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>From West Sytem web page: http://www.westsystem.com
ADHESIVE FILLERS
403 Microfibers
403 Microfibers, a fine fiber blend, is used as a thickening additive =
with resin/hardener to create a multi-purpose adhesive, especially for =
bonding wood. Epoxy thickened with microfibers has good gap-filling =
qualities while retaining excellent wetting/penetrating capability. =
Color: off-white.
404 High-Density Filler
404 High-Density filler is a thickening additive developed for maximum =
physical properties in hardware bonding where high-cyclic loads are =
anticipated. It can also be used for filleting and gap filling where =
maximum strength is necessary. Color: off-white.
405 Filleting Blend
This strong, wood-toned filler is good for use in glue joints and =
fillets on naturally finished wood. It mixes easily with epoxy and lets =
you create fillets that are smooth and require little sanding. Its color =
is a consistent brown, so 405 can be used to modify the shade of other =
WEST SYSTEM fillers.
406 Colloidal Silica
406 Colloidal Silica is a thickening additive used to control the =
viscosity of the epoxy and prevent epoxy runoff in vertical and overhead =
joints. 406 is a very strong filler that creates a smooth mixture, ideal =
for general bonding and filleting. It is also our most versatile filler. =
Often used in combination with other fillers, it can be used to improve =
the improve strength, abrasion resistance, and consistency of fairing =
compounds, resulting in a tougher, smoother surface. Color: off-white.=20
Their products are excellent. I have been using them for more than 20 =
years in marine applications. They have excellent technical support and =
are willing to help you with any questions by email or on the phone. =
They do not charge for a brief dose of expertise - but I think they make =
up for it when selling you the epoxy! Their variety of hardeners really =
lets you control things also. I keep three types on hand: Slow cure, =
Extra Slow cure, and Coating hardener. Their handy pumps for the =
hardener and resin are a MUST!
I often use the #404 High-Density filler for big cracks. Maybe it is =
overkill. I do know it mixes a lot easier than the #406. It sounds to me =
like Del was recommending the #403 and #406. Maybe next time I will try =
that.=20
Roger - I think Del was pointing out that West System with no filler may =
be a bit too plastic when one is trying to actually repair a broken =
bridge - one that is cracked to the extent that it needs to be held back =
together - as opposed the the more common case where we are filling a =
small crack next to the bridge pin. I think when you have a large crack =
(although I can't imagine a large crack on a not-terribly-old Bozy =
across only 5 or 6 notes) you will be able to stuff the non-wicking =
thickened, not-so-plastic, epoxy into the crack efficiently. Maybe that =
should be the deciding factor - if the crack is big enough to get =
thickened epoxy into it - do it. If the crack is so small that you need =
the wicking action of the unthinned epoxy, then go that route. I agree, =
put the pins into the uncured epoxy.
Regarding clamping. Del is right on. Epoxy requires a minimum thickness =
of product in the joint. For the bridge, if the bridge is cracked so =
much that you need to reposition the two halves, yes, of course clamp. =
But clamp to position things correctly only. Do not clamp so hard as to =
squeeze out too much epoxy. You gotta leave a good coating in the joint. =
Do not clamp it like you would clamp a bridge cap to a root with hide =
glue. Sometimes, if I am jointing two perfectly mating surfaces together =
with epoxy, and the situation is such that it will be hard not to squish =
the two joining surfaces together tightly, I will actually drill a bunch =
of shallow holes, route out a series of shallow troughs, or whatever to =
be sure that I have sufficient joining surface area that has a good =
1/16" or whatever layer of epoxy retained in the joint.
Regarding solvents. Del is right on with his description of using a =
solvent for cleanup, as opposed to using it as an additive for thinning =
the epoxy. For cleanup, I use acetone. It works excellent on non-cured =
epoxy. It works well even when the epoxy is semi-cured into a rubbery =
state. That is what West System recommends as a cleanup solvent. I don't =
know how laquer thinner would work - never used it. I do know that I can =
tolerate a little acetone vapor better than laquer thinner.
Terry Farrell =20
----- Original Message -----=20
From: Tom Servinsky=20
To: pianotech@ptg.org=20
Sent: Saturday, September 01, 2001 8:36 AM
Subject: Re: split bridge
Del,
Might want to mention that West does provide the thickening material =
for changing viscosity. #403 Micofibers Adhesive is the name.
Tom Servinsky,RPT
----- Original Message -----=20
From: Delwin D Fandrich=20
To: pianotech@ptg.org=20
Sent: Saturday, September 01, 2001 12:49 AM
Subject: Re: split bridge
----- Original Message -----=20
From: David Love=20
To: pianotech@ptg.org=20
Sent: August 31, 2001 7:51 PM
Subject: Re: split bridge
Joe:
Why would you not clamp epoxy? The bridge needs to be pulled back =
together, among other reasons, to get the pins back in the right =
position. My conversation this date with Roger Weisensteiner confirmed =
my belief that this would be the method of choice for making this =
repair. He suggested using a two part epoxy (e.g. West System type) and =
clamp it back together reinserting the pins either before or after it =
dried. My concern with after is that if I have to redrill the case =
might be in the way. So I will probably reinsert the pins before it =
dries.
Unlike nearly all other adhesives, epoxy is an excellent gap filler. =
In fact, it actually requires a rather thick glue line for best adhesive =
strength. Rather than say "don't clamp at all," I would say clamp =
lightly--just enough to bring the crack just shy of fully closed.=20
West System is a good epoxy for this repair, but it should be used =
with some kind of filler to improve its resistance to cold flowing--it =
is a plastic, after all. I would suggest a bit of micro-fiber (ground =
cotton fibers) to add strength and some colloidal silica to add =
hardness. Try equal amounts of each, adding just enough to bring the =
matrix up to the consistency of warm peanut butter.
You'll want to insert the pins before the epoxy hardens. And you'll =
want to clean up the excess and squeeze-out before it all fully hardens =
as well. Things can get pretty difficult after the whole mess gets hard.
Regarding solvents and epoxy, I have, in the past, repinned =
bridges putting a drop or two of epoxy in the bottom of the bridge pin =
hole prior to inserting the pin. The squeeze out I have cleaned up by =
brushing it onto the notch using an acid brush with a bit of lacquer =
thinner. I think I may have been introduced to this technique by Bill =
Spurlock in a Journal article in fact. Though I recognize the =
controversy surrounding epoxying bridge pins in, I wasn't aware that a =
bit of lacquer thinner was compromising the strength of the epoxy. =20
Joe was referring to the practice of adding a thinner such as =
lacquer thinner to the epoxy to thin it out and get it to flow into the =
cracks more readily. It is true that you can thin epoxy in this manner, =
but it does chemically weaken the material and introduces a certain =
amount of shrinkage as the thinner flashes out of the mixture. It is =
doubtful that you will get enough thinner into the epoxy mix using it as =
you describe.
Incidentally, epoxy cures chemically, it does not "dry. It is this =
property that keeps it from shrinking as it sets up. There is no--or at =
least, very little--solvent to flash out.
Regards,
Del
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