Another BFN Rebuild

Morfoot wrote: The mix ratio of microballoons to resin is ( according to GE) 22% of your resin wt.

And microballoons don't weigh much!

Tim M, do yall use cabosil? What do you think of my theory above?

Waterdog wrote: If you look at it under magnafication.,the mil fiber tears out when it fails (adds strenght)and cabosil just shears off in the resin. Smae with any "sphears" round shape filler.

I agree on the fiber shearing VS: just shearing off at the bond. Any fiber type filler will act similar to a glass fabric and it really the fiber that's gives the strength so it's a higher strength. My concern and comment is just don't use something real weak meant for easy sanding like a wood flour under the glass. Go with one of the less expensive higher strength fillers.

Greg, Mike- we’re making enough changes to the structure of the boat that it makes sense to lay it out first to get an idea how all the new pieces will fit together. Like I told Alan, there are enough inconsistencies in the hull that we’ll be spending a lot of time with a tape measure and cardboard to build everything!

Tim, thanks for the info! Interesting stuff here...

Andy, Joe- thanks for the offer on the milled fiber! To answer the question, I have NO IDEA how much I would need. With all the bedding and fillets on the boat, probably a lot! From what Greg is saying, it sounds like its quite a bit denser than cabosil- does that mean it would go farther (based on volume)? I suspect not... A mixture of those 2 plus talc might be just the ticket- thanks for the idea Greg! Do you think a 50 lb bag of milled fiber, 10 lbs of cabosil, and 50 lbs of talc would be somewhere close to the right amount? What kind of ratio did you use (by volume)... somewhere around 2:2:1? Ill probably pick up 4 gallons of glass bubbles for final fairing.

BuffaloBFN wrote: Tim, I ordered everything in the 2.5 qt size and had to re-order cabosil, mil fiber, and talc. I re-ordered in the same size and used about half of each.

Hmmm... does that mean you used a ratio closer to 1:1:1?

Id wager a guess that I'll use about twice the amount of fillers as you did since I have about twice the number of ribs and bulkheads... that gives me an idea of what I need. Thanks!

I think you are going to need WAY more brushes than that.

Man that resin in the 5 gallon kits is the way to buy it. Actually makes it look cheap.

Tim, If you have a harbor freight store around check them out for your disposable supplies, I bought a 36 pack of 2" brushes for $9.99. They have larger sizes as well. Won't save you much in the grand scheme of things but it helps.

Waterdog wrote: So whats the reason for using talc? A stringer job is a high performace application. Talc is one of the main constituants of bondo.

Greg mentioned way back in the thread that it smooths out the consistency but I too would question it blended in on a high strength application. I've never used it and have always relied on West #410 Microlight for fairing. I bought a large container way back and it's lasted for many projects!

Yes the 5 gal. epoxy kits are the way too go. The pump kits come with the suction tube extensions to get to the bottom of even the large containers.

All the repairs I've done with thickened epoxy, milfiber & cabosil no talc, microbeads or microballons. Thou we do use a couple of epoxy adhesives that have glass beads already in the mix .05% for bond line control.
Your going above and beyond with cosa and epoxy using the best materials available, I think it's a no-brainer to use the strongest fillet materials also.
I would use 100% milfiber in the first layer or two of glass tape for the main stringers / hull fillet.

Tim,
When you lay the first layer or two of glass tape in the fillet (main stringer to hull)prep the surface by lightly sanding with 220 grit to give it the proper tooth (both layers) Use a little milfiber in the resin but be sure it still has good wet out. Shape a couple of old paint brush handles to fit the radius. Lay the first layer of tape and roll it in. Use the shaped paint brush handle to debulk it (force it down into the radius) Repeat on the second layer of tape. It will nest the plys of material, force it into the radius and give it
qusi-isotropic strenght to defeat the harmonic vibrations in the hull (more resistant to harmonic delamination failure over the life of the part) Aircraft quility baby...
Eric's right thou it's a boat, the extra detail costs nothing but time.

i have resin and talc droppings on the floor, and the only way to get it off the floor is with an air hammer, or a sledge, resins have changed in the last 25 years and CC felt back then they were strong enough but didnt factor in foam rot. your re-building these boats becasue or rot, not because of strength issues, there are places where epoxies are needed and places where polyester is very suitable. obviously bonding a stringer to the hull you would go straight epoxy. using fillers such as talc is reccomended without disregard to strength from the manufacturer. a good polyester resin is 28.00 bucks a kit. and it does have a use where epoxy is not needed. the stringers in these boats are 90% for holding the engine in or you would have seen 10000 CC's crack in half at this point. setting a prescedent is fine but also polyester is also a proven less expensive product that can be used in these boats. some guy's are on a budget and may mis-costrue that 700.00 bucks worth of epoxy is not him worth doing the boat and may opt to send it to the dump. point being, these boats can be done economically and it may be "scaring" a prospective CC rebuilder away

