[tap]

I'd like to patch over an old below the water line through-hull. Actually, I rather not, but I've been advised that the insurance company might expect me to. I'm not sure why a capped off through-hull is unsafe but once you stick a seacock and hose on it, clearly adding more points of failure while removing none, it's ok.

I was planning to use system 3 epoxy and 1708 (too heavy?) biaxial cloth with mat. I was also planning on doing the patching from the inside since I have easy access and there will be a lot less fairing and painting to do that way. Also easier to keep the glass in place with gravity working for me instead of against me. It's a small through-hull, probably 1". On the outside I was planning to fill with epoxy thickened with phenolic microballons (e.g. west 407) and then fair.

What, if anything, do I put on after fairing and before bottom paint? I was planning on using gel coat, but I've since found that polyester gel coat does not adhere to epoxy very well. Should I just use nothing before the bottom paint? Or just paint on some unthicked epoxy over the faired epoxy?

 

[scottyt]

Tap there are many threads here on this, do a search using google and the key word epoxy and thru hull

also west systems has videos on you tube about this too

yes the biaxial is too heavy 7 oz glass is perfect, and the best is to do the repair from both sides. also gelcoat will stick just fine to sanded epoxy for what you are doing.

quote from the how to sticky on searching

How to Search Sailnet's Forums

Since Sailnet's internal search function isn't usable for most people, I thought I'd post a tip on how to search for past posts and threads on Sailnet using Google.

It is pretty easy to do.

First, open a web browser window to Google. If you have a search toolbar that uses Google, you can use that instead.

Then, in the search box, type your keywords and then type Quote:
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and click on search or hit return.

This will cause Google's search engine to search just Sailnet's forum pages for your keywords.

While, you can't search for posts by specific username-it will generally give you better results than Sailnet's search function will.

 

[sailingdog]

You really should patch it from BOTH sides...as that will create a much stronger fix than patching from just one.

You don't need to prime the epoxy, but can prime it with something like Interprotect 2000E barrier coat.

The reason the capped off seacock is seen as a danger is the cap may deteriorate over time, for instance, a bronze one may de-zincify and fail... and that would lead to the boat sinking.

 

[sailingfool]

I've painted extensive bottom areas what were faired with epoxy/microballoon mix, just sand and paint. The paint held the same as other parts of the bottoms. Gelcoat is a waste of time and materials.

 

[mitiempo]

I agree with the dog - both sides is the only good way to do it. Grind a taper on the outside only, probably 3/4" larger than the hole. Tape the inside with duct tape and do the outside first. 1708 is good as it's strong and has some resistance to wrinkling which thin cloth does not. Lay the larger precut circle in first and go progressively smaller. This way when you sand you won't go through the strongest piece. After fairing with thickened epoxy coat with straight epoxy and wash blush off before bottom paint. Apply 2 or 3 coats to ensure the surface is impermeable to water. Barrier coat isn't necessary as the epoxy is the barrier. Gelcoat is unnecessary and is water permeable which epoxy is not. I'd mix the fairing coat with colloidal silica which is tougher to sand, but won't absorb water like sanded microballoons will. If you're careful with the fairing coat and it's mixed to a peanut butter consistency not much sanding will be needed. On the inside sand the area an inch or so larger all around than the hole. Fill any dip where the hole was with thickened epoxy and lay a couple layers of cloth over the area wet out with straight epoxy, the smallest in size first, then the larger. Make sure there are no rough spots after it's set and coat with straight epoxy. No fairing required inside as cosmetica aren't an issue in the bilge.
Brian

 

[tap]

I've searched quite a bit already, my plan so far didn't come out of thin air after all, and watched all the videos I could find on youtube. They never say exactly what glass to use for a repair, though what I found about glass types seemed to indicate that stitched biaxial would be stronger than just cloth. Also that mat has better adhesion than woven fabric, so boat hulls are usually made with alternating layers of woven roving and mat. So stitched biaxial with mat backing seemed like the right choice. I don't see anyone selling 7oz fabric, mostly just 4, 6 and 10. I take it four layers of 6 oz fabric should be about as thick as one layer of 1708?

West's boat repair manual, section 2.2, says "these finishes are recommended for above the waterline only. Use west system for all repairs and coatings below the waterline, prior to applying bottom paint." It's not entirely clear to me if the warning about below the waterline use applies only to polyurethane paints or if it includes polyester gel coat as well. The section on repairing keels and rudders says to apply several coats of epoxy after fairing, then wet sand, then bottom paint. No gel coat or barrier coat.

