Need help breaking the "fiberglass code"

[RandyH]

I am the new guy who is "thinking" of trying to build this boat. I have never built a boat before and have not worked with wood or fiberglass. I am, however, good at following directions and am just now finishing a thre-year long project of building an all aluminum airplane ( a Van's RV-12) from a kit. (Plane will be finished and flying this summer so I need to get thinking ahead on next project for next winter).

In the summer I volunteer crew for people who race their sailboats for fun. I think that given enough time and patience I could build a boat of my own. I have purchased the build manual for the Pocketship and have read it through. The only thing scaring me off is the fiberglassing! Although I have read the manual a few bits are still not clear to me:

1. I understand that the first coat of resin on the cloth is just to "wet it out" and that I must thereafter apply a second and third coat of resin. Is the desired result to get the cloth to turn "Clear"? Is that when I know that I will have enough resin?

2. Is there a MINIMUM time to wait before applying the second and third coats? Is there a MAXIMUM time to wait between coats? Does each coat have to fully cure or is the goal to get the second and third coats on BEFORE the entire layup cures so that the entire thing can cure together?

3. Am I supposed to sand the surface between each of the coats OR can I avoid all but a final sanding if I get the second and third coats on quickly enough?

Thanks,

Randy

[chaertl]

Hi Randy,

Love to see that RV-12, I come from a family full of A&P's. The first coat will cause the cloth to turn from white to clear but the biggest thing to watch for is any air bubbles between the glass and wood. They'll show up as a whiteish spot and are usually caused by somthing trapped under the cloth or not sanded smooth. There really isn't a minimum or maximum time for the fill coats but you should sand lightly if you let the previous coat set up completely. Personally I've skipped that on the fill coats and never had a problem though. The fill coats don't do anything structurally, just smooth out the weave for painting. I usually give eight to twelve hours between coats. Fiberglassing is realy quite easy after the first time. Just don't follow marine advice for aircraft, you'll never get off the ground.

Chris

[JonLee]

Yeah, the first coat, the "wet-out coat", basically sticks the fiberglass to the wood (or whatever you are sticking it to) and makes the glass turn clear. For strength, you are pretty much done at this point. However, it ain't all about strength, as you really want a smooth, paintable or varnishable surface. Since you want to minimize sanding later, you'll have used just enough epoxy in this first coat to make the glass clear. Hence, the weave of the glass is still very prominent after the first coat, and if you try to sand it smooth at this point you'll end up cutting into the glass, greatly reducing it's strength. Bad, bad, bad.

Now , the fiberglass pros will tell you that there are ways to get around this, and get a really nice surface after one coat, but for amateur 'glassers like us, it is best to go the "fill coat" route. So, after the first coat cures (more on that later), you apply another thin coat of epoxy. It'll take maybe 1/3 of the epoxy that the first coat took. Once that coat cures, you'll do one more thin coat. one more time with the third coat. Once that cures, you'll have a nice layer of hardened epoxy over the 'gless that can be sanded to a beautiful smooth finish without cutting into the epoxy.

So, how long between coats? The answer is, it depends. Again, the pros may offer other opinions, but for the amatuer, you'll be happiest if you wait until it cures...in other words, until it is no longer tacky to the touch. This usually takes somewhere in the 8-12 hour range; the exact time depends on things like whether you use a fast, medium, or slow hardener, the initial temperature of your epoxy, the temperature of your shop, etc. You can still recoat when it is a tacky, but I've found that for me it is a little easier to just wait until it feels dry.

Is there a max time between coats? Depends on the type of epoxy you use. If you use an older/cheaper epoxy, then you really have to recoat sometime before 12-24 hours (agin depending on temperature. After that time the epoxy will "blush" and you'll have to sand before the next coat. This, of course will hose you, because you'll remember that sanding will cut into the glass and seriously diminish the strength of the glass. BUT, tf you use a no-blush epoxy, like the MAS stuff included int he PocketShip kit, or System3 Silvertip, then (theoretically) you don't have to worry about this, so your recoat time can be huge. Despite this, I'd probably still recommend recoating under 24 hours if possible, just as a good-practice guideline. I can't speak competently about the chemical bonds between coats or whatever (my gut says waiting too long could eventually cause problems there), but if nothing else recoating in fairly short order reduces the chance for dust contamination.

