Urac question

[ErictheViking]

I have looked through 5 or 6 how-to threads that mentioned urac and none of them mentioned how to prep the wood. just sand with 80grit? I plan to wipe down with acetone but I heard somewhere (I thought) that the epoxies need too have something to grip so they recommend grooving the wood with a toothing plane or hack saw blade. any tips will be helpful as I have only used tbIII. it has worked well, just wanted to test this out on an easy one first then try someting harder. r/d possibly, thanks in advance.

[Pat B]

For Urac you need to rough up the surfaces. Unlike TB glues Urac has gap filling properties. A toothing plane or hacksaw blade will do. You drag the hacksaw blade sideways down the limb so it acts like a toothing plane.

[ErictheViking]

Thanks Pat, that is what I thought.

[eflanders]

With all due respect, I will challenge Pat's answer some here.  I spoke with the folks at Nelson (who make URAC) and they had some differing opinions on whether toothing was necessary.  Apparently they have done some shear testing and they had little differences in the woods that were scored versus the woods that weren't.  However, some woods are more oily than others and these woods did shear quicker without being scored.  So, given the stress that a bow undergoes, and the various woods used, it certainly would be safest to score the glued surfaces some for best adhesion.

[Pat B]

I'm always happy to learn new info, eflanders.  It good to know Urac works just as well on smooth surfaces.  I believe Urac was used to hold wooden air plane propellars together. 

[hillbilly61]

Were the heck do you get Urac? I've looked all over town  and no one seems to know what it is

[ErictheViking]

Thanks for the info eflanders, I plan on using two different oily woods, IPE and garapa. hillbilly you can get it at nelsons website, they are a forestry supply company that sells tree marking paint, even paint balls, and other stuff. I went there to get a quart of urac185 and they wanted $17.99 for shippping. then I read Eric Krewson say that a pint is more than enough glue for the shelf life. so I bouught it on the big auction site. It was a full pint not the baggies one fella is selling on there. is was cheaper there I just hope they hadn't had it for too long.

[ErictheViking]

Scott ,thanks for next time. .  can't believe I didn't call(hits self in head with hand).  Always learnin', always learnin'.lol

[Josh]

You can order the pint sized ones from 3 rivers that's how I get mine.  Usually gets to my house within 2 days of ordering too.  Shipping last time was 6 dollars.

[Hexrod]

A couple comments that may help with the use of Urac 185 from Nelson:

 Follow their mixing instructions.  Urac is pretty forgiving, but if you stray too far from their recommendations, you will weaken the glue.  I think the can says to mix 12 parts catalyst powder to 100 parts resin, by WEIGHT.  A reloading scale is useful.

The catalyst powder consists of about 15% ammonium chloride, and 85% walnut flour.  The walnut flour is a filler.  The ammonium chloride is the catalyst that will activate the urea formaldehyde resin.  Stir the powder before mixing to make sure the ammonium chloride is well-mixed into the walnut flour.

For best bonding, the glue requires a certain moisture content in the pieces to be glued up.. IIRC, 12% is optimal.  Happily, that is where many woods equilibrate when exposed to a moderate environment, more or less.  Don't try to glue up strips straight out of a drying oven.  if you live in an arid climate, mist the strips with water 5-10 minutes before glueing up.  if you glue up in winter in a heated building (i.e. very low relative humidity), mist the strips.  Every URAC 185 failure I've heard of has had to do with too-dry pieces.

The mixed glue lasts longer in the pot than it does spread out.  It also holds longer in cooler rooms than in very hot rooms.

Urac holds well even with smooth surfaces.  Can't say whether rough sanding or running a hack saw blade down strips helps or hinders.  Also can't say how it deals with oily woods like Ipe.

The Urac resin is about 2% formaldehyde, IIRC.  Formaldehyde is a carcinogen.  2% of maybe an ounce that you will mix for glue-ing up a bow is not much, but you have to decide how careful you want to be.  Personally, i wear latex gloves when i glue up, and try to do it with decent ventilation.  Some people seem more sensitive to formaldehyde than are others.  I also believe that if you live in a new house, you probably are exposed to more formaldehyde from the construction materials and paint off-gassing than you will ever encounter using URAC 185, but that's just my opinion.

I've only used URAC to glue up one bow, but have used it on maybe 30 split bamboo rods I have made.  (They are all smooth-surface joints, by the way, not roughed up in any way, but the stresses may be different between rod and bow...)

The glue will set properly at room temperature in 24-36 hours, but as indicated on the can, this can be sped up if you slightly heat the glued piece.  Don't flex the bow until the glue has fully set.

It's a great, strong glue which doesn't have the problems with "creep" that non-catalyzed glues like titebond 3 can have, but it requires that you do what it takes for it to work properly.  I hope these recommendations may help make it as good as it can be for you.

Lee

[Gordon]

Excellent post Lee. Thank you.

[Pat B]

I never mixed Urac by weight but always by volumn and never had a failure.  I also keep Urac in the frig for longer shelf life but also mixed it cold. This seemed to give me a longer working time. Immediately after glue up I would put the glue-up in the hot box over night at about 90 to 100 deg(F).

[Hexrod]

I agree with you, Pat.  It's entirely possibler to mix Urac 185 correctly by volume rather than weight.  All you or someone else has to do is to do it by weight one time, then figure out what that translates to in volume.  I know that Weldwood Resorcinol tells us how to mix their glue both ways, printed on the can.  I didn't think Urac does, but could be wrong about that  Regardless, once someone figures what the equivalent ratios are (by weight and by volume) there is no difference between the 2.

I too store my Urac resin in the fridge.  Nelson says at room temperature, the resin should have a shelf-life of at least 6 months, but they will tell you on the phone that if stored in a fridge, it can be much longer, years.  In my experience, the more times you open the can and expose it to air, the less time it will hold, even in the fridge.  I have never tried using bloxygen on it, but probably should. The longest I've had a can stay good was about 3 years (when it turns from creamy yellow to dirty tan/brown, I figure it has oxidized and I throw it out.)

I also mix it soon after it comes out of the fridge, when it's still cold, and agree that that extends pot life.

I cure my rods in a similar hotbox, with 1 60watt light bulb that pushes temps up around 100.

BTW, there are other Uracs not made by Nelson.  They may be made differently and behave differently.   I had a bad experience with one of them, found Nelson Paint, and have never considered looking for another maker.

Finally, any yahoo (like me, for example  ) can write anything he wants on the internet and that doesn't necessarily make it all true.  Customer Service at Nelson Paint has always been patient and helpful when I've called them with questions, and I'd suggest bowyers interested in Urac 185 consider doing the same and get info regarding their product straight from the horse's mouth.  That service alone is worth whatever they charge in shipping in my opinion.

Lee

[Pat B]

Lee, my cans of Urac have mixing directions for weight or volumn.
  Another product I used a few years ago was Weldwood Plastic Resin. It comes in powder form and mixes with water. From what I could tell it is very similar to Urac(urea) and worked well for me. I learned about this from a past PA member from Italy. He couldn't get Urac there and built very nice, highly stresses R/D type bows as well as standard longbows and recurves.

[Hexrod]

There you go!  Instructions for mixing either way on the can.  You can tell that I habitually mix by weight, and so had forgotten the can also said how to do it by volume.

Lee