New mold damaged after 1 use

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#1

I am new to the forum. I run a composites shop in Point Richmond CA where we work almost exclusively on racing sailboats. Recently we decided to build a fiberglass mold for making emergency rudder blades. We made our plug and pulled a mold off of it. We sprayed the plug with Duratec Hi-Gloss Vinylester orange coating (1908-045 orange).

We built the molds using vinylester resin. We screwed up in that we should have used an ISO resin that doesn’t shrink but in the end the part was stable enough for the application (ie emergency rudders don’t need to be beautiful).

We had no bonding issues when separating the mold halves at all. We used Part-All #2 wax, seven coats to be exact. After separation it was time to crank out our first blade. (We made sure the mold had adequate draft to get the part out when we build the plug btw). I polished the mold surface to a really high gloss. We waxed the mold 7 times again, with the same wax. The e-rudder blade is carbon (first layer is 90-degree plain-weave) and subsequent layers are bi-axial and unis. We used epoxy resin (US Composites), and vacuum-bagged the part. We went with a carbon-apparent finish, so we did not spray any kind of surface layer in the mold.

On one half the mold, the part popped off with some difficulty and I had only small chips on one of the edges. On the other half, the mold is basically beyond repair. Huge bummer obviously as this was a very expensive part for us to build.

Despite many years of composites experience, we seem to be having big problems when it comes to molds. Did we trap solvents? Did we screw up by not using PVA? It seemed adequate to wax the mold 7 times, but when I look at the skins of the rudder, it’s like they bit into the mold in splotches here and there and just wrecked the surface.

Any help will be greatly appreciated. See attached pics.







#2

I have had problems with wax release… I now always use a semi permanent release…

#3

I had problems one time when using wax and epoxy. I now use semi perm release and have 0 problems. Also important is to use a sealer first. Frekote is the brand I use. Not to mention it’s less work. When I put so much into a mold I’m not taking any chances. I can’t believe people build parts out of carbon fiber and then think semi perms are expensive.

#4

Epoxies usually release well since there are no solvents trying to attack the mould.

These days I always use at least semi-permenant sealer on the mould first to ensure any porosity is filled and then your waxes. Or semi-permmenant sealer, release and waxes. Frekote or Zyvax etc.

Was the wax well cured or did you maybe layup too soon after the last coat was applied?

#5

I think the last layer of wax went on something like 2 hours before we started the layup.

#6

Thanks for the good advice. So something like Chemlease R&B EZ would qualify, and first apply a sealer like Frekote?

Wish I had done this right away. The mold is pretty beat up, and what’s worse, we damaged our plug too.

#7

Epoxy layup resins and only wax will typically stick on new molds. You need to use PVA during the break in period of the new mold. Wax cannot block the linking of active sites on mold surface with the fresh layup resin. Not all of the epoxy molecules in the vinyl esters chemically link… especially if the mold hasn’t cured for many days. The epoxides within the layup resin link with those in the surface coat of the mold. The result is a stick up that wax cannot prevent. PVA needs to be used until the mold surface is no longer reactive. Often the wax or waxing technique is blamed which is rarely the problem. Heat curing the mold can help because is progresses the cure of the resin resulting in fewer reactive molecules. The reason that one side released easier is that it probably had more time to cure which reduced it’s reactivity. Proper mixing of the mold surface coat can play a role in its reactivity as well.

PVA is often thought of as the devil, at least on compositescentral, but it probably would have saved you.

Many semipermanent systems (sealer and release) have the ability to block this reactivity as well.

#8

Just an observation which may be wrong but the gel coat looked quite thick so that might have also been contributing to the gel pulling off as there was no glass to bind it together… I have started to use chopped ends of glass in tight radius areas more as that was one problem I had with a couple of moulds… my mould making is still awful but I have learned that if I am going to damage a mould it will be the first time I use it due to poor waxing or releasing… I tend to over release the first time and really make sure it is ok. I then make a glass part out of the mould just in case the release causes some fish eye issues with the gel coat.

#9

#10

Btw, parts made with epoxy are signicantly more prone sticking than PE or VE. The release practices used with PE and VE with often not directly translate to epoxy.

#11

third photo lower right next to fridge/oven…

#12

The gel doesn’t look too thick to me based on a comparision with the carbon weave but looks can be deceiving. Regardless, the gelcoat is stuck. Too thick gel would tend to chip and/or crack through use. Sticking is a whole other animal.

One of the standard practices in composites, at least as it relates to the marine industry, is to first put on a “blow coat” on a new mold to test the release and maybe season the mold some (not totally convinced on the last part). Everyone has there own method for the blow coat. Some will let it fully cure and then blow it off, some will wait for it to gel to a fairly hard surface and then blow it off, thinking that if there is a problem the blow coat can be pulled/scraped off before it has a chance to really stick. That being said, I’ve kind of gotten away from blow coats since switching to polymer release agents many years ago. If you are spraying and getting fish eyes, you can try to just mist on the gel for a couple of coats and then load the surface to the proper thickness. Most times it works, sometimes not.

