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Thread: Primary vs. Secondary Bonding
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18th June 2009, 12:01 PM #1SENIOR MEMBER
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Primary vs. Secondary Bonding
For Mik especially: What is the latest in the debate on this topic? I was trained in the WEST system way, to saturate the wood, then add the thickened epoxy, and complete the glue joint using all primary bonding. So, let coatings, etc. "go green" -- that is let it get tacky and then do the next coat or add the thickened glue and make the glue joint final.
The other way is to let the epoxy cure and sand it. The glue joint is this a secondary bond.
I heard that there was no appreciable difference in bond strength, but really wonder what the data says.
The answer would have an impact on the whole approach to prefinishing parts to build a boat. If the secondary bonds are not any weaker then it seems like precoating the wood and doing a lot of the sanding and prefinishing on the bench is the way to go. I'm thinking of an example: the side planks for a Goat or similar Storer build. If we coat the panels on the bench and allow it to cure and sand it well, we've done a lot of great prefinishing and made for a more efficient build process later. We would not need to mask off for the bulkheads and other glue joints. Just coat, sand, and move on. If primary bonds are a must, then the consequence is that we really ought to be working within the window of epoxy (sometimes a challenge) or masking off faying surfaces such as in coating the side planks.
Thanks.
Cheers,
Clint
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19th June 2009, 12:08 AM #2
I asked PAR about this a few days ago. In the building subforum ... the thread about "what should I epoxy"
Michael
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19th June 2009, 08:06 PM #3
Mik, Clint's a yank, he's probably not used to being 'handballed'
Richard
for the non Oztralians, our weird local game involves passing the ball from one player to another via the 'handball' whereupon you punch the ball with one one hand while supporting it on the other. In the local vernacular, refusing to answer a question by referring it elsewhere is called being 'handballed'
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20th June 2009, 10:53 AM #4
Howdy,
My belief is that it is perfectly fine from both experience and observation of others.
But was PARTICULARLY interested in Paul's (PAR's) experience because he has done so much building over such a long time and also has the chance to see his work again through the years.
He is also a damn fine analyst with few biases as he has used most types of glue and chooses what does the job ... as perfectly as possible. I've learned a great deal from him.
Yes ... I handballed it
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20th June 2009, 05:20 PM #5Novice
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- Santiago, Chile
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Handball link
G´day all!
Being at home, possibly swine flu, I guess there´s not much more to do than offer a link,
G'luck with PAR's, Daddles' and Mik's advice...
Cheers,
PDJ
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20th June 2009, 08:01 PM #6
P = Pig
D = Disease
J = ?
Hope you are hale and hearty soon.
If you are providing links it can't be toooo bad. Which is great.
So from the other thread
Originally Posted by PAROriginally Posted by PAR
The only exceptions are usually the outside of the hull, which is so easy to coat anyhow and often has some glassing that can happen at the same time.
Most components I like to coat and sand while they are on the flat. Whether they get masked for further wood to wood gluing or any framing is done with a brush at the same time. Sand ready for painting or varnishing before the item is glued into the boat. HInt do any bevels after the item is coated - that way you create clean surfaces - The plane is the fastest way to remove epoxy.
Often with the documentation of a particular design it is possible to know where the frames are going to go. These areas can be masked up quite quickly. Eg chine log positions, frame positions on bottom and side panels. If it takes you all day to work it out it is probably most sensible to go for a secondary bond by dewaxing and sanding the whole surface.
Other tricky ways is the wet on wet then glue scenario. Really useful for closing in decks etc when it is going to be the last time you will see inside. Underside of deck and all framing inside the compartment is given three coats wet on wet (waiting between coats to allow the epoxy to go tacky) and then glue spread on mating surfaces and the deck or compartment face dropped and screwed into place.
But everything PAR said too.
MIK
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20th June 2009, 08:02 PM #7
P = Pig
D = Disease
J = ?
Hope you are hale and hearty soon.
If you are providing links it can't be toooo bad. Which is great.
So from the other thread
Originally Posted by PAROriginally Posted by PAR
The only exceptions are usually the outside of the hull, which is so easy to coat anyhow and often has some glassing that can happen at the same time.
