Which sealant to seal a deck hatch?

[Southern Boater]

I need to re-seal my three Vetus alloy framed deck hatch’s to a GRP/gelcoat deck.
The grp molded cabin top plinth has developed gelcoat cracks from screw fasteners for covers, drawing rainwater along and up slightly to the failed, cracked sealant and down into the cabin.
I will of course repair the gelcoat cracks, but not decided on which sealant to re-bed the hatches.
Some say Sikaflex 291, but don’t really want the full adhesion factor, or a silicone?
Wayne Canning on YouTube suggests Dow silicone 795?

What have others used successfully?

TIA

 

[Bacchus]

Many swear by silicone while many herevswear at it, including myself. I dont think thetevare enough positives to offset the negatives of silicone on most applications.
I have switched to using butyl tape for most bedding situations and found the tape available from Compass Marine Services the best.... There are differences.
https://marinehowto.com/bed-it-tape/
https://marinehowto.com/

Rod (the owner and commercial member here on TF) is out recovering and unfortunately his online store is down, we hope temporarily. The How To is still very applicable and helpful.

 

[FF]

Flexing is the cause of gel coat cracking so unless you beef up the mounting area, you will be resealing often.

I prefer old style Dolphinite , its a sealant , not a glue, so scrapes off very quickly/easily when its re bedding time, again.

 

[DegoRed]

First off, never use Sikaflex for anything, that stuff is complete trash.

The Best is a product called NP1, but it kind of hard to find, but if you can find it, that is hands down the best, end of story. This product is what we use on most every commercial building, especially high rise stuff that gets slammed with driving wind & rain.

A good product, that is a little easier to find is called Quad OSI, which can be found at Home Depot.

You want an Elastomeric, polyurethane sealant. This stuff will remain flexible and move providing some give while remaining water tight. Make sure you put down masking tape prior to placement, this stuff is hard to get off once its placed, so no fat fingering it, and don't get it on your clothes, it does not come off ever, use rubber gloves as it hard to get off your skin. All these products come in various colors, so you can get one pretty close to what you need.

 

[Southern Boater]

Thanks for the responses so far, I will grind out the cracks and fill with thickened epoxy, but keen to find the best(-ish)sealant to prevent future leaking. Even with waterproof vinyl covers over the hatches, the water tracks uphill, about an inch, in a capillary effect.
The boat is thirty years old and the hatch sealant appears original, and once disturbed, crumbles, which I guess you would expect after UV exposure.
Thanks again for those who have commented, I appreciate the feedback.

 

[Comodave]

I used to use 3M products but have switched to Sika products several years ago and have been very happy with them. I use 291 for general caulking where things are screwed down. I use butyl from Compass Marine where things are through bolted sine it will properly squeeze the butyl.

 

[Southern Boater]

Many swear by silicone while many herevswear at it, including myself. I dont think thetevare enough positives to offset the negatives of silicone on most applications.
I have switched to using butyl tape for most bedding situations and found the tape available from Compass Marine Services the best.... There are differences.
https://marinehowto.com/bed-it-tape/
https://marinehowto.com/

Rod (the owner and commercial member here on TF) is out recovering and unfortunately his online store is down, we hope temporarily. The How To is still very applicable and helpful.

It looks as though I have made a blunder!
Before leaving the boat I temporarily filled the gelcoat cracks with silicone to slow down further leaks until I can get back to effect a proper repair, reading Rod’s impression of silicone “contamination” I’m up for a big job!

“Silicone contamination of gelcoat is very, very real. It is nearly impossible to clean and remove silicone from gelcoat. Auto body products intended for metal are not generally safe for gelcoat. To effectively remove silicone from gelcoat requires judicious manual cleaning then wet sanding rinsing the paper frequently to clear it of silicone traces so you don’t grind it deeper into the gelcoat. To test if the silicone is gone spray the area with a misting bottle of water. If the water beads it is not clean.”

As I don’t live in the USA, I will struggle to find his Bed-It butyl tape no doubt, and even he thinks all butyl tape is not created equal.

