visible weave in fiberglass

Discussion in 'Materials' started by sean-nós, Apr 3, 2012.

  1. sean-nós
    Joined: May 2010
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    sean-nós Senior Member

    Hi guys anyone have any ideas on what to do, it looks like the weave was not wet out enough or some moisture got in.If I sand down to the weave is it possible to get a clear finish again. There are a few of these marks around the boat so if it cant be fixed I will have to sand it back to the wood and start again :( something I really don't want to do "I hate sanding fiberglass"
    Any tips would be great thanks.

    [​IMG]

    There is another patch to the left top of the transom that is really annoying me:mad:

    [​IMG]
     
  2. Petros
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    Petros Senior Member

    I am not composite expert but I know a little. If you sand it and cut the fibers you will weaken it. looks like it was not wet out good enough, the smaller areas not so much a problem (except for the appearance). Try painting it with a clear finish, if that does not work use opaque paint. For the larger areas, there would not be a good bond between the surface and the composite, giving an area where moisture would get trapped, and without a good bond it would be weaker.

    Seems to me if strength is the concern that it should get removed and replaced. If you can not put resin in it now to get a good bond, than it has to get replaced.
     
  3. Yellowjacket
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    Yellowjacket Senior Member

    You've done a beautiful job on the boat and it's a shame that you have the problem. I don't think there is anything you can do but take it down to at least to past the glass and reglass it. If you are careful you might be able to take it just to past the glass and not to the wood. Depends on how much resin there is under the glass.

    What weight of fabric did you use? It's a lot harder to get a clear wet out anything more than a 6 oz cloth. Even with 6 oz cloth there are different weaves and finishes. You need to look for a light cloth like is used for clearcoating kyaks, otherwise you run a high risk of not getting a good clear wet out. A silane finish also helps to get the kind of clear finish. Using an 8oz tight weave cloth it's just hard to get it to wet out clear everywhere.

    The resin and hardner is important too. I use Raka epoxy and they have a low viscosity resin wets out really well. In addition Raka has a very slow hardner and that prolongs the pot life and helps a lot with making sure everything gets well wetted out.

    In looking at your pictures, it appears that you laid the fabric over the unfinished wood and then wet it out from above. That makes it much easier to get the fabric set where you want it, but there are downsides to doing it that way. What often happens if you do it this is that some of the resin soaks into the wood and leaves the layup a bit dry. I've seen some publications where they recommend painting a thin coat of epoxy on the wood first, letting it get past the tack stage and then, before it fully cures, lay the fabric and wet it out. This prevents the resin from soaking into the wood and keeps the fabric wet.

    Lastly, to avoid a lot of sanding you should get some sheet mylar and put it over the wet layup. This will compress the weave and leave you with a smooth finish. Here is a link to the technique.

    http://duckworksmagazine.com/03/r/articles/glass/bottom.htm

    There was also a lot of discussion about using peelply, but for what you are doing I think the Mylar is better, since it is clear and you can see what you have going on under it, but here is a link to a discussion on peel ply.

    http://www.boatdesign.net/forums/materials/peel-ply-14461.html

    One last thing is that it could be printout of the glass because you didn't have enough resin over the glass to seal it well and water has gotten into the fibers, can't quite tell but it could be that too. I don't think it matters but you always want to make sure you have enough resin over the glass even after sanding or this can happen too. If you get too close to the glass you need to recoat with resin to seal it well.

    I'd probably mask around the area you want to clean up and sand it down to past the cloth, then cut a piece of cloth that will fit inside of the "hole" you are cutting out and then use the mylar or PTEG material to compress the wetted out cloth and just do patches. On your boat you aren't really looking for cloth to help the strength, you just want some damage protection that is better than plain epoxy, so it isn't that important to overlap it. Get some light cloth and some slow hardner and try again.
     
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  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    That's "print through" and what happens if the finish is applied without post curing the resin. It's a common problem. You can strip the varnish off the clear coated areas post cure, then reapply the clear coats. You may have to add more epoxy, then post cure if you need to level the surface any.

