Epoxy on gelcoat and installing thru-hull fittings with epoxy

[TobiasLager]

Originally Posted by Lake-Effect

Seeking clarification - is Tru-Design recommending that one epoxies their thru-hulls into place - eg epoxy is what you goop the fitting with before you place it and tighten up the mounting nut?

Originally Posted by bil56

I am very surprised by this recommendation to put thru-hulls with epoxy !
For me, thru-hulls are always fitted with PU or MS polymere seal.

Tru-Design recommends the use of epoxy since it bonds very well to the fitting and they make a rather large promise: “the epoxy has now made the skin fitting an integral part of the hull and will last the life of the vessel.”

As second choice, they recommend Sika or similar sealer. Since I need to use epoxy on the outside (removed the gelcoat (this was recommended in another forum and might have been a bad idea…)) it is not that much effort in following their instructions and use epoxy for the fitting as well. I have previously only used Sika so this is new to me as well.

The following is quotation from their brochure:

“Tru Design suggest using Epoxy-West system or similar two pot epoxy that mixes to a paste and not a liquid type resin, as this will run and will create an undesirable finish.”

“Smear the epoxy paste on the underside of the skin fitting flange and a small way up the threaded diameter but no further than the thickness of the hull. Insert the skin fitting through the hull from the outside. The paste should be thick enough to hold the fitting in place and not drip or run down the hull.”

“If there is a large gap between the hole in the hull and the skin fitting carefully fill this gap with more epoxy paste.”


Thank you for all the answers on handling epoxy and how it should/can be done.

[barnakiel]

Originally Posted by zedpassway

Seems to me like you went way overboard. If your fitting is has a flange that is a good bit bigger than the hole and the hole goes through solid and there is not a balsa or plywood core, then just cut hole and seal it on both sides with butyl tape and screw it tight and then use a dull knife to scrape the butyl tape off the fitting.
If you are going through a core then you need to drill a hole about 1/4 to 1/2 inch bigger than the hole, fill the whole thing with epoxy(digging out the core about 1/8, and then re-drill the hole). But it doesn't look like that's what you have.

I think you prime the edges of the cut first. Any epoxy primer will do.

b.

[Lake-Effect]

Originally Posted by TobiasLager

Tru-Design recommends the use of epoxy since it bonds very well to the fitting and they make a rather large promise: “the epoxy has now made the skin fitting an integral part of the hull and will last the life of the vessel.”

... interesting. Thanks.

Last weekend I helped a friend change a thru-hull (new transducer). Because the old one was sealed with a urethane sealant, it was fairly easy to dislodge and remove. I expect that with an epoxied-in thru-hull, you'd just about have to drill it out. But up until that point... yup, great seal.

Originally Posted by zedpassway
If your fitting is has a flange that is a good bit bigger than the hole and the hole goes through solid and there is not a balsa or plywood core, then just cut hole and seal it on both sides with butyl tape ...

I have never heard anyone suggest butyl for use below the waterline. Are you certain that it's ok for that?

[mitiempo]

Originally Posted by zedpassway

Seems to me like you went way overboard. If your fitting is has a flange that is a good bit bigger than the hole and the hole goes through solid and there is not a balsa or plywood core, then just cut hole and seal it on both sides with butyl tape and screw it tight and then use a dull knife to scrape the butyl tape off the fitting.
If you are going through a core then you need to drill a hole about 1/4 to 1/2 inch bigger than the hole, fill the whole thing with epoxy(digging out the core about 1/8, and then re-drill the hole). But it doesn't look like that's what you have.

Butyl should only be used above the waterline.

[Thumbs Up]

Someone suggested using acetone to remove blush, this is incorrect. A little bit of Dawn and water with a scotchbrite is the preferred way. Wet sanding with Dawn and water also works. Rinse thoroughly. Anytime you bed a fitting with epoxy you are going to want to mask the edge of the fitting as well as the perimeter. Then you gloop on a copius amount of thickened epoxy and squish it into place. How are you going to mask freshly applied epoxy barrier? My advice is wait for it to cure, deblush and sand, then mask everthing off and apply the sealant of choice (5200 or thickened epoxy) install the fitting and remove the tape. It is not that important to get a chemical bond here. A well prepped mechanical bond is plenty good for this, and any other repair. Sure a chemical bond is more convenient because you can skip the prep but once again how are you going to mask the tacky epoxy and if you don't mask how will you deal with the ooze out. (you need the ooze out factor to be sure there are no gaps). On second thought there is a way though, if you are feeling brave you could just mask the outer flange of the fitting and squeegee the ooze out into the still tacky barrier coat. On third thought, the down and dirty way (I am not recommending this) would be to use the ooze out as the barrier coat but if you do this do not tighten the fitting all the way.

[Lake-Effect]

I read somewhere that vinegar is good for removing blush.

Some info here from an older CF thread.

[Suijin]

Originally Posted by alexanick

Suijin,
Please explain the"hot coat" process.
Thank you, Ken

Any kind of epoxy, be it a system like West System, Marpro, etc., or a two party epoxy paint, like barrier coat, does not dry, it cures.

It has a "working time" during which you can manipulate it (e.g.. brush it on, paste it on if it has thickening filler in it, etc.). At a certain point it will "kick" or start to cure and harden more rapidly. This period extends until the point where it is fully cured.

"Hot coating" is when you apply subsequent layers of epoxy, or epoxy paint, or even compatible anti-fouling or other coatings, before the epoxy has fully cured. This allows the coats to bond chemically to each other, providing a very strong bond. If you wait until the epoxy has fully cured you have to sand it/roughen it to ensure a mechanical bond since the chemical bonding window has closed.

