Boat Builder Central - Builder Forums

Posted: **Thu Feb 13, 2020 11:53 am**

I'm at the point where I need to put something on my bottom. I'm planning on using an epoxy/graphite coating(or 3) without paint on top of it. Am wondering if there is any need/benefit to putting primer on before the epoxy. I know that people use high-build primer to handle the final fairing but I'm not too concerned about that, it's as fair as I care for it to be. Just not sure if there are other reasons I need to/should add primer before the epoxy.

As always, any/all opinions welcome.

Jeff

Posted: **Thu Feb 13, 2020 12:02 pm**

VT_Jeff

IMHO there is no need prime before the epoxy/graphite coating. Primer is meant as a final coat/sealer before paint.

Make sure, if you haven't already done so, to read Cracker Larry's graphite application method.

Good Luck,
Reid

Posted: **Thu Feb 13, 2020 12:49 pm**

My mix as follows: 8 oz of resin and 4 oz. slow hardener, then 1/2 cup of graphite power.

What I used;

BBC's Graphite, MarinEpoxy with slow hardener

What I did;

Shifted graphite a few times.
Mixed epoxy and hardener.
Added graphite slowly as I mixed.
Rolled on slowly.
Wet on wet, 1/2 to 1 hour between coats.
Total 3 coats, maybe 4?
Did not sand at all.

I guess we shall see if this holds up. So far, I dropped the boat on it's transom (no skig), hard!
Nothing cracked or chipped off! Also, it's very slippery!

Update, I hit a big log on the river at full speed with two of us in the FS14 (SandPiper). We came out of the water, I very slowly turned around and went back to the ramp to pull the boat out.... Checked bottom and inside, no problems!!!

: normal_56.jpg (43.32 KiB) Viewed 1115 times

Posted: **Thu Feb 13, 2020 1:11 pm**

Agree with the above. I put primer on but not sure why.
It isn't bulletproof and unlike the good Captain, I've scraped it but I drag my boat across rocks and gravel sometimes. Easy to patch, though.

Posted: **Thu Feb 13, 2020 2:12 pm**

Reid wrote: ↑Thu Feb 13, 2020 12:02 pm IMHO there is no need prime before the epoxy/graphite coating. Primer is meant as a final coat/sealer before paint.

Make sure, if you haven't already done so, to read Cracker Larry's graphite application method.

Perfect, will do, thanks!

Posted: **Thu Feb 13, 2020 2:14 pm**

Capt UB wrote: ↑Thu Feb 13, 2020 12:49 pm Rolled on slowly.

Appreciate the input, Capt. I suspect I will avoid the roller, apply with squeegee and then tip/smooth with a foam brush, 3 coats wet-on-wet. I have never had any luck with a roller and epoxy, have had decent success with a squeegee. Let know if you think that's insane.

Posted: **Thu Feb 13, 2020 2:37 pm**

terrulian wrote: ↑Thu Feb 13, 2020 1:11 pm Agree with the above. I put primer on but not sure why.

More support for skipping the primer, awesome, appreciate it!

terrulian wrote: ↑Thu Feb 13, 2020 1:11 pm Easy to patch, though.

Interesting side topic: Do you carry an emergency patch kit? I'd be interested to know how people do field repairs on these cored-composite boats, and what they carry in the boat for emergency "get back to port" repairs.

Posted: **Thu Feb 13, 2020 3:11 pm**

VT_Jeff wrote: ↑Thu Feb 13, 2020 2:37 pm Interesting side topic: Do you carry an emergency patch kit? I'd be interested to know how people do field repairs on these cored-composite boats, and what they carry in the boat for emergency "get back to port" repairs.

When sea kayaking, we always carry some Denso tape - basically a strong fiber tape with a thick bitumen layer that sticks to the hull, even when wet. It comes in 6" wide rolls and has a plastic film covering the sticky side. Just cut off a piece, peal the covering, and slap over the hole.

Posted: **Thu Feb 13, 2020 3:21 pm**

I think Tony was talking about "patch" in the context of top to mid layer. Not a hole in the hull. To fix the graphite finish, just sand a bit, mix a bit and apply a bit. Simple.

When it comes to holing the hull, the better option is positive floatation for boats of "size". Even if you know you holed it, how do you get under it to apply the patch? Capt UB is a highly experienced captain and you'll notice he just slowed and got to shore. With positive floatation you know you can get to shore even if you are a little wet. for us small boat guys... we still need to get to shore but we are able to roll it over and slap some tape on it.

Posted: **Thu Feb 13, 2020 3:58 pm**

Jaysen wrote: ↑Thu Feb 13, 2020 3:21 pm Even if you know you holed it, how do you get under it to apply the patch?

That's a good point: not much of the hull below the waterline is accessible from inside the boat on some/many of these designs where flotation is sealed in.

