From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Black Water tank leak
Date: Mon, 08 Sep 2003 22:19:47 -0400
Message-ID: <tucqlvkro3hp0u87t3se42vn3r866vs1se@4ax.com>

If JB weld doesn't stick to the tank, which I suspect it won't since JB weld
is rigid and the tank flexible, the best solution is to find an auto body shop
with a plastic welding kit and have the crack welded shut.  The welding kit
consists of a soldering iron-like hot air wand and filler rods of the various
thermoplastics.  The kit is sold to body men to fix plastic bumpers with but
it works equally well on tanks.

Harbor Freight occasionally sells a plastic welding kit out of their stores
and catalog.  I looked at one in the store in Chattanooga.  Typical chinese
knockoff stuff.  Probably OK if you're not in a hurry.

There are specialty adhesives that will stick to the low surface energy
plastics like PET or HDPE but the use is tricky, almost always involving the
application of something to increase the surface energy of the plastic being
bonded.  this may be the very brief application of a very hot (oxy-hydrogen or
oxy-acetylene) flame (not much energy imparted but simple) but more preferably
an electron or plasma beam. Intense very short wave UV (UVC) will also do the
job. There is a lot of info on the net regarding this topic.  Google is your
friend.

If you want to just kinda jerry rig a patch, rather than JB weld, try a
technique I've developed that works fairly well.  This involves applying a
fiberglass/RTV composite to the fault.  RTV does not itself stick very well to
these plastics but it can be mechanically bonded in place.  The idea is to
poke multiple shafts of RTV through the tank wall so it can mushroom out on
the inside, forming a mechanical lock.  Fiberglass gives it strength.

You'll need some fiberglass tape.  I get my 1" X about 25 ft rolls from an
electric motor shop.  This tape contains no adhesive.  You'll also need some
conventional silicone RTV and some thin self-leveling silicone RTV.  I can get
you a Dow number if you're interested.

First step is to empty and thoroughly clean the tank.  Clean the leak and
identify the hole/crack.  Gouge this out so that there is clear passage to the
inside of the tank but try not to make the gouge too large.  Drill a series of
small holes through the tank close together around the fault.

Squirt some conventional RTV into each hole and the fault.  Using a large
sewing needle with half the eye cut off to form a tiny fork, push strands of
fiberglass into the holes, leaving some protruding on both sides.  Squirt in
some more RTV, leaving perhaps 1/16 layer around the area.

Roll out the fiberglass tape on some scrap material, squirt on the
self-leveling RTV and work it in the fabric with gloved hands.  This material
is fairly thin and easy to work with.  Wrap this impregnated material over the
holes, preferably wrapping it around the tank nipple for more mechanical
strength.  Apply several layers.  After the last layer, apply a uniform film
of thin RTV to the fiberglass.  Allow to cure overnight.

If you have a suitable torch, try to activate the surface before application.
Clean the surfaces as good as possible.  Very quickly wave an oxidizing (lean)
flame over the material.  It should NOT melt the stuff, just turn the surface
a different, somewhat more dull texture.  The best flame on an acetylene torch
is one that is so lean it is just about to blow out.  As I understand it, this
"activation" breaks some of the long molecular bonds on the surface, leaving
chains dangling that the adhesive can bond to.  This very superficial
activation doesn't last long and is totally reversed by melting but it is
better than nothing.

I've used the silicone/fiberglass composite technique many times with
practically 100% success.  Using fuel resistant caulk I've even patched
plastic gas tanks.

John

On Mon, 08 Sep 2003 22:14:02 GMT, "Tom J" <tomjanis2@att.net> wrote:

>
>"Richard Ball" <richb@u.washington.edu> wrote in message
>news:bjitfd$mrq$1@nntp3.u.washington.edu...
>> While spending a week out on the Washington coast we noticed a small leak at
>> the connection between the tank and the pipe running to the valve.  Any body
>> have a preference as to what sealant to use on this joint.
>
>JB Weld
>Follow directions closely. Get from hardware or auto parts store.
>
>Tom J
>

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Grey water Black Tank Repair??
Date: Sun, 19 Mar 2006 22:55:58 -0500
Message-ID: <d89s12puqbqm5rb7dlol7if6avrmo9lud5@4ax.com>

Like others have said, I'd be looking for warranty adjustment.  That
plastic should not be that brittle.  In the meantime....

Slathering gunk onto an 8" long crack isn't going to work.  Here is a
commonly used industrial patch technique that will work here.

You'll need some 1/2" plywood, enough toggle bolts to place one about
every inch and some 3M marine polyurethane caulk.  I believe the
number is 6500.  It will be listed as the maximum strength,
non-removeable version.  This is available at Wallyworld in the boat
department.

Cut one or more strips of plywood to fit over the crack.  Preferably
long and no more than 2" wide.  Drill holes in the plywood about an
inch apart, alternating sides in a zig-zag pattern.  Select a drill
diameter so that the shank of the toggle bolt will just pass.

Drain and dry the tank.  Use a heater, hair dryer, etc to drive off
all the moisture around the crack.  Hold the plywood up to the crack
and using the holes as guides, drill through the tank.  Remove the
plywood and enlarge the holes until the wing part of the toggle bolt
will pass through.

Remove the wing from each toggle bolt and after placing a fender
washer on each bolt, pass it through the plywood.  Then re-attach each
wing.

