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Fiberglass/ epoxy tecnique


Mr. Scott

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OK I have a question for anyone that has an idea. I want to know if you can spray epoxy or fiberglass, and if you can how do you do it? I have a large air compresser, and good ventilation in my shop. I have painted quite a few cars, but I don't think that the above materials can be mixed the same (ie thinned down enough to spray like paint) :? I am not at this stage yet, but if I can spray, I want to practice to get good at it.

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Not a good idea, IMHO. The only time I've heard of spraying epoxy, it was done with a little spray bottle to get to an area that was too small to get at with a brush. I don't think it's a good idea to spray it on fiberglass. It would have to be severely thinned, making it runny, very difficult to wet out the glass properly and, worst of all, weakening it chemically.

Have you read the West System manual? I think you'll find it time well spent.

http://www.westsystem.com/webpages/userinfo/manual/

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first- you can't spray fiberglass. it's a cloth or a matt like a roll of cloth. Ya gotta roll it out or spread it out.

Picky HUH? I think you mean the difference between polyester resin and epoxy resin. Both use fiberglass.

Second - Polyester resin can be sprayed with the right equipment. Usually the guns I see doing it are set to draw from a 55 gallon drum and inject the MEKP from a 5 gallon bucket as it's being sprayed - BIG bucks.

Third- the manufacturers of common boatbuilding epoxies - such as WEST and MAS strongly recommend AGAINST thinning it enough so it can be sprayed. You would lose strength in the cured resin.

The plastic technique is really interesting - I intend to try that myself next I get a chance. I already use somewhat the same technique doing repairs on small holes. I can't conceive that it will totally eliminate sanding prior to paint or varnish but it looks like it will certainly minimize the work.

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The "el cheapo" boat mfg. use fiberglass chop which is a thread of glass that comes in huge rolls. It is fed into the feed end of a "Chop gun" which feeds the glass along with the polyester resin/MEKP mix at the gun. The glass is chopped into short fibers and sprayed into the female mold which has been preped with Gel coat to be the finish for the glass panel. It is quick and dirty mfg. of fiberglass boats or other parts. A quality job uses mat and cloth to "lay up" within the forms or over a form which it may or maynot be bonded to. No shortcuts to good quality.

The Chop gun, polyester resin/MEKP equipment ain't cheap. Requires various Hazmat permits and controls and isn't at all what you want to try to do at home.

Use the compressor, if it is large enough capacity to run a Random orbital sander or a straight line sander in your finish work. Then with a good spray gun to spray the hull with the finish coats of your chosen paint. For most trailerable boats, the better quality Exterior House Paint Enamels work very well. They don't need to be sprayed, roll and tip out with a brush works well. Even with the Polyurethanes until you get to the 2-part LPUs. And there really isn't any reason to go to them on these boats.

Also don't even think about automotive finishes on this type of boat. It just won't last.

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Barry - Chopper gun use doesn't necessarily denote "el cheapo" If it is used correctly by someone who cares about what he''s doing, a chopper gun does a great job. Some very good boats used a partial layup done with chopper gun in between layers.

It's a sad note that a relatively few incompetent builders gave the equipment such a bad name - It's rarely seen anymore except for small part layups.

And Jack- no- not referring to Peel ply. There was an article mentioned recently I think on the B and B board about someone using 30 mil polyethene rolled on over the wet glass/resin layup and carefull flattened that gave a truly remarkable finish.

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Certainly there are very competent builders that use chop guns as a part of the layup. There is a place for chop. Unfortunately it is all to often seen as the one ply fiberglass cheapie. On the well done jobs, the average buyer wouldn't have any indication that it was used.

My point is that all too often it was used as a substitute for layups of mat and glass with good building techniques as it was quick and less expensive to build that way. As a part of this discussion it was in reference to having a compressor at home and looking for a way to spray glass and epoxy. Neither of them appropriate for use at home with any equipment that I am aware of.

I think we are on the same page, just different paragraphs.

We used a lot of "peel ply" in layups in the past, unfortunately none of it outside a vacumn bag situation. We also used heavy guage poly sheeting occasionally for the same application. It did leave a really smooth surface that required little further prep work to be ready to finish. I think it would be interesting to try on one of these to see if it does speed up the process or if you end up with a leveling challenge instead of just sanding/filling challenges. The biggest potential issue I see on hull surfaces is consistency of thickness and eveness. A fair curve is just that. I can envision enough variance under "peel ply" just laid over the epoxy and glass and rolled down that I just wonder if it would be even and not wavy, hill and dale type of really smooth ssurface.

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Yep- I think we're in agreement.

