16' fiberglass hull painting questions

[jherlyn]

Hello, I have completely rebuilt the inside of my chrysler '77 tri-hull, stringers and everything. I now have decided to paint the outside of the boat

i am not daunted by the work, in fact I love it. Just was wondering how far I have to sand down the topside and hull to repaint. How far is too far? If I take the old shiny gelcoat layer off is that too much. Do I take just as much off on the hull (which is painted too, btw)?

The other question I have is with hairline stress cracks in the hull, will primer hide those or do you recommend filling in EVERY crack on the boat? This boat has some hairline cracks do to the transom being shot. It is now new, and I want to make it look good. The paint I am using is the interlux perfection 2 part and I will spray. I have the tools and the know how. The boat is trailered after every use and not in the water longer than eight hours at a time. All we use it in is freshwater. Let me know if there is anything else you need to know.

Thanks in advance for the help!

 

[phillyg]

Re: 16' fiberglass hull painting questions

My recollection is the Interlux website gives you all the info you need for preparation. You definitely do not want to remove the gelcoat, however.

 

[jherlyn]

Re: 16' fiberglass hull painting questions

I have watched the videos on the interlux site and they show how to sand, but they don't really say when to stop. I guess my confusion is what is defined as the gelcoat. I know that the fiberglass and the resin are different than the gelcoat layer, but is the shiny laminate finish the gelcoat, or is it the pigmented stuff underneath it. If I sand the shiny layer off, am I past what is considered to be the gelcoat that protects the fiber in the resin from wicking up water while in a lake. I guess I want to know because it would seem like to me that if you were to sand off this "gloss finish layer" down to the pigmented "stuff" the paint would form a better bond, but if the "glossy finish" layer is what protects the boat from the water, than I am just shooting myself in the foot.

I know it might be a wierd question, but I need this defined before I make an irreversable mistake

 

[archbuilder]

Re: 16' fiberglass hull painting questions

First make sure you get any silicon or oil off the surface before you sand. I started by washing it with dish soap and water. The soap is great at breaking down the wax and oil. I followed that up with the pressure washer. Later when it dries I would wipe it down with some acetone. Careful, it is nasty flammable stuff. Make sure you use it in a WELL ventilated area and with gloves, safety glasses, etc. Just wet out a rag, then wipe it down.

After it dries, you need to provide a mechanical tooth for the paint to bond to, translation sand the hull. Unless you are sanding out a defect, just sanding till it is dull is fine. Usually that only takes a few passes of an air sander or a dozen by hand. One critical thing is to sand it down with the grit recommended by the paints manufacturer. If you have the right grit and it is clean you are good to go. Just make sure you have all the surfaces sanded, to give that mechanical tooth.

Try to sand as evenly as possible, if you stay in one area too long you can "dish out" that area. That is usually more of a cosmetic issue that structural. If you are sanding by hand I recommend a wrapping the paper around a paint paddle and tearing it off as you go, this is called blocking. It will help you keep the flat parts flat! curved surfaces I use a 3m rubber "squeegee", more or less a foam block about 3/8" of an inch thick. With power sanders, just keep them parallel to the surface and always moving!

I try to stick to wet sanding when doing it by hand, no dust and the paper last longer.

Probably more info than you wanted, but hopefully it will help. Key to any good paint job is prep, prep, prep!

 

[jherlyn]

Re: 16' fiberglass hull painting questions

Thanks for the tip. Yeahs I know acetone is nasty. I am a plumber and use it all the time at my job. It sucks because you can't always use it in a well vented area, but it is amazing stuff.

alright, so sand until the shine is gone and I will be okay. If I sand to where I see resin and fiber then I've gone too far and I will have to patch. the hard part about that on this boat is that the luster of the old gelcoat is not only cracked but completely gone in some areas I am lucky because after looking at the hull's condition with paint there still was absolutely no osmosis.

So the hairline stress cracks, do they need to be completely sanded down or filled, or will primer fill them in during the paint process? I just want to make it look as good as possible.

Once again, thanks for all your help in advance.

 

[Woodonglass]

Re: 16' fiberglass hull painting questions

As long as your Hairlines are NOT REAL DEEP then using a High build primer should take care of them. Two coats with wet sanding in between should give you great results.

I'm just sayin...

 

[jherlyn]

Re: 16' fiberglass hull painting questions

ok, they are real deep, so i'll fill em in. Like I said the transom was mush and the guy who owned it didn't know anything about boats, so everytime he revved it up out of the water, it was essentially trying to break the boat in half

I have brought it back from the grave with about 100 hrs. of my life, so I'm not going to skimp on the fixes now. This guy is a coworker of mine, so when I get it done, I'm going to show him what a boat SHOULD look like

Another off question about this paint. With the interlux, does the paint add a little bit of a "barrier" in itself from water once it's painted on? I realize it's not meant as a waterproof coat, but does it kind of act like a gelcoat in keeping moisture out of the fiber and resin?

 

[Woodonglass]

Re: 16' fiberglass hull painting questions

Yes, but do NOT use bondo to fill in your cracks. Use this instead.
http://www.amazon.com/3M-Marine-Premium-Filler-Pint/dp/B0000AZ4YS

It is for marine use, works great

I'm just sayin...

 

[jherlyn]

Re: 16' fiberglass hull painting questions

Can't I just use the resin that I was using in the boat for the stringers, of course mixed to a thicker form.

 

[lonewolfed]

Re: 16' fiberglass hull painting questions

The jellcoat was actually sprayed into the mold before the fibergalss part when the boat was built. Its like the fiberglass resin but retains the pigment all the way through in that it is a two part process with a catalyst and dries like plastic. The ultrasmoothness of the mold is responsible for the shine . roughing it up by sanding with a 220 grit paper is all that is needed.

Fiberglass resin is NOT recomended for stress cracks. They need to be dished out (I used a dremel rotary tool) and filled in. I used the fiberglass resin in some areas, they looked fixed, but the paint and primer soaked in and you see them now. Make sure you use a good marine filler. I think mine was made by Evercoat.

 

[Woodonglass]

Re: 16' fiberglass hull painting questions

Yes, if you mix in some 3M Glass bubbles to make it easy to sand. If not you wil have a MESS on your hands.

I'm just sayin...

 

[jherlyn]

Re: 16' fiberglass hull painting questions

Thank you for all the help. I think I will order some marine filler tonight so that I can do it right. I did not realize that dishing out was needed to fill in cracks, but now that you say that it does make sense. thanks all and I have a lot of work ahead of me.