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  • Russ Murphy says:

    Great test. Enjoyed the videos and the information

  • Mike Tinsley says:

    It appears to me you have put an old wives tale to rest about gelcoat not bonding to epoxy.It was a great experiment. I will now use epoxy resin without worry. Thanks,Mike

  • Byron Schluter says:

    Andy, Thanks for the great test and video. As a long-time diyer and Assistant Mgr at West Marine, this info backs up what West Systems has been saying for years. I am now telling my customers that you can (with proper prep) apply gel-coat over epoxy. I recommend a couple of days cure time to eliminate any possible off gasing from the curing process.

    I will use epoxy for the modifications and repairs to both my power boats over polyester to ensure a stronger repair.

    Thanks again,


  • You give us more confidence in using an epoxy coating. But it should be done properly. And always make sure that the surface is clean before the application. Thanks!

  • Todd Dunn says:

    I have a question about the procedure for the shear test where you bonded polyester and epoxy based substrates together with gel coat.. When you did the gel coat bonding, did you apply the gel coat to one surface and then press the two substrates together? If you did that did you always apply the gel coat to the same substrate (i.e., applied to epoxy in all cases, or vice versa)? I can see a reason for the difference in the results if you applied the gel coat to the 207 and 207 and then pressed the poly into the gel coat, but applied the gel coat to poly and then pressed the 205 substrate into the gel coat. I suggest this because flashing off of the gel coat might effect its bonding properties.

    Alternatively, did you apply the gel coat to both substrates at the same time then press the two gel coated substrates together. If this was the case, there may well be a difference between adherence to 205 based epoxy and polyester.

    • ~Andy says:

      Hi Todd,

      I applied gel to both surfaces (poly and epoxy sides) and positioned them on top of one another using shims to maintain even and proper gelcoat thickness for curing (roughly 20 mils thick). I made sure there was enough gelcoat applied so that both sample faces were completely covered. Any excess gel was squeezed out which was why there was gelcoat visible along the sides of each sample. The edges were sanded after cure to remove this excess. All the gelcoat was applied from the same batch / mix at the same time. Unfortunately it was these details that had to be edited out of the video for length (plus it wouldn’t be interesting / exciting for most people to watch.) In total I believe I had close to 3 hours of raw video that eventually was edited down to 2 segments; (1) 7 min video and (1) 17 min video.. Hope this answers your question 🙂

  • Todd Dunn says:

    Thanks, you nailed it Andy. Well done.

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