As I said earlier- I can't conceive how the plastic applied over wet glass can give you a surface that is ready to paint without at least SOME fairing. Particularly when using a high gloss finish. It has GOT to have some waviness in it. Now if they were using something with some stiffness to it, like a heavier Mylar I could see it. That would be somewhat like a mold. But they show plastic on a pretty small roll, and all the heavy mylar I've seen would take a much larger roll.

But I intend to give it a try when the right application shows up. It IS an interesting concept.

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Lifted from the West System website westsystem.com

Spraying epoxy

We do not recommend spraying epoxy products because the health and safety risks are enormous. As epoxy leaves a spray gun nozzle, it is reduced to tiny droplets (spray mist). You can easily inhale epoxy that is suspended in the air. It can cause extensive lung damage and other health problems. The spray mist can settle on your skin, causing sensitization and allergic reactions. It can settle on your eyes, injuring them.

Compared to other application methods, spraying increases the amount of hazardous volatile components released from the epoxy. Using solvents to thin the epoxy for spraying adds to the health and safety risks. These hazards are similar to those of any spray painting operation, involving both health and flammability concerns.

If you are determined to spray epoxy, control hazardous vapor and spray mist by using isolation and enclosure, such as a properly designed, ventilated and filtered spray booth. In any case, if you spray epoxy, you must use an air-supplied respirator and full-body protective clothing!

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When our layup crew did hatch covers they used the "release films" (peel ply) as part of the layup. The heavy guage films were then overlaid with something else to give them a stable surface to be drawn down by the vacumn press. It seems to me that they quite often used high pressure laminate (countertop covering such as WilsonArt or Formica) and backed that up with a sheet of closed cell foam. The combination brought them a wave/ripple free surface when the "peel ply" was removed. I don't think that any of the parts being done with "peel ply" were flat, I think all were a curvalinear surface for additional strength. All that was generally required after that was a wet sanding session to make it ready for finish. Most of the finishes being applied were sprayed on gel coats after that.

We had the capacity to vacumn bag panels as large as 8' X 26' and occasionally did just that. These large panels were almost always composites of marine ply (if being used for boat building), foam or balsa core and a finished high pressure laminate surface. These were then cut to size for the finised applications. Anything from sound deadening office dividers (covered with a fabric) to bulkheads or decorative panels.

I don't recall any of the large panels just being glassed with "peel ply" but that doesn't mean it didn't happen. I also don't ever recall it being used in our shops other than in a vacumn press or for small spot repairs.

I will have to check with the guys that did the layups, they were a pretty talented crew with a lot of epoxy/glass/resin experience. It would be interesting to see if they had any open area work experience with "release films" or "peel ply" such as on decks, or hulls. Since most all of the boats essentially came out of molds prefinished, I would doubt that there was an application for it in our shops. I know that a couple of them were strip kayak/canoe builders as well, maybe they have some experience with it.

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Wow! :shock: Lots of info. Thats what I meant...spraying the resin...anyway I found a friend who srays varnish and epoxy for a living. This means I have an "in" ( if I choose to be lazy and have someone else do the work!) Now next question...Do I paint over the epoxy, or under it? :shock: Thanks again all!

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Mr. Scott

Epoxy doesn't adhere well to any finish. It adheres best to unfinished "clean" surfaces with a little tooth to grab onto for a mechanical bond. One of the mistakes a new builder will make is to over sand the surface to be bonded. It really doesn't have to go any further than 50 grit to be ready for epoxy and glassing. Same with assembling parts. Don't get them too well finished if you want a good bond between parts and don't over clamp. The epoxy has to be there to bond. If you squeeze it out, it is not nearly as strong.

It will adhere to itself if it hasn't cured and you don't have the blush on it. Then it is a chemical bond which is a superior bond as it becomes one solid material.

No...it won't prevent checking of the plywood under it without fiberglass over the plywood. And it has no good UV characteristics on its own.

So....Paint over not under, same with varnish. Caulk over not under.

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Barry,

In your last post you said epoxy would adhere to itself if it is uncured, or not blushed. I have several areas, like the fillet along the keel, and some uneven seams that I have used thicken epoxy on already. Do you think I'll have a problem with the subsequent layers of epoxy/fiberglass sticking? They are cured! Also I have epoxy coated one side of the hull, and am waiting for more resin from Raka to begin glassing. Larry from Raka recomended epoxy coating before glassing.

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Rough the surface up with some 50 grit to give the new a textured surface to bond to and you should be ok. Save all the fine sanding until you are done and getting ready to paint. Even applying the first coat of primer paint you don't want anything smoother than 150 grit to allow the paint something to grab to.

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