Gorilla glue and African mahogany....

[chris_goris]

I recently needed to make some raw blanks to turn some exterior porch components for an architectural restoration job. The job required the blanks to be 10-1/2" square x 2-1/2" thick when finished. Having mostly 4/4 stock, and narrower than 10-1/2", I needed to edge glue, plane, and laminate to get get my width and thickness. Sounds good so far, right?. Well, I rough planed and edge jointed one edge and glued up the pieces, I used 6 x 22 long pieces as to get 2 from each. After spraying water on the edges and gluing and clamping, I left them for 3 days, I wasnt able to get back them until them. My next step was to plane them and then laminate the pieces and clamp. Well, when I was planing them, one of the joints failed, it completely came apart , and the boards were fairly uniform thickness and flat etc, as they had been rough planed. So I took one of the other glue ups and sure enough, I was able to lightly tap the joint against a hard surface and it too failed..... Im kind of at a loss here. Any ideas?

 

[toolferone]

Did the glue foam up? I would call Gorilla tomorrow and ask them.

 

[chris_goris]

Yep, it foamed up. I had glued up some other blocks too a couple weeks ago, same material too, and no problems. Weird part is, the glue fractured, none of the wood failed.

 

[ehpoole]

I'm not an expert in working with these woods, but I will share what I do know.

It is the oily resin in your wood that is preventing your glue from bonding properly. If you will wipe the glue surfaces down with acetone, give the acetone a minute or two to flash off, then promptly glue the two surfaces with Titebond III and clamp tightly you *should* get a good bond.

As always, test the advice before you trust it as I have not had to work with these woods much myself.

 

[chris_goris]

I'm not an expert in working with these woods, but I will share what I do know.

It is the oily resin in your wood that is preventing your glue from bonding properly. If you will wipe the glue surfaces down with acetone, give the acetone a minute or two to flash off, then promptly glue the two surfaces with Titebond III and clamp tightly you *should* get a good bond.

As always, test the advice before you trust it as I have not had to work with these woods much myself.

Thanks Ethan, but I need to use the polyurethane glue for outside. Its the only thing I trust for exterior. Ive tried different glues tightbond exterior etc) and they just dont hold up (just my opinion, dont rant back please.)

 

[JJD]

Check out the new Elmer's glue. I'm told that it is good for outdoors and moist conditions, although I've not tried it myself.

 

[Jeff]

Chris,

A weird problem indeed because glue line failure is not usually a problem unless the joint was glue starved to begin with or it didn't properly cure because of other factors. Personally, I don't care for the glue expansion of Gorilla glue, but can't dispute your personal experiences with it. Is this your first glue experience with an "oily" exotic wood like African mahogany and Gorilla glue specifically?

Fine Woodworking did a glue type strength comparison test a few years ago: Mark Schofield; titled "Your Glue?. In particular, using a dense tropical wood like Ipe, they found that Titebond III outperformed Gorilla glue (100% vs. 58%, respectively). With Ipe the glue line failure was 100% along the glue line with the latter.

So maybe you should reconsider and have a go with Titebond III and it's extreme qualification as an ANSI Type I waterproof glue for exterior use. :icon_scra

http://www.titebond.com/Libraries/LiteraturePDFs/FF681_TBIIIUltimateBrochureTB.sflb.ashx

 

[bluedawg76]

sounds like the glue didn't cure properly. i would test this first to see. I realize you'd used it previously, but it's the most obivous culprit. I haven't worked w/ african mahogany before, only the south american cousin, but I don't recall it being particularly oily. Out of curiosity, why did you spray the edges w/ water prior to glue up? I have no experience w/ gorilla glue here, so does this raise the grain in hopes of getting a better bond?

Sam

 

[SkintKnuckle]

Chris, without seeing the joints, it's difficult to say, here's my guess:

1- did the joints have really good fit? polyurethane glues do not work well as gap fillers
2- did you have good clamp pressure, this is even more critical than when using plain old wood glue

hope this helps

 

[chris_goris]

sounds like the glue didn't cure properly. i would test this first to see. I realize you'd used it previously, but it's the most obivous culprit. I haven't worked w/ african mahogany before, only the south american cousin, but I don't recall it being particularly oily. Out of curiosity, why did you spray the edges w/ water prior to glue up? I have no experience w/ gorilla glue here, so does this raise the grain in hopes of getting a better bond?

Sam

Sam,
When I said previously, I meant last week, and it was alot of the same lumber. Polurethane glues need moisture to cure, that is the catalyst for curing. The manufacturers recommend this with dried lumbers.
Chris

 

[chris_goris]

Chris, without seeing the joints, it's difficult to say, here's my guess:

1- did the joints have really good fit? polyurethane glues do not work well as gap fillers
2- did you have good clamp pressure, this is even more critical than when using plain old wood glue

hope this helps

Martin,
Thanks for the reply, but this wasnt my first rodeo. The joints were only about 24 inches in length and had been jointed. They were clamped as tight as I could get them with 4 "K" Body besseys on each glue up. Im not sure what more I could have done. May have to just right it off as one of those unsolved mysteries
Chris

 

[Berta]

What was the temperature of the shop during this process, including the curing? I suspect a temperature culprit!

 

[chris_goris]

What was the temperature of the shop during this process, including the curing? I suspect a temperature culprit!

Its quite possible Berta, but I dont know for certain, but it did get cold, I do know it wasnt "cold" when I glued them

 

[Berta]

The temperature gave me problems when I was doing a simple glue up. It was 70, then colder at night. I am now waiting for spring!

 

[DWSmith]

I use TiteBond III for all my glue ups. A good amount of those glue ups and boards are mahogany, Sapele and Khaya, both known as African Mahogany. I can't remember one glue joint failure in the past 8 years and over 5000 boards. Just my 2 cents worth.