[Suijin]

Originally Posted by bil56

I am very surprised by this recommendation to put thru-hulls with epoxy !
For me, thru-hulls are always fitted with PU or MS polymere seal.

The epoxy is for seating the the-hull fixture into the GRP. I suspect that they recommend epoxy because their thru-hulls are composite materials; now bonded with the hull, if there is any flexing it's all one unitized piece, which would not be the case with bronze, for example. You would never mount bronze with epoxy.

However, if you read their whole instruction sheet, the backing and nut should be installed with an adhesive sealant.

Personally, I would never use one of these below the waterline, in part out of concern about breakage (a misplaced foot jammed against it, a heavy tool box dropped on it), but also because I bet you basically need to drill it out and grind the flange off if you ever need to replace it. You're not going to be able to twist it out, lol.

[TobiasLager]

Originally Posted by Suijin

However, if you read their whole instruction sheet, the backing and nut should be installed with an adhesive sealant.

Where do you find this information? In the info sheet they do not suggest using adhesive sealant for the backing and nut, when installing with epoxy, as far as I am concerned. They do suggest using Sika 291 as sealant when mounting the valves, which is another thing.


From the info sheet:
"Smear the epoxy paste on the underside of the skin fitting flange and a small way up the threaded diameter but no further than the thickness of the hull. Insert the skin fitting through the hull from the outside. The paste should be thick enough to hold the fitting in place and not drip or run down the hull. Go inside the hull to fit the lock nut.

If there is a large gap between the hole in the hull and the skin fitting carefully fill this gap with more epoxy paste. Drop the washer over the top of the thread and push to the hull. Now hold the thread down near the washer and screw on the lock nut. Once the nut is screwed down far enough so you can hold the fitting above it do so and continue to screw the nut down onto the washer ensuring it is only finger tight. On the outside of the hull clean off any excess epoxy.

After recommended curing time tighten the nut to about 15ftlb.
There is no need to over tighten the locking nut as the epoxy has now made the skin fitting an integral part of the hull and will last the life of the vessel."

[minaret]

Originally Posted by Suijin

The epoxy is for seating the the-hull fixture into the GRP. I suspect that they recommend epoxy because their thru-hulls are composite materials; now bonded with the hull, if there is any flexing it's all one unitized piece, which would not be the case with bronze, for example. You would never mount bronze with epoxy.

However, if you read their whole instruction sheet, the backing and nut should be installed with an adhesive sealant.

Personally, I would never use one of these below the waterline, in part out of concern about breakage (a misplaced foot jammed against it, a heavy tool box dropped on it), but also because I bet you basically need to drill it out and grind the flange off if you ever need to replace it. You're not going to be able to twist it out, lol.

For the record, I grind off the mushroom on about 80% of the bronze thru hulls I remove. If it doesn't come off real quick, out comes the grinder. Removal time is generally five minutes or less. Anything else is unacceptable because the cost of a new skin fitting is substantially less than the cost of paying a pro to be careful removing the old one. About $35. This means that at yard rates, if it takes more than about 20 minutes to pull it, you are losing the client money. JMHO. I wouldn't hesitate to use one of these on the grounds of difficulty to remove...

[ramblinrod]

Originally Posted by Suijin

Technically you can dispense with the barrier coat altogether. It's just epoxy paint, and it's purpose is to prevent water penetration into the gel. 80 grit is plenty rough enough. If it were me I would install the through hull per their instructions, although I would probably brush on epoxy neat on the hull before topping with filled and installing to ensure the best bond with the GRP. Then barrier coat the surround and up to the flange. It's really up to you, both approaches amount to the same end result.

If you do barrier coat before the install, you want to hot coat your coats, I would do at least four, and then install the thru hull after the last coat has kicked but before it's fully cured. That will ensure a chemical bond between all the layers and the bedding epoxy as well.

I install a lot of thruhulls.

I can't really tell, but it sounds like you are considering bedding the thruhulls fitting with thickened epoxy, instead of a resilient underwater
sealant. Don't do it. There are many resilient sealants that will work fine.
While maybe not inuitive, some flexibility in the thruhulls / hull interface, is important.

Materials manufacturers tend to recommend use of their product when other
Products are vastly superior.

[mitiempo]

Originally Posted by ramblinrod

Materials manufacturers tend to recommend use of their product when other
Products are vastly superior.

It isn't the epoxy manufacturer that is making the recommendation. It is the manufacturer of the through hulls - Trudesign - that is recommending epoxy.
I would think the maker of the through hulls knows best.

Skin Fittings Threaded | TRUDESIGN

scroll down to the questions.

[DeepFrz]

Originally Posted by Suijin

Personally, I would never use one of these below the waterline, in part out of concern about breakage (a misplaced foot jammed against it, a heavy tool box dropped on it), but also because I bet you basically need to drill it out and grind the flange off if you ever need to replace it. You're not going to be able to twist it out, lol.

There is now available a load bearing collar that strengthens the through hull and brings them up to ABYC standards.

[lateral]

Vinegar saves on acetone when cleaning brushes, squeegees, etc but you must clean with acetone after to remove the vinegar or you risk contaminating your next mix.

Warm water & 3m pads are best for removing amine blush (peel ply is better still) or cleaning hardner pumps but be careful to dry the pump carefully before reusing.

DONT use acetone for cleaning amine hardner pumps as it eats the check ball.

[ramblinrod]

Originally Posted by Suijin

Any kind of epoxy, be it a system like West System, Marpro, etc., or a two party epoxy paint, like barrier coat, does not dry, it cures.

Interlux Interprotect E2000, must be exposed to air to cure, and thinner coats cure faster. This is more like drying than curing, despite being 2 part. PS, mixed product can be kept in a closed container for quite some time.