Hull Epoxy Undercoating

[Rick D]

I am going to have to have my bottom paint removed, the bottom prepped and repainted next year after the boat having had seven bottom jobs since 1994. I noticed some flaking the last time it was hauled. I asked for a price from a yard in Mexico where I have had work done in the past and which I respect. Anyhow, they recommended sanding to gelcoat, putting two coast of epoxy on, fairing that and then two coats of bottom paint. Seems typical.
However, after I brought the boat in 1998, I asked Hunter about epoxy. They said then they didn't recommend it until, as I recall, after seven to ten years, believing their chemistry would do a good job of blister protection for at least that period. In later years, I was told not to put on epoxy until the bottom had dried for six months or so. Further, that there was a danger of sealing in moisture and causing more problems if the bottom was not fully dried out.
However, when I read the instructions for Pettit's version, it seemed to me they were talking about treatment for blisters which might be a different animal. I sent an e-mail to the yard, but anyone have advise here? I know it's done all the time, but that may not make it right.

 

[Rick D]

Got a reply back from the yard. He explained the drying is to solve a humidity problem (blisters) and the gelcoat has to come off in that regard if extensive. However, if I don't have a problem with humidity (I don't), then it is a simple application and fairing. Good to have that clarification.

 

[DArcy]

I can't make a recommendation on drying time but I have done extensive testing on moisture barrier coatings. The one that stood out above the others was Interprotect 2000e. We tried several epoxies, vinylester, polyester, polysulfide. Interprotect 2000e was noticeably better at protecting against water migrating into the laminate than the other coatings.

 

[Charlie Jones s/v Tehani]

My go to coating also- interprotect 2000E

 

[windward54]

Hey Rick, sounds like a lot of work to be done. When we’re you thinking of going down to get it done?

 

[Rick D]

Hey Rick, sounds like a lot of work to be done. When we’re you thinking of going down to get it done?

Probably early April. It may be less than here, but you have to add all the visas, permits, lodging (altho you can stay on the boat) and slip fees. With all that, the best you get is a free vacation. But, it is a great yard and a good excuse for a trip (or race).

 

[Davidasailor26]

My understanding is that newer hulls use vinylester which is relatively blister resistant. When that’s done, it’s often wth only a thin layer of vinylester, and if that is compromised by sanding or blasting you’ll need a barrier coat. The reason the coat is not recommended when the hull is new is that to properly prepare for the epoxy you need to sand the bottom, compromising the factory vinylester layer.

 

[Crazy Dave Condon]

What year is your boat? I am asking that to see if vinylester was used in your hull. A lot will depend on the moisture in the hull if any. If so, the hull needs to dry out completely first. Mositure meters are fine but the old way was to tape up plastic to the hull and see what if any moisture is on the inside the following day. Removing all the gel coat, that may or may not be necessary as I do not have any idea if blistering is thru out. In addition, I would put on four coats of epoxy using 2000E vs. two coats when I was a dealer in my yard. Yes it may be more costly to add but warranty usually suggested four coats if stripping all the gel coat off.
There is a lot more to consider but at least food for thought.
There is another possibility as to the vinylester being used starting when. Ask the forum store as the new owner can probably answer that question as to the year first introduced on the Hunter boats in construction.

 

[Rick D]

I am pretty sure my 94 has vinylester. No blisters. Just flakey bottom paint that has become too thick.

 

[Sumner]

I'd personally want the bottom to dry for as long as possible, blisters or no blisters, but realize that isn't always done.

.... they recommended sanding to gelcoat, putting two coast of epoxy on, fairing that and then two coats of bottom paint. Seems typical.....

I disagree with the "two coats of epoxy" depending on whose paint you use. Most recommend 5-6 coats. I used Sea Hawk's Tuff Stuff which goes on much thicker per coat than most of the others. They say at least two coats, but recommend 3 coats. Three coats of their high build is equivalent to 5-6 coats of most others. This can cut down on labor costs.

Also the epoxy coats and the following bottom coats have to all go on in a time window so that you have a good 'chemical bond' between them. If you have to apply on separate days it is better to go overnight between the epoxy coats. If you don't hit the time windows you then have to sand to create a 'mechanical bond' between the coats before going on.

If you are sanding (fairing) the epoxy coat smooth for some reason, racing?, then you would be removing some of it and decreasing the thickness and effectiveness of it so then I'd apply at least an additional coat to make up for that. I didn't sand my epoxy but did get it and the subsequent bottom coats on in the required time periods.

I was quoted about $2000+ for sanding the old bottom paint off (37' boat). I paid $1200 to have it blasted off. In Florida there are people that have media blasting rigs that are specifically designed to do this with boats. The guy who did ours did a great job. Not sure if they can do this in CA? You might save labor wise in Mexico, but wherever you decide to do this, I'd make sure you personally know how the materials that are used should be applied. You want the job to last.

Here is a link to the steps we went through ...

http://purplesagetradingpost.com/sumner/endeavour-outside-mods/outside-index.html

Give us an update later on the job,

Sumner
=================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Sefuller]

I believe Interprotect calls for a certain micron thickness, which the yard must feel they can reach with two coats. I rolled mine on and did 6 coats after scraping the entire bottom down to gelcoat. I don't believe our O'Day is vinylester so not sure what other factors may be in play there. I did the scraping during the winter, outdoors, and applied the Interprotect when the temps were in the 60s in the spring. I removed 20+ years of ablative bottom paint and VC-tar which was applied when the boat was new. There were no blisters at all when I scraped it, and I have been very happy with the Interprotect, which we cover with VC-17.

 

[Crazy Dave Condon]

1994 you are correct on that year.

 

[Barnacle Bill]

Having done several hull jobs, I know a thing or two about a thing or two. First there is blister prevention and then there is blister repair. If you wish to prevent blisters (and you don't have any), then applying protective coats of epoxy is not a bad thing at all - especially if you have all the previous cocktails of paint applications removed. It is wise to check the hull for levels of moisture. You don't want to apply epoxy over a wet hull, or you will, in fact, seal in this moisture and that would be a waste of someone's money and effort. If you have higher levels of moisture evident in your hull, then you may have a blister problem which you may not see if the gelcoat was sanded smooth. Gelcoat, they have found out, is not a great water barrier as it is porous and can take on water. Early gelcoats were called orthothalic and they were very susceptible to water osmosis and later they developed isothalic resins which were not so susceptible. Later came vinylester resins which were epoxy modified polyester resins. Anything with epoxy in it means more money. It is too expensive to build a boat entirely with epoxy resins and so polyester is still the best product. Some manufacturers use vinylester resins below the water line to prevent blisters. Some apply an epoxy water barrier where they are built and some don't leaving it to be done on the dealer level. Because gelcoat has been found to be porous, sanding the hull to bare sort of makes it a bit more vulnerable, so epoxy is not a bad idea if the hull is dry and you wish to prevent blisters. Stick to the manufacturer's recommendations when it comes to number of coats, windows between coats (based on air temperature), etc. Often there is a window where the antifouling paint can be applied directly over the epoxy without having to sand assuming there is no compatibility issues (which can be determined with the paint manufacturer's product info) and the epoxy application is smooth enough to satisfy you. If you have blisters, then you need to sandblast the hull, or strip it, let it dry and then do all the steps to rebuild the surface including epoxy, fairing, etc. as described in the product info of the product you are using. Interlux Interprotect is recognized as one of the best and they are coming out with formulas that require fewer coats of epoxy in comparison to their original offerings.

 

[Rick D]

Thank you everyone for your thoughtful and reasoned responses. It will give me the tools I need when I haul out.