Andy Miller's Lesson in Thickening Epoxy Resin – TotalBoat

Andy Miller’s Lesson in Thickening Epoxy Resin

It’s great to be back inside Andy Miller’s boat shop where he is filming his Boatworks Today video series. Andy is still working on his Bertram Moppie rehab, and this episode finds Andy at the transom again, working through a repair that didn’t go quite as expected. He teaches us a few lessons about thickening epoxy for strength and for straight-up thickness, using Milled Glass Fibers to add strength to his mixture and then Silica to actually add the thickness he needs to avoid sagging on his vertical surface. His application doesn’t go as planned and he explains how, but he can save it easily and plans to attack it again with a thicker epoxy mixture to fill in the gaps behind the coosa board. We admire and thank Andy for choosing to share this lesson with us all anyway, keeping us informed, and teaching us about real-life boat repairs and the mistakes that commonly plague even the best of them.

Tune back into Andy’s videos to follow along as he gets back into the trenches of this Bertram restoration series. The boat is a classic that deserves Andy’s attention as well as yours. Give  a “thumbs up” to Andy’s video to help it find other boaters looking for great repair content on YouTube. Thanks for watching.


12 responses to “Andy Miller’s Lesson in Thickening Epoxy Resin

  1. When the epoxy is cured enough to not be sticky, but still soft enough to dent with your fingernail, you can shape it. Sanding won’t work, it will make a mess, but you can cut it with chisels, knives, etc. Even a very rough carving job to remove the very high spots would save a lot of sanding later on. Most importantly, it might get the surface close enough to where you want the high spots that it is worthwhile to put another layer on the low spots before it hardens enough that you need to remove the amine blush and sand. You really should try peel ply. Yes, it does help hold epoxy in place so you don’t get these big sags. It also leaves a surface that requires MUCH less fairing so you may have to throw away the peel ply, but you save epoxy, fillers, sanding materials, and loads of time.

  2. Very interesting, I’m not into Marine environment’s, mainly mechanical, but that pushes me into odd situations, and the MORE info I have to what is available t\for any different situ, helps me out immensely.
    I had never heard of Coosa Board, Nor the Peel Ply. So a lil quick Google search gave me a few more item’s to add to my virtual” TOOL BOX”. And I loved the thought process to reduce cost’s AND reduce waste in the project.
    Thanks, I enjoy watching your thought processes….

  3. Thanks for the video.
    Could you have used a cheese grater (Stanley SurForm file) to knock the high spots down while the epoxy was still soft?

  4. Always love your videos. Just a quick question, sometimes we look at a
    project from one side and miss the other. Would it have been easier and
    possibly stronger solution to structurally enhance the outside of the transom, spreading out the load over a larger area and then fair out and spray new gel coat. I am not a structural engineer by any means, but with all the new composite board materials it would seem to me to increase surface area, therefore distributing more of the load. Just looking for your insightful feedback. Happy 2022!

  5. Rather than just use filler why not build that void up with fiberglass cloth and resin which would be much stronger than just filler. By making a fillet the cloth would lay down smooth and help hold the resin in place. In my opinion filling the void without cloth is not the strongest solution and I think that was the main goal on reinforcing the transom

  6. I guess the lesson to be learned would be ” when working epoxy over a large vertical area,consider peel away technique “. It’s nice to see a pro get in trouble too. Mike

  7. I like Dave Lansky’s idea. I use a surform plane to shape while stll slighly workable, which is an old body shop trick. Surforms come in several configs – flat, curved, circular etc. I use a slightly curved 8″ without the handle.

  8. Hi Andy. A couple of years ago some one let my boat loose and it hit he rocks and holed the hull in a few places, most on the port stern quarter and transom, I built it all back up with, resin, silica, cs mat, bi axial sheet, 1in marine ply and a lot of sweat. It was all done on the bank side car park while she was on the trailer during 2019 and 2021. The North east coast of England is not the best place for regular fine weather. The mix of 8mm chopstrand with silica is magic to work in any position.
    The boat is a 22ft cabin boat built 1982.

  9. A big yes on using the rasp-style tools to shape still soft epoxy. But the additives in the epoxy will trash your tool – don’t be afraid to throw the old rasp out and start with a sharp one.

Leave a Reply

Your email address will not be published. Required fields are marked *


Free Shipping On All Orders!