Water tank adhesive question

centerline · Jun 27, 2015

it appears to be a poly tank so if its leaking around the sealant, you may be able to give the screws an eighth of a turn and get it to seal without further problems. if not, remove it from the tank and clean it all up and use silicone to reseal it.... if its the o-ring on the cap leaking, replace the o-ring.

Ralph Johnstone · Jun 27, 2015

Ken Cross said:
Hi all. I just filled our water tank to the top for the first time and found it leaks around the ring of the cleanout. The white adhesive isn't bonded to the tank. Clearly I need to drain the tank and remove the cap and ring and clean the faying surface.

My question: After I clean it up, what shall I use to seal it?

I know someone will have the answer.

The boat is a 1989 Hunter 30.

Ken

Without seeing the construction of the cleanout ring, it's hard to offer anything too concrete.

Most adhesives just do not stick to poly. The only one I have found that sticks like "you know what" to a blanket is Permatex #2. Great for holding tanks and fuel tanks but not so good for potable water.

If, after taking it apart, it comes out as a simple screw on flange, you may want to look at installing something fancier with a backing ring. There, the non-sticking sealant is held solidly in place by the backing ring as the tank flexes from both filling and general flexure. The split allows for entry into the tank and a little ingenuity keeps it from falling to the bottom of the the tank while installing. The attached pic shows a small backing ring for a depth probe.

Chief RA · Jun 28, 2015

Ken: I'm with Centerline on this one. Silicone should work but if you have problems with proper adhesion you might buy a tube of Shoe Goo as it sticks like crazy to plastics.
Chief

centerline · Jun 28, 2015

Chief RA said:
Ken: I'm with Centerline on this one. Silicone should work but if you have problems with proper adhesion you might buy a tube of Shoe Goo as it sticks like crazy to plastics.
Chief

the silicone does not even have to stick or adhere to the surface... if its assembled with the right amount of silicone, and then the screws are left a bit loose for a couple of hours til the sealant sets, when the screws get screwed in another half of turn or more, the seal will be under compression like a true gasket or o-ring seal would be.... this is what you need for that type of application. (do NOT over tighten it as it could warp the tank or cover)
you dont want it to "stick" as it is supposed to be able to be easily removed when needed without destructive or damaging means....

Steve Dion · Jun 28, 2015

You may also want to check out some butyl rubber gasket material too. The softer the better.

centerline · Jun 28, 2015

Steve Dion said:
You may also want to check out some butyl rubber gasket material too. The softer the better.

but NOT butyl tape in this application... the poly tank needs a sealant with a high amount of resilience. some forms of butyl do have it, and butyl tape does have to some degree, and more or less at times depending on the temperature, but the resiliency of silicone is unaffected by even abnormal high and low temps....

jibes138 · Jun 28, 2015

Wouldn't a gasket be a better choice than a sealant? You can buy a sheet of gasket material and cut it to fit the ring and use a drill for the screw holes.

Chief RA · Jun 28, 2015

The way Centerline is explaining it the silicone becomes a gasket plus molded to all contours. I like it! Chief

centerline · Jun 28, 2015

jibes138 said:
Wouldn't a gasket be a better choice than a sealant? You can buy a sheet of gasket material and cut it to fit the ring and use a drill for the screw holes.

the silicone is softer and more resilient than any common pre-made gasket material. and being in a gel form during application it will form to any imperfections or warping there may be in the mating surfaces.

centerline · Jun 28, 2015

jibes138 said:
Wouldn't a gasket be a better choice than a sealant? You can buy a sheet of gasket material and cut it to fit the ring and use a drill for the screw holes.

the silicone is softer and more resilient than any common pre-made gasket material. this makes it strong, and being in a gel form during application it will form to any imperfections or warping there may be in the mating surfaces.

jibes138 · Jun 29, 2015

The only trouble with silicone is it skins over so fast so you don't get much working time. How about that thick foam gasket material they use to mount caps on pickup trucks so they don't leak? I used it on a deck plate that goes over my rudder post and it seems to work well. This isn't a high pressure application, leakage should only occur when the boat is heeling or if the tank is overfilled. This stuff is 0.200 thick and soft enough to conform to any surface. It is EPDM rubber similar to what is used in car door seals and a huge assortment of sealing applications.
http://www.amazon.com/Premium-Width...=1435580914&sr=8-6&keywords=pickup+truck+caps

sailortype · Jun 29, 2015

I used silicone for my water tank port, years of use and no problem with leaks. It does not adhere to the poly, it acts as a gasket. Btw, Goop is one of the most tenacious sealant/adhesives I have ever used. Sticks to pretty well anything and clings like grim death. Use the Marine Goop variety, it is u/v resistant for any exterior uses you may have.

Lander · Jun 29, 2015

It's likely to be a polyethelene tank and there are very few sealants that will adhere to that. Call Ronco Plastics, who make them, and ask for the correct product.

bobbyfingers2001 · Jun 30, 2015

Ken Cross said:
Thanks, I haven't torn it apart yet. So do I assume the white gunk doesn't belong there? It doesn't feel like silicone, more like 5200.

Ken

Ken,

If it was sealed with 5200 it would feel like hard plastic, and would probably never come off.

If it has any pliability then it is either 4200 or silicone, either way if the seal is failing then you need to remove the inspection cover and ring assembly.

First you will need to drain the tank and place some towels under the ring to catch any debris that may fall into the tank.

Then thoroughly clean the entire surface including an area about 2 inches wider than the base plate.

Get some new screws with nylon stop-nuts and either a silicone gasket ring or food grade clear silicone, if the surfaces are prepared correctly you should only need a thin bead around the flange, remember to put the bead towards the inside of the screw holes and place just a tiny amount on the screw before inserting them.

Use a shop-vac and some clean rags to remove any debris from the tank so you don't wind up clogging the pump strainer or worse.

You should sanitize the tank before disembarking again. Using a solution of 1 cup bleach to 1 gallon of clean water on some towels clean the inside surfaces including the underside of the top where you installed the ring, flush out the tank and then refill with clean water.

Also be sure to examine the o-ring on the cover itself, check for pliability, porosity, cracks, cuts, etc. If it is OK then reuse or replace it, spread a small amount of petroleum jelly on the ring and re-install it.

You should be good for 10 years...

Happy sailing!

***One last tip:

If you have a poly-tank (or even an aluminium tank) with flimsy walls then get a second flange, make a slit between two of the screw holes, insert it into the tank and bolt through the top flange, the tank then the bottom flange. This will stiffen up the tank to flange joint and prevent warpage in the future.

SamLust · Jul 2, 2015

having done this more times than I can count I can assure you Centerline is 100 percent correct. Follow his instructions line by line and you will be fine. Doing so you are forming a custom molded gasket in place, and once it is CURED you snug down on it. Simple.

Water tank adhesive question

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