Posted: **Thu Feb 13, 2020 4:10 pm**

BrianC wrote: ↑Thu Feb 13, 2020 3:11 pm
VT_Jeff wrote: ↑Thu Feb 13, 2020 2:37 pm Interesting side topic: Do you carry an emergency patch kit? I'd be interested to know how people do field repairs on these cored-composite boats, and what they carry in the boat for emergency "get back to port" repairs.
When sea kayaking, we always carry some Denso tape - basically a strong fiber tape with a thick bitumen layer that sticks to the hull, even when wet. It comes in 6" wide rolls and has a plastic film covering the sticky side. Just cut off a piece, peal the covering, and slap over the hole.

Going to look into that, at least for our SUPS which we need to field repair from time to time. I know some whitewater kayakers who use something like Bitchathane(no idea on spelling, I just recall te conversation about it) for emergency repairs on plastic kayaks, I guess it's some type of roofing material. Maybe related to Bitumen?

Edit:

Looks like it's Bituthene I was thinking of and it is related to Bitumen.

Posted: **Thu Feb 13, 2020 6:15 pm**

VT_Jeff wrote: ↑Thu Feb 13, 2020 4:10 pm
Looks like it's Bituthene I was thinking of and it is related to Bitumen.

This reminds me of the time I described something as "bitulithic" to a friend of mine.

Of course he heard "bitchalithic", which he understood to be sort of like monolithic, but...

Posted: **Thu Feb 13, 2020 6:56 pm**

Jaysen's right...I was talking merely about touching up a scrape that went through the epoxy.
If you hit something hard enough to put a hole in your boat, a patch is going to be the least of your problems, after an ambulance. These boats are made of iron. Don't know how the Captain did it without injury.
I had my hull crack on my 39 but it wasn't because we hit something. There's some fool on You Tube who powered his bateau design into a log and jumped it with no damage.
The question of a repair kit for putting a hole in your boat reminds me of the movie "All Is Lost" with Robert Redford, which is a collage of some of the most ridiculous sailing scenarios ever put on film. At the very beginning of the movie, he is asleep and wakes up to find he's hit a container, and there's a large hole in the hull. Two things: One, if you hit a container in a bluewater boat hard enough to put a hole in it, you're going to have a concussion and a dislocated shoulder. It's not going to be like your cat licked your face and awakened you. Second, he looks around and the sea is calm So...how was he going fast enough to rupture the hull at impact? Somewhere I have a list of all the nonsense in this movie, and it isn't a short list.
That said, you can buy epoxy that cures underwater for this sort of thing. I carried some aboard, as I did tons of emergency gear. We didn't need that particular thing, nor hardly anything else.
https://www.amazon.com/TotalBoat-Underw ... ive&sr=1-1

Posted: **Thu Feb 13, 2020 7:30 pm**

terrulian wrote: ↑Thu Feb 13, 2020 6:56 pm ...he looks around and the sea is calm So...how was he going fast enough to rupture the hull at impact?

Hilarious! I spent the whole movie trying to figure out exactly what boat he was sailing as I was shopping for a boat at the time. I ended up with a C&C29 MKII, I think his was a Sabre 34 or something, been a while.

Appreciate the info on the patching, I'll take a look, and wear a helmet!

Edit - Apparently it was a Cal39

Edit: https://www.sailfeed.com/2013/11/all-is ... ing-movie/

Posted: **Fri Feb 14, 2020 9:20 am**

terrulian wrote: ↑Thu Feb 13, 2020 6:56 pm Jaysen's right...I was talking merely about touching up a scrape that went through the epoxy.
If you hit something hard enough to put a hole in your boat, a patch is going to be the least of your problems, after an ambulance. These boats are made of iron. Don't know how the Captain did it without injury.
I had my hull crack on my 39 but it wasn't because we hit something. There's some fool on You Tube who powered his bateau design into a log and jumped it with no damage.
The question of a repair kit for putting a hole in your boat reminds me of the movie "All Is Lost" with Robert Redford, which is a collage of some of the most ridiculous sailing scenarios ever put on film. At the very beginning of the movie, he is asleep and wakes up to find he's hit a container, and there's a large hole in the hull. Two things: One, if you hit a container in a bluewater boat hard enough to put a hole in it, you're going to have a concussion and a dislocated shoulder. It's not going to be like your cat licked your face and awakened you. Second, he looks around and the sea is calm So...how was he going fast enough to rupture the hull at impact? Somewhere I have a list of all the nonsense in this movie, and it isn't a short list.
That said, you can buy epoxy that cures underwater for this sort of thing. I carried some aboard, as I did tons of emergency gear. We didn't need that particular thing, nor hardly anything else.
https://www.amazon.com/TotalBoat-Underw ... ive&sr=1-1

: unnamed.gif (235.94 KiB) Viewed 963 times

Posted: **Fri Feb 14, 2020 9:40 am**

Oh.

