Unibond 800

[Lee Lobbestael]

I bought done unibond 800 for a bamboo osage glue up. I have never used it before. Do the surfaces need to be roughed up prior to gluing? My father in law who is a woodworker says it's a misconception that wood should be roughed up before gluing and that they should actually be as smooth as possible. Possibly he was only talking about wood glue tho

[Eric Krewson]

I have made about 50 BBOs, I started with Urac and have since used Unibond after they quit making Urac. I roughed up the osage backs and bamboo bellys of every one of the bows I made with a toothing plane iron, I have had no glue failures .

[High-Desert]

I've never done any actual testing of this, but a smooth back does make more sense. A smooth back is a clean cut on the wood vs roughing the back which is tearing the fibers, making them weaker. Using a toothing plain is cutting the fibers,  as well as increasing gluing surface, which is beneficial. Is there really a loss of holding power from the glue with a smooth surface vs roughed up with sand paper, it's probably negligible. If you are going to do something to the back, I'd say a smooth surface or toothing plain like Mr. Krewson said. Just my 2 cents.

Eric

[Lee Lobbestael]

The gluing surfaces are just so smooth and tight fitting, it seems like a shame to gouge them  all up

[Aaron H]

I like to use 80 grit sandpaper on the mating surfaces.  Unibond is a gap filling glue, compared to say titebond 3 which prefers a smoother surface

[PEARL DRUMS]

The manufacturer suggests a roughed up surface, so I always have from the URAC days up to the UniBond days.

[Lee Lobbestael]

So just roughing them up with 80 grit will be fine?

[PEARL DRUMS]

Straight strokes that make linear grooves. Don't swirl the paper around. I usually use a block so the pressure is even and consistent.

[Aaron H]

I agree with pearl, long linear strokes.   I have also heard of guys using a hacksaw blade pulled the length of the limbs as an impromptu toothing plane

[PEARL DRUMS]

Ive done that with no negative results.

[PatM]

Smooth is fine but linear "roughing" increases surface area and helps prevent glue starving. The main point is that you don't need or want to make the surfaces ragged with torn fibers standing up all over.

 That's about like throwing a layer of sawdust in your glue line.

[bubby]

Yup 50-60-80 grit all will work

[Onebowonder]

I used to have a toothing plane, but the one I had has gone missing somehow.  I've used a hacksaw blade many times since with good results.  It's about increasing the surface area in the glue line as was mentioned before.  The matrix created between the exposed fibers and the set glue is actually quite a bit stronger in shear than the natural lignin in the wood's own fiber matrix, so there is really no risk created by using the toothing plane if you a reasonably careful.  The process is particularly effective for gap filling type glues and works exceptionally well with Bamboo's extra strong and long fiber matrix.

OneBow

[Wooden Spring]

So why don't you do a glue up specifically for destruction testing? Test a few samples to breaking point with smooth joints, and then test a few samples to breaking point with roughed joints.