Is wax alone good enough?

General Composites Discussions Composites Talk
#1

OK, let’s be honest, I’m just scared. I have finished my plugs for a hood and dash so it’s time for some mold making.I’m trying really hard to not use PVA so I can be like the other cool kids but I’m afraid of having a plug permanently attached to a big chunk of fiberglass. I would love to use some semi-perm but I can’t justify the expense with the quantities I need to buy it in for only a couple parts. The plugs are primed with a 2K urethane primer (Pro-Form) and then sanded and polished. There isn’t the same shine as a polished clear but I figured since I will be painting or clearing the final pieces that I didn’t quite need the same gloss in the mold. This is not to say there is no shine, they are still baby smooth, just not a schwanky clear gloss. That being said I do understand that the better the finish the easier the parts will come off.

So the big questions is am I just a chicken and I will be fine with 7 good properly applied coats of wax on my plugs, and subsequently the molds later, or is there some merit with my gut wanting to use PVA? I was intending to use Mequair’s Mirror Glaze 8 for a release wax. As always thanks for the priceless advice.

#2

Shoot a 1’ x 1’ scrap with your primer, prep it just like plug, apply the wax, and test the exact resins that you will be using. If the release is good you know that the wax/paint/resin combination works. If the release is sketchy then you need to use PVA.

#3

A test is always a good idea. Be carefull with your plug materials, they can react with your resin. Especially paint. I had a lot of problems with paint, even from professional painters (I’d rather do it myself nowadays).
A good hardened PU paint, with m87 or m88 (last one’s a bit slippier)should provide no problems and a high quality mould surface.

#4

For what ever reason there are allot of guys here that simply hate the use of PVA. Bad experiences and such. Wyowindworks is right; the only way to really know is to test.

I use PVA from time to time and can actually improve the finish of a plug with a couple decent coats, which will actually improve the quality of the mold. I think one of the biggest factors of people having issues with PVA is the inability to spray it correctly. Before I got into composites work I did quiet a bit of painting so applying PVA came natural to me. Other guys that may have started in composites are used to spraying gelcoat with dump guns which just isn’t that precise, so when they try to spray PVA they can’t get it to lay down correctly.

The trick with PVA (other then cleanness, and the basics) is applying enough to allow the PVA to flow and create a glossy film over the entire part. Depending on what you’re spraying there can be a fine line between enough and too much.

#5

You are going to have a few problems spraying PVA on Meguiar’s #8 if you need to use PVA. The PVA is going to want to bead up on the wax. The way to get around it is to very lightly mist/fog on the first coat. I do this by just barely open the product release stop on the spray gun. Then let it set-up and do a slightly heavier coat. Once this sets up you can shoot a nice flowing coat. If you don’t want to mess with flowing coats the use Part-all Paste #2 release wax. With this wax you won’t have to worry about PVA beading.

If you are spraying in warm temperature and a dry climate you can reduce the PVA with about 10% water. This will slow the set-up of the flowing coat and allow it to flow out flat and glossy. If you reduce the PVA too much you can get excess shrinkage and the PVA will pull out some tight corners. The PVA barrier will also be thinner. I like to use a gravity feed gun and about 35-40 psi. I shoot with the gun about 8" away from the object. The PVA is going to go on looking very milky when shooting a flowing coat. Don’t panic, this is how it’s supposed to look when applying a proper flowing coat. If the PVA doesn’t set-up too quickly the PVA will clear up and look really nice. If the temps are too high the PVA will get “stringy” coming out of the gun and the PVA won’t have time flatten out. If you don’t put on a heavy enough flowing coat the PVA will look rough. If you put it on too heavy it will run.

I’ll agree that PVA, if sprayed correctly, can improve the finish of the plug or a mold finish. Below is a photo of PVA on a little home project.

#6

Thanks for the responses. I was planning to do up a test panel but didn’t know the correlation between a small piece and a larger one like a hood. As was stated one reason was to also test the reaction between the gelcoat and the primer.

That piece looks great wyowindworks. There is definitely no surface degradation from you ability to use PVA that I can see. The last time I sprayed PVA I use a gravity feed HVLP with 10psi at the gun and a 1.8 tip. I seemed like it wanted to dry and “string” in the air before it got to the part. I was thinking of experimenting with a 2.2 tip but I don’t know if that would make a difference when it comes to a mist coat. I’d imagine adding a touch of water would help with that so I’ll have to give it a try. I also have honey wax mold release. Would that be a better alternative under PVA or are they both relatively the same?

I think I may be getting a touch over nervous as this is where all the hours of work either make it or horribly fail. :slight_smile:

#7

I shoot Part-all Film #10 (PVA) with a 1.4mm tip.