 

[fgarriso]

If you want it to stay on and sealed try 3M-5200

 

[Comodave]

Yes, getting silicone off is almost impossible. I scrape it first with a sharpened putty knife and sort of shave it off. After getting off as much as possible then I use something like acetone to clean it up. Then usually have to sand the area to get off the lingering residue. It is a real PITA. But if you don’t get it off nothing else will stick where you used the silicone. I don’t even keep any on the boat just in case I might be tempted to use it.

 

[SteveK]

First off, never use Sikaflex for anything, that stuff is complete trash....................................

Well then, after many decades of using the product I shall immediately stop. I heard it on the internet after all so it must be true.

 

[BruceK]

Sikaflex is fine imo, a good product. Parfix in Australia makes a polyurethane sealant/adhesive too, not as good imo, and the white "yellows" with age.

As regards the silicone, all may not be lost. The "Roof & Gutter" variety takes paint whereas the "bathroom" type won`t take anything at all, so check what you used. If it takes paint etc, you may be ok. And there are silicone removal products. I used the "R & G" variety to fill gaps in a black "rubber" hatch seal,it flows better than polyurethane and is generally more co-operative to use. And it worked! It`s not necessarily a product of Satan Inc.

I`m about to use a Selleys brand adhesive/sealant called "Marine Flex". The tube says it is "an advanced polymer" "superior to traditional polyurethane" which can be applied and will even set underwater. We`ll see, I`m just using it on a dock wheel(above water) I installed at the marina, not on the boat.

 

[Southern Boater]

Sikaflex is fine imo, a good product. Parfix in Australia makes a polyurethane sealant/adhesive too, not as good imo, and the white "yellows" with age.

As regards the silicone, all may not be lost. The "Roof & Gutter" variety takes paint whereas the "bathroom" type won`t take anything at all, so check what you used. If it takes paint etc, you may be ok. And there are silicone removal products. I used the "R & G" variety to fill gaps in a black "rubber" hatch seal,it flows better than polyurethane and is generally more co-operative to use. And it worked! It`s not necessarily a product of Satan Inc.

I`m about to use a Selleys brand adhesive/sealant called "Marine Flex". The tube says it is "an advanced polymer" "superior to traditional polyurethane" which can be applied and will even set underwater. We`ll see, I`m just using it on a dock wheel(above water) I installed at the marina, not on the boat.

It appears there is no easy answer unfortunately, as far as bedding the hatches is concerned.
Of course the silicone I used as a temporary gel crack stopper was a bathroom version, just because it was there after the install of a new vanity. Hopefully the dremel and the good advice from TF will result in an adequate clean up.
When we found the leak source, on a rainy day, I got some waterproof tape from Bunnings which is supposed to stop a flowing water tank leak, then changed my mind and decided to keep the tape for a proper boat emergency when the rain stopped, and used the silicone.

 

[Bacchus]

It appears there is no easy answer unfortunately, as far as bedding the hatches is concerned.
Of course the silicone I used as a temporary gel crack stopper was a bathroom version, just because it was there after the install of a new vanity. Hopefully the dremel and the good advice from TF will result in an adequate clean up.
When we found the leak source, on a rainy day, I got some waterproof tape from Bunnings which is supposed to stop a flowing water tank leak, then changed my mind and decided to keep the tape for a proper boat emergency when the rain stopped, and used the silicone.

I have used some metallic foil tape as a temporary stop for hatch leaks until I could remove & rebed and it worked very well and easily removable. It was also helpful when trying to pinpoint the exact leak area by taping off areas and testing for leaks.

 

[Southern Boater]

I have used some metallic foil tape as a temporary stop for hatch leaks until I could remove & rebed and it worked very well and easily removable. It was also helpful when trying to pinpoint the exact leak area by taping off areas and testing for leaks.

Yes, the tape route would have been the better option for such a short term period. I guess it wouldn’t be a boat job without developing into a few more degrees of difficulty ;-)

 

[sbman]

For a bolted down hatch, bolted onto a GRP deck, I would only use Butyl tape. It never hardens, will allow for flex and movement, provides very little adhesion so you can remove it quite easily later. There's really no comparison to the messy tubes of oozy stuff. I also use the go2marine brand of butyl tape, it is easier to work with than other off brands I've tried, and it also cleans up easier.

