Thin Gelcoated Panels, how to Improve?

I did my first PET resin panel with gelcoat last night. It tured out a little rough and I am seeking advice to make it smoother/better the next go-round.

My initial guess is that the gel coat was not firm enough and/or thick enough to resist print-through as a main problem and that the bag film also contributed to a general lack of 'smooth' on the panel.

The intent of this panel is for practice and patching a small boat project with a similar layup, eventually I will need to make some hatch covers for my boat using the same or fresh gel coat. Would another layer of gelcoat help to fill in the imperfections? If so, how to handle the unwaxed gelcoat exposed to air?

Please see the pics and information below. Appreciate any thought/advice, thanks!

-Shop temp was 70F/21C (wish I could say the same this morning, outside is 40F/ 4C...)
-Gelcoat seemed to take forever to get 'tacky', started after lunch and did not laminate until after supper.
-molding surface was vacuum bag film stretched flat and tight over a smooth melamine MDF surface
-Gelcoat is unwaxed, color-matched to my boat, never opened, and freshly shaken at the paint counter of a big-box store. The laminating resin is Bondo from a big-box store. Both resins were 'older' maybe 1 year but did not seem to have gone off in the cans
-I had two sets of MEKP, one in 8oz bulk and a small tube of Bondo liquid. I used the Bondo as it seemed to be be less exposed to air. The bulk one had spilled once and is 'contained' in a larger glass jar where the leaked material turned brown, the unused material is clear, and the plastic cap is eroding My plan was to test the unused bulk MEKP with the Bondo resin to see if it still works.

 

The layup does not require a sheet membrane between the mold surface and the gelcoat.
I would prefer a coat of PVA for mold release.

 

Like kapnD said, you can never get a plastic film smooth, Me3lamine mdf or not.
Get some of the sealant tape, or similar flexible "joiner", and wax the Melamine

 

Thanks kapnD, thanks rwatson.

The melamine surface is on a cart usually used for other things so I was hoping to get away with not waxing or coating it. I will try again without the film, either straight on the cart or get another piece of something.

Sealant tape, would this be for making a dam around the working area? I have been using butyl roofing tape from the big box store for sealing vacuum bags for the infrequent times I bag stuff.

I was able to clean up and test the other bottle of MEKP and it's working fine so my experiments can continue.

To reduce the latent image of the mat in the in gelcoat, should I be waiting longer to laminate? Thicker gelcoat? Try adding some veil? Or will this improve once I have a stable mold surface?

Thanks!

 

The squirrely surface definitely has some affect on fabric print through.
PVA is water soluble, will not damage your mold surfaces.

 

I am giving it a second try, coating the melamine with PVA. I should have enough of everything for a second panel, then I will need to get more resin, MEKP, and Partall.

 

I don't see a reason for using sealant tape around the panel.Just lay up an oversize part directly on the melamine and trim to the required size.If you need a moulded edge,things change and strips of PTFE sheet or even sealed plywood will work.When you find yourself doing a hull repair,it all becomes a bit more challenging and I suggest posting a few images of the boat in question before advancing too far with the project.

 

The reason for the panels is to fill in bigger holes, 100-150mm (4-6") diameter in boats like a Sunfish where the parent material is missing. The lams are only 2.5mm (.093") or so thick. For these repairs, there is a method of hanging the new patch in with battens and only grinding, filling, and fairing a small seam (sometimes called the Shoreline method after the shop that posted YouTube videos of the same). Since I have a batch of gel coat and resin about to age out and the reinforcements, I thought I'd try the panels.



My 'big' boat is a 6.4m (21') day sailor and there are a couple dozen pukkas where the gel coat was not back up by fiber enough in the corners of the molds to prevent it from chipping away and a hatch that I unceremoniously bounced off the asphalt driveway from about 1.7m (5' ) off the transom. Part of me wants to remake the hatch as a learning exercise, the bigger part of me wants to just fix it and go sailing. Any tips on these two types of repairs would be appreciated.

 

The corner chips are cosmetic only.
I would
-open them up with a small bit
-over fill with thick gelcoat
-cover with a thin plastic film
-while at softserve ice cream hardness hand plane to approximate surface
-wet sand and buff.

For the hatch I would do a quick repair to get sailing again while rebuilding it properly.

The round hole in the blue sunfish looks like an inspection/deck plate would be an appropriate repair.

Good luck

 

Thanks Blueknarr, I will try that with the gelcoat chips.
That Sunfish has a nicer deck and sketchier bottom so I added the holes on the bottom along with a computer fan, battery, and solar panel to move air through the hull.

I did another gelcoat panel and some carbon fiber using the Partall as mold release. Pretty happy so far with how it behaved with the epoxy and carbon fiber. The red weights are re-gluing the corners that did not grab during the lamination (there is a wooden frame behind the carbon fiber).
I did the gelcoat thicker, shooting for 21 mils (strong .5mm) wet and it cured much quicker. I took a Surform type tool to the high spots (I applied with too small of brush, not so smooth, and it was thick enough to not flow out so much) and went after the mat and woven roving after supper. I will pull it in the morning.

 

You are demonstrating the benefits of doing some experimenting before diving into the main project.Any trials that don't work can go in the bin and not have to be remedied while the successful version can be used on the project with no further rectification.

For that hole in the bottom I'm wondering if you could make a small section of mould from the opposite side of the boat and lay up a light panel from it.The change of curvature over the length of the hole doesn't appear to be that great and you would be much closer to a decent finish and given a light enough laminate,you could push it to the correct shape before adding some bracing.It might seem like a longer process but it could save a lot of finishing work.

 

Sureform-hand plane
Same-same

So no inspection ports on the underside

Your work looks great.

 

Thanks Everyone, I appreciate the encouragement.

I pulled the panel this morning. It is much better than #1, thanks to the help from the group.
I am surprised how well the Partall worked, the film formed is quite durable and easy to release with both PE and epoxy. My bottle is a few years old, so also happy with the shelf life of the product.



Making small molded pieces off a hull to patch those big bottom holes is a great idea. I did that to fix a bow of one that was too far gone, repairs on top of repairs and the wooden blocking for the hardware had fallen away.

 

Print-through is one of the downsides of vacuum bagging. Resin rich laminates tend to show the fabric less. That is the reason to lay gelcoat, then a resin rich laminate with veil, and finally the structural laminate.