Fiberglass basic questions 101?

[B.Mac]

I do have a couple questions?

After I remove the inner skin and wet transom core I will have access to the inside of the outer skin. This outer skin has a diagonal crack in it clear through the gelcoat below the waterline.

My plan is to apply resin and mat to the inside if the crack and then lay some more over the whole interior of the exterior skin before I begin replacing the core. Is polyester resin and mat the correct material? Do I need some light cloth and/ or epoxy resin there? I get mixed up as to the application of polyester -vs- epoxy resins. I believe polyester is cheaper but does not have the "bonding" properties of the epoxy resins?
If I am correct, mat is primarily for "finishing" and cloth is for structural integrity?

2.) How do you bond the bottom of the stringers to the hull? I assume it's "glued" down to fresh ground "pink" glass with epoxy resin mixed with some kind of filler (caposil?) Then you lay bidirectional cloth up and over the whole stringer and out 6" in each direction onto the hull?

3.) When I bond the new 3/4" plywood core to the outer skin, do I apply wet mat to both surfaces then clamp it all together. Repeating the process for the second 3/4" plywood core? Do I use epoxy here or polyester?

4.) When applying bidirectional cloth that has mat integrated on one side, can this be appled directly over raw (resin coated) plywood or do I need apply resin & mat to the plywood first?

5.) Some guys say use only marine plywood, others tell me marine plywood doesn't bond to resin and glass as well as plain old exterior 3/4" CDX?

OK....thats enough question for now... I appreciate you reading this far into my madness :eek:

I'm taking all this to the glass forum so don't flame me yet please? Thanks guys.......

B.MAC:D

[175checkmate]

- Epoxy is more flexible and bonds better than poly but these qualities aren't always needed. The crack should be key out with something like a can opener then filled with mat. Cover the fix with cloth or mat. Poly is fine.
Mat has a higher resin content and a random fiber lay. Cloth has a higher glass to plastic ratio so is stongerfrom this and has a definate tension direction. So is stronger in those 2 directions.

2- I would mix an epoxy filler for bonding the stringers to the hull, there are a few flavors available from structural bonding to light wieght fairing. When the filler squeezes out use a large popsicle stick - something with a largeish radius and drag it along the squeeze out to produce a fillet.
2a- You can laminate the stringers outside the boat first or laminate them down then wrap. I wouldn't try doing the whole thing in one wrap from tabs over the top and down the other side, tab. It's too hard to do. Radius the tops for the cloth to form easier. The fillets make it easier for the cloth to change direction and add strucurally too.

3- Epoxy the layers of plywood and clamp them together outside the boat. Seal the surfaces first, let setup or cure. Then mix a thin filler up, squeegee on like a tile floor with those nothced things. Clamp it up. Seal the wood with epoxy all around before installing. If covering the inside side then glass before installing, it's easier outside than stuffed inside the boat.

3&4 If the wood is epoxy coated you don't need the mat, if your using epoxy to install it (again with the thickend epoxy). If installing with poly most say the mat is needed for a good bond. If it's on the cloth already then you don't need a 2nd layer first.

5-Look at the edge of regular plywood and marine plywood. Marine and furniture grade plywood has no voids and no bark filler. You can see both on any other kind of plywood except baltic birch. For 3/4" CDX with voids a (I'm guessing) 1/2" marine would be just as strong. This is close though. CDX is mentioned because it's available,cheap and says it for outside use.



Epoxy is the same stuff used for bonding nose cones on and all the other magic bonders. Marine tex all that. Aluminum filler brass...They just sell it by different names with different fillers.

I use epoxy whenever in doubt. Always for wood. Some disagree but poly doesn't bond to wood. It will seem to for some applications but I don't take the chance. Either seal the wood with 1-3 layers of epoxy and do everything else with poly or just stick with epoxy.
Epoxy can produce what is called AMINE BLUSH(doesn't always). This should be wiped off with a damp rag and wiped dry. Thats it. No solvent needed. Poly cures with a wax additive and this needs to be cleaned off with a solvent( if it cures sticky then its a laminating resin without the wax additive). Scratch both before bonding to.
If you do use an epoxy get some pumps for them or it's hell mixing it. With the pumps you pump one each or several each and no measuring and quick & clean. There should be a gougans or west systems (same thing) pamplet where they sell that epoxy, Either buy it or leaf through it. Goes through the basics and the fillers for epoxy. Don't need to buy thier product. Good hints and filler uses + how thick you need it.

Anything that can be done outside the boat comes out better and is done easier. You can install wood parts already glassed over.

[Liqui-Fly]

Did you see my post or did it disappear when the forum went down?

David

[Reese]

We lost a bunch of posts when the forum crashed so I may be repeating myself; also I’m sure you know most of this stuff anyway.

My own project started out very similar to yours…wet transom, wet floors, wet foam and delaminated stringers.

The best advice I can pass on was from a local boat builder who told me “don’t be in a big hurry to fix and encapsulate wet wood that is still in the boat”. Like you, I began removing fiberglass to survey and expose the wet areas as much as possible…and then I did nothing, just let the exposed wood sit in the 90 degree CA sun for about a month.

On most boats there is a gap between the floor and the stingers that is usually glass over (in your case the inside). I filled mine with fiberglass kitty hair and covered it with cloth.

Checkmates suggestions seem very sound…but I have never used epoxy for fiberglass or bonding. Generally I use 5200 or polyurethane glues to bond/sandwich wood to fiberglass.

CDX is a perfectly good material if you take the time to seal it…I use thinned (acetone or styrene monomer) polyester resin for first coat followed by un-thinned resin for subsequent coats.

I generally find good construction techniques far outweigh the advantages offered by epoxy or marine ply. But that is not to say they don’t work…they do. I’m just comfortable with the cheap stuff.

Here is a picture of my knee brace transom using CDX (home depot)…it will be sealed with laminating resin followed by polyurethane primer and paint. Green stuff is fiberglass bondo for a nice smooth finish.

Good luck with your repairs and post some pics.