Evercoat's gel coat information says quite clearly on the first page, "IMPORTANT: GEL COAT SHOULD NOT BE APPLIED OVER AN EPOXY."

So the gel coat maker says you can't put gel coat over epoxy and the epoxy maker says you can (but maybe not below the water line). That really clears things up. My searching found a lot more people saying not to put gel coat over epoxy than the other way around.

This west video says after fairing, coat with two coats of epoxy with a white pigment added. Of course it doesn't go into any detail about what happens after you're done using west products. Maybe you go direct to bottom paint or maybe there is something else? This west video just says to paint or apply gel coat after the last glass layer is dry. No fairing even. This other west video says to finish with six coats of epoxy combined with 422 barrier coating additive (aluminum & mica powder), then bottom paint. I'm pretty sure I've seen videos involving gel coat after fairing too.

I haven't see any guides describe patching from both sides. It's always just one, though I have found discussions about which side is better. Any links to a patch from both side guide? I've looked at tons of them and don't recall any, yet now two people suggest it.

Both sides has an appeal, as half the hull thickness to taper will give a patch with half the radius, which is just one quarter the area. Two 1/4 area patches is still just half the total patch area vs one side patching. The problem is that any grinding on the outside of the boat is very costly. Full tent, vacuum sander rental, etc. Hundreds of dollars. Assuming the boatyard will even allow it in the first place. Plus I have a bigger spot on the outside to fair and paint.

 

[tap]

The reason the capped off seacock is seen as a danger is the cap may deteriorate over time, for instance, a bronze one may de-zincify and fail... and that would lead to the boat sinking.

Thanks for the explanation. Still, it seems like the rubber hose for an open cockpit drain is much weaker than a bronze cap. I'm seriously considering putting a new through-hull and seacock on if I can get away with that. Much cheaper and should only take a fraction of the time. If a capped seacock is also too dangerous, maybe I need another cockpit drain somewhere, or a raw water inlet for the galley sink, I don't think the boat has one, or a fish finder transducer, I think the hole is near the center line... all much cheaper than patching over the hole.

 

[mitiempo]

tap
Gelcoat is NOT necessary underwater. It's because of gelcoat that people have spent thousands in some cases and countless hours barrier coating their gelcoat with epoxy. You don't even need the white pigment. After fairing 2 or 3 coats of straight epoxy is all the barrier coat you need. Wet sand and any bottom paint will adhere. By the way you can apply gelcoat to epoxy as outlined by West but not underwater. When you do the inside there is no reason to grind a taper as you're not trying to make the surface perfect - that is only for the outside and a little raised section of the bilge is not important. If you want to learn about patching both sides go to The Plastic Classic Forum • Index page
or Northern Yacht Restoration | Tim Lackey: One Man, One Boat at a Time where every job is documented step by step with pictures.
Brian

 

[scottyt]

7 oz glass is what the packs of glass from west marine are, they are a good middle of the road. the problem with the thicker stuff is getting it properly saturated with out having too much resin. yes thicker is stronger until its not totally wetted out, or too much resin.

you are right about the out side fairing and sanding issues. one way around is to just do the tappering on the side, then 2 layers of thinner glass on the out side, to "lock" the inside repair in place. just some minor sanding out side before and after glassing is all it should need

 

[mitiempo]

But you have to grind and sand fair outside no matter how you do it, so might as well do it right.
Brian

 

[captainmurph]

Patching from both sides is a good idea for both strength and possible cosemetics. When you grind the outside for the taper, you 'll be getting the inner edge of the hole down to minimum thickness, but your first layer (largest piece of cloth) from the outside will not completly be flush with the inside.

When you are done with the outside, scuff sanding (and wiping down with acetone) the area around the patch will promote adhesion of the inside layers. In this case, you use the smallest piece first and then one that overlaps the hole edge by 1/2".

This inside is certainly optional, but very easy to do and really doesn't require fairing.

You may want to check out these articles about hole repair - particularly #9-12.

By the way, the reason one normally uses only cloth on these repairs is that there is a special (and very expensive, hard to find) type of matte to be used with epoxy. Normal matte is not to be used with epoxy due to erratic saturation. The strength of the repair is not in the epoxy - or just in the cloth - its the properly impregnated cloth.

Good luck. Don't make it more complicated than it is.

