster way?
Am I smarter to get some Lexan and vacuum form the part?

Please advise a guy doing this for the first but hopefully not the last time.

You are on the right track. Put a layer or two of 2 ounce cloth on the plug soon, and do all of your final sanding after that. Get some laminating resin. Minute epoxy is junk. Use the resin you get to make your finished parts with as well. Finish your plug with primer and sand as necessary to 1000 grit. put 6 to 8 coats of mold release wax on and coat with PVA. Your plug is now ready. A 1 piece mold is easier if the shape will allow removing the plug.

For the mold, coat the plug with resin and lay 2 layers on .5 ounce cloth. Follow with 4 to 6 layers of 2 ounce cloth, and finally 8 to 10 layers of 6 to 8 ounce cloth. Cure for 3 days and remove the plug. Cure the plug for 1 week. Wax 6 to 8 coats and PVA. Pull your first part, wash the PVA from the mold, apply PVA fresh, and pull another part.

Scott

what is PVA?

Poly vinyl alcohol. It's a water/alcohol base parting film. Generally you spray it, but it can be brushed. The older product is green, the new stuff purple. The new stuff came into being for environmental reasons. Commercial boat builders in my area just use wax as a release agent, but our models are a slightly different application. We are trying to build small light parts that don't shrink as much as a say a boat. The greater shrinkage of the bigger parts helps to break the parts free from the mold. The PVA is not affected by the resin, or solvents, but can be washed off with water. Business like Fiberglast products sell PVA in quarts, or you could try to find some local fiberglass shop that would give you a cup full. Making molds, and fiberglass parts is not difficult, but there are many different ways, and tricks, to getting the best results. Good luck, Greg

Thanks for taking over Greg. Horrible day at work and I had no time to check in here. While some pros use wax only, I will caution against it. Wax provides slip on a mold (Making it slippery makes the parts come out easier), wax does not provide any chemical barrier. If there is ANY polyester of any sort (fiberglass resin, Bondo, etc) you will experience styrene migration where the mold will not release due to a chemical bond. PVA, when applied properly, will provide the chemical barrier needed to ensure release.

Note that I said use the laminating resin to finish the plug and use the same resin to construct your finished components? Now you know why. If you finish your plug with auto primer, your plug will not stick in your mold and your components will not stick in your mold.

Greg, how new is the purple PVA? Mine is still green. Is this a California thing, or did I just buy old PVA?

The color of typical PVA release film (old or new) is usually no color at all to my experience, but I have a bottle of the Partall brand (Rexco) that is purple, this is a special PVA made to provide a particular thick coat. Rexco might have other PVA formulas as well to provide the usual thin coat. I don't spray it on, I use a sponge and I apply it swiftly 1 coat wet on wet. If you go back with wet PVA on top of dry PVA with a sponge it makes sort of a mess. The reason I don't bother to spray it on is because the standard kind evaporates to a very very thin film making any streaking marks more or less invisible anyway.

If your last finishing coat on the plug is 1-component primer or paint you should take special care with the waxing, the solvents in the wax might penetrate the surface of the primer/paint so it needs plenty of time to evaporate before the next wax coat. I would look at it like this; when my plug is finished I deserve a week break before starting to make a mold, so in that week I wax the plug once in the morning (takes 5 minutes) and once in the evening, having the plug in a tempered room (not too cold) just like I would with drying paint so that the solvents evaporates properly. After perhaps 3-5 days you will likely notice a difference in the surface, let it be for a day or two before starting with the mold.

When you have applied the PVA release film to the plug and you are ready to start I would first apply a surface coat of some sort, in the smelly world of polyester this is known as Gel coat. Gel coat made to be used with epoxy is often quite expensive so perhaps others will be able to say what they have been using with success, a thickened epoxy mix of some sort might be adequate. This surface coat should be applied as a thick coat and let cure to soft plastic before proceeding with epoxy and fiberglass, it should make the mold inside surface nice and free of air bubbles and it will prevent the texture of the fiberglass to become visible in the mold surface.

Finally if the plug should seem stuck to the mold when it's time to part it don't panic, this would be quite normal for a first time. It only means that you should take two steps back, take a deep breath and start carefully to remove the plug the best you can. If you made your plug base in foam and not from something like MDF you will be quite happy you did, the plug might not survive but the mold will likely be perfectly fine as long as you take your time to carefully remove parts of the plug or primer/paint from the plug that may be still in there. Making your first molded part is quite an experience and when you know how to, it's something that you take with you as an additional skill that will advance your possibilities for future projects.

