Thoughts on this technique by Andy Miller?

This is the place to post your ideas, thoughts, questions and comments as relates to general boatbuilding and reconstruction techniques and procedures (i.e. recoring, epoxy, fiberglass, wood, etc.)
Post Reply
smcgrath67
Bottom Paint Application Technician
Posts: 12
Joined: Wed May 29, 2019 2:00 pm
Boat Name: Leah Mae
Boat Type: C&C Corvette
Location: New Hampshire

Thoughts on this technique by Andy Miller?

Post by smcgrath67 »

https://youtu.be/ihhr283aW1A

Any thoughts on this technique of laying CSM over the entire cabin top in order to “stabilize” the surface, which is the typical very old gel coat with millions of little checks in it? I like the idea, but wonder if it’s necessary. Won’t a high build primer do the job?
Thanks for any input.
Sean.
svMira
Master Varnisher
Posts: 104
Joined: Wed Aug 08, 2018 10:16 pm
Boat Name: Mira
Boat Type: Pearson Wanderer 30
Contact:

Re: Thoughts on this technique by Andy Miller?

Post by svMira »

I haven't tried fixing any of my crazing. But the places that I have had to rebuild, like my mast step, I have reglassed and they are now completely stable and haven't done any crazing after.
I just wonder how to account for the flex. Once it is all checked, you simply have to flare all the cracks or grind down till they are gone. I don't know what I can put on top of there that will adhere and absorb the abuse from the flex that caused the cracks in the first place. If is is serious, you need to cure the flex, but you just can't do that everywhere there's a little bit of movement.
I wonder how related this is to sealing plywood. On one of my small boats, I covered my marine plywood benches with epoxy and varnish. They checked over a few seasons, or was it just one winter. I don't recall, but I remember being surprised and very disappointed. Other parts that I had covered with thin cloth and then epoxy and varnish were perfect years later. I realize the substrate is quite different, but movement is movement, and all it takes is a crack in the finish for water to get under and then it all starts breaking down.
Also looking for wisdom.
Marvin - s/v Mira - 1971 Pearson Wanderer #174
svmira.ca
User avatar
atomvoyager
Moderator | Revitalizer of Classics
Posts: 421
Joined: Thu Jul 12, 2018 7:48 am
Boat Name: Atom
Boat Type: Pearson Triton
Contact:

Re: Thoughts on this technique by Andy Miller?

Post by atomvoyager »

Looks like one good way of repairing the damaged gelcoat. I believe that particular boat has crazing mostly from weathering possibly coupled with a defect in the original gelcoat that made the UV and weather damage worse than normal for its age and not primarily caused by flexing. If it was flexing damage it would be longer cracks that are much more limited in number and could be repaired as in this video:

https://www.youtube.com/watch?v=x_uvonIHJpo

Once you identify the cause then you choose the appropriate repair technique. Some old gelcoat surfaces have thousands of tiny pinholes with or without crazing. In that video, he said he wanted to "stabilize the surface". His technique of fiberglass mat was chosen because he likes how it is easy to lay down on curved surfaces. I'm guessing he used polyester resin because CSM absorbs a lot of resin and epoxy was too expensive and he felt he had enough strength and adhesion from the poly. That will probably do the job fine. If the crazing was caused by weathering he might have gotten away with sanding the gelcoat until it was mostly gone, applying a thin coat of epoxy fairing compound such as West 407 and then painting. Although easier to do, that may or may not prevent it from recurring so it's safer to add the CSM. Oer you might use a thin fiberglass cloth that absorbs less resin and wet it out with epoxy.

In this clip he shows repairing actual flexing damage:

https://www.youtube.com/watch?v=i9HbPP8A0Fo
smcgrath67
Bottom Paint Application Technician
Posts: 12
Joined: Wed May 29, 2019 2:00 pm
Boat Name: Leah Mae
Boat Type: C&C Corvette
Location: New Hampshire

Re: Thoughts on this technique by Andy Miller?

Post by smcgrath67 »

I don't think he is talking about stress cracks, but just the tiny little cracks in the old gel coat. My boat, a 1969 C&C, is in need of this kind of repair so I was curious about this technique. James, would you say that a heavy sanding of the old gel coat, followed by rolling on a coat of neat or slightly thickened epoxy would be ok? Then follow that with primer?
User avatar
atomvoyager
Moderator | Revitalizer of Classics
Posts: 421
Joined: Thu Jul 12, 2018 7:48 am
Boat Name: Atom
Boat Type: Pearson Triton
Contact:

Re: Thoughts on this technique by Andy Miller?

Post by atomvoyager »

You might be alright with heavy sanding then a coat of epoxy resin only. I don't think thickening it slightly will work since it either won't lay flat with a roller, or will add too thick of a brittle epoxy coating that is susceptible to cracking later. And it won't fill as well as putting on a thin layer of thickened epoxy with a wide putty knife and sanding most of it off to get it thin and level. I'd try the resin first and after a light sanding apply the thickened epoxy after if it looked like it needed filling. I mentioned that this method probably would work in most cases but no guarantee and that is probably why this guy used fiberglass. I've gotten away with using fillers and resin without glass on boats with similar problems.
Post Reply