Thanks everyone for your comments. I have been researching adhesives quite extensively lately, ( I started with a term paper in chemistry about 50 years ago) and am gathering manufacturers data for my presentation in Seattle in July. I appreciate the specific comments about Bolduc and I guess it will remain a mystery. For that reason, I doubt I will include it in my presentation. If a manufacturer (or distributor) won't supply any technical data on their product, I for one, will not promote it. There is enough mystique going around already as many of you have noted. For what its worth, just about all of the adhesives that we would use on pianos are thermoplastics except hide glue. I was following this topic on a violin makers site. Even those guys, who are the purists of the pure admit to using modern adhesives for some uses. The big issue is whether the piece will ever have to be taken apart in the future. If it might, then they use hot hide glue. It is not for the acoustic properties which I think Delwin stated very well, it is so they can get it apart later. Actually PVA glues are soluble in acetone and it would be possible to break the bond even with these modern adhesives. It may mess up the finish though. For those concerned about creep, the addition of finely ground pecan shells used in Better Bond adhesives for veneer work will prevent creep. Hardness can also be achieved by adding silica (sand) as in the West system hardener. However, West System data states that it will actually weaken the bond slightly if used. Hardness is really overrated. (Shore is a measure of hardness) Hardness means brittle. If you have two pieces of wood expanding and contracting or being impacted as in hammer shanks, brittle is not really what you would want. Some slight flexibility will allow the bond to give a little and not break. Almost every adhesive we use is stronger than the wood we are gluing. The most important part, as pointed out so well by several of you, is not un-clamping the part too soon, particularly if the parts are under stress. Most adhesives will have sufficient tack to hold in 30 minutes but for maximum strength almost all manufacturers suggest at least 24 hours, in the fine print. For larger surfaces, double that, at least, since most of them are water based and the water has to evaporate. The larger the glued surface, the longer that will take. Thank you all for your comments. I think this will be a lively session in Seattle. I will present as much of the science as most of us can tolerate so that you can interpret the manufacturer's data sheets and make up your own mind. Doug Gregg Classic Piano Doc Message: 1 Date: Fri, 24 Feb 2012 12:04:38 -0800 From: "Delwin D Fandrich" <del at fandrichpiano.com> To: <pianotech at ptg.org> Subject: Re: [pianotech] Bolduc glue Message-ID: <010b01ccf32f$8a596a70$9f0c3f50$@fandrichpiano.com> Content-Type: text/plain; charset="iso-8859-1" It does creep. Given enough time, enough stress and/or enough heat--PVAs are thermoplastics--all PVA adhesives will exhibit some creep. At question is whether or not these things will exhibit enough creep in ways that will be of any consequence to us as piano technicians and rebuilders. Years back I used to worry about this stuff but then I actually started to think--I know, unusual, but it does happen--about how we use adhesives in real life and these days I don't waste a whole lot of worry time on them. With very few exceptions glue joints in pianos are not subjected to high sheer-stress loads. The most obvious exception might be the rib-to-soundboard panel joint of a compression-crowned soundboard system. Here, I would argue, age- and compression-related long-term creep--i.e., compression-set--within the soundboard panel itself is going to be a far bigger concern than any relatively minor amount of creep that might be taking place in the glue joint. And in some applications a bit of creep might actually be to our advantage; a large cross-lapped joint, for example. PVA adhesives are not approved for use in structural, load-bearing laminated beams such as those used in some building designs (many churches, for example) or for similar beams used in road bridges and railroad bridges. The concern in building beams is not so much that they will creep over time but what will happen to them in a fire. PVAs soften when exposed to heat and it's not a good thing if structural beams fail while the fire department is trying to put out the fire. Laminated structural beams used in road bridges are subjected to heat from the summer sun, not to mention water from periodic rains. PVAs are not generally recommended for use in bent-laminated structures such as grand piano rims or vertically laminated bridges. Still, CP Adhesives (http://www.cpadhesives.com/) lists CP-0200, a cross-linked PVA adhesive similar to Titebond II, as one of their recommended adhesives for curved laminations. And I have to confess--please don't tell the glue police!--I've used Titebond II to glue up more than one vertically laminated bridge body and, as far as I know, twenty and thirty years later they haven't yet come apart or straightened out. If I start building curved laminated structural beams for a railroad bridge to be installed in Arkansas I'll probably consider using some other type of adhesive. There are other adhesives that would better stand up to those extremely hot and humid summer days. I also don't use PVAs for gluing up grand rims. For one thing, the open-time for most PVAs is not long enough; they start to skin over before the whole book of veneers could be assembled and loaded into the press. But the shear stress on the glue joints in some areas of the bent laminated rim are extremely high. I doubt this would be a problem once the belly structure was fully assembled but until then I'd think spring-back might be a problem. It would be an interesting experiment and I might well be surprised. It wouldn't be the first time. So, to your clavichord; as long as you don't put those parts you've glued up with Titebond outside in the summer sun or the winter rain they should work just fine. Ron's point is well taken, though. It would be nice to have access to a lot more information on the adhesives these companies are trying to sell to us. You have to figure it exists somewhere. There is some information available but you have to search for it. I've attached the product data sheets for Titebond Original, Titebond II and Titebond III. (Does this list still accept attachments?) Chapter 10 of the Wood Handbook is all about adhesives and the bonding of wood. Either specific chapters or the whole book can be downloaded (free) as a PDF file from http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id= 100&header_id=p I may have some additional information somewhere. If I come up with anything I'll add it to the list. But I don't think I've ever seen a Shore hardness rating for any adhesive.... ddf Delwin D Fandrich Piano Design & Fabrication 6939 Foothill Court SW, Olympia, Washington 98512 USA Phone? 360.515.0119 ? Cell 360.388.6525 del at fandrichpiano.com ? ddfandrich at gmail.com
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