Voids in gel coat on molded part

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#1

Very new to composites so please excuse the questions.

Working on molding wakesurf boards on of a mold using vacuum for pressure.

Mold was CNC cut and then we used filling primer and wet sanding to get a nice finish. This mold is just considered our prototype mold so we decided to just make the negative rather than a plug and a fiberglass mold.

Foam was cut on CNC allowing 0.020inch clearance all the way around… Since its foam this number is not perfect but we wanted some clearance for the layup.

Board came out very good, we just have some voiding along the rails of the board. Looking for any advice on how to keep this from happening in the future. We hand brushed in a layer of epoxy as a gel coat and confirmed that the entire rail was well covered. I was thinking on the next one to add some extra epoxy right down the middle of the mold. Then as the pressure pushes in the middle it would push epoxy out to the rails? Again first mold and first time using vacuum with composites so any help is greatly appreciated…




#2

Does your mold hold vacuum? Pull full vacuum with a gage attached and shut vacuum off. Does the gage hold still or do you have leaks?

#3

I can only see the first three pics - is that the same for others? Can you repost? Are the voids in the gel-coat or behind the gelcoat?

#4

jrandsu’s question is a good one. If you cut the mold out of a porous material, like MDF, there is a good chance it is not airtight, which means that until the resin gels, things will move around causing issues.

#5

Wet laid bagging is often not so good for getting a porosity free finish.

I think you should use your same mould and vacuum infusion process instead. You have all the gear, just change your methods.

#6

Simply put, you don’t have enough resin to fill the gaps, but using more resin isn’t the answer. If you just use more resin, you’ll fix your problem with voids, but you’ll have thick, unsupported cured resin that’s likely to chip. It looks to me like you’re using unconventional methods to produce the board. You’re encapsulating the foam core and using half of an outer two piece female mold. If you’re going to use matched molds, where the part is sandwiched between molds, they have to be perfect so there’s only enough room left for the perfect balance of cloth and resin, and the mold has to surround the entire part so you would typically have another mold similar to your existing female mold that would be used on top, which eliminates the need for a vacuum bag. Creating a foam core perfectly matched to an outer mold through trial and error is impossible. This would be a two piece mold with a sacrificial core. You haven’t selected an easy part to make. I see a lot of reading in your future.