I was just going to say the same thing as I read down the thread. Although I don’t use a lot of epoxy, I do have some experience with it. Frekote has a special release topcoat (770-NC) specifically designed for epoxy release. It is very slippery. I’m using it as a release on some deep draft male molds and it doesn’t take much to get a release. Previously I was using Frekote WOLO-HL and having a heck of a time getting the parts off (not sticking, just tight). The sales rep suggested the 770 and it was like a bolt out of the blue. Very slippery.

#13

Wait, I think I know why this happened. You have a tool full of styrene and you’re trying to pull an epoxy part.
This explains why one halve was harder to separate. Let me guess… The bottom halve? The styrene would have fallen and deposited in those areas that the part bit into.
You need to post cure the mould and cook the styrene out of it before you let epoxy go anywhere near it. (Ok, it can go near it, just not on it). You could also leave the mould with concave sides facing down for a couple of weeks. A semi perm can help, but its not as sure fire as nipping the root cause.

I suggest while the mould has some styrene left in it, take some of the same red gelcoat and mix it with some silica to make a putty. Lightly acetone the problem areas and apply the putty to reshape the mould. Make sure there’s too much on there rather than too little. I would mask off areas around it with some tape. Once cured, sand it back to shape, polish etc.

After all that hard work, post cure it. If you don’t have an oven large enough to do so, you can try putting in a container under the sun for a couple of days. Temps can reach up to 50C in one of those. If that’s not an option, use a poly or VE infusion resin.

Saying that, I would have used a semi perm anyway.

#14

How does styrene and epoxy cause a stick-up?

#15

Yeah… I know. A gallon of PVA.

#16

Yeah. I know. A gallon of PVA.

#17

Styrene is a solvent that keeps poly and VE in suspension, and its their thinner. If there is styrene on the surface, or that could move to the surface, it will keep a small percentage of the resin uncured. It can also attack cured resin. The epoxy is making a chemical bond in these areas.
Thinking about it, you have several options:

  • Post cure to the HDT of the resin you used ramping at 2C/min. This will reduce the styrene to an insignificant level (you will never get rid of 100% of it)
  • Leave the moulds with concave sides facing down for a week, prefereably in a warm environment with air flow or recycle the air every now and then.
  • Use a semi perm. Like peeps have suggested above, this will help and you could have flawless success. But that doesnt solve the fact that there’s styrene in the tool. What if you accidentally use cheap/out of date semi perm? What if a tiny little corner only got a couple of coats, not 4?
#18

Gcrigs,

Allow me to take a stab at this. It appears that you’ve used the Duratech in place of gelcoat. Well, that can be done, but if thats the case you need to let the duratec stand for 24 hours at 25degC and then lightly sand the Duratech, say with 320grit, till all becomes opaque. Then leave it another 24 hours, at at least 25 Deg C. This is because the high gloss additive leaves a shiny sheen on the exposed side, that blocks any further evaporation of the solvents in the duratec. The sanding gives the solvents the path to evaporate and this process according to hawkeye (manufacturer of duratec), needs around 24 hours.

Now if you didn’t do all that and laminated your mold on top of that, you didn’t have a good bond of the mold reinforcement with the duratec layer and it just came off with your part.

I also believe that you should have used a mold sealer after the polishing of the duratec, then applied the wax/release agent. It would have given you at least one pull off of your mold. For more pulls, you need to work with the duratec system as I’ve described.

We use duratec extensively on our master plugs.

Secondly, I believe that if you’d have sprayed the duratec on the master plug and polished it, then taken a mold off of it, using a regular gelcoat, it would’ve helped. But apply the skin coat after the gel coat has kicked in well.

Hope this helps.

#19

Styrene isn’t just a carrier nor doesn’t keep the polyester/vinyl ester in suspension. It is vital to the cross-linking of the polyester molecules. It would never become hard without it.

Why Molds Stick - http://www.rexco-usa.com/why-molds-stick/

#20

We tried letting the duratec cure and harden before laminating the reinforcement and it pre-released. It is so brittle and shrinks up so much that it basically shattered on the plug. (mind you this is vinylester high-gloss tooling duratec). After that experience, we re-shot it and this time we glassed over it right when it was starting to harden. As I repair the mold it seems to me we got a very good bond.

It is becoming more and more clear to me that what happened: first, the mold was new, and thus still reactive. We should have used pva for the first few pulls, and a semi-perm system instead of our usual part-all wax. Second, we should have cured the mold surfaces after wet-sanding to release the trapped solvents. We had one of the halves stick way more than the other… Turns out to the be the half we used to build a return flange (to glue the the two blade halves) tool using the plug, during which we used heat and had a problem with the resin attacking the plug and to some extent the edges of the mold. I think we re-activated that half by heating it when there was really no escape for the solvents (it was polished, waxed up, and had a plug in it).

Definitely will use duratec for future plugs. We used an epoxy primer that we buffed out for this one and it got damaged when we built the flange tool.

Thanks again for the great advice.

gcrigs