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Good day all, from the hurricane infested lands of Florida. After an unseasonable dry summer, we have been getting absolutely drenched over the past three weeks. This has created a humidity disaster in my otherwise well-conditioned shop.

Fast-forward to now, having finished bracing the tops of 6 guitars in the last week. Though I store them in the house, the time in the shop for gluing the braces down and setting was enough to expand the tops. Now that they have been back inside for a few days the lower boughts have flattened (they were glued into a 40' radius dish).

I've had this problem in the past, and was able to "re-set" the lower portion of the x-braces and the tone bars by using an iron, but with scalloped braces it was difficult. Plus, trying to heat from the top always makes me nervous about destroying the glue joint down the center.

I've not tried a heat gun before, but though it might be an easer and more controlled way to go. Anyone have suggestions from trying different approaches? I definitely don't have time in my build schedule to scrap them all and order new materials...

They are glued on with HHG 315.

I'm no expert, but I use hot hide glue a lot. Just to be clear: are you planning to add more hot hide glue after you take the joints apart, or not?

I think the heat gun idea is great for when the glue is still in the gel state, and you need to either move the brace a bit, or make sure that a good glue joint was made (i.e., the glue might have gelled before the parts were put together, so after clamping, you use the heat gun to make sure). But that strategy has to be applied really soon after the original joint was put together, while the glue is still in the gel state.

If the joints have had time to fully dry, I think you should add new glue after you take the joints apart. That's what I do: I take a heat gun to a dry glue joint, and that helps the parts come apart. Then I use more hot hide glue to put the parts back together.

The things with a heat gun are that you have to keep it moving, and pay attention to scorching. I use the low setting on mine more often than the high setting. It takes a little longer, but there is less chance of scorching.

Well, the good news *ugh* was that one of the six was to by my first personal guitar.... long overdue. Anyhow, I tried that one first by heating with an iron from the top side. Got the braces loose but then the heat ended up sucking out so much moisture that the darn thing cracked up the right side about 5". It's trash....

I went after the next one with my typical method of touching the iron on a small part of a brace at a time and using a spatula, moving very slowly. It worked.

And, yes, I definitely added more glue after I got it apart. In fact, the tone bars were completely removed, re-sanded, top re-sanded and glued like they were new.

Man, this is gong to take a lot of hours I wasn't planning on. I guess this is why I call the first 10 "prototypes" and why the customers pay less than have of our final sell price.

Back to the iron!

I'm curious about your choice of 315 gram strength for brace work. The higher the gram strength, the shorter the working time. I normally use 192, and it is plenty strong for this task. I would only be tempted to use a higher gram strength for gluing on bridges, and so far I have just stuck with 192. Can you share why you went with 315 for braces?

Why not take a small plane and plane away the braces? Much less chance for damage to the top.

Actually, I use 315 for braces, kerfings, bridges, bridge plates and attaching the top and back... anything I think might ever need to come apart. For things that I assume will never need to come apart, I use other stuff. For example, I use Epoxy on Fretboards and carbon fiber rods, which I figure will be there forever, or you need a new neck. For things that take a "long" time, like bindings and perflings where I need to glue most of it and then trim and fit at the end of the process, I use titebond 2 or 3, depending on the color of the woods involved. It would be nice to use HHG for those too, but honestly, I just don't see myself ever being fast enough for that. Plus I want the glue still setting when I rope the body after I've taped on the bindings. Might seem redundant, but I like taping to get them in place and then really clamping everything down with 100' of cotton rope in the traditional fashion. This allows me to remove the tape before the glue dries and clean off any excess. Plus it leaves the surfaces mostly exposed for drying.

Anyhow, with the HHG, I just figure if I'm gonna use a form of glue, might as well be the strongest version I can get my hands on. For me, I have my braces very well marked and fit before heating up the glue pot, so I only need enough time to spread the glue, place the piece and put in a couple go-bars. That's never more than about 10-15 seconds. In fact, I usually can't clean up any squeeze out until I'm about three or for braces past the one I want to scrape, or the glue hasn't gelled up enough to come off clean. I probably spend less than 15 minutes bracing an entire top, once I start applying glue. Backs are actually a little more because I cut the reinforcement strip to fit between the braces after they are placed.... so there's a bit of trimming and trying to get them all just right.

That's a good idea if I was willing to completely remove the x-brace, and everything touching it. Which would be basically everything except for the Transverse Brace. At this point in the process, the entire tops have been braced, including the bridge plate. Taking it down to a raw plate is probably possible, but man...

The good news is that the upper bought didn't move as much (after all it's smaller, and has the Transverse Brace and a sound hole) so all I really needed to deal with was everything below the bridge plate. Fortunately, I shape the bridge plates to match the 40' radius, so that portion of the tops remained pretty good. It was really that large "mostly" unsupported area where the legs of the x-brace and the tone bars are that really went flat on me.

For taking things loose (fingerboards, braces, removing backs, etc) I like to use a heat gun, Baker's palette knife, and a small amount of water.
I wet the joint I want to take loose, then heat the palette knife with the heat gun and wiggle it into the joint, adding moisture and reheating the knife as necessary.
I haven't had much luck heating the wood with a heat gun (I'm too heavy handed with it). The wood seems to dry out and scorch before the joint gets hot. A hairdryer is probably more my speed.
Stainless palette knives allow you to use a little vinegar if you are taking apart AR type glues. (carbon steel leaves black stains when used with vinegar)

https://www.amazon.com/LEGERM-Decoratin ... 6R8YP5JMDA

I can't believe I hadn't thought of that.... heating the tool instead of the wood. Brilliant.

