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Blistering on Viega Fostapex

A customer of ours has Viega Fostapex installed in her home. After it was installed about 4 or 5 years ago, she noticed a blister on the outside of the pex. In 2013, she contacted her plumber, who contacted the manufacturer, who sent her a letter saying that it was purely aesthetic. Attached is a copy of the letter. She called us because she's concerned that she can now see many more blisters, and some are starting to split and crack. I read a couple of articles concerning pex and oxygen diffusion, but I'm not sure how that comes into play in this situation. Is anyone familiar with these blisters? What is the scientific reason they occur, and do they compromise the integrity of the pex?


  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    edited September 2015
    I have occasionally seen some delamination on older Fostapex, outer jacket only, and it showed when prepping a section for assembly. Sometimes a little wrinkling when bending to form it. Nothing where you'd see the entire "sleeve" seperate and slide off the pipe however, just small areas like your picture. I do not believe the O2 barrier was compromised. I have not seen blistering when in use, if I did, I would cut a cross section to see how deep//how many layers the blister involves. It still could be just the top layer.

    Anything out of the ordinary on site? Pressure/temperature/environmental?
  • jonny88
    jonny88 Member Posts: 1,139
    Interesting.I plumbed a house all Fostapex to manifolds and was impressed at the time.Rep said Viega have a lifetime warranty etc but unfortunatly everything is behind walls.Now you got me worried.Anyone else out there have this problem.Viega are supposedly the best of the best.If you need reps number pm me.
  • RobG
    RobG Member Posts: 1,850
    edited September 2015
    It sounds like it may be a high temp bang bang on and off issue? Maybe the big temp swings cause the issue? After all, aluminum and pex have different expansion rates so something has to give.
  • Fireflies827
    Fireflies827 Member Posts: 2
    I didn't think of the temperature swings, but they do mention that in the letter. This pex is installed on a baseboard system, not radiant. I'm wondering if it was ever even rated for anything but radiant to begin with. Does anyone have this installed for something other than radiant?
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    I use it exclusively for baseboard and other high temp applications, since it came out about 12 or so years ago. No issues at all in my experience, except for what my previous post said.
  • spectrumenergy
    spectrumenergy Member Posts: 4
    I have blistering on a customers Viega-FostaPex 1". Brown bubbles. I am worried based on looks and on material failure. Have not consulted with customer yet as I am trying to get all my facts straight. This application is for a a high temp 150-170 degree F radiant and fan convector system. A reps contact info would be good to have. Thanks, Ben
  • j a_2
    j a_2 Member Posts: 1,796
    I became concerned when I realized the joints where sensitive to movement especially when heat was on....I had a couple leaks and decided I did not want to use it....but that's just me as I am sure there are countless installers with no issues