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Glue sizing end grain question


MikeC
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I use a dilution which will just barely begin to gel after a minute or two, when a couple of drops are placed on a piece of aluminum foil. If there is any remaining on the surface of the end grain after glue of this concentration has been applied and has barely started to gel, I wipe this off while it is still easy.
Then I let the area dry completely (maybe a day or two), and do it once more.

Same thing for the end grain of the blocks.

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I use more-or-less the Burgess method.  There are two basic purposes of sizing:  1) To keep the final glue-up from soaking into the endgrain and ending up with a dry joint, and 2) Keep the final glue-up from getting into the wood and having it swell up and then shrink when it dries, leaving potentially crack-causing stresses or distortion.  I don't think the size needs to soak far into the endgrain for these purposes, so thick-ish is better, with less coatings required.

And yeah, it has to be completely dry before the final glue-up.

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In my experience, if you glue size once with pretty medium glue (dilution-wise), and really dib in in there with your finger until it gets, you should be good to go once that dries. 

If I'm not mistaken, as long as you've got a barrier keeping subsequent applications from soaking in before they gel, you'll be okay. 

 

But a second sizing is never a bad idea just to be safe at critical spots. 

 

I've been sizing basically every joint these days. Crom center joints to rib tops to fingerboards. You can't really go wrong with that. 

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3 hours ago, Don Noon said:

Am I the only one that sizes purfling grooves?

Not a bad idea. I do this from time to time on the spruce endgain areas, which are very absorbent and the glue could be sucked in and not glue the purfling. But usually, it is enough to be careful not to use too diluted glue and to insist on in those areas.

If I remember correctly Roger Hargrave does, but his purfling gluing system is different.

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11 hours ago, MikeC said:

Thank you all for the advise.  I have now glue sized the end grain on the neck but may apply another coating before final glue up.   

If you do it another time, do not do this just before gluing the neck, as the accuracy of your neck joint will most likely be gone. Do it before gluing the fingerboard to the neck, because you will have to let it dry and check that the heel has not been distorted, and in any case re-flatten it, which is not very comfortable to do with the fingerboard in place.

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4 hours ago, Davide Sora said:

Not a bad idea. I do this from time to time on the spruce endgain areas, which are very absorbent and the glue could be sucked in and not glue the purfling. But usually, it is enough to be careful not to use too diluted glue and to insist on in those areas.

That takes care of the problem of a dry joint, but I worry about the residual stress problem.  The spruce endgrain areas will expand with the hot glue, and then shrink as it dries.  The purfling is all long-grain, and will not expand or shrink appreciably along its length.  When it dries, the spruce crossgrain will be in tension, and initiate cracks more easily... kinda the opposite of what you want the purfling to do.

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16 minutes ago, Don Noon said:

That takes care of the problem of a dry joint, but I worry about the residual stress problem.  The spruce endgrain areas will expand with the hot glue, and then shrink as it dries.  The purfling is all long-grain, and will not expand or shrink appreciably along its length.  When it dries, the spruce crossgrain will be in tension, and initiate cracks more easily... kinda the opposite of what you want the purfling to do.

Good point.

Even if I am not sure that these residual stresses can be so important as to create problems, perhaps it is better to prevent them anyway by using preventive glue-sizing, at least on the spruce.

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20 hours ago, Don Noon said:

Am I the only one that sizes purfling grooves?

 

16 hours ago, Davide Sora said:

Not a bad idea. I do this from time to time on the spruce endgain areas, which are very absorbent and the glue could be sucked in and not glue the purfling. But usually, it is enough to be careful not to use too diluted glue and to insist on in those areas.

If I remember correctly Roger Hargrave does, but his purfling gluing system is different.

I apply glue to the purfling channel and clean out the excess and let dry. Once dry I fit the purfling and apply very thin hot glue/water. No glue ghosts remain after the channel is finished, all gets carved away and I lightly size the spruce with Gelatin/Alum.

I started doing it this way after reading Rogers bass thread. For me its much easier to fit the purfling, especially the miters, in a dry channel then it is trying to align  everything quickly before the glues starts to gel. Once everything looks good just brush on the hot water/glue to reactivate. Never had a problem with loose purfling or cracks so far. I learned several other tricks that I use in my building since Roger posted that excellent thread. I'm glad I was around when he was sharing all that information here. I wonder what he's doing now...

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Not a big fan of sizing the channel anymore, I find it not needed, time consuming, messy and as Don points out potentially mis-shapening things.

I do the reverse of charliemaine and apply the glue to the purfling that way I'm not slopping on the plate and worrying about deep hidden glue ghosts or unwanted swelling on the end grain particularly. I cut my purfling, dry fit it lightly to make sure everything is good, then coat the purfling, let it dry on plastic pen stickers, put it in the channel, seat it, brush on boiling water , clamp it, and its done, perfectly clean with no excess on the plate. This also allows for glue to be on the end grain of the mitres once activated by water

A really good way to check the "does this work good enough'ness" of this method is to simply make several practice channels in scrap material ,with and cross grain, and simply glue in as suggested, then do some sized channels and glue it that way so you have both styles of application, then do 2 types of demo...1 the I don't care demo where you just hack at it with a purfling pick trying to jack it out and then 2 the "restoration demo" where your trying to be careful and preserve the channel and purfling with no damage.

In my experience I'm not really seeing a big difference in the amount of force needed to remove the purfling one way or another, this assuming you have a proper fit, so therefore ergo I do it the fastest, simplest, cleanest way that works.

 

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