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Fiberglass/ plywood/ help


striperick
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Probably a couple weeks away . But food for thought before I get there....

 

I am nearing the end of side planking on the OB20 (maybe 4' from the bow)  I have  used fairing  to fill staple holes and fill any imperfections and fair as I go along. I plan to radius all sharp edges an to get as"fair" and filled as best as humanly possible before even purchasing glass.

 

I am a research  freak . But I am looking for direction on applying the glass to the Hull . I have watched U tube and have downloaded Gougenon book online but I am looking for more specific info on plywood boat finishing. Can someone walk me through the process of wetting down hull?

 

1)  80 grit to prep hull?

 

2) Should I cpes hull and let dry ?   then let glass rest on hull to "relax" then fill the weave ?  I plan working alone so I dont want to put the glass on "wet"

 

3) I understand the directions on the drawings where the chine gets overlapped  twice (overlapping by the glass from bottom and side)  . I will purchase material long enough and wide enough  to glass the boat in 5 glass pieces. 2 for sides 2 for bottom and 1 for transom. 

 

4) I dont want to paint the transom. I want to show wood like "princess"  (Chicks  build) . Does it matter if transom is glassed first or last?  Or is the thickness really not an issue to feather in in the sides and bottom (assuming transom is glassed first)

 

5) Should I glass tape all plywood intersections before cpes and large glass sheets ?   meaning  side/transom    bottom/transom    bottom / bottom  at centerline ?

 

6) How much to "fill the weave" ? do I not totally fill the weave and then use fairing compound ?  do I fill the weave in several applications and use peel ply at the last application?  I thought I read somewhere that the glass is stronger when its not totally filled ?    I am really confused . 

 

 

 

 

 

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1)  80 grit to prep hull?

 

Yeah that'll work, though 100 will do too, but I wouldn't go much higher in grit.

 

2) Should I cpes hull and let dry ?   then let glass rest on hull to "relax" then fill the weave ?  I plan working alone so I dont want to put the glass on "wet"

 

CPES is worthless in this application and basicly has no real place on a taped seam build, so save your money for other stuff. Regular epoxy resin is what you 'glass with, not magic diluted goop (CPES) in a can.

 

3) I understand the directions on the drawings where the chine gets overlapped  twice (overlapping by the glass from bottom and side)  . I will purchase material long enough and wide enough  to glass the boat in 5 glass pieces. 2 for sides 2 for bottom and 1 for transom. 

 

'Glass is available on rolls, so just order the yardage you need and cut off the length required for each flank or panel. Butt joints are okay, but if the piece can be continuous the better.

 

4) I dont want to paint the transom. I want to show wood like "princess"  (Chicks  build) . Does it matter if transom is glassed first or last?  Or is the thickness really not an issue to feather in in the sides and bottom (assuming transom is glassed first)

 

Use 4 ounce (135 GSM) or lighter cloth to cover the transom, as this will become transparent. Heavy fabric will show the weave. Work the edges (tape them off) during the other 'glassing operations so you don't mess up the pretty stuff. It doesn't mater, first or last, though if done first, then protected (plastic sheeting works good) then you can tape off the sides and bottom as you continue the sheathing. This said, you don't have to sheath the transom and can just epoxy it and apply varnish/urethane, knowing it will not have as much abrasion resistance as a sheathed transom. Of course this means you need to somehow "tab" the transom to the hull shell, which is easy enough on the inside, but not so much on the exterior. I did it by applying a mahogany veneer, after the transom was filleted and tabbed.

 

5) Should I glass tape all plywood intersections before cpes and large glass sheets ?   meaning  side/transom    bottom/transom    bottom / bottom  at centerline ?

 

Yes, tape all the seams first, then fair the hull to remove humps and hollow spots, then apply the cloth fabric.

 

6) How much to "fill the weave" ? do I not totally fill the weave and then use fairing compound ?  do I fill the weave in several applications and use peel ply at the last application?  I thought I read somewhere that the glass is stronger when its not totally filled ?    I am really confused .

 

It depends on the weight of the cloth, how much goo it will take to fill the weave. Yes, the fairing compound fills the weave, except on bright finishes, where you have to use straight epoxy, preferably a special clear formulation. Generally you fair the hull twice: the first time is to get the raw wood, screw holes, seam taping and other imperfections as fair and smooth as practical. This saves a lot of work when applying the sheathing, as you'll lay it down on a fair, smooth surface. Once sheathed, you'll fair again, but because you put so much effort into this already, the second time is really just prep for the finishes. You can use peel ply on any application. I'm not sure where you read this 'glass is stronger thing, but try to avoid that publication again. In an ideal world, we try to control resin/fiber ratios, but with hand laid applications if you can get 50/50 you're right there.

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  • 3 weeks later...

I would only add one thing on #6. 

 

When first applying the glass it is very important to completely saturate the glass until no white is seen. 

 

Once the saturated glass has soaked into the wood. Then you must do one of the most important steps.  That is take a squeegee to all surfaces.  With each stroke clean off excess epoxy off squeegee into a paper cup that has been slit down the sides.(do not re-use this waste epoxy). 

 

You are doing this step to accomplish two things. 1. To remove excess epoxy, because if you don't it will puddle and the glass will float off the surface.  You do not want it floating.  Second you want to remove enough epoxy to clearly see the weave even dimples between the weave but not starve so it turns white again. 

 

Then once the epoxy has set up as soon as possible probably within 24 hours you should apply a coat of epoxy to fill the weave.  If you do it within the 24 hours or whatever your epoxy says timewise, then you do not have to sand between these two coats.

 

The above is very hard for me to describe but in practice not that hard.

 

Hope this helps.  My 2 cents worth.  Maybe PAR can explain it in a better way.  He is good at keeping explanations simple.

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" Glass is stronger when the weave is not totally filled"

 

My understanding is that the fiberglass reaches a high percentage of strength well before the weave is filled. So when taping seams in areas that will not be seen there is no need to completely fill the weave. Saturating the tape as you apply it and then coming back while the epoxy is still green with another coat is plenty. Filling the weave in these areas is just adding unnecessary weight.

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Filling the weave is purely a cosmetic thing. Filling with a lightweight fairing compound can dramatically reduce the additional weight. Only on very small craft is a weave filling coat's weight a real concern.

 

The elongation of 'glass fibers in resin is about the same, regardless of fiber to resin ratio. When formulating resin for use with various fabrics, ideally the modulus of each reaches the fatigue limit at about the same time. This way both the resin and fabric can have the most exposure to strain. This is why you see high tech fabrics used with epoxy and vinylester resins, because polyester resin would fail long before the elastic limits of the carbon or other fabrics, so they wouldn't be able to impart their full physical attributes.

 

This comment "Glass is stronger when the weave is not totally filled" would be best written as "Glass in no more stronger with the weave totally filled". On a technical level, there may well be a measurable difference (quite slight), but for most practical rational, a filled weave is a fairing, smoothing and cosmetic issue though a resin rich fabric (filled weave), will have better abrasion resistance, if only from the additional mass of the extra resin.

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