Andy, great info- thanks for the description! I have a couple questions about the following things:

Waterdog wrote: 1) When you lay the first layer or two of glass tape in the fillet (main stringer to hull)prep the surface by lightly sanding with 220 grit to give it the proper tooth (both layers) 2)Shape a couple of old paint brush handles to fit the radius.

1)Are you suggesting I let each layer of cloth dry completely, then sand, then lay the next one? My understanding is that if I were to lay subsequent layers in while the previous was still tacky, I get both a mechanical and chemical bond. True or false?

2)I read somewhere on here (Roger?) that a piece of PVC pipe (not sure what diameter) to shape the fillet is a good, simple method. Perhaps I could use the same piece of pipe instead of shaping a paint brush handle? If Im understanding you correctly, the purpose of this is to remove excess resin in the glass layup. Is that right?

I used frosting spatulas to shape the fillets. Cheap and they leave a nice uniform, clean shape.

Edit: apparently they called "spoonulas"

Hey Waterdog,

I've read posts where you've spoke about Airplane repair. Is there a lot of fiberglass on military or commercial planes? I don't know anything about airplanes except when I fly on them it all looks like riveted steel or aluminum. Just curious.

BKH

BKH,
The V22 Osprey is 80% composite, AV-8b Harrier is mostly composite. Rotor blades my gosh, a titainum spar like a hollow 2X6 down the lenght and a composite leading edge, blade pocket and tip cap. No adhesive likes to bond to titainum. In the desert we get very little time on a set of rotor blades. Lots of blades removed for over haul with less than 10 hrs. ($300,000)But the bad boy is the C-5a the biggest we have (reworked in Ga.)20,000 sq ft of bonded surfaces.

Ok, Ive detuned my glass order due to the changes. No more mat in the stringer/rib/bulkhead schedule. Added a bit more cloth tape for good measure. Got rid of the talc. Ive removed the incedentals for the time being- Im going to check Harbor Freight for them next time I pass by.



Revised plan:

Before installation:
- Main stringers (3 layers of ½”) will be laminated together with cloth
- Front bulkheads will get a layer of cloth on both sides (to prevent buckling)
- Floor panels will get 2 layers of cloth on the underside (for screw retention)

Stringer Installation:
- Mains will go in first, followed by secondaries, then bulkheads and ribs.
- Mains and secondaries will be bedded with a combination of epoxy mat and epoxy resin thickened with mill fiber and cabosil (to take up the gaps).   
- Main stringer layup: 2 layers of 2" cloth, 2 layer of 4" cloth, 2 layers of 8" cloth, 1 layer of 12" biaxial. Top will be wrapped with the biax.   May add a little mill fiber to the resin.
- Secondaries: : 1 layer of 2" cloth, 1 layer of 4" cloth, 1 layers of 8" cloth, 1 layer of 12" biaxial. Not wrapped.
- Ribs (alongside secondaries): Not bedded or filleted. 2”,4”,8” cloth tape only.
Front bulkheads: Every other bulkhead will be bedded and get the same schedule as the primary stringers. Every other will not be bedded or filleted and will get a 2”/4”/8” cloth tape schedule (same as the ribs).

Floor Installation:
- Each panel will be bedded with epoxy mat or thickened epoxy (mill fiber/cabosil). Still undecided on which one (or both) and whether or not to use screws as well.
- Filleted to walls with thickened resin (milled fiber/cabosil)
- Taped to the wall with 2" cloth, 4" cloth and 8" cloth.   
- Taped to the secondaries with 2” cloth, 4” cloth, 8” cloth
- The top of the floor will get 2 layers of cloth and one of mat, except up front where its foamed- which will get an extra layer of mat for thickness.

The idea behind the reduced schedule (fewer layers of glass and no bedding) on the ribs and every other bulkhead came from my conversation with Joe. I have no problem with taking advice from those smarter than I am! The main idea is to prevent gel damage in the event of a hard strike (running the boat aground, bouncing on the trailer, etc) by allowing the hull to flex a bit during these situations. The coosa and glass schedules I have planned should be more than strong enough to support the floor and hull, even at 60+mph.