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Old 03-14-2005, 12:04 PM
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TexasJack TexasJack is offline
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Join Date: Apr 2004
Location: Southeast Texas
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Years ago, I worked in the research lab for a pipeline company. (Back when those companies actually did research.) One of the groups did a lot of coating testing. How does that relate to adhesives? Well, good coatings are also good adhesives.

Some of the tests they ran:
- small pieces of pipe were coated and put on a carosell with a mercury street light shining on them. That gave them the equivalent of years of sunlight exposure in a few days.
- Pieces of metal were coated, except for a corner or tab, and a very small hole was drilled into the coating. It was placed in a brine solution and connected to a dc power supply to make the pinhole corrode. Then the plate was removed and an "X" cut across the pinhole. The tech would see how far back the coating would peel from the hole.
- A spinning wire brush was used to bombard pieces of coated metal with gravel and concrete
- Coated metal was bent to see how the coating stuck under stress

After years of testing coatings - and every new coating that came out - it was determined that underground piping should be coated with epoxy and aboveground piping with urethane coating. (Epoxy didn't hold up as well in sunlight and was more susceptable to mold damage. Epoxy 'stuck' better under stress.)

Another thing that was a big factor was mixing those '2-part' coatings. A bad mix ruined an otherwise good coating.

From all this I would say that I'm not surprised at some of the conclusions so far in this test. There are many factors in play with adhesives. (Color, for example, could be an important one in some cases.) No adhesive will overcome bad preparation - of either the glue or the surfaces. Some adhesives will not hold as well in a thick layer as in a thin layer. (Epoxy does well thick; acrylics don't.) Water resistance claims are often useless (as has been pointed out.) Shrinkage (epoxy) and expanding (urethane) seriously affect the application.

Just my 2 pesos! I look forward to more results!


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