Most components I like to coat and sand while they are on the flat. Whether they get masked for further wood to wood gluing or any framing is done with a brush at the same time. Sand ready for painting or varnishing before the item is glued into the boat. HInt do any bevels after the item is coated - that way you create clean surfaces - The plane is the fastest way to remove epoxy.
Often with the documentation of a particular design it is possible to know where the frames are going to go. These areas can be masked up quite quickly. Eg chine log positions, frame positions on bottom and side panels. If it takes you all day to work it out it is probably most sensible to go for a secondary bond by dewaxing and sanding the whole surface.
Other tricky ways is the wet on wet then glue scenario. Really useful for closing in decks etc when it is going to be the last time you will see inside. Underside of deck and all framing inside the compartment is given three coats wet on wet (waiting between coats to allow the epoxy to go tacky) and then glue spread on mating surfaces and the deck or compartment face dropped and screwed into place.
I liked Daddles stuff about not getting too frantic about cleaning anything but yourself
Originally Posted by Daddles
But everything PAR said too.
MIK
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21st June 2009, 01:13 PM #8
Vinegar is actually really only good at cleaning up resin (without hardener added) or stopping the reaction of a mix. It does do a fair job at cleaning up people as it's reasonably benign to put on your skin, though you'll smell like a pickle fro the rest of the day. Some residue will remain from vinegar clean up of tools.
I long ago stopped trying to save brushes and use a good quality chip or foam brushes. Both of these brushes need attention before use. Chip brushes are given the "tape" treatment, which is box tape (clear plastic packaging stuff) is wrapped around the bristles, then pulled off with a firm yank. This removes any loose ones. Then I clamp the bristles between two boards and cut them about half their length out of the metal binder. This makes them stiff enough to spread epoxy, rather then slather it about.
Foam brushes can be shaped to suit tasks, like reaching into holes or applying coatings to highly curved surfaces. Both chip and foam brushes come in two varieties, cheap and a little better then cheap. I've managed to find a local big box store that just happens to carry the good foam ones, so I buy them out each time they stock up. If you place the good ones, next to the poor ones, the good foam looks clearly more dense, which much smaller holes. Chip brushes also need to be ferreted out for good ones. Good ones will have twice the bristles and better binders, with less bristles falling out.
West System has technical data on sheering load for both mechanical and chemical bonds. In both cases all the test subjects (bits of wood of varying species) failed in the wood fibers, meaning the bond is sufficient, which ever you choose.
This said, some designs, particular high speed powerboats and high performance sailors will ask much more, in terms of loading on say a structural fillet, then some oak samples in a testing jig. By this I mean, if your mast step on your pocket rocket with a SA/D of 42 and a D/L of 29 (the exact figures of my little 16' hot rod, by the way), is bonded to the hull's centerline seam, which happens to be a large fillet of thickened goo and a 25 knot gust catches you with your paints down, which type of bond would you prefer to have working for you. It's these sudden, unplanned loading situations we try to design for when working up scantlings. High speed power and sail take bigger engineering risks, so the margins are smaller and things can break. If a simple technique can offer a marginal increase in strength, then take it.
Not every joint or bond will need it, but some should be highly recommended. Which ones? Each design is different. Hopefully the plans will tell you, mine do, but this isn't always the case.
As far as coatings, wet on wet is superior for long life and durability. Mechanical bonds can introduce containments or other surface prep "errors" that can challenge the integrity of the layers within the coating. I've seen three coats of mechanically bonded epoxy, flake off after some use. In one recent case, the epoxy was finished bright with good varnish, but the second to last epoxy coat was sanded very fine (600 grit) and insufficient "tooth" was available for the last coat to grab a hold of. The result was UV damaged the top coat enough for it to lift off the coat below. Fortunately, he got at it quickly and I sanded off the top coatings, down to solidly bonded epoxy, then progressed up to 320 grit for the last coats of epoxy. I don't recommend finer grit then this and most can live with 280 or 220 if done properly. A wet on wet approach, literally makes the whole of the epoxy coating, molecularly bonded to itself.
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