For a surface coat on the mold, I use laminating epoxy thickened with some microballons and carbon powder. The carbon provides the hard surface for scratch resistance.

Unless you are going to make lots of parts I see no need to use any surface coat other then a few coats of the same resin system you will be using to make the remainder of the mold. I will usually do a couple coats of straight resin with a tint added allowing the resin to tack up between coats and then a couple coats with tint and some cabosil added. After that tacks up I do a final thickened coat and lay down some light cloth followed by heavier cloth until I get the build up of thickness needed. If I am doing just a one off part I will usually skip making a female mold and just fab up the part on the plug. Red mold is one made using my described method. The other pictures are a one off part using the plug as a male mold.

I make my molds similar to ibuild. My molds are two pieces with a parting board at the split line. Once I have the parting board in place I wax and PVA the plug and parting board. Then I mix up epoxy and West Systems Colloidal Silica to a peanut butter thickness. I use a cake decorating through away bag to fillet the corners ware the cloth will not go. Then mix up a surface coat with carbon power so it will stay on the vertical sides. I let this setup until it becomes tacky and does not come of on my finger. Then recoat with epoxy and apply the cloth, 1- 4oz, 2- 6oz. let set up again. This is where I differ I use a layer of Coremat core material cut in strips. Then 1- 6oz and 2 layers of 8oz crowfoot cloth.
Laying up the part is similar. I will use some color pigment for the surface coat. 1- 4oz, 1- 6oz cloth then in areas additional glass cloth, carbon fiber, Cormat or Divenacell core material. I never had a part stick in the mold. I have only made two fuel tanks before I started my A10. I just finished laying up the front half of the fuselage. The fuselage, nacelles and wheel covers are done.
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I think I have about 12 layers of wax on the plug so far, it is about as perfect as I can make it at this point. As this is my first attempt, I will not be upset if it has some issues, but think it will be ok. I actually have a second plug started as well, needs a bit more sanding but should be ok.

As far as my process so far:

1) used blue 1" insulation foam, covered first with 30 min epoxy, then a layer of 6 oz fiberglass cloth, covered with a good quality laminating epoxy. Then did a second coat of laminating epoxy.
2) sanded between each set with 80 grit, 150 grit, 220 grit and 600 grit, filling in any imperfections.

3) Waxed with mold release wax, 12 + coats, careful to get all corners and seams really well. At this point it is SMOOTH! I think it is ready to make the mold. I am thinking about getting some PVA - sounds like a good idea, but it is a long haul to the composites store for me so I may not bother.

I do like the idea of doing the first coat with some micro balloons - think I will try it.

One more thing, I did not prime the plug, is this good or bad??

I prime and fill all the bad spots until I am satisfied. Then a last coat of primer and final sanding. I put six coats or Wax ( Partall Hi Temp.) Then I spray one to two coats of Partall Coverall Film on. I use to brush it on with a foam brush but got bad runs. No runs with spraying. I let it totally dry before I start laying up. I never had anything stick.

I started the mold last night, it has set up ok, not the cleanest, but not bad for a first attempt.

I checked it this morning, it is still tacky, once it has cured a bit more and the tackiness is gone, I will sand the and put on a couple of more coats of 6 oz glass. Then I will let it sit for a few days to fully cure, sand again and pop if off he plug.

Just for fun I am also starting a second plug for another mold. This one was easier, now that I have a better idea what I am doing and am getting better with the materials.

I used to view this type of process as a real pain in the ___ but I am now seeing the pride of doing this type of work.

Really enjoying it so far.

OK, so the wax that I put on the plug did not work well at all. I had to gut out the foam plug. The but here is that the mold looks really good, there is a bit of sanding an some bondo needed but over all it looks really good.

Once I get the mold smooth I will prime, sand, fill, prime sand and then lay on 10 - 12 layers of wax, then I will PVA the mold. Don't think that I will be fabricating a part until next week. I am also started to make a second plug for another mold - already started to wax it, I will PVA this one as well.

I see a problem with your plan. Notice I said on post #5 not to use any bondo or polyester? Styrene migration is a real problem and could cause your finished parts to stick in the mold if you use bondo on the mold. If you go that route, be sure it is well covered with 2 part epoxy primer, and don't sand through the primer anywhere. I would repair the mold with filled epoxy if necessary.

