Which "Butyl Rubber" for Freshwater Tank Seal?

Jan 24, 2009
450
1981 Cherubini Hunter 27 Shipwright Harbor Marina, MD
Hi,
I have a 1981 Hunter 27 with a seldom used fiberglass molded-in-place freshwater tank that has a fiberglass lid screwed down with a bunch of screws. I've been using Google Advance Search and reading through old posts on pulling the lid and scrubbing it out. I keep seeing comments about making a new seal out of "butyl rubber" and I'm not seeing details on what exactly this refers to:
1. Is it the sticky butyl rubber tape like I got from MaineSail?
2. Is it a "gasket" type rubber and if so, do I have to buy a whole sheet and cut out one large gasket? (more expensive)
3. Or can I just buy a roll and cut strips to length?
I've already pulled the lid on the holding tank using a heat gun to soften the 5200, so I'm comfortable doing that, the butyl rubber idea just seems easier to work with than re-doing the seal with caulk every time.
Thanks in advance for any help you can give me,
Dan
20170408_142033.jpg
 
Jan 7, 2011
4,727
Oday 322 East Chicago, IN
I don't know that I would use butyl rubber tape for this application. It would certainlily seal, but I would be worried about toxicity. I would use an FDA approved caulk, maybe silicone.

Just my opinion. Your boat, your decision.

Greg
 
Jan 24, 2009
450
1981 Cherubini Hunter 27 Shipwright Harbor Marina, MD
Thanks, Tally Ho. One of the people who suggested it was Mistress Peggie, so I assumed it was a legitimate idea, but there were no details beyond "use butyl rubber." I'm leaning towards silicone only so I don't have to worry about it not sealing well. It shouldn't be a big hassle to re-do the caulk if I have to ever pull the lid again, so maybe I will go ahead with caulk and not agonize over it.
 

NYSail

.
Jan 6, 2006
3,048
Beneteau 423 Mt. Sinai, NY
I am not sure what you are asking, possibly you mis-typed something.
I guess I don't understand what you are doing. I assume you have an inspection port in your water tank that screws into the frame (picture shows cap off the screwed-on frame of inspection port). I am not sure what you need to reseal... just unscrew cap.... stick arm in and clean then when done screw cap back on...... Guess I'm missing something.
 
Jan 24, 2009
450
1981 Cherubini Hunter 27 Shipwright Harbor Marina, MD
Thanks for the link Chris, that's very helpful. I figured it wasn't something I could readily find, thanks for saving me the time.
 
Jan 24, 2009
450
1981 Cherubini Hunter 27 Shipwright Harbor Marina, MD
I guess I don't understand what you are doing. I assume you have an inspection port in your water tank that screws into the frame (picture shows cap off the screwed-on frame of inspection port). I am not sure what you need to reseal... just unscrew cap.... stick arm in and clean then when done screw cap back on...... Guess I'm missing something.
There's a baffle in there and I'll have to pull the lid to reach the space behind. Haven't decided on whether or not to install a second inspection port. Once I've cleaned it good, if I keep it clean I shouldn't have to re-do it again. I wish it were as simple as just reaching in with a long brush and scrubbing it out.
Thanks for the reminder to replace the inspection port seal, I'll put that on my list.
 

NYSail

.
Jan 6, 2006
3,048
Beneteau 423 Mt. Sinai, NY
Right... removing the top! I had a glassed in tank but was a complete tank (no baffle) with only the small inspection port..... removing the top will be nice! Good luck!
 
Sep 8, 2014
2,551
Catalina 22 Swing Keel San Diego
I'm 99.9999999 % positive you can safely use Butyl Tape for sealing a potable water tank, especially if you got the "Bed-It" tape from Mainsail which is where I got mine too. Although food-grade silicone is also a great choice, it isn't for fiberglass tanks... its great for plastic or metal tanks, just not GRP tanks. If you pull the cover annually to clean/disinfect, go with the butyl tape. Once silicone gets on GRP (even on the gelcoat) it pretty much contaminates it forever and nothing will stick to it again except more silicone. One of my (loosely enforced) rules is that there is no place on a boat for silicone except DOW 795 for windows/port-lights and food-grade only in galley equipment as required. There are a few engine room applications too, but they generally don't touch fiberglass.
 
Oct 6, 2007
1,023
Hunter H30 1982 Chicago IL
There's a baffle in there and I'll have to pull the lid to reach the space behind. Haven't decided on whether or not to install a second inspection port. Once I've cleaned it good, if I keep it clean I shouldn't have to re-do it again. I wish it were as simple as just reaching in with a long brush and scrubbing it out.
Thanks for the reminder to replace the inspection port seal, I'll put that on my list.
Add the second access port so you don't have to do this again. The tank in my H30 has two baffles and three access ports, two of which appear to have be added by the P.O. after he had removed the top and re-sealed it at least once. It makes it pretty easy to clean the tank with a brush and a small mirror.
 
Jan 24, 2009
450
1981 Cherubini Hunter 27 Shipwright Harbor Marina, MD
Thanks Dalliance, sounds like it's worth the effort to add extra access ports, I'll have to do that when I get the lid off.
I will try MaineSail's tape also, maybe use it and then fill the tank and go sailing and see if it leaks.