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Help finishing gasp in shrinking bubinga

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Forum topic by XOXO posted 11-02-2017 09:11 PM 1281 views 0 times favorited 12 replies Add to Favorites Watch
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XOXO

3 posts in 43 days


11-02-2017 09:11 PM

Topic tags/keywords: gaps finish veneer

New to the site and looking for help:

I know this is long but I wanted to give as much info as I could
I’m having problems filling the seams between strips of bubinga veneer on 30” x 60” coffee table.  The veneer is laid on a 1 1/2 substrate of baltic birch ply.  I sliced the veneer to between 1/8 and 3/32 and ran it through a drum sander to remove saw marks and even the thickness of each piece.  I laid out the sequence of strips and ran a strip of heavy clear packing tape along each seam.  I’ve done this many times before with no problems.  Glue was rolled on bottom of the taped up panel which was then transferred to the substrate, covered with a plastic sheeting and a plywood caul and placed in the bag. The problem began a few days after the veneered piece was taken from the vacuum bag.  At first all was fine.  A few days later gaps (about 1/32) formed between each strip of veneer.  My solution was to fill all of the seams with Timbermate (a grain filler/wood putty) which I’ve also used on bubinga before.  They have a color which is a great match to the bubinga.  Again the panel looked great.  Off to the finisher who sprayed on a catalyzed finish.  When I picked up the panel the gaps had returned.  It made the panel look as of it was intended to be viewed as “rustic”.  Not what the client was expecting.  I removed the finish (scraped and sanded), tried to refill the gaps with more Timbermate, brushed on shellac to see what it looked like.  Still gaps but not quite as bad. More like indents than gaps but still readily noticed.  Now the gaps look like pores (like oak but longer) which I can’t seem to fill  Seems like surface tension prevents penetration.  My client isn’t happy.  I’m not happy.  At this point my only solution seems to be removing the existing veneer and starting over.  But I’m hesitant because I don’t know what happened and I do not want a repeat of the problems.  Notes:  The veneer had been around plenty long enough to be acclimated,  we had been going through a triple digit heatwave, maybe I could have edge glued the strips of veneer but this method hasn’t failed me until now,  the Timbermate is hard and isn’t supposed to shrink but by now I should have filled the gaps, maybe the filler sands away faster than the surrounding wood keeping the gaps fully filled while sanding.

Any fresh eyes out there with suggestions on how to fix/fill my gaps and how to prevent this from happening again???


12 replies so far

View Mike54Ohio's profile

Mike54Ohio

120 posts in 316 days


#1 posted 11-02-2017 09:16 PM

Pics of the trouble piece might go a long way in someone being able to give you “fresh eyes” on the project. A long of talented people on this site and I am sure a couple pics will get you lots of responses for the issue

Good Luck

-- It's only a dumb question if you ignore the correct answer

View Loren's profile

Loren

9631 posts in 3486 days


#2 posted 11-02-2017 09:51 PM

Perhaps the moisture in the glue caused
the wood to expand and stretch the packing
tape.

View TungOil's profile

TungOil

747 posts in 333 days


#3 posted 11-02-2017 10:06 PM

Paul (Shipwright) would be a good resource here, but a few things come to mind.

1/8” is on the heavy side for veneer. It’s my understanding that it starts to behave like solid wood around that thickness although I’ve never gotten a definitive answer to ‘how thick is too thick’

What kind of glue are you using? Is it PVA? PVA glue is flexible, combined with the thickness of your veneers the wood might be moving. I usually use a urea formaldehyde glue like CAT-5 or Weldwood Plastic Resin glue for veneer work.

The last table I veneered I used shop sawn sapele that finished up around 1/16” thick after the drum sander and it worked out well so if you wind up redoing the top consider going thinner.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View XOXO's profile

XOXO

3 posts in 43 days


#4 posted 11-03-2017 02:29 AM

Thanks Folks for the speedy and worthy replies.

I will post pics as soon as I figure how. This was my first post.

I thought about the moisture in the glue (PVA/Titebond) but if anything I thought that would result in the pieces expanding not shrinking and the tape is pretty stable I don’t think it shrunk any.

Who is Paul (Shipwright)? I’ve never figured out “how thick is too thick” either. But actually by the time it was being glued up the pieces were thinner than the 1/8, probably less than 3/32. I usually use a resin based glue when I’m concerned about wood movement. But for flat surfaces Titebond has worked well until now. Obviously the wood did move but would a stiffer glue have prevented that or would something have just split?

If I must redo the veneer I’ll probably use a different glue and try to glue the edges together prior to bagging the top. How have you found the CAT-5 or Weldwood resin to work with? I’ve not used either.

View shipwright's profile

shipwright

7779 posts in 2636 days


#5 posted 11-03-2017 03:05 AM

On the topic of “how thick is too thick” …. when I was building boats and gluing with high quality adhesives the general standard for teak overlay decks was epoxy up to 1/8” and polysulfide or polyurethane (both flexible) over 1/8”.
If decking over 1/8” was epoxied the bottom would be held by the glue but the top would shrink a tiny bit and open up cracks.
Fast forward to veneer, TungOil has covered it pretty well. I would however use hide glue (either hot or liquid), my preference being hot. Like plastic resin glues it is a hard dry unlike pva (which I just don’t use for veneer ever) but unlike plastic resin glues it doesn’t require high clamping pressures and it can be reversed if there are problems.
I have had both bumps and indents on thickish veneer seams with pva. That’s why I don’t use it anymore.
What you are experiencing is extreme but I think the answers lie in the kind of glue and the thickness of the veneer.
Pictures would help.