Scott

Manks7477, you have gotten past the first barrier that is actually to do the work, the next time you already know what to do and it makes it alot easier. I wish you did use the PVA the first time, it would perhaps still not part perfectly but we would have a better reference to give you advice. I know it might take the air out of the balloon if people say like you should have done this and not that and so on because obviously we all know the effort involved, also I know you would want to manage and get started with what you already have on your shelf rather than buy a lot of other stuff that costs money and perhaps takes time to get hold of.

The advice Scott is giving you about getting some 2 part epoxy primer is a good one. I get it from the car/auto shop and it is not particularly cheap, but it is something else than the epoxy used on the plug and mold and it makes a secure base for the wax as the finish coat on your plug. You have done just the right thing starting with a reasonable simple shaped cowling, some people goes through all that with something like a complete fuselage and the effort as well as disappointment could take the breath away from anyone. Just look at the pictures from Speedracerntrixie, this is what you will be capable of doing.

I do appreciate the help! Overall I am very happy with the results, the mold is in good shape, not perfect but pretty close, any defects can be fixed with some more sanding and maybe filling with a bit of epoxy and filler. I will prime the mold as per the comments and then put in many, many layers of wax, then PVA. Even if the parts pulled from the mold are not usable, this was a really good learning experience.

I have a second plug that is almost ready to go, this one again is simple, only going to pull one part from it, but it is more good learning. By the time I do my third plug I think I will have the process pretty much down.

I may try to do the hull of a boat before trying a fuse - just seems like it would be a bit easier to do. I am actually finding the process to be very satisfying. I thought I would go crazy making things perfect, but it is oddly enjoyable.

I really hope you are NOT going to prime your mold!

I was going to, with a 2 part Epoxy Primer - is this wrong?

I usually do repairs to my epoxy molds by 1. clean with acetone, 2. clean with soap 3. clean with acetone again 4 sand the problem area (even dremel out any bubbles or where you can't get sanpaper)5 apply epoxy and thickener to any divots or small problem areas (I am talking about small little problems, not resuracing the entire mold) attempting to make level 6. cure 7. sand with fine grit to level 8 sand with finer grit 9. wax and PVA. Low spots in the mold will be high spots in the part.They can be sanded down before priming the part. Your mold doesn't need to have a perfect surface finish. Being too perfectionist when beginning will drive you nuts. Learn from your mistakes and go on. It's gonna take a few times around the block before you work all the bugs out. Being too cheap can drive you nuts. Been said before and I'll say it again, wax AND PVA works for beginners, some people can make only wax work, some people can make semipermanents work, beginners can't seem to get good results with any thing but wax AND PVA.

Did my second mold using wax and PVA - same problem, plug had to be cut out. The good news is that the mold turned out really good, much better than the first. I will take more time and effort waxing this one and making sure the PVA fully covers the mold.

I am getting better, it will take some time - but improving as I go.

Gotta think you put a thin coat of PVA on, must have been too thin. Doesn't have to be thick, but one full wet coat. A dry thin coat that dries almost immediately is too thin. It looses allot of it's thickness when it dries. Yes it is a little bit of an art to get a full coat and no runs

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It's a little mysterious this particular subject to get a nice release when making a mold, one should think there is a simple receipt to make it work but it's just not that simple. Some people like Jefff goes through it with no problems and hit the bulls eye right away, but I think most of us needs to make some experiences and get it in to the hands. It's basically about that and what goes well on top of what, buffing the wax lightly to a shine without buffing it completely off and have the patience to let it rest between coats. If it's any comfort the more mistakes you make the more you will eventually know about it, personally I always makes a lot of mistakes before I get there with anything - it should make me a professor by now hahaha :)

Anyway, if you have a mold now thats great news! It would be good for you to progress with the actual part, if you stay for too long with one particular stage it will certainly as Rudy says drive you nuts.

I just read my own post and that doesn't sound encouraging at all does it, I guess my strong ability is honesty more than tactical...
Anyway, I think that in most cases the release is easier from the mold than from the actual plug because the mold is made from a waxed and smooth surface already, also I am beginning to think that perhaps using a spray-gun of some sort to apply the PVA might not be such a bad idea after all. It should be easier to apply a fully covering coat and it should even make it possible to apply two coats to be absolutely sure.

The spray gun that I use to spray the PVA on is just a cheap gun from Harbor Freight for about $12.00. I set the compressor to 40-45 psi and the fluid control wide open. This solved my runs.