Se we finally finished a new (and time consuming) MDF mold with an epoxy gelcoat. Before layup 4 coats of Smooth-Ons Sonite Wax were applied and buffed. Finally a coat of Price-Driscoll Ultra-3 Epoxy Parfilm “Paintable Mold Release” was sprayed on and allowed to dry. We then did a wet layup and bagged it. The layup was heated at 110F for 4hrs (plenty of time for our resin to harden) before ramping to 180F.
The part stuck…well. The good news is that after chipping gelcoated MDF chunks off of the part for the next couple of days we were able to save the part. Bad news is we have to completely rebuild the mold. So the big question is, why did it stick and what superior mold release can we use next time that will part CLEANLY?
When I’m scared of breaking plugs I use lots of PVA.
Yep… Try freekote. It isn’t scared of heat one bit. Most waxes dissolve with heat. Is this the first time this happened? Also the epoxy gelcoat probably absorbed some of the release and that why the part stuck…
10 layers of a carnuba based wax and a misting of PVA does the trick. But dont apply too much heat as the wax and pva melt
At least you have a decent part to make the mould on.
Semi-permanent release would have been a better choice. Much more reliable IMO.
I do not know the releases used, are these suitable for high temp?
Also, my experience with high temp epoxy resins is that it needs a GOOD cure before you can use it for molding on them.
I also like the semiperms, preferably with a good sealer.
Before knowing I used the agent “mother” from the “in-law” company. That hated me as well… 
Glad to hear I am not the only one with the “mother” of all experiences. So what is the semi permanent releases? and what does the sealer do (I am assuming this is different than wood sealers since the mold is presumably already gelcoated)?
The sealer isn’t something you can buy at Home Depot. You buy these semi perms as a kit, use the sealer first to seal the mold, then apply the semi perm.
So is the sealer applied over the gelcoat or is it the gelcoat? How often do you have to reapply the semi perm? Do you use any other release agent with the semi perm?
You’re a bit confused.
The semi perm is applied directly to the mold, independently of what you’re going to do with the mold. After that you can layup w/e you want however you want without having to worry about the part sticking. The semi perm is the release agent, it’s a bit of work at the start. You need to seal the mold, then apply the release agent, after that you apply the semi perm every so often.
I don’t have personal experience with the stuff but it’s what I’ve read here. Please correct me if I’m wrong.
semi permanent sealers and releases chemically bond to the surface of the mold to form a thin film which resins can not bond too. The sealer fills micro-purosity in the surface of the tool. This is a important step to add longevity to your tools while aiding in better release of the part. the release agent is applied anywheres from 2-6 coats intially depending on the brand and type. typically u can pull anywheres from 1-10+ parts before reapplying a coat of release agent depending on your application. Frekote is the most well known of the semipermanents, and it works very well. That being said there are many different ones out there that work well too.
Ok, that clears up a lot. The only question that I still have is regarding the sealer. Is the sealer applied in addition to a gelcoat or is it an alternative to gelcoat? From my perspective the gelcoat is filling the porosity of the MDF mold…so I just want to be clear that I am guessing this semiperm sealer is further sealing the gelcoat? Lastly if it lasts for 1-10+ parts, how do you know when its time without it being too late?
Thanks for all the info, this is a huge help.
you apply the sealer and release agent to the surface(gelcoat or surface coat)of the tool after it has been made and fully cured. you can do a tape test after each pull to help determine if you need to reapply release. Use 3/4" masking tape stick it to the surface of the mold. the amount that the tape sticks will help determine if you need more release.
MDF is extremely porous. That is why you applied the epoxy gelcoat over that.
But the epoxy gelcoat is a bit (micro)porous as well, just as aluminium, glass, polyester gelcoat, etc. This microporisity is filled by the sealer from the semi-perm kit. It is a very important step and basicly is your insurance policy.
As for knowing when to reapply: You get a feel for that. If you sense that the part needs more force to release than previous, reapply release agent.
In a production environment, I always order the people who do the demoulding to also do the application of release. It is these people that know where to put in extra effort with certain moulds. (unless the shop owner only hires brain-dead people…)
Throw away any PVA.
Apply wax and do not expose to heat.
Or, apply liquid mold release and don’t go over the service temp.
Are the “high-temp” waxes (like TR104) any good? Again, we are pressing at 180F. So the PVA is a product like Partall Film 10?
Partall is a PVA. I’ve seen people use waxes like Worlds Finest mold release in ovens with no problem but they were making flat plates that are easy to release.
As mentioned above semi perm sealer is the way to go if you’re doing multiple parts. Applying mold release everytime, praying that the part will release, and hoping for a consistent finish is just a massive waste of time. Go with semi perm.
What he said. PVA is crap in most cases. Using PVA in moulds is like using carbon fibre with polyester: a waste of time and money.
A semi permanent is by far the best release possible. Wax is nice if you need a high gloss finish. not really important with epoxy products, they need paint anyway, in most cases
I like PVA for the protection it offers to the materials underneath to styrene attack. For instance when making a mould using Gibco Flexmold for anti skid areas. (this stuff does not like styrene, PVA is recommended.)
Or when molding from a really bad mould, or making trailer supports on a boat you do not own, or even has been sanded with grit 180 for the last paint session. Or when making a mould from a towing tank model of Brunel Sunergy…
But for decent moulds it should not be neccesary.
Has anyone used Frekote’s FMS sealer on metal molds? Most of our molds are epoxy, so I dont want to spend $200+ on a 4-pack of B15 sealer for a couple of small metal molds.