The stringyness is from spraying in too warm/dry climate. I like to spray in cool temps. Try shooting in the morning while it’s cool if you can’t control the temps. You can also humidify your environment by misting the air with a spray bottle. This will also pull dust out the air. If you are still getting strings you can reduce with 10% water. DON’T reduce it with alcohol. This will only compound other problems. The PVA needs time to flow out on the surface. You want to slow the set-up time. Alcohol can accelerate it which the opposite of what you want.

You are taking the right approach about being cautious. I’m always shocked at the number of people who do not test when working with new paints, resins, and releases. So many disasters can be avoided by testing. I always test the release with trying a new release agents, plug finishes, mold surface coats, and layup resins. Change any one and the combination many result in sticking.

If you are concerned then use the PVA. The role of the PVA is to create a barrier that will block any reactivity between the plug surface and the layup resin. Wax provides the slip but it cannot block reactivity…no matter how many coats you apply.

#8

I second everything wyowindworks is saying here except the thinning. I’ve never had the need.

With two other little comments - when I use PVA i don’t use any wax before applying the PVA, I just make sure the surface is perfectly prepared and well polished. I use a gun with a 1.8mm tip and no thinning, just make sure to spray when its cool with no direct sun light.

#9

I typically never thin either. Thinning should only be done if the operator has no way of reducing the ambient temperature or raising the humidity. If you have no control over these variables then thinning can be the difference between getting a nice finish or not.

Interesting about not using wax under the PVA. I guess I’ve always used PVA when the surface is less than perfectly prepared. If I’ve prepared the surface then I go with a wipe-on wipe-off semi-permanent release. Good to know that it’s possible.

#10

I have used PVA on a grit 80 sanded epoxy boat, to make trailer moulds. (no wax used). Even that works…

Still what I like to use for plugs is PU paint, semiperm sealer, and high temp wax over it, to prevent gelcoat beading. Works everytime, in the largest projects.

#11

I have seen some epoxy resins stick pretty firmly to the PVA and the only way to get it off was to wash it off with water. In fact, the white PTM&W epoxy surface coat will have a permanent “green” tint after being applied over PVA. No amount of washing with soap and water will get it off. If the PVA bonds to the plug due to the scratches and sticks to the molding resin then I would think that the release would be pretty difficult. Again, I only use epoxy surface coats so this could be the difference.

#12

The last mold I made had only PVA applied to the plug. When I demolded the PVA largely stayed with the mold which was VE including VE gelcoat.

The PVA would tear off the mold as a thin film. There’s something strangely satisfying about removing PVA in this way… Kinda like putting rubber cement on your hands as a kid and pealing it off. Weird.

#13

Haha, yes it is strangly satifying.
But I hate using it in high quality production though. applying with a brush, sponge, paintgun, etc. I never ever get the result I need. Same with some semiperms by the way, they leave stripes.
I never have real problems with wax or semiperms, so I stay away from PVA as much as possible.

(but somehow the can in my garage seems to get more emty anyway, especially when I use someone others (bad) moulds.)

#14

Devil’s advocate here, but you really can’t afford to pay $20 for a pint of Frekote and $35 for a pint of sealer?

#15

Maybe I didn’t look hard enough but I only found it in gallon quantities north of the border. If I have to ship it across the imaginary line you can at least double the cost. That being said if anyone knows of pint sized retailers in Canada then let me know.

#16

I’m surprised no one has mentioned using a microfiber towel to wipe on PVA, especially on a waxed surface. I’ve done it on several molds so far with good success with both polyester and epoxy resins. It takes a little practice at first to reduced the streaks, but a clean, soft towel will definitely help.

#17

I had to test this. :smiley:

I sanded a scrap with 120 grit sandpaper. I waxed one half and left the other half unwaxed. I shot the scrap with PVA and then preformed a little layup on top of this with an epoxy resin. I was quite surprised to see that both halves released. The waxed side definitely released easier but the unwaxed side did release.

I learned something today. :smiley:

#18

When I make quick molds, (you didnt hear it from me) I usually never use wax. I just go straight to PVA.

However, now all of our molds are made with perfection. We have the flanges milled, then we apply a polyester paint, then we wet sand and buff, then seal, wax 10 times, let it dry over night, then spray on the gel coat, fiberglass it, and tatda! Finished mold.

#19

PVA dissolves in water. If you cannot get the part loose, soak it in water, pry an edge loose, add more water, and with some patience, or even soaking for a day, you get the stuff loose without damaging anything.

#20

I never had any good experiences with waxxing. I use to follow the book when it comes to release waxing. This guy will tell you 2 coats that one will tell you 6 cotas and then you get someone that tells you 8 coats. never the less it never worked. so then I decided to go 25 coats!!! after the 5th coat it became so hard to buff to a shine that i had to buy a car buffing polisher machine. 2 days later and 25 coats , i started building a mold for my buffed up hood. a couple of days later my mold was finished and i had to demold. when i turned the mold around the plug fell out by itself!!! So somewhere between 1 and 25 coats lies the perfect number. take a guess?