 

[sailingdog]

Yes, but hoses are supposed to be inspected regularly...and a visual inspection of a hose is fairly easy to do...is it swollen, is it soft, is it dried out and cracking??? A visual inspection of a small bronze cap in the bilge is much more difficult to do. Dezincification of the bronze piece will not be apparent unless you remove all the corrosion from it...and by the time it is apparent without removing the corrosion, the boat is sinking.

Thanks for the explanation. Still, it seems like the rubber hose for an open cockpit drain is much weaker than a bronze cap. I'm seriously considering putting a new through-hull and seacock on if I can get away with that. Much cheaper and should only take a fraction of the time. If a capped seacock is also too dangerous, maybe I need another cockpit drain somewhere, or a raw water inlet for the galley sink, I don't think the boat has one, or a fish finder transducer, I think the hole is near the center line... all much cheaper than patching over the hole.

 

[sailingfool]

I've searched quite a bit already, my plan so far didn't come out of thin air after all, and watched all the videos I could find on youtube. ....It's not entirely clear to me if the warning about below the waterline use applies only to polyurethane paints or if it includes polyester gel coat as well. The section on repairing keels and rudders says to apply several coats of epoxy after fairing, then wet sand, then bottom paint. No gel coat or barrier coat.....So the gel coat maker says you can't put gel coat over epoxy and the epoxy maker says you can (but maybe not below the water line). That really clears things up. My searching found a lot more people saying not to put gel coat over epoxy than the other way around.

.....The problem is that any grinding on the outside of the boat is very costly. Full tent, vacuum sander rental, etc. Hundreds of dollars. Assuming the boatyard will even allow it in the first place. Plus I have a bigger spot on the outside to fair and paint.

Absolutely just forget about gelcoat, it has no place in a bottom repair, there is no need to put any on, hey, everyone els eis taking it off or spending $$$ to cover it up. Not a consideration at all.

Gringing the outside shouldn't be an issue, I'd get one of the air vacuum grinders and go at it ( early some morning). Many yards rent these grinders for bottom work.

Use microballoons for any filling that you will need to sand, collidial cilica is very difficult to sand. You can put a couple final coats of epoxy over the faired microballoons, to resolve any concerns about moisture, this is the West recommended approach.

 

[sailingdog]

If you're using a thickener other than colloidial silica, please don't forget to seal the sanded repair with some epoxy. Many of the thickening agents, including microballoons will absorb water otherwise.

 

[Waltthesalt]

You may want to check out a current edition of Don Casey's book "This Old Boat"

 

[nightowle]

it's definitely recommended by most fiberglass experts to use a barrier coat like the 2000e. A quart is slightly expensive but worth the peace of mind.

 

[mitiempo]

I agree that if you are working with gelcoat or polyester you should use a barrier coat like 2000e. But if you're using epoxy it is a barrier coat as good as 2000e (which Interlux states is epoxy). From the West repair manual "below the waterline apply bottom paint directly over thoroughly cured West System Epoxy". 2 coats minimum, 3 if sanding between coats. While 2000e won't hurt, all you're doing is applying a very expensive epoxy over a moderately priced epoxy.
Brian

 

[tap]

So, no gel coat it is. Two coats of neat epoxy after fairing and then bottom paint.

Still not sure about the glass. I've found some recommendations for biax with mat and some for straight cloth. Some mat uses a styrene soluble binder to hold it together that will dissolve in polyester resin but not in epoxy. West system has an article about it, and concludes you can use epoxy with mat, even with the binder. Of course they say you can use gel coat on epoxy too, doesn't mean it's a good idea.

An epoxy works article about filling holes had an interesting idea. They use a solid epoxy puck to partially fill the hole, then taper on both sides. For a 1" hole, a single side 12:1 taper on a 1/2" thick hull gives a 133 sq in patch. A taper on both sides would give a 38.5 sq in patch on each side. Stick a 3/16" thick puck in the hole and taper both sides and the patch is now only 17.7 sq in on each side. Seems like a good way to not grind off so much perfectly good fiberglass.

 

[mitiempo]

tap
Here's a link to pics and description of how an expert does this. It's Tim Lackey's site Northern Yacht Restoration. At the bottom of the page you can go forward or back. This is a 1966 Pearson Triton he's working on. She is undergoing a complete restoration - inside and out.
Brian
Northern Yacht Restoration | 1966 Pearson Triton Circe