Pete S-RCU

I've noticed some kits I've built with fiberglass fuselages say to sand the inside of the fuse with 80 grit to remove the mold release before gluing in formers etc.
Why would there be mold release inside the fuse?
The gel coat on the outside I can understand having mold release on it, bu the inside s/b just plain fiberglass, right?
Am I missing something here?
I guess roughing up the gluing surface is a good idea, but is it really necessary?

Just wondering,

thunderjet

My Feedback: (1)

I believe that when a part is molded. That a type of wax comes to the surface oppisite of the mold. ie inside of fuse. This wax must be removed for proper bonding. This may be wrong. I only know what I have been told.

Harley Condra

My Feedback: (4)

Pete,
The reason that the manufacturers instruct you to sand the inside of the molded parts interior, is to provide a roughened surface that will allow the secondary bond to have some "tooth" to hang on to. Prior to sanding, the interior surface has a somewhat smooth surface that will not allow adequate adhesion.
Some faying surfaces, particularly in vacuum bagged parts, have a layer of "peelply" added, which, when removed gives the surface the appropriate and correct texture to allow and promote good secondary bonds.

BVM, for example, tells the builder to rougen the inside surface with 80 grit wherever a bond will occur, to give the surface some "tooth" for bonding.


The wax coating that "thunderjet" is referring to, occurs in polyester laminates when a "finishing" resin is used. "Finishing" resins contain wax which rises to the surface in order to form a barrier between the resin and the atmosphere. This assists the cure.

The "mold release" wouldn't be "mold release" if it migrated through and into the resin.....


Hope this info is helpful...........

Harley Condra
BVM REP

Vincent

My Feedback: (61)

Pete,

I learned a long time ago to just take the glass parts out of the box and wash them off with soap and water with the garden hose. Yes, rough up the interior with 80 grit to get some weave showing for the glue to hang on to. If I am using a pfm type glue I will just wipe the area down with acetone first, no need to sand with that type of glue.

Vin...

Pete S-RCU

Thanks for the information guys, I am sanding the glue area's, just wasn't sure why it was necessary.

Vin, what's pfm glue?
I'm using aeropoxy and I also have some methacrylate adhesive which is supposed to be good.
Anybody used the methacrylate?
It's also supposed to be tough and flexible, but it smells when curing.

Vincent

My Feedback: (61)

Pete,

PFM is kind of a silicone looking type stuff, almost like "goop" or what ever else they call it. I use it for a variety of things, not on formers though, aeropoxy on those.

Vin...