Gel Spraying Techniques

SkiBum, Stick with the epoxy for structural repairs and the polyesters for the gel repairs and you won't have any problems. If you do or have used epoxy for the repair of cracks in the gel, then you will need to prime first with a vinyl ester before the poly ester gel. Call your supplier and tell them exactly the products you have used to make sure what to apply next.

The polyester gel coat will stick to epoxy repairs a$$uming certain things have been done:

1. After the epoxy has cured, wipe it down liberally with Acetone to remove the oily residue that forms on the surface of cured epoxy (I forget the name of this residue). Do this before sanding so you do not sand the residue into the surface.
2. Roughen the surface of the epoxy with 60 grit or heavier paper to provide tooth for a good mechanical bond with the gel coat.
3. Wipe again with acetone to remove sanding dust, etc.

Now you can apply the gel coat without worries.

When the boats are constructed, the gelcoat is first sprayed into the mold. Then, before the gel coat has fully cured, the fibergla$$ composite is laid up. This result in a chemical bond between the polyester gelcoat and the polyester resin. However, with epoxy resins, you cannot create this chemical bond. Correct Craft uses a modified epoxy resin that will chemically bond with the polyester gel coat.

Yep, that it...important thing is to get rid of it.

The smart guy at US Composites was in favor of the vinyl ester as well. I keep the garage at a min of 80 f but I don't have a way to get 100 f. For my stringer repair I have been using acetone to clean the areas I used epoxy but I did this after sanding.

Thanks for the help. I'll start in an area that cant be seen and work my way out into the open.

Just might have to try that. Thanks

Bill, you can definitely be more aggressive than the 600 youve been using. I went down to 320 on my deck to restore the color.

Skibum, You're finally getting to the spraying. Great progress. I've been watching what you have been doing and feel you've gone beyond what most would do. Great job!

2nd coats of gel can be sprayed as soon as most of the solvent (styrene) has flashed off. This can be in as little as 20 minutes but it depends on the heat and humidity.

David is right that nothing can be done with the orange peel except sand it off after it cures. If you reduce it too much, you will not get the dry film build that is needed. The stuff doesn't like to be sprayed. It's like trying to spray a solvent based contact cement.

The wet sanding is going to be time consuming. You will need to get a feel for what grit paper you can start with and feel comfortable that you won't sand too far. Only HARD block sand untill the orange peel is removed. This can be tricky on concave and convex surfaces. I have used all sorts of things laying around to use as shaped sanding blocks. If you use your orbital first, you will be left with orange peel bumps. Go with the hard block wet first.

When you get the orange peel knocked off, there are 2 products that woodworkers supply carries that I have found to be very helpfull. They are hook and loop sanding pads that will go on your random orbit electric sander that can be used wet. They are available from 320 to 10,000 grit. I gave up on my air DA sander simply because I don't have a 20HP compressor to keep up with it! With the electric in one hand and a spray bottle of water in the other, it really speeds this up. You also don't sand off the skin on you fingers! I've done so much that I don't think I have any finger prints anymore!!

Thanks to both of you. I really appreciate your expertise. I do not know what "tracer" means. Can you explain that one to me? Thank you again.

bkhallpa$$ wrote: Tracer - you spray a very light light coat of black spray paint over the gel, to expose the low spots. Than as you sand it down you can tell if the surface is becoming flat. BKH

Okay, got it. Thanks.

No to both. I agree that you should sand to fibergla$$ where there are stress cracks. If no stress cracks, then you really only need to take off the surface of the existing gelcoat...i.e the oxidized part. If there is an area of significant stress cracking, then you may want to consider what I did. Since my boat was involved in a collision with rocks, the fibergla$$ that was not destroyed was severly flexed to the point the gelcoat was crazed/cracked like broken tempered gla$$. I ground off all the gelcoat and then brushed on very thin epoxy resin. I applied heat with a heat gun as I applied to make it flow better. My theory was that the thin and flowing resin would fill the stress cracks that were no doubt present in the fibergla$$ composite. Hopefully, this method would produce a strong enough mechanical bond within the composite to prevent future stress cracks within the new gelcoat. Two years later so far so good. The thinned resin was then faired out with bondo providing the final fairing. I found that grinding off the gelcoat created a very bumpy and irregular surface. bondo took care of the issue.

I am not sure if I understand correctly, but here is my plan. On the exposed fibergla$$ I will apply thinned epoxy resin. Over that I will use Bondo filler. I will not sand all of the gelcote to the gla$$, only that with cracks. But I will apply resin to the areas where the cracks are located.

When grinding the gelcote I am able to make a reasonably smooth surface. Any indentations are taken out with the 40 grit. Now, there are low spots extending to the gla$$ that will need to be epoxied and filled.

Eric, when you talk about using a long sanding block are you refering to sanding the new gelcote?

It almost looks like it's had part of the transom replaced at one point in time. Looks like distinct line in the gla$$ on both sides like a panel waas installed in the center.

Bill, I wonder if the cracks in the gla$$ below the gel were caused by moisture? Also keep in mind that Bondo is a polyester and it too will absorb water. For fairing, I think I would stick with the epoxy with a filler that is sanded easily.

You can definately see that where the wood was laminated into the stern the cracking is substantially reduced as apposed to where there is no wood backing. I applied one layer of epoxy resin to the stern. I'll do two more layers followed with a thin layer of Bondo that will be mostly sanded away. Will this create adhesion issues with the polyester gelcote?

I know it is a bad picture. Worked late tonight but I was determined to get the boat on stands. It was not the best job of boat stand making in the world. Two stands in the back, two toward the front, and two sets of blocks; one under the front and one under the back are supporting the boat now. The boat is stable, the system isn't pretty. Made a lot more room to work around the boat.

David, I understand what you are saying about the heat gun and the epoxy. My first layer was 635 thin epoxy 3:1 with no fillers and the garage was 80f. I will start using a heat gun in future epoxy applications.

I will keep plugging away. Thanks for all the help. I am sure I'll be asking more questions time progress.