Posted: **Fri Feb 14, 2020 9:58 am**

I like that solution to the problem. If I had a family motto it would have to be “hold my beer and watch this”

Posted: **Fri Feb 14, 2020 3:02 pm**

The SandPiper (FS14) was built heaver, with a cockpit deck (sole), no center bench, but more ribs/frames under the deck, 2 part foam, glass went up to the gunwales inside and out....

Posted: **Wed Feb 19, 2020 10:10 am**

Capt UB wrote: ↑Thu Feb 13, 2020 12:49 pm My mix as follows: 8 oz of resin and 4 oz. slow hardener, then 1/2 cup of graphite power.

What I used;

BBC's Graphite, MarinEpoxy with slow hardener

What I did;

Shifted graphite a few times.
Mixed epoxy and hardener.
Added graphite slowly as I mixed.
Rolled on slowly.
Wet on wet, 1/2 to 1 hour between coats.
Total 3 coats, maybe 4?
Did not sand at all.

I guess we shall see if this holds up. So far, I dropped the boat on it's transom (no skig), hard!
Nothing cracked or chipped off! Also, it's very slippery!

Update, I hit a big log on the river at full speed with two of us in the FS14 (SandPiper). We came out of the water, I very slowly turned around and went back to the ramp to pull the boat out.... Checked bottom and inside, no problems!!!

normal_56.jpg

Posted: **Mon Jun 29, 2020 9:22 am**

I just finished the graphite this morning. Wasn't as close as I thought when I started this thread. I went back and forth in my mind over and over whether to go the expoy/graphite route or some other route. I had talked myself into cheap black paint(an unfortunate fact is that this boat just won't be in the water a lot: I live in VT, it's a short season, and I have quite a few other water-craft) and was on my way to the hardware store to buy it. Luckily it's a long drive and before I got halfway there I had re-talked myself into the epoxy/graphite and here's why:

1. The cheap paint would not offer any protection to the soft, fairing compound areas and I remembered that when i did a neat coat of epoxy on the hull a few months ago, I skipped the bottom, planning on epoxy/graphite. I still had the option to neat coat and then paint but...

2. Paint would scrape easily and leave very visible marks that would bother me, but not enough to flip the boat and fix them, which means that within a short period the bottom would look like !@$ and probably stay that way.

3. With expoxy/graphite, I could get the bottom started and finished within a day or 2 with multiple coats, where paint would take days and days to cure, then would need to be sanded before the next coat and just generally be a lot more work.

So, epoxy/graphite was the clear winner.

I didn't use rollers. I tried in one small section and it just was not working for me at all. I heqated the epoxy in my cooker, mixed in un-sifted graphite from BBC until the mixture looked very black, poured it out(all of it), spread it with a knife or a fat stirring stick, then tipped it with a foam brush. I went through about half a box of foam brushes as they fatigue pretty quickly.

It came out.......OK. As someone else said, from 10 feet it looks pretty good. When you get close you can see imperfections in the tipping and the odd clump of graphite. But: it's black, fairly smooth/shiny, it's tough, it's going to stay mostly that way, and ................it's DONE!

Posted: **Mon Jun 29, 2020 9:58 am**

It looks great. No one has ever, to my knowledge, reported getting a glass-like finish with epoxy. But only the fish see it.
Good job!

[edit: I mean with graphite/epoxy. You can get glass-like with neat epoxy. But it involves some tricks.]

Posted: **Mon Jun 29, 2020 5:40 pm**

Thanks Tony, let's hope a lot of fish see it, with approval or not!

Posted: **Mon Jun 29, 2020 7:19 pm**

Looks great and FINISHED from Florida!

Posted: **Mon Jun 29, 2020 8:33 pm**

No one, absolutely no one has ever looked at my boat and said that the bottom was ugly.

Posted: **Sat Sep 18, 2021 3:15 pm**

I know the thread is a bit old but with the info in here I thought it was better to add to it.

Do you sand the bottom before applying the graphite mixture? I just finished laying the fiberglass on the entire bottom and I'm assuming I sand it with something like 80 grit before applying the graphite but want to make sure.

Thanks,
Bill

Posted: **Sat Sep 18, 2021 3:22 pm**

Like any epoxy you want to sand the old coat to get a good mechanical bond with new.

Posted: **Sat Sep 18, 2021 3:28 pm**

cape man wrote: ↑Sat Sep 18, 2021 3:22 pm Like any epoxy you want to sand the old coat to get a good mechanical bond with new.

Thanks Cape,I assumed that was the case but you know what they say about assuming...

For those that have tried both Capt and cracker Larry's methods, was there any noticeable difference?

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