-- Paul M ..............If God wanted us to have fiberglass boats he would have given us fibreglass trees. http://thecanadianschooloffrenchmarquetry.com/

View Aj2's profile

Aj2

1177 posts in 1636 days


#6 posted 11-03-2017 04:23 AM

My guess is your material was too far apart in Mc. Being the veneer was not as dry as the plywood and when you added moisture to both the plywood absorbed the water away from the veneer. So basically your veneer dryed and shrank while the plywood kept sucking out the water.
It’s also not good practice to test Mother Nature when ever we get the Santa Ana winds and the temp from day to night is a good 30 degree swing I can hear my lumber stack cracking and poping. As the surface losses moisture fast.
Your solution is to use a different glue I do like old brown glue.So that’s my vote.
Controlling the Mc is difficult.
Good luck

-- Aj

View Kazooman's profile

Kazooman

867 posts in 1790 days


#7 posted 11-03-2017 12:30 PM

I agree with Loren, the moisture in the PVA caused the veneer to expand and after the glue had set the moisture content came back down and the veneer strips shrunk. I agree with others, you need to use a different glue.

View TungOil's profile

TungOil

747 posts in 333 days


#8 posted 11-04-2017 01:46 PM



Who is Paul (Shipwright)? I ve never figured out “how thick is too thick” either. But actually by the time it was being glued up the pieces were thinner than the 1/8, probably less than 3/32. I usually use a resin based glue when I m concerned about wood movement. But for flat surfaces Titebond has worked well until now. Obviously the wood did move but would a stiffer glue have prevented that or would something have just split?

If I must redo the veneer I ll probably use a different glue and try to glue the edges together prior to bagging the top. How have you found the CAT-5 or Weldwood resin to work with? I ve not used either.

- XOXO


You have good guidance above.

Shipwright is a member here, he replied to your post a few responses above. He has a LOT of veneering experience, way more than most here so he speaks from significant experience.

I used Weldwood on the curved panels for my sleigh bed 15 years ago. It has held up perfectly so far. Earlier this year I used the CAT-5 on a veneered dining table top and it also worked well. They appear to be the same product from what I can tell. Vacuum bagging with either is a must in my opinion. You can see both of those pieces in my projects section if you are interested in seeing the final result.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View Loren's profile

Loren

9631 posts in 3486 days


#9 posted 11-04-2017 05:07 PM


I agree with Loren, the moisture in the PVA caused the veneer to expand and after the glue had set the moisture content came back down and the veneer strips shrunk. I agree with others, you need to use a different glue.

- Kazooman

I didn’t express it very well. I thought maybe the
glue on the bubinga made it swell, then when
it shrunk again the packing tape stretched. I
wonder if paper veneer tape would not stretch
and so pull the pieces tighter together as the
bubinga moisture content dropped.

It sounds outlandish I know, but that’s my theory.

The thickness also may be a problem.

View XOXO's profile

XOXO

3 posts in 43 days


#10 posted 11-06-2017 02:44 AM

Folks, thank you one and all for sharing your very helpful thoughts and experience. Here’s just a bit of feedback.

I neglected to think about the moisture in the glue transferring to the veneer thus swelling it and then shrinking when that added moisture left. That could have been the whole problem. I stand be the packing tape though since the gaps didn’t appear until after the tape was removed. Maybe I would have been better off leaving it on longer giving the veneer more time to gradually lose the moisture. It was frustrating though to have the veneer shrink twice on me, once after vacuuming and again at the finisher.

The more I have sanded the narrower the gaps become so they seem to behave a little like Shipwright’s thicker teak strips.

My current strategy (looking for any way to avoid replacing the entire top) is to try building up the gaps with successive coats of shellac since the gaps look more like indentations than gaps. It seems to be working somewhat but I’m having trouble filling the tiniest splits with anything, finish, epoxy or filler. It seems that surface tension just won’t let any material settle in the vacancies. Any thought on that?

If I do meed to replace the veneer I will be making it thinner and will use different glue . The heat won’t be as much of a factor. In fact it’s now cold and wet.

Thanks again. I hope I can add something as a member. I’ll still try to add some photo’s, I’m just a little behind the curve on that.

View Lazyman's profile

Lazyman

1504 posts in 1225 days


#11 posted 11-06-2017 02:21 PM

If you have already applied a finish it may be too late but I’ve filled small gaps using slivers of veneer with similar grain and color. I was using hot hide glue to apply the veneer which allowed me to sort of slide it into place or remove it if it didn’t look good and use another sliver. Without seeing it, it is hard to know whether this would have worked for your situation.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View TungOil's profile

TungOil

747 posts in 333 days


#12 posted 11-06-2017 11:53 PM

If you have finish on already you might try a grain filler. Depending on how big the Gaps are it might be enough to do the trick.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

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