To tape, or not to tape...?

Topics pertaining to fibre glassing, finishing issues, concerns and tips, epoxies and epoxy problems/resolves
groper
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To tape, or not to tape...?

Post by groper » Wed Jul 03, 2013 8:25 pm

Have been building interior furniture and stuff like that recently and was thrown by a few comments by a composites engineer down the gold coast...

The discussion was around whether or not glass taping was required over the adhesive coves of T-jointed panels, such as bulkhead to hull joints etc. The engineer said that even survey was letting through non taped joins provided the bond could demonstrate adequate strength, usually accomplished via 3rd party testing - which he was involved in.

I also rang ATL and had a chat with them about their rubberised HPR5 epoxy adhesive for this purpose alone. The long and short of it, was that they agreed it would probably be ok in most instances provided a large enough cove was used. But they stopped short of backing it with a guarantee. It was way too expensive, so i didnt pursue it any further...

So this got me thinking, whilst im not prepared to go out on a whim on what 1 guy said, im not going to leave out the glass tapes on anything that has structural importance. However, what about the non structural stuff like interior furniture etc? This would save alot of fairing - all those taped edges and the bumps left near the cove.

So Ive decided to try something on my cabin setee... i might do it elsewhere too... ive decored the vertical panel and the horizontal seat panel, both edges where they meet. Im going to fill both decored edges with epoxy/microfibres to form a solid internal join, then cove the inside where it cant be seen. The vertical panel is coved to the floor (no tape) This means no fairing to do as the panels are already sweet.

So what did you guys tape, and what did you not tape?

Has it lasted?

Would you do it any differently next time?

puremajek
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Re: To tape, or not to tape...?

Post by puremajek » Thu Jul 04, 2013 1:05 am

All structural were glassed, then coved (as opposed to cove, then glass). Some internal non-structural were also done this way (saloon ceiling, lower bridgedeck, bow lockers etc). All others - coved only. Some cases where I wanted extra strength, a thick glue-mix cove, left till tacky. Then a thinner finishing cove with microbaloons to get a clean edge.
James
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groper
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Re: To tape, or not to tape...?

Post by groper » Thu Jul 04, 2013 12:22 pm

Can you give examples of what was not glass taped?

There is often some confusion about what is structural and what is not...

Also can you clarify what you meant by glassed then coved - not the other way around? What i mean is, how can you get the glass to sit in the corner without air bubbles if there is no cove in there beforehand?

puremajek
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Re: To tape, or not to tape...?

Post by puremajek » Thu Jul 04, 2013 1:35 pm

Can you give examples of what was not glass taped?
Inside/outside cupboard frames, bench tops, saloon seat, toilet setup and shower arrangement, galley cupboards, nav table, cabin soles etc.
There is often some confusion about what is structural and what is not...
What is on the plan (with my design anyway) I considered structural.
Also can you clarify what you meant by glassed then coved - not the other way around? What i mean is, how can you get the glass to sit in the corner without air bubbles if there is no cove in there beforehand?
I cut strips of glass, resined the area to be glassed, lay glass-strips in the corners and dabbing with a paintbrush, removed any air bubbles. Most of the time I let that dry before coving, but occasionally coved once it was tacky.

While on coving, a billiard ball with a bolt screwed into it. Also seen others using a SS ice-cream scoop.
James
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sea_bee
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Re: To tape, or not to tape...?

Post by sea_bee » Thu Jul 04, 2013 5:11 pm

Keep in mind that James built in ply and Groper in foam core. Joints in those materials are quite different.

I'm building in ply, and coved before and after glassing. It is easier to get the glass to take the corner when it has been rounded with a small glue cove (and stronger), and that then gets a microballoon bog cove after.

Chris

Finally
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Re: To tape, or not to tape...?

Post by Finally » Thu Jul 04, 2013 6:17 pm

Chris

You mentioned you are laying down a glue cove before glassing over.

I am building a Pacific 40 in Polycore and my plans specifically mentions, to quote "Don't be tempted to use a glue mix for filleting thinking the join will be stronger, it won't. We want the stress path to follow a smooth curve from one glass face to the next through the glass tape. A hard glue mix fillet causes a stress concentration". I don't know if this would also apply to a ply built boat.

For what it's worth I am coving and taping (in some places dummy tapes) all joins because the plans say so. Over the top but I'd rather be safe than sorry particularly if there is a falure of a non-taped join and the insurance company uses that as an "out" when the plans say to tape.

David

groper
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Re: To tape, or not to tape...?

Post by groper » Thu Jul 04, 2013 8:55 pm

Dave, where's your boat being built? I'd love to come take a look.... I'm out Smithfield if you wanna check out what I'm upto, always cold beer here too :)

James, I've never heard of that method before... Hope it's going to be ok as I've always read that the smooth transition of glass from one surface to the next transferred the load stresses. With a sharp corner, like a kink, it can simply crack or fold...

Structural cove and tapes can apparently be too stiff, the correct amount of flex is ideal. Some rules recommend foam spacers under bulkhead to hull joints to allow a small amount of flex. Then you see all the duflex boats being built with hard structural epoxy coves, other boats use pre fabbed glass hat section bulkheads bonded to hull via plexus. Seems there is so many different ways... End of the day I think most boats are probably WAY over built and so matters little, hence everything works...

I bought some plywood today, just going to build the interior cabinetry from it, everything else is foam core sandwich... I think I'm just going to use the AV515 polyurethane adhesive for all this stuff, epoxy seems overkill and more inconvenient having to mix it up every time...

puremajek
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Re: To tape, or not to tape...?

Post by puremajek » Fri Jul 05, 2013 9:40 am

I would talk to the Designer. They all have their own preferences.
James
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groper
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Re: To tape, or not to tape...?

Post by groper » Fri Jul 05, 2013 8:10 pm

I talk to myself all the time james, doesn't seem to help no matter how much I wave my arms around in descriptive mannerisms, some questions always remain... Some questions not even competent engineers get it right all the time either, no matter how good they are, some things just aren't very well understood by mankind yet... Go and ask 3 different naval architects for a solution to a problem and you will likely get 3 very different solutions... :mrgreen:

kjay
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Re: To tape, or not to tape...?

Post by kjay » Sat Jul 06, 2013 8:35 pm

Groper,

Have you had a chance to research the gougeon brothers book? they go into epoxy fillets and their strengths. I am sure that you have however I thought i would throw my hat into the ring.

Nice build by the way.

John
(Sunday Morning)

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