Oak, glue and black lines

[Richard_C]

This isn't really finishing but this seems to be the best place for it because it shows through the finish.

I glued up some small piece of oak and ash ( chosen becauseI had some) as a proof of concept test for turning a segmented vase. I used evo stick wood glue - pva - also because I had some, clamped up etc. and all went well. When I came to finish the test piece there were fine black lines along the joints, and I can only assume that it was the tanin in the oak reacting with the pva as it set. It wasn't just on the surface, it was still visible after turning to shape.

I cut the oak on the diagonal and inserted the ash so whan it was turned there would be a 'stripe' effect. That means there was some oak end grain exposed to the glue. Horrid it is.

I want to carry on and do a full sized one. Should I use a different glue (Titebond?, I prefer not to mess with 2 part epoxy unless I have to) or is glueing oak to something else a hopeless task?

 

[eribaMotters]

I moved to Titebond 3 as soon as I heard of it some years and have not regretted it. Yes it is expensive but a bottle of glue goes a very long way and accounts for a tiny cost of the project. The only negative is a slight staining to porous softwoods occasionally.
What I would add is, and this could just be your photo, is that your joint is not as tight as it could be. Aesthetically this is annoying, practically I'd have thought it could be a danger when turning. I'm sure the experienced turners out there might correct me on this one.

Colin

 

[Richard_C]

is that your joint is not as tight as it could be

Fair point, it was a try out. It was only 35mm diameter and glued over a decent length so I went with it. This is the worst section, selected to show the most blackness. I will give Titebond a go on the next trial before I go to anything bigger. Will be a while though - its minus 5 inside the garage/workshop right now.

(on dangers, don't the people of Hatherleigh regularly fling themselves in front of burning tar barrels rolling down a very steep hill ?)

 

[eribaMotters]

The barrel roll is a yearly event that they got back into operation this year. We only moved in recently and were looking forward to it, but after preparing the garden for 380 beech hedge were knackered. Next year will be a different matter. We might even see the 48hr pub opening back in future years.

Colin

 

[profchris]

I recently glued oak to mahogany using Titebond Original- no visible glue line. So I guess it's something in your PVA reacting.

 

[kinsella]

This isn't really finishing but this seems to be the best place for it because it shows through the finish.

I glued up some small piece of oak and ash ( chosen becauseI had some) as a proof of concept test for turning a segmented vase. I used evo stick wood glue - pva - also because I had some, clamped up etc. and all went well. When I came to finish the test piece there were fine black lines along the joints, and I can only assume that it was the tanin in the oak reacting with the pva as it set. It wasn't just on the surface, it was still visible after turning to shape.

I cut the oak on the diagonal and inserted the ash so whan it was turned there would be a 'stripe' effect. That means there was some oak end grain exposed to the glue. Horrid it is.

I want to carry on and do a full sized one. Should I use a different glue (Titebond?, I prefer not to mess with 2 part epoxy unless I have to) or is glueing oak to something else a hopeless task?

Richard, how did you apply the glue, i've had a few occassions where i've used metal application tools and the metal and tanin will react and i recall i got a black line on one or two occassions. I use oak around 70% of the time on my projects and never (with above exception) get a reaction from the oak. (i use american white oak and antique english oak).

 

[Richard_C]

You got me thinking, and maybe led me towards the cause of the blackness. I used pva straight from the plastic bottle which has a dispenser, maybe used a SHF to spread it a bit. (standard human finger). But, I do recall giving one piece a quick rub on the belt sander. Didn't change the zirconium belt for just one job, and it had been used to put an edge on a woodturning chisel. So, even though I wiped the joint with a dry piece of paper towel there is every chance that some fine steel particles got embedded in the grain. More tests will follow, but that might be the cause. From what others have said there should be no fundamental problem with pva and oak but I now own some titebond and will take care not to 'infect' the join with anything metallic.

 

[Sachakins]

Only time I got black marks on oak was when I inadvertently had the clamp bars touching the surface as it dried, looked a right mess, but only on surface, a 1-2 mm pass on jointer cleared it. So yours does sound like contamination.
I only use silicone pastry brushes now, never loses brush and no metal like on normal brushs.
On anything wider than 100mm I use a notched spreader, as used for gluing lino down.