Reply
 
Thread Tools Search this Thread Display Modes
 
Old 06-28-2012, 09:36 AM   #1
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
Adhesive to bond polyethylene flange to fiberglass tank

I'm working on my Cayo C-11. The blackwater tank on these is made of fiberglass and is notorious for developing leaks over time. Mine has already been repaired once, by a previous owner.

The repair involved, among other things, replacement of the outlet flange with a piece that appears to be made of polyethylene. This is a poor choice of materials because of the difficulty of bonding polyethylene to fiberglass (or, for that matter, much of anything else besides other pieces of polyethylene) and because of the cold flow problems posed by this material. The flange is only partly surrounded by fiberglass and epoxy.

Predictably, the epoxy holding the flange to the fiberglass portion of the tank has given way leading to a crack and an odoriferous drip.

Here are the alternatives as I see them:

1) Remove the tank, cut out the flange, and glass in a new flange using PbearSailor's excellent photo essay on this sort of thing as a guide. I haven't done any fiberglass work myself in the past, and removing the tank is an involved process, so this is a last resort. Chemical prices being what they are this would involve over $100 worth of marine epoxy and another $100 of glass mat, mixing, handling, and safety materials.

2) Clean the exterior of the joint and carefully sand it down to a rough surface, and apply a specialty structural adhesive intended for polyethylene. I'm looking at 3M DP-8010, which is expensive but appears to be the only thing that will work. The adhesive itself is $40 for a 35 mL syringe, and the application gun, plunger, and nozzle are another $150 or so.

3) Duct tape and gorilla glue.

Any advice?
__________________

__________________
Jammer is offline   Reply With Quote
Old 06-28-2012, 12:38 PM   #2
Rivet Master
 
danlehosky's Avatar
 
2012 25' FB Flying Cloud
Gig Harbor , Washington
Join Date: Oct 2011
Posts: 780
Jammer, is there enough tank material to make a gasketed connection? A flange of any type with rubber gasket with screws holding everything in place. This will only work if the tank material is strong enough to support everything. Or you could also add some additional hangar support so the pipe weight is not stressing the tank. Polyethelene by it's very nature is difficult to make connections with.. Maybe a bulkhead fitting if you can get a hand inside.

Dan

Dan
__________________

__________________
TAC
Hope is not a plan.
danlehosky is offline   Reply With Quote
Old 06-28-2012, 01:17 PM   #3
Rivet Master
 
68 TWind's Avatar
 
1968 24' Tradewind
Oxford, , Mississippi
Join Date: May 2009
Posts: 1,420
West System Epoxy makes some stuff called G-Flex. It is made for use on various types of plastic. You can go to youtube and see some videos on applications. Any Marine dealer should have it. Might be what you need.
__________________
__________________
Bruce & Rachel
__________________
68 Trade Wind
2001 Toyota Tundra
68 TWind is offline   Reply With Quote
Old 06-28-2012, 02:05 PM   #4
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
Quote:
Originally Posted by danlehosky View Post
Jammer, is there enough tank material to make a gasketed connection? A flange of any type with rubber gasket with screws holding everything in place. This will only work if the tank material is strong enough to support everything. Or you could also add some additional hangar support so the pipe weight is not stressing the tank. Polyethelene by it's very nature is difficult to make connections with.. Maybe a bulkhead fitting if you can get a hand inside.
Dan

I'll try to post some photos at some point next time I'm out at storage.

Design wise the connection is a gasketed one between the tank flange and the Thetford valve. That part is all good as far as it goes.

The trouble is that the flange is the part made of polyethylene. It's more or less part of the tank in the sense that it's kinda epoxied in there, with the idea of some glass around it in a couple of places.

There is excessive length of 3" ABS attached in a rigid fashion to the dump valve which is probably contributing to the problem. I'm thinking of addressing this by replumbing the greywater and dump valve system in a more sensible way including some mission fittings (the clamp-type rubber ones) to provide a degree of flexibility. While this may reduce the likelihood of future problems it won't fix the crack though.
__________________
Jammer is offline   Reply With Quote
Old 06-28-2012, 02:08 PM   #5
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
Quote:
Originally Posted by danlehosky View Post
Maybe a bulkhead fitting if you can get a hand inside.
The wall of the tank is irregular in thickness and so getting a bulkhead fitting to seal would pose its own problems. I suppose it could be done with a thick enough gasket, maybe just by using five or six of them stacked up each other with some washers in between. There's no good way to get a nut in there though since there are no openings larger than the outlet.
__________________
Jammer is offline   Reply With Quote
Old 06-28-2012, 03:02 PM   #6
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
Quote:
Originally Posted by 68 TWind View Post
West System Epoxy makes some stuff called G-Flex. It is made for use on various types of plastic. You can go to youtube and see some videos on applications. Any Marine dealer should have it. Might be what you need.
I'm checking into it. Might be just the thing. They claim it will bond as long as the polyethylene is flame treated first.
__________________
Jammer is offline   Reply With Quote
Old 01-28-2013, 06:54 AM   #7
Wise Elder
 
Jammer's Avatar
 
2010 30' Classic
Vintage Kin Owner
South of the river , Minnesota
Join Date: Dec 2009
Posts: 4,119
Ultimately I was able to get this to seal properly using about five coats of G/Flex and a little bit of glass mat to reinforce it. I did flame treat the polyethylene.
__________________

__________________
To learn to see below the surface, you must adjust your altitude
Jammer is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



Virginia Campgrounds

Reviews provided by




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 12:53 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.

Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.