Flex-Seal tape experiment..

[1911tex]

Hey folks...I did a test this morning, got on my wet suit to do a double duty...got a piece of highly advertised Flex-Seal black tape that is supposed to stick underwater (yea, sure!). Jumped in, and slapped it over the galley sink thru-hull which valve I had previously closed and disconnected the hose to the sink drain. While wet...scrubbed the bottom with a brush to rid slime, etc.. Then got out, opened the valve with a bucket handy. A quart of water came out, then STOPPED! I am going to wait the day while working on other boat chores before going down and removing the Flex-Seal. Just want to see how long this tape keeps from leaking/deteriorating, etc. I will report back later today. No I don't work for that outfit!

 

[kapnkd]

Hey folks...I did a test this morning, got on my wet suit to do a double duty...got a piece of highly advertised Flex-Seal black tape that is supposed to stick underwater (yea, sure!). Jumped in, and slapped it over the galley sink thru-hull which valve I had previously closed and disconnected the hose to the sink drain. While wet...scrubbed the bottom with a brush to rid slime, etc.. Then got out, opened the valve with a bucket handy. A quart of water came out, then STOPPED! I am going to wait the day while working on other boat chores before going down and removing the Flex-Seal. Just want to see how long this tape keeps from leaking/deteriorating, etc. I will report back later today. No I don't work for that outfit!

Looking forward to hearing back more about how well this tape really works.

 

[1911tex]

I forgot to mention in post 1; before I applied the Flex-Seal tape, I brushed off the slime as well as I could from the area to be applied...to give optimum chance for adhesion. Going to give it minimum 6 hour trial. Be back with you.

 

[1911tex]

Continued from post #1: Just re-opened the galley sink thru-hull valve, tilted the hose (already removed hose from sink drain in post #1), into a bucket and got only about 2 coffee cups full of water into the bucket! I am amazed. That's about 6 hours of test for this Flex-Seal tape. Sooo, bottom line it works for at least 6 hours with minimal leakage. I purchased the roll in the sailboat department at Ace Hardware. The 4" wide black roll is expensive and is much more difficult to pull product off the roll than duct tape; however, I will keep this roll on the boat for emergencies...really tough stuff...it works! I don't know how difficult it would be to pull off the roll if the roll was stored in a hot summertime cabin. Hot stored duct tape is very hard to pull off the roll. But great peace of mind! Now to put on the wet suit, jump in and try to peel it off the underwater thru-hill ! I hope the anti-fouling bottom paint does not come off with the tape...never thought about that potential problem....

 

[toddster]

Good info!
I’ve heard that the adhesive membrane material used to waterproof house foundations will also work for boat damage control. Odd pieces and roll ends might be had for practically free, if one has the right connections. I had several yards of it, but by the time I obtained a boat and learned of this use, it had hardened into a rock-like state, after ten years under the porch.

 

[Christian Williams]

A few square feet of any membrane that could stick underwater--now that would be good to have.

 

[1911tex]

Follow up...the process of peeling off the 4 sq. inches of tape from the thru-hull very carefully with a dull knife did the job and did not harm my relatively new bottom anti-foul paint. It took 25 very careful tedious minutes and many dozen gulps of air from my mask snorkel. Not something I want to do on a routine basis for sure. Getting too old for such experiments. Yes I did remember to re-hook up the hose to the sink drain prior. Side note while down there, I saw what looked like a 15#+ large mouth Bass and several massive goldfish (I mean Carp) making springtime love just under the surface...ignored me totally as I did them.

 

[goldenstate]

A few square feet of any membrane that could stick underwater--now that would be good to have.

Flex seal tape is pretty close (in my experience) to the WR Grace construction material sold in big rolls as 'Bituthene':

GCP Applied Technologies Bituthene 4000 36 in. x 66.7 ft. Roll System Waterproof Membrane and Conditioner (200 sq. ft.) 5003004 - The Home Depot

Use this Grace Bituthene System Waterproof Membrane and Conditioner for positive-side waterproofing applications over concrete, masonry and wood surfaces.

www.homedepot.com

It seems like it could be a great thing to have on hand in large-ish pieces, for the Robert-Redford-bashes-a-shipping-container scenario.

I (my building contractors) have used it to waterproof retaining walls that hold back moisture-laden soil. Also roofing flashing. I have little doubt as to the ability of the membrane to keep water out. The question for me would be if the native adhesive would hold sufficiently to the fiberglass (bio-growth laden?) hull in saltwater. Maybe a good argument for getting your hull power-washed before a long passage.

Tex's positive experience may reflect his recent bottom-paint job. Great contribution, Tex, thank you.

 

[goldenstate]

Apparently smart people using bituthene under teak decking to prevent leaks under deck teak:

One of a Kind Part 2

Part 2 of the story of her restoration by Gannon & Benjamin Marine Railway

www.soundingsonline.com

Also widely used as kayak repair method.

 

[1911tex]

A 4" roll of this stuff will last a lifetime...stick it in a drawer for emergencies or whatever....I would put it in a zip lock and store on a flat surface...I cannot state how long it will last in heat; my roll did not have an expiration date...but add it to your duct tape backup supply.