202GF, A miracle glue?!

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The Garrett -Wade catalog has a PVA glue that it claims: 1) It fills gaps with strength 2) Squeeze out does not penetrate the wood and easily chips off when dried, no need for scrapping.
If it actually does this I will certainly use it, but it seems like bull when an obsure brand is radically superior to the successful brands.
Has anyone used it. (Hey, occassionally my joints have gaps...)
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Well if it is like the Lee Valley 202GF, then yes. Fills gaps with strength? I've never tested it, but it does indeed fill gaps. I like the brown colour too. I have to shake it up real well before use as it the solids settle out.
John
toller wrote:

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toller wrote:

I wonder how it holds a joint together if it "does not penetrate the wood and easily chips off when dried"?
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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Yeah, I was thinking, what good is a glue that will chip off wood when dried?

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How about glues that hold metal pieces together. They don't penetrate the metal. The problem is the strength of the glue bond to each piece and the internal strength of the glue layer itself. A roughed up surface holds better than a smooth one because there's more glue in the between pieces volume, ain't it?
If it chips off easily, it doesn't seem to mean that the bond itself will be weak. The stresses would be different, wouldn't they?
Agkistrodon
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A roughed up surface does not necessarily mean a better bond. Have you ever laid a pane of glass on top of another with water between the two? Almost impossoble to pull apart because of the surface tension.
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But that's a different physical phenomenon.
Agkistrodon
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Is it? The water like glue displaces the air that is between the 2 surfaces. If there is a spot in a glued up joint that has an air space, the joint is week at that point

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Well when the glue dries, then it is a different phenomenon.
John
Leon wrote:

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wrote in messagenews:aKqEc.2199

I don't want to be seen as a pedantic jerk by you chaps even though my students often called me one but:
Glass sheets are held together by water between them because the water has driven out the air and occupies the space between the two sheets. The sheets themselves are then forced together (and against the water lamina) by the air pressure that pushes them together at about 14 lb/sq in. The only mediating pressure is the very slight air pressure on the thin lamina of water between the sheets of glass that forces the water to push outward against the sheets by pushing inward on the water. Surface tension has not much to do with it unless there is an interactive attractive force in the glass (or whatever) that pulls the water molecules toward the sheet but this would be very slight in almost all cases of materials. Air pressure is the force both holding the sheets together and, to an extremely small degree, pushing them apart by pushing on the water lamina. If the glass sheets are uniformly flat and measure, say 10"x10", each sheet is 100 sq in. The air pressure produces 14 lb/sq in on each sheet so the total is [14 lb/sq in x 100 sq in/sheet x 2 sheets] - [the pressure on the water from the sides], or 2800 lb. (I ignored the very very slight pressure on the water lamina because it close to zero). 2800 pounds is the amount of force needed to separate the sheets if there's no other factor. We don't need that much because when we slide the sheets over each other we reduce the amount of air pressure push against them at the places where they are together. Finally, by sliding the sheets enough, the holding pressure is reduced to an easy force to apply.
Glues work differently and don't depend on air pressure to hold things together. There are essentially two aspects, the adhesion of the glue to the surfaces and the internal bonding strength between the molecules that make up the glue itself. The solvent for the glue (water, alcohol, whatever) is just a carrier. The glue dries by losing its carrier and (in some cases) the chemical nature of the glue itself changes when that happens. When it dries, it bonds to the things being glued and internally inside the dab of glue between them. In the old days, both these bonds were relatively weak and either the glue's internal bonds broke or the bond with the material broke. Some glues produce bonds to materials that are stronger than the material itself is internally AND the internal glue intermolecular strength is also stronger.
Spaces in glued up joints produce weakness because theres no glue in the spaces to form a bond.
Agkistrodon
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Yea, that's just what I was gonna say. :-) -- ******** Bill Pounds http://www.billpounds.com
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What? The part about being a pedantic jerk??? Hell, I know it! And I don't give a flip, either.
Agkistrodon
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.

Now you are beginning to show signs that you understand the point that I was trying to make. You stated,
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news:4TCEc.20861$bs4.13057

Now you are showing signs that you might understand the point that I was trying to make.
You said,
"A roughed up surface holds better than a smooth one because there's more glue in the between pieces volume, ain't it?"
Roughed up surfaces often cause spaces in the glued up joint. A smooth surface is Ideal for glue.
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wrote in message

That is really debatable, mein Herr. It depends. If the glue can get into the roughed up spaces, it will be stronger because there will be more glue in the joint as a result of the increased surface area caused by the roughening up. The gap causes a weakened area of the joint relative to the rest of it because there's no glue there. This calls for scientific investigation!! Roughed up vs. smooth glued surfaces. Aha, something I know about.
If I do some sexperiments, would anyone want the results? How would you design the set of experiments? I'll do them this weekend.
Agkistrodon
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I believe the glue companies already have this data. IIRC their recommendation is a smooth surface. Hence there are rip blades made for glue line ripping that produce smooth surfaces. Jointers straighten a board and produce smooth surfaces for gluing. Thick glue in a joint is not desirable. It is usually an indicator of a poor joint that does not fit well. Roughing up a surface has little value for gluing as the surface produced from roughing up leaves loose and weak fibers of wood.
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I checked several maufacturers and other sites and found it about equally divided between smooth and roughed up. Who knows? I did not find any raw or reduced data but didn't look that hard.
Agkistrodon
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First step - glue together two end-joint pieces. The ends are always rougher than the sides. So the glue should hold better according to the theory you are testing.
Some of you may have already done this... :-)
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wrote in message

I think it depends on how rough and what sort of glue. With most any glue but epoxy the roughness must be small enough that you have a very thin layer accross the interface. If you roughen the surface to the point that the glue is filling gaps the result will be a weaker joint than if you just planed the surfaces smooth and glued them because the glue in the pockmarks will be weaker than the wood it replaced. I dunno where you cross the line between giving the glue tooth, and weakening the joint by requiring the glue to fill a gap.
I _think_ that a planed or scraped surface has the correct level of roughness for most glues, and does not have as many loose fibers or dust particles in the pores and does a surface roughened with sandpaper.
With epoxies, the glue in gaps is stronger than the wood and the strength can be maximized by eliminating the wood altogether, though the resulting furniture may leave something to be esthetically desired.
--

FF

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Forget the physics... wood fibers are held together by lignin and xylan, woodworking glues mimic natural glues by bonding the wood fibers together. That's why it isn't necessary for the glue to soak in and why a smoother (planed) wood surface holds better than a rough (sawed/sanded) surface.
--
Mac Cool

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