Two fiberglass questions

[irish24]

I'm currently about to glass a new deck in my boat. I've got an 87 Starcraft with a fiberglass hull. Do I need to sand the deck first then treat with epoxy or can I just go 4 it? Also when glassing the floor to the side walls what grit sandpaper do I prep the existing glass sides with? Finally, when double layering do i need to let the epoxy set between layers, do I need to sand and if so what grit?

 

[Bob_VT]

Re: Two fiberglass questions

If you are attaching fiberglass to fiberglass (or epoxy to fiberglass) I would use 80 grit to provide more bite.

As far as putting resin on plywood...... there is no need to sand but a light touch with 80 grit will not hurt. Make sure the wood is dry and you can even clean it off a bit with some acetone (let it dry) and go for it.

Yes, you can adhere multiple layers of cloth but be careful for air pockets forming and stay on it until it flashes.

 

[BuzzStPoint]

Re: Two fiberglass questions

If you do get air bubbles, And sometimes you see one or two, perhaps the dreaded fold in the cloth, don't spend to much time trying to get it out. (Dont that, then the resin starts to set up and you waste a 1/4 cup. Although I do have a nice Hockey Puck sized paper weight made out of resin)
Let it dry and you can use a grinder the zap them out.. A dab of resin and a square section of cloth.

 

[irish24]

Re: Two fiberglass questions

Thanks Bob and Buzz. I was thinking of using 2oz csm for my floor with an epoxy resin and overlapping into the walls to waterproof. Should I also use a woven cloth where the csm meets the walls as an overlap for added protection? My intention is to completely waterproof the subfloor.

 

[drewpster]

Re: Two fiberglass questions

A couple of things about using Chopped Strand Mat and Epoxy;

Traditionally CSM is not used with epoxy. The binder that is used to hold the fiberglass strands together in to a uniform cloth is not compatible with epoxy resin. CSM was originally developed for use with polyester resins to provide a random pattern in the mat for better adheasion and waterproofing. CSM is also used as a finish layer and as a way of conforming fiberglass into complex shapes and tight corners. CSM used alone is generally weaker than woven roving or cloth, so it is usually used along with a woven fiberglass product to provide strength. (this is the accepted thinking)

HOWEVER- I have been told that the binder in CSM IS compatible with epoxy and it can be used with it. So, I recommend that you verify with the vender or manufacturer of your particular CSM that it can be used with epoxy. It is my understanding that modern CSM binders are made to work with both resins but there are manufacturers that still make it the old way. It is best to check.

Personally I see no reason to use CSM with epoxy given that the advantages of using CSM are not needed when using epoxy resin. The only benefit I can see is that it is easier to get CSM to conform in to corners and weird shapes. Epoxy is stronger, it bonds better and it is far more watertite than polyester. So the benefits of CSM are not really needed. I generally recommend using a fiberglass cloth (weaved fiberglass, not woven roving) with epoxy resin. If you get print-through of the cloth weave on the surface you can use an epoxy based fairing filler to cover it before you paint. (because you cant use gelcoat over epoxy, you have to paint) But that is another debatable topic.

 

[NSBCraig]

Re: Two fiberglass questions

why spend extra for epoxy?

 

[irish24]

Re: Two fiberglass questions

Thanks Drewpster, I ended up purchasing a 12oz biaxial fabric with a .75oz CSM sewn into it. I was considering using a 6" bi/triaxial tape for the first pass around the perimeter of the floor, followed by the actual glass for the floor tapered up the walls and another layer of 6" tape around. I intend on using a thickened epoxy to create a nice big fillet around this edge too. My intent is to completely waterproof this boat. Under all floors will also be 2lb expandable foam for flotation and hull rigidity.

Side note: Why do the front seats on bowrider boats typically open towards the centerline and not the opposite?

 

[oops!]

Re: Two fiberglass questions

the bi axe cloth you got for the deck will be good enough for tabbing in the perrimiter.....just cut some strips of it....(cut with the grain and lay them in length wise).

the bi ax tape is expencive

 

[irish24]

Re: Two fiberglass questions

Thanks OOPS, I'm always looking for places to save!!

When prepping for glass, is it ok to let the epoxy dry on the wood before laying down and wetting out the glass? If so, is there any prep work I need to do before laying and wetting out the glass?

 

[Yacht Dr.]

Re: Two fiberglass questions

Hello Irish..

Um..no you should not let it dry..

If epoxy cures then your next step is to reprep b4 the next coating(s).

YD.

 

[irish24]

Re: Two fiberglass questions

Ohhh.....big thanks Yacht Dr!

Anyone have a cost effective alternative to micro balloons/epoxy fillers?

Also, check the pic below. The previous owner glassed the stringers. Note the 1" gap between the stringer and skin of the boat. Is this gap too big? The visible glass in the gap is on the back side of the wood. Cut a shim to fill the space and reglass maybe, replace stringer? Any thoughts?

 

[irish24]

Re: Two fiberglass questions

Any thoughts on the previous post?

 

[oops!]

Re: Two fiberglass questions

glass bubbles and milled fibers are cheap and good.

as far as a one inch gap between the stringers and the hull....that is wayyyy too much.

you just need the thickness of a Popsicle stick or less. the rest of the gap is filled by peanut butter or pl construction adhesive.

 

[Yacht Dr.]

Re: Two fiberglass questions

Your 1" gap may or may not be ok..

There are some that say "floating stringers" are better.. ( I tend to agree ).

Meaning that any wooden stringer or bulkhead should not actually touch the hull. Its the fiberglass that takes most of the energy transferance..

Imagine formed stringer systems.. they were designed to transfer the energy load of your drives to the hull with ONLY glass .. no wood involved here..

So If your glass is good and thick/solid then ... why would you need wood in the first place ??

If you do fill the stringers/bulkheads directly to the hull.. make sure its Soft filler.

YD.

 

[irish24]

Re: Two fiberglass questions

That is reassuring to hear YD. It appeared to be something else I had to worry about on this project. It would be nice to know if it was truly designed this way though. What is soft filler? Is that the same as a Fairing filler or Micro-bubbles?

Next question: I've constructed my new Transom and drilled all the thru-holes oversized. I was going to fill them with some West Epoxy and High Density filler, install the Transom and then re-drill the holes to the correct size. When filling transom thru holes on a horizontal surface, what is recommended to seal the back side of the wood to keep the epoxy from going everywhere? Is it also recommended to put a chamfer or countersink these holes before epoxy fill? Input appreciated....

 

[Yacht Dr.]

Re: Two fiberglass questions

Yea.. Micro Ballons would be fairing compound .. soft filler.

As for you next question .. I recommend you repost so others may get an idea and chime in .

YD.

 

[irish24]

Re: Two fiberglass questions...Transom Complete...pics

Re: Two fiberglass questions...Transom Complete...pics

Thanks YD. I think I'll just cut that stringer out and redo it. Why not, right I'm already here so....
Finally finished this Transom. Cut new transom pieces, drilled thru-holes 1/4" oversized, bonded the two halves with a thickened epoxy (West Systems 404 filler for high density bonds) and clamped together, used engine mount bolts to apply pressure with two 4' pieces of angle iron to keep transom true while it set up, backfilled all thru-holes using the 404 filler and will re-drill holes to size tomorrow. This transom is hard as a rock and is now the last thing I will ever worry about on this boat. Very pleased with the outcome.