 

[Southern Boater]

For a bolted down hatch, bolted onto a GRP deck, I would only use Butyl tape. It never hardens, will allow for flex and movement, provides very little adhesion so you can remove it quite easily later. There's really no comparison to the messy tubes of oozy stuff. I also use the go2marine brand of butyl tape, it is easier to work with than other off brands I've tried, and it also cleans up easier.

Thanks for the advice.

 

[sbman]

Thanks for the advice.

I had the brand I like wrong. It's compass marine, and it's called 'Bed-it'. Unfortunately I believe it is not available at this time.

https://shop.marinehowto.com/t/bed-it-tape

I'm not sure what brand I'd use at the moment, I still have some bed-it left. (I keep it in the fridge).

 

[Southern Boater]

I had the brand I like wrong. It's compass marine, and it's called 'Bed-it'. Unfortunately I believe it is not available at this time.

https://shop.marinehowto.com/t/bed-it-tape

I'm not sure what brand I'd use at the moment, I still have some bed-it left. (I keep it in the fridge).

It seems finding the right butyl tape is nearly as hard as finding the tube sealant. The fridge seems the best place to keep all sealers for sure.

 

[Southern Boater]

Thought I would update the thread, as I know folks sometimes are doing general research.

My boat has GRP moulded decks, no external teak, so I assumed the hatch plinth would also be GRP, but turned out the teak box inside under the hatch meets fairing compound with gelcoat externally.
The deck level cracks bought the water along and up, past the degraded sealant and down past a combination of fractured fairing compound and gelcoat where it meets and breaks away from the teak internal hatch frame, dribbling down the frame into the cabin headlining…..and onto the bed!

First fix the initial source of the leak, the gelcoat plinth cracks which involved using a dremel to enlarge the cracks and expose any voids around timber and fairing compound and fill with thickened epoxy. I used the West System Six10, very easy to use from a pre-mixed cartridge.

The removal of the hatch itself took a bit of work because it was bedded with a strong adhesive, removed all screws, used a flexible putty knife with rounded corners and belted it with a rubber mallet.
After working what I thought was the entire perimeter, forced a heavy duty plastic scraper with a decent wedge taper to lift the hatch away from the plinth, but I had missed a couple of inches on one section, the strong adhesive pulled a wedge of teak up from the frame! The lesson here is keep working your way around several times with the flexible putty knife if your hatch has a strong adhesive compound used, before lifting.

Once the hatch was up and surfaces cleaned, I could see the leak point from where the fairing compound had broken away from the teak, so dremeled any shattered compound anywhere around the entire frame and filled with thickened epoxy to create a flat, smooth bonding surface for the sealant between the hatch and deck plinth.
Worth noting, after watching Boatworks Today, if you are wanting an neat finish, run masking tape around the outside perimeter of the hatch on the deck to create a neat line when cleaning up excess sealant, same as masking off when anti-fouling.

For any Australians, I ended up using FixTech 15 as sealant, on advice from local shipwrights

 

[mysticdreamer]

hello,I have a steel boat and I'm replacing my 30 yr old hatch on the upper deck what is the best sealant for steel and what outside temperature does it need to cure

 

[Bacchus]

I had the brand I like wrong. It's compass marine, and it's called 'Bed-it'. Unfortunately I believe it is not available at this time.



https://shop.marinehowto.com/t/bed-it-tape



I'm not sure what brand I'd use at the moment, I still have some bed-it left. (I keep it in the fridge).

Update: I have noticed a recent post by Rod at CMS and I see he has announced that Bed-It Tape is once again available on his website.

See. https://marinehowto.com/

https://shop.sailboatowners.com/prod.php?55717/Rod+Collins+and+apos;+Bed-It+Tape

I have used a couple different tapes but have to say the CMS variety is the best I have found and always keep some on hand.

 

[Comodave]

hello,I have a steel boat and I'm replacing my 30 yr old hatch on the upper deck what is the best sealant for steel and what outside temperature does it need to cure

I would use butyl tape. With the steel deck and some other material like aluminum hatch they may not expand and contract at the same rate. Butyl tape will have waaay more ability to move with the materials without breaking the seal. Post above about Bed-it butyl tape on marinehowto.com is the way to go IMO. There is an excellent article on that website about bedding things.