Darryl Keil Last Activity 2025-02-12 2:48 PM
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Gregg

Posts: 12

Joined: 2006-03-03
Location: chicago

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Subject : Possible leaching?
Posted : 2010-07-15 11:34 AM
Post #36113
Did the wine rack last year, put it away for 6 months and pulled it out recently and now there is spots.
Here is the process.

Veneers glued on ultralight MDF with unibond 800. The white and grays are dyed veneers, everything else is natural (anegre, burls in the hands).

Top was sealed with a thixotropic poly acrylic (ICA), sanded down for a full grain fill, then top coated with 5 coats of ICA polyacrylic.

What is confusing is I have done this process on many pieces, with no problems, but nothing this light, mostly darker veneers like sapele. So I am trying to think back on what made this project different.

I sanded the sealer back to the actual wood. Normally I leave more sealer material. But I have the same problems on the sides of the unit, where it was an open grained finish, and with the curved nature of the sides, I hand sanded so I left a lot more sealer material.

I talked to the ICA product specialist, and he thinks it is coming from underneath.

Like I said, this problem wasn't there when it was sprayed. It was stored in complete darkness.

Thoughts?
Attached file : leaching 1.JPG (34KB - 68 downloads)



 
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Don Stephan

Posts: 825

Joined: 2003-07-18
Location: Cincinnati, Ohio

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Subject : RE: Possible leaching?
Posted : 2010-07-15 6:48 PM
Post #36114 - In reply to #36113
Gregg:
In the picture, I can't tell what is unexpected spots and what isn't. And I've never heard of, and don't recall seeing any posts of, your finish.

Are the spots in the area of just one species of veneer? Just in the area of dyed veneers? Are the spots in an area of veneer you've used before under the same finish without problem? Have you used the same finish over Unibond before? Over Unibond on ultralight MDF before?

Could the area of complete darkness have introduced high humidity or particular solvent or other vapors? It does sound puzzling.

For info on the finish itself you might post on the forum at Homestead Finishing Products.


 
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Gregg

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Joined: 2006-03-03
Location: chicago

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Subject : RE: Possible leaching?
Posted : 2010-07-15 7:09 PM
Post #36115 - In reply to #36114
Hi Don.

The bleeding is happening in the anegre and the dyed white veneer. I think I used the medium catalyst which mixes thinner than the dark. But when I sanded and sprayed, there was no spotting. There is a much more detailed picture here (500k vs 50k). I always use ultralight mdf and unibond on everything.

http://www.woodweb.com/cgi-bin/forums/finishing.pl?read=659823

I guess the question is does unibond bleed become more pronounced over time. Six months in this case. I rarely, if ever get bleed through (at least as it applies to showing up in the final finish) and I lay the glue on pretty thick to help fill the gaps. But I also work with darker woods in my field work.

The project was stored in the garage and in the winter it gets cold. But I have many projects stored there with the same finish and they had no issues.

I have used this finish on many pieces including lighter woods like ceylon, holly, lemonwood, eucalyptus and pear but most of those veneers have a much denser grain than anegre. But the dyed white is a pretty dense grain. I have had bleeding with fiddleback english sycamore. You can see a reply from the above post over at woodweb recommending a blocker.


 
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Darryl Keil

Posts: 1454

Joined: 2003-05-22
Location: Maine

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Subject : RE: Possible leaching?
Posted : 2010-07-15 8:51 PM
Post #36116 - In reply to #36113
Gregg,

Is there somewhere I can see a bigger picture of the veneer in question?

Darryl Keil


 
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Gregg

Posts: 12

Joined: 2006-03-03
Location: chicago

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Subject : RE: Possible leaching?
Posted : 2010-07-15 10:31 PM
Post #36117 - In reply to #36116
http://www.woodweb.com/cgi-bin/forums/finishing.pl?read=659823

then you can click on the image. It is 500k. You can see the spots on the white veneer, the anegre is a little harder to see. I can email them to you as well, but yahoo does a compression.


 
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Darryl Keil

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Joined: 2003-05-22
Location: Maine

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Subject : RE: Possible leaching?
Posted : 2010-07-17 5:26 PM
Post #36118 - In reply to #36117
Gregg,

Ah, now I see. These spots are caused by undissolved crystals in the catalyst, let me explain. The powdered catalyst of Unibond is made of mostly walnut and pecan shell flour with an acid salt as the actual catalyst which is a small part of the powder. These acid salt crystals are similar to the size of common table salt. If you put your hand in the powder you can feel them. If, when mixing the liquid resin in with the catalyst, these crystals are not fully dissolved, then they sit under the veneer in concentration and slow leach out over time leaving spots in the veneer.

You tend to see this mostly on lighter woods especially bleached and these white stained veneers. The solution is to be sure these crystals are fully dissolved by mixing with a electric mixer in a drill then let the mixture sit for a few minutes and then mix again. To be absolutely sure you could put on a thin glove and feel the mixed glue for any undissolved crystals.

The unfortunate thing is nothing can be done at this point because it is a chemical staining between the veneer and the acid salt crystals.

Darryl Keil


 
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Gregg

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Joined: 2006-03-03
Location: chicago

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Subject : RE: Possible leaching?
Posted : 2010-07-18 1:36 AM
Post #36119 - In reply to #36118
Thanks Darryl, that's got to be it. Often I have chunks of catalyst that I just smear around with the roller to help dissolve. I have never had a problem in the past, but now I know the cause and effect. I am going to copy this to the wood web forum so maybe I can help someone else out.

Thanks again.
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