    Under paint you can often use a building primer (after post curing) to hide any print through.

    What resin system did you use, as I would suspect Dublin's weather wouldn't make natural post curing as practical as it is here in sunny Florida.
     
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  5. sean-nós
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    sean-nós Senior Member

    Thanks for the help "print through" could be the one alright. I used 4oz cloth and west systems 105 resin and 205 hardener it looked fine when it was done.

    [​IMG]

    But when I was done I covered the boat in plastic for a few weeks to do the bottom and that may have trapped some moisture allowing it to get into the epoxy before it was fully set.

    [​IMG]

    The mylar looks like a good way to go, I can't find any .030 but found this it is 38/40 microns thick and is used for wraping flowers, will that do ?http://www.ebay.com/itm/17072620530...AX:IT&_trksid=p3984.m1423.l2649#ht_1289wt_964

    Thanks again.
     
  6. Herman
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    Herman Senior Member

    I wonder which picture you did see? I see a picture with a starved glass laminate. Very probably due to resin that soaked into the wood.

    Another option is that the epoxy has not been thoroughly mixed. Especially for transparent work, use a 2 pot mixing system: measure and mix in 1 pot, then pour into another, and mix again. All to avoid the risk of adding unmixed resin into your project. A surplus of hardener can affect water resistance considerably, as a surplus of resin can make things brittle. (general guide)
     
  7. Yellowjacket
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    Yellowjacket Senior Member

    Really thin stuff like that may work, but I'd for sure look for something thicker, too thin stuff tends to wrinkle, which leaves you sanding off the resin that built up in the wrinkles.. Don't ask how I learned that one.

    I didn't know if you could salvage printthrough with just recoating the epoxy. I'd sure like to know if that works, usually you see printthrough coming out of the surface, and recoating would give you a smooth surface, but maybe Par can shed some light on the clarity of the layup after you do that. I always thought that if you got either starved layup or printthrough, you couldn't salvage a clear finish.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Herman is correct in that you should use an epoxy formulation designed for clear finishes, such as West 207.

    What I see in the picture looks like an abrasion that's down to the fabric (though it certainly could be resin starved), but mostly I see fabric weave, which you really shouldn't with 4 ounce cloth.

    Now that I've blown up the picture, I'm inclined to agree there are starved areas as well as print through.

    Yes, you can save a clear finish once sheathed, but it's not an easy task. Often in restoration work I've forced to pull a sheathing, with minimum damage to the substrate. There are some techniques, all with various degrees of success that can be used, some damage should be expected if the novice laminate is attempting it.

    Lastly, the really thin plastic sheeting material doesn't really work like a Mylar sheet does in producing a smooth finish. The exotherm will move or distort it as well as wrinkles that can't be fixed before cure. The sheeting material has to have some weight to it and also has to be applied as a "developed" piece. On a round bilge, this means dry runs with the sheeting, so you know where it's got to live, as adjustments in wet goo is self defeating.
     
  9. sean-nós
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    sean-nós Senior Member

    I have decided to sand it back to the mahogany and down to the waterline that way if the overlap is showing I will just make the waterline bigger "If at first you don't succeed" :mad: I will also try the 207 and wait till the weather warms up a bit, in the link yellowjacket posted http://www.boatdesign.net/forums/materials/peel-ply-14461.html duckworks say the used .030" and then rxcomposite said it looks like 0.003" any ideas on what I should look for in mm, microns or inches or what has worked best for you.
    Thanks again " I hate sanding " :D
     
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  10. PAR
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    PAR Yacht Designer/Builder

    Mylar usually comes in 5 mil (.005") or 10 mil (.01"), though you can order it in many thicknesses.. You can get polyester and acetate films fairly easily, with thicknesses that range from very thin (.0005") to 20 mils (.02"). I don't know what the thickness of peel ply is, but it wouldn't be my first choice for a clear finish, as it leave a considerable texture in the cured epoxy. There are quite a few plastic films to look at and several ways to find it. Drafting film, decorative films, landscaping films, etc.
     
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