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Re: [PSUBS-MAILIST] Mini Nautilus Minisub

Hi Doc,
 
OK, I see what you're saying.  Admittedly, 'glass on epoxy isn't the best bond one can get, but in the case of the sacrificial foam method it doesn't matter since the epoxy only serves to keep the foam from dissolving while the resin cures; and then the foam will be dissolved away leaving only the fiberglass shell. 
 
Lately I've been working on a part made from cardboard and heavy posterboard; sealed with epoxy; and covered with 'glass.   (The intent is to make a male plug for a female rubber mold.)  I toothed the epoxy with 36 grit sandpaper before applying the polyester.  Some time ago I wasn't happy with the shape of a section of it, so I cut it off and rebuilt it using the same process.  I've got that section here with me now, and I'm putting it through a destruction test.  With considerable effort (twisting and breaking the part), the paper core separates, but the epoxy stays with the 'glass.  A bit more work with a sharp blade and I can get the epoxy layer to peel away from the glass; but it takes some doing.  So. for the purposes of producing a plug from which a mold can be made, epoxy and glass work well enough. 
 
Of course, the part I'm making now is strictly decorative and won't have to withstand the stress of high speed operations your Bionic Dolphin must experience.  If the final product needed to be something that could stand up real punishment in the water, I wouldn't rely on glass over epoxy, either  I might use it to make the mold (as above), but the actual working part produced from that mold would be made of something much stronger: I might mold a polyurethane foam core and cover that with 'glass; or shoot a matrix of glass fibers and resin into the mold with a chopper gun.
 
VBR,
 
Pat
 
 ----- Original Message -----
From: Doc
To: personal_submersibles@psubs.org
Sent: Saturday, June 15, 2002 10:38 PM
Subject: Re: [PSUBS-MAILIST] Mini Nautilus Minisub

I've sometimes used a weak bond of polyester on a lightly sanded (120 grit) epoxy to test experimental fairings.
When the tests were over, a few minutes with a BIG rubber mallet and the fairings popped off.

Doc
 

Captain Nemo wrote:

 
----- Original Message -----
From: Doc
To: personal_submersibles@psubs.org
Sent: Saturday, June 15, 2002 5:34 PM
Subject: Re: [PSUBS-MAILIST] Mini Nautilus Minisub
 Just a quickie, then back to the boat.
I've found epoxy will stick to polyester and vinylester, but, polyester and vinylester will not bond well to epoxy. Go figure! As to the styrene foams, if you're just building a quick plug, cover the foam with a thin layer of FixAll plaster, then paint, wax
and lay up with polyester or whatever. Later,

Doc  Right on Doc, I should have mentioned that, while epoxy sticks well to most surfaces, almost nothing sticks to fresh epoxy; not even masking tape. It dries with an almost "oily" feeling to it.   What one can do is (1) wipe the fully cured epoxy surface down with Acetone on a paper towel to get rid of the "slickness" and let that dry; then (2) sand the surface well with extra coarse sandpaper to give it a "tooth" the resin can "fill in" and bond to, and then apply polyester resin and glass cloth.  Works fine. Yep, I've heard about the plaster coat method, too.  And I've heard one can even use regular house paint on top of that.  Sounds economical for large projects. For the general info of anyone thinking about this kind of project: when making a foam plug out of multiple layers of that 1-inch thick extruded styrene foam insulation available at hardware stores, it might become necessary to glue the stuff together.  There are glues especially designed for use with styrofoam, but one "all purpose" cement that I've found to work well is Elmer's PROBOND polyurethane glue.  Doesn't contain any volatile spirits that "eat" foam; and will adhere to most anything.  When dry, it can be sanded during the forming process, too; but be sure you're working in a well-ventilated area and wearing a dust mask.  You don't want to breathe this stuff. Of course, when in doubt about any of this, one should take a small amount of the material(s) being used and test them to see how they behave. VBR, Pat