Hi Terrence,
I changed the link to palette knives with rivets and wooden handles - the polypropylene handled ones might be O.K. ,but then again, not take the heat.

I'll be the odd man out and suggest, respectfully that you do what it takes to have the humidity controlled in a proper range in your shop and throughout the build process. Seems to me the underlying problem here is a lack of RH control. If addressed none of this, resetting braces is necessary.

And although I'm very well versed in reactivating HHG it's done in the repair world at times but it's not ideal in my view. We do it when we have to, when it's appropriate for the instrument...., and when we have access issues to the object being glued. When we build or glue a new brace in place we go to a lot of trouble to have the correct RH, pressure, temp, temp of the glue, properly prepared surfaces and proper cure time. Resetting braces really sounds like a compromise to me that should be avoided at all costs.

Also what does 315 gram strength glue do for you beyond the typical plain Jane HHG and isn't this less serviceable since more heat is required to soften it?

And please I am not being critical or a jerk here. I just wonder why you have to deal with all this at all and feel bad for you that you do when RH control can get you back to building and end the repairing.

PS: 315 HHG has been promoted for bridges here in the past and I think that's a fine and thoughtful application for it. I would push back that anything difficult to access such as internal braces need to remain serviceable with lower gram strength, easier to release glue.

HHG is an excellent way to do bracing, I/ve switched to fish glue. several years ago. When I was in KC I had a recurring problem of hhg braces going wonky on me during the cold winters when the humidity would drop to 25% on the main floor and bsmt, I dreaded the loud pop of bracing. I switched to fish glue. Which i prefer , as it gives me 25 to 30 min of open time. When we moved to the OKC metroplex I decided to use a dedicated dry room . It Is humid here summer spring winter an fall. The winters are mild, enough that a humidifier is rarely needed . Our dry room remains at mostly 40 to 45% yr round. with a dehumidifier. I am currently experimenting with a combo of clear gelatin and 192 hhg . I have a glued a maple sample outside that is 50 % clear gelatin an hhg I want to see how long it will take to delaminate Our avg aft humidity outside is over 65%. in summer.. In summary. having a dedicated dry room that is used for all phases of the building process is the way to go, in terms of having more control over the building process., and getting less surprises.

I think the best solution to the problem of controlling RH is very situation-dependent, so I hesitate to recommend any strategy in particular. In my situation, I work in my walkout basement, and it would be extremely difficult to isolate the environment of my shop from the rest of the house. So, I control RH for the whole house, not just my shop. It’s not cheap, but neither are the renovations (and second set of HVAC and RH control units) that would make it possible to isolate my shop. With a high capacity Aprilaire whole-house humidifier in the winter, and whole-house dehumidifier in the summer, I can keep the whole house, including my shop, hovering in the 40-45% range all year. I would not enjoy trying to do part of the work in a controlled environment, and the rest of the work in an uncontrolled environment. But that’s me and my situation.

I’ve built guitars on three continents and nowhere was relative humidity within a range where I could do assembly all year round. I store my wood and do all assembly in a separate room with controlled humidity. I share space with the well pressure tank, hot water tank and electrical panel.
If it were me, I’d remove the braces, and reinstall after acclimatizing all parts at a known RH. A cracked top is heartbreaking — I do my best to avoid these.


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Regarding the use of a heat gun for localized heat in undoing a hot hide glue joint: Just this afternoon, I used a heat gun to unglue a completely dried glue joint where the tail block meets the sides. It had a wonky placement the first go-round (my own fault). A little water, a little heat from the heat gun, a flexible icing spatula nudging its way into the joint . . . relatively easy. On a soundboard, it would be good to be very mindful of the center seam, and the relative fragility of the spruce. But the job can be done with a heat gun with no serious problems, if you stay alert to what the wood is telling you.

I can't believe I hadn't thought of that.... heating the tool instead of the wood. Brilliant.[/quote]

Someone here suggested some time ago to keep the palettes in the hot water in glue pot. Very useful tip, too.

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Pierre Castonguay

Agree with Mr. Breakstone on correcting the humidity control issue before worrying about anything else. As to trying to remove or slip the bracing...I suspect you will spend less time and do less damage to the top and center seam by using a chisel to strip off most of the bracing (down to less than 1/64"...closer to 0.010"), leave the bridge plate on, then clean off the remaining spruce with warm water.

The first time I had to strip a top of bracing, it seemed daunting and so impossibly vindictive on the part of my former boss that it occasioned a moratorium on any and all baked goods deliveries to the shop for a few months afterwards (Mr. Morelli once commented that my lemon bars were a clear example of American Exceptionalism). After stripping that top a few times - six times in total - I got much quicker and much more accurate in trimming down to leave just a whisper of spruce.

On glue...we used 315 gram strength glue for bridges only - it was considered overkill for other guitar applications. 192 gram strength high clarity glue has a good balance of strength, ease of use (a gel temperature of about 95 deg F), and ease of removal. 315 is - to be quite frank - a pain in the rear to use (gel temperature of closer to 130 deg F) and makes a bridge installation or removal a more involved process than with other adhesive. Offsetting that pain pill is a history of zero bridge joint failures - even when one of our customers decided to use his vehicle's trunk as an Easy-Bake Oven for his brand new instrument...in Dallas, TX...in July.

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If you want to save your braces you can tear up strips of paper towel and soak them in vinegar and place them against the glue joint. The vinegar will soak in and soften most organically based (hide , fish, bone) glues and "white" and "yellow " glues (as previously mentioned) and allow the braces to be removed nondestructively without heat. The surfaces need to be washed thoroughly to remove any vinegar residue and then allowed to dry before regluing. Again, be sure to use stainless steel to avoid black staining.