"tabbing" versus "fillets"

[F14CRAZY]

I'm finishing up my seat boxes and boxes that support the cabin cushions. I've used peanut butter epoxy to bond the boxes to the deck. I've created "fillets" (what the West System manual calls them) where the plywood is bonded. If I hadn't heard of the "fillet" term I would just call it "caulking"...pictured below:

note: I bond stuff together with peanut butter between them, not just the fillets, so you know.

As I understand it, epoxy itself is very strong, but with West System "colloidal silica" the epoxy binds the fibers together and is even stronger. In this case, is there a need for me to still "tab" it in with like 4'' fiberglass tape? I would imagine the fillets are much stronger. I haven't closed up anything yet so if I'm seriously wrong in my thinking it isn't too late to add tape.

Thanks again guys



another note: there is a steel L bracket pictured if you look close enough...it's only there temporarily to hold things in place until the peanut butter sets up.

 

[erikgreen]

Re: "tabbing" versus "fillets"

Well, terminology differs.

But, what west system calls "colloidal silica" we here usually call cabosil, or fumed silica. It's cheaper to buy it as "cabosil" than "West System Colloidal Silica" by the way.

Adding it to epoxy thickens the stuff... makes it, in technical terms, "thixotropic". It also makes it harder to sand. It does not add any significant strength, actually... that's done by fibrous fillers like milled fibers, cotton or acrylic fibers, etc.

That said, just gluing your non-structural wood elements in place with epoxy is tremendously strong. If you're happy with the way it looks, you may be ok just using the thickened epoxy. If you want to be completely safe and ensure that your boxes actually do contribute to the overall strength of your boat (bonding all parts of a boat together into one piece is sometimes called "monocoque" construction) then tab it, or more accurately glass over the hull/box joint with a section of fiberglass cloth. You can use a section of glass "tape" to do this, or you can cover the whole box with cloth and overlap it onto the hull.

The main thing fillets (that's the right term, by the way) are used for is to provide a nice smooth transition between two surfaces for fiberglass cloth to follow. If a transition isn't smooth or is right angle, the glass forms a bubble when wet out, which doesn't add any strength and looks bad.

The best, strongest way to use fillets is to form them and then immediately lay glass over the top of them. The resin, fillet, glass, wood, and hull then all become one piece, with an extremely strong chemical bond.

Letting the fillets harden first will glue the parts in place and still let them be removed relatively easily, which can be nice sometimes, and adding the glass after still adds strength, just not as much as laying glass on uncured fillets (what we call "working wet on wet" here).

Erik

 

[F14CRAZY]

Re: "tabbing" versus "fillets"

thanks for the awesome reply. I actually started out with a 2 gallon bucket worth of cabosil but ran out and have been shelling out the cash for the stuff from West Marine...I'll be getting some more from US Composites when I order more epoxy later this week.

To me a fiberglass boat is similar to a unibody car, and stuff like the seat boxes and cabin cushion boxes do add to the strength that the deck and stringers mostly supply.

I might as well overdo it and add in some tabbing. I've actually added a few 18 oz fabric tabs to the cabin cushion boxes and used some of my 4'' tape (6 oz) inside the seat boxes.

 

[danond]

Re: "tabbing" versus "fillets"

I love epoxy. I wish I had a reason to use it more often. Don't tell me to get another boat....I just might do it.

 

[proshadetree]

Re: "tabbing" versus "fillets"

Get another boat.I dare you.Then post pics here I dare you.F-14 thats a awesome job.Your going to be riding the waves soon

 

[F14CRAZY]

Re: "tabbing" versus "fillets"

Get another boat.I dare you.Then post pics here I dare you.F-14 thats a awesome job.Your going to be riding the waves soon

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