You Can Teach an Old Dog a New Trick!

by Dale on October 7, 2013

There’s Always Something New!

Well, I just learned something. I have been gluing up wide boards out of narrow boards for more years than I would like to admit. Up until about 5 years ago I used pipe clamps, made with black pipe. I always used some type of spacer to keep the pipe from touching the squeeze of glue.

Then five years ago I acquired a bunch of ½” galvanized pipes (more clamping pipes! and free!) Remembering I had read somewhere that you shouldn’t use galvanized pipe because it slip I decided to find out for sure. I made one to check. It did not slip. Then I made about two dozen ½” pipe clamps about three feet long.

A very handy length in my business and the lighter weight over ¾” pipe was another plus.

Galvanized pipe doesn’t rust, right?

So I thought that the pipe could touch the glue and it wouldn’t make a black mark. Well, this method worked fine for over five years, until today.

I glued up a bunch of 1” thick cherry for a table top, usual method. Alas! Dark grey marks everywhere the galvanized pipe touched the glue squeeze out. Why did it work all those years before but not this last time? I was using Titebond II Extend, which I haven’t used before … maybe that is the reason.

Oh, now I remember, I was teaching a class recently and told my students that galvanized pipe won’t leave a black mark. One of them disagreed and said it would! Well, it never had before but rather than make a long discussion longer, we just put some paper between the pipes and the glue. Then – now, a few weeks later it happened to me. Must be the power of suggestion!

It wasn’t a big deal, I just removed the dark stains in about 1 minute using oxalic acid power dissolved in water.

This is an old refinisher’s trick.

What I cannot figure out is why? Why after five years of working did it stop working after the student adamantly said it would stain? Maybe it was something like the placebo effect, or eggs are the greatest food until you find out about cholesterol and all that so now they are bad.

Whatever the cause I’m back to using paper between the pipe and glue. Any thoughts or ideas about why this method quit working? Add your comments and let me see what your experience has been out there in woodworking land.

{ 2 comments… read them below or add one }

Rod Smith January 28, 2014 at 3:16 pm

I could only suggest that the black marks may be related to the galvanize pipe reacting with the wood. For example different wood species will definitely cause black marks on wood when brought in contact with galvanized. Remember those galvanized nails in cedar siding. If you use galvanize on exotic hardwood decking it will cause black marks. The moisture content of the wood would also have an impact on how quickly the marking would result. Kiln dried wood usually has a high percentage of acetic acid which may impact the marking. Kiln dried wood is more acid and more immediately corrosive than air dried. Zinc and Zinc alloys are very susceptible to reaction with acetic acid.
The black comes from any iron coming in contact with the wood and the acidic properties of the wood and amount of moisture present. The shiny galvanized pipes are electroplated and have a very thin coating. When you buy nails there is a difference in the performance of hot-dipped instead of the electroplated. I use the same galvanized pipes and haven’t had a problem. It could show up depending upon the variable factors, acidity of the wood, moisture levels, any potential iron content in the wood, and the uniformity of the galvanized plating on the pipe.


Dale February 4, 2014 at 3:09 pm

Hi Rod, Thanks a lot for the technical info, I knew hot dipped galvanizing is better than other types just didn’t know the cheaper version was electroplated. The galvanized pipes were pretty old, came out of older building probably hot dipped but from your comments all the variables involved tells me that to be on the safe side just don’t let the pipes touch wet glue in any case, which is my method now anyway. I’m glad now to know the reasons why, Thanks for commenting! Dale


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