composite repair question

[Longboatin]

Ok, time to clean up the cracks on the MJM. All have been patched well on the inside so i just want to clean up the exterior cracks on the hull. Previously the cracks were just painted over with resin. What weight glass should I use to make some nice neat patches?

[KNeal]

It depends on how detailed you want to be with the finished project. I tape off the work area with "blue" tape (used for painting), then sand the work area to prep. If the crack(s) go deep, I use the sander (random-orbiter) to grind deeper and open it up more. After wiping the area clean and it is dry, you can do two simple repairs:

1). Since you repaired inside the hull, you may only need to mix your epoxy-resin with a thickener (I typically use microfiber filler) then spread it around the work area, using a plastic squeegie to work it around and smooth. Cover the area (I use Saran Wrap, but it creates wrinkles; you can also use a sandwich bag, plastic garbage bag, or purchase some peel-ply), and tape the whole thing down firmly. Again, use the plastic squeegie to work out bubbles and excess resin as well as you can. Clean up any spillage outside the work area and let it cure. Remove cover and tape. Sand area to smooth rough spots.

2). Same thing as above, but apply epoxy-resin to fiberglass strip (you can go to a local boat repair shop or Davey Hearn's site and purchase the material). Fiberglass strips are necessary for structural needs. You will only need enough size to cover over the crack in the hull with one strip since you did the repair inside. Everything else stays the same as above. Thickener is an option with the fiberglass strip.

Like I said, you can get into as much detail with the repair as you like, such as adding color to your mix to match the hull (kinda hard to be accurate with a good color match though). Have fun with your project. Remember to wear a particle-filtering respirator when sanding the hull. So, what is the "MJM"?

[KNeal]

What weight glass should I use to make some nice neat patches?

Since you repaired inside the hull, one layer of "S" glass, or even "E" glass may be sufficient. Maybe someone else has a more informed and knowledgeable recommendation.

[Longboatin]

Kneal, thanks for the info. +1 on the respirator, and maybe longsleeves and pants too... felt like I workd on a bunch of cacti, after sanding in shorts an Tshirt.

MJM is Berry design before ME I believe.

[Sir Adam]

MJM is a sweet design - I know of one or two locally. John Berry's longtime OC2 partner once told me it was one of, if not the, favorite solo boat.

KNeal is right on it when it comes to prep etc... What I do is very similar:

1) Tape off area (newspaper on rest if there is any chance of getting resin where I don't want it. It WILL go where you don't want it to, when you don't want it to!
2) Materials - West Systems epoxy and some type of glass. I'm a big fan of S-glass, as it is lighter and stronger then E-glass. Better abrasion resistance too.
3) Sand down area as KNeal mentions, especially "removing" the crack if you can (get it all down to good material). Often dirt / water has gotten in there, and if you can you want to get it all OUT.
4) Wipe area down with acetone on a rag or shop towel - this removes fine particles and any oils, and can make a big difference to get a good bond.
4) I like to put my patch(es) in the cup of resin I've mixed, then squeegee them with my hands and place them on the boat. If you ended up with any sort of crack left put resin on the boat first, otherwise I usually don't.
5) If it was a big crack perhaps two patches, otherwise if it is well reinforced inside one should do just fine.
6) I like to put peel-ply over the patch - this is a fabric that releases after the resin has cured and leaves a nice finish, and can help you work out the excess resin and all air bubbles that may be in the cloth. If it's a smaller area Saran wrap does work well - just try and get ALL the wrinkles out (difficult enough a lot of the time I'll use peel-ply)
7) If you used peel-ply when it's cured lightly sand, then coat with just resin using a gloved hand. You just want a skin coat on it to make it smooth and glassy / glossy. Same trick as with wooden canoes...

I like respirators that have particle and chemical filters, and recommend working out doors. Long sleeves are indeed a good idea too!

Good luck, and post images if you can!

[RodeoClown]

Adam and Kneal have it covered pretty well. I'd second grinding off anything that's not solid- it's not doing much, if anything, for you. My preferred weight of fabric is whatever i have scraps of. Absent that, I'd say 6oz.

I'd also recommend the disposable Tyvek coveralls (I get several uses out of them before the disposable part is needed) to minimize fiberglass contamination with other laundry.

[Longboatin]

6oz cloth, check
+1 on sanding the junk away.
Boat is laid up with partial glass layer on inside, kevlar, then single glass layer on outside. I sand into the cracks to remove any dark material an expose clean Kevlar.
I will git some pics together to post.
Thanks for all yins info an help!