I definitely agree that you'll do most of youre learning on the first job. After that, you won't even think about it.

[RandyH]

Many thanks for the information!

So now I have three more questions:

1. When doing the fiberglassing between the narrow spaces on the floors, (pages 78 and 79 in the manual) I noticed that the top of each section is meant to overlap the one next to it. Do you do one section at a time, allowing it to cure to dry before you start the next section - OR - Must you get the adjoining section laid and overlapped quickly so that the cloth of one is actually touching the cloth of the other?

2. Do you lay all of the cloth sections on the floor first and then apply the second and third coats of epoxy to the entire bottom section?

3. In many of the photos posted on this forum I see Blue painter's tape. Is the tap used to hold the cloth steady while you do the intial wetting - OR - is the colth laid over the top of the blue tape. If the latter, do you only wet the cloth up to the line of the blue tape? Do you cut of the excess dry cloth at the tape line after the first coat hardens?

Thanks Again,

Randy

[chaertl]

Hi Randy,

Here we go,

1. You can go either way. If possible lay the next layer of cloth onto the wet resin but it's more improtant to get the cloth to lay flat against the wood. If you've got an akward postion trying to work around the wet areas it's best to let it set up until it's safe to touch without lifting or sliding the cloth around which will cause wrinkles and air pockets.

2.Probably best to get it all down before doing the fill coats, I wouldn't recommend filling one section before overlapping the next one but you could do up to the overlap area.

3. Blue painters tape is usually used in the filleting steps to help keep things neat. There might be some technique for making cleaner edges since fiberglass supposeably won't stick to it but I'm not familiar with it.

Chris

[JonLee]

Yeah, I'd agree with that.

There is a technique for using tape to get a cleaner line on the glass, but I haven't seen anyone use it on PocketShip yet. Basically you lay down a strip of masking tape where you'll want the glass trimmed back to. You then lay your glass cloth down (with the cloth overlapping onto the tape, and wet it out. In about 2-3 hours, come back and with a razor knife and cut through the glass along the tape line. You have to be careful to cut all the way through the glass, but not push so hard that you damage the hardened fiberglass/epoxy that would underneath in the case of these overlap regions. Then peel the tape up, taking with it the ragged edge of the fiberglass. This leaves a really nice seam that will require very little feathering. Proceed with the fill coats as usual.

[garciaa]

Looking at Jeff's beautiful work in his blogspot http://www.flickr.com/photos/35243545@N02/page11/ , I think he used the technique that JonLee described.

[jwv630]

Has anyone experimented with applying a seal coat of epoxy to bare wood prior to laying down the fiberglass/epoxy? This seems to have the potential to limit the absorption of epoxy when wetting out the fiberglass later.

Also, I recently read that MAS Epoxy had been reformulated so that even with the slow hardener, the cure times are now somewhat quicker. They say that now the Slow Hardener will be tack free after 5 hours and 'after 8 hours you should hand sand to create a mechanical bond before applying the next coat.' (They did not refer to a temperature for this new info...) Comments?

Rule of Thumb Test (per MAS): If you can press your thumbprint in the epoxy - but there's no tack - then you should do a scuff sand, but will be getting both a chemical and mechanical bond.

Jimmy Vitale

[Shudoman]

For my PocketShip I used the masking tape method. For me it gave much better results than I had on my other two small boat builds. It yielded clean edges that were/are much easier to fair in. Less unraveling at edges and a far more positive placement of the glass. The two things I did different on this boat from the other builds were the edge taping method of fiberglassing and the use of peel-ply on the flat surfaces. These two techniques have made this build go with a lot less angst (and sanding)!

http://pocketship.blogspot.com/search?u ... -results=7

[jwv630]

Hi Shudoman:

Thanks. Went to your link; nice procedure; will try it. Didn't see any mention of the peel-ply. Heard it was hard to work with.
Any comments or suggestions regarding it?

Regards,
Jimmy V