Slather marine caulk along the crack and in the holes.  Apply more
caulk to the plywood, especially where each bolt comes through.  Hold
the plywood next to the tank and insert each toggle bolt.  Make sure
they all expand and grab.  Make sure there is plenty of caulk around
each toggle bolt shank.  Push the plywood up against the tank.  Make
sure caulk oozes out all around.  If not, lower it and apply more
caulk.  Tighten the toggle bolts.  Allow the caulk to cure and you're
set.

The marine caulk probably won't stick very well to the tank material,
particularly if it is polyethylene.  The combo of the toggle bolts and
the plywood makes a mechanically sound assembly.  The caulk doesn't
really have to stick, just fill in the gaps.

This should be good indefinitely, particularly if you can find
stainless toggle bolts.  You'll have plenty of time to wrangle a new
tank out of the mfr.

John

On 18 Mar 2006 19:55:58 -0800, "joebedford" <i_mongo@hotmail.com>
wrote:

>Yeah - I already looked at that thread and dismissed it because I came
>across the same old posters talking about the same old subject as the
>last time I looked 4 months ago (tires).
>
>I took your advice, looked again and found some good info.
>
>Problem right now is that I have one more month on this trip and I'd
>like to do at least a temproary patch to hold me (well, hold the galley
>waste) until we get home.
>
>Cheers, Joe

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Grey water Black Tank Repair??
Date: Mon, 20 Mar 2006 17:58:31 -0500
Message-ID: <ticu12pde5fegd117im18pdq3243jcdf1u@4ax.com>

On Mon, 20 Mar 2006 09:18:18 -0700, Gio <giomedici@sumware.com> wrote:

> Neon John <no@never.com> wrote:
>
>>Like others have said, I'd be looking for warranty adjustment.  That
>>plastic should not be that brittle.  In the meantime....
>>
>>Slathering gunk onto an 8" long crack isn't going to work.  Here is a
>>commonly used industrial patch technique that will work here.
>>
>>You'll need some 1/2" plywood, enough toggle bolts to place one about
>>every inch and some 3M marine polyurethane caulk.  I believe the
>>number is 6500.  It will be listed as the maximum strength,
>>non-removeable version.  This is available at Wallyworld in the boat
>>department.
>>
>>Cut one or more strips of plywood to fit over the crack.......
>>
>>.....The marine caulk probably won't stick very well to the tank material,
>>particularly if it is polyethylene.  The combo of the toggle bolts and
>>the plywood makes a mechanically sound assembly.  The caulk doesn't
>>really have to stick, just fill in the gaps.
>
>I guess the key is a caulk that dries a little flexible and that fills
>voids well. And I think you saying that a urethane based caulk is more
>compatible than silicone with most plastic, (?)

It's not a compatibility issue but a strength one.  That tank bottom
move around as the tank fills and empties.  Silicone is so weak that
it would pull loose.  The urethane is VERY strong once it cures.
Urethane is also resistant to just about everything once cured.
Silicone isn't.

>Can you see any advantage or disadvantage to using one of the engine
>gasket/sealants, like Permatex?

Gasket sealers solidify by solvent evaporation.  That is, they lose
volume and shrink.  Not very good for gap filling.  Plus, with little
exposed surface area, solidifying would be very slow.

Urethane and RTV cure by catalytic reaction and partially by
evaporation in the case of Urethane.  In both cases, moisture from the
air triggers the reaction.  There is no volume loss with RTV and
almost no volume loss with urethane.

Cost and availability are almost identical for all the products
discussed so there is no reason not to use the proper material for the
job.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Grey water Black Tank Repair??
Date: Wed, 22 Mar 2006 00:39:33 -0500
Message-ID: <pnn12256mmiu56n0eoprn68no63an1m2ht@4ax.com>

On 21 Mar 2006 14:07:25 -0800, "joebedford" <i_mongo@hotmail.com>
wrote:

>Thanks for the input. I think I'm going to try something like you
>suggest. As it happens, we would have to turn handsprings to get our
>rig over to a repair shop at this time. I want to make a "repair" that
>will hold for at least a month, then when we get home I can take our
>rig to the dealer where we bought it and leave it for months if
>necessary (hopefully not).
>
>I spoke to the manufacturer today and they said that the tank is ABS.
>They recommended that I go to a local repair shop.
>
>I went to Tri-Am in Ocala and they recommended using a product called
>Meta-Lox. Here's a link to the manufacturer's site:
>
>http://www.chemsearch.com/productDetail.asp?pName=Meta%2DLox%3Csup%3E%3Csmall%3ETM
>
>Anybody know this product? It looks pretty much like JB Weld. Tri-Am
>said 8oz of parts A & B is about $60 but they'll sell me a couple of
>ounces for proportianately less.

Youch!!!!  That's expensive.  Since the tank is ABS, something like JB
Weld might stick.  I prefer an industrial maintenance epoxy make by
Dexter (now part of Loctite) that is sold at most every industrial
supply company around here.  Cost is in the sub-$10 range for two
large tubes.

You might want to check with the local car parts store that sells
bodywork supplies.  Many exterior parts on a car are ABS.  There are
some pretty good patch adhesives available for ABS.  The body on my
CitiCar electric (at least the original panels) are ABS.  I've had
good success on small defects with a 2-part patching material sold by
the local NAPA.  I use the Urethane supply plastic welding technique
on larger defects.

You might also test that 3m Marine Caulk for adhesion.  I think that
it will adhere strongly to ABS.  Even without my reinforcing technique
(meant primarily for polyethylene to which very few things stick) the
caulk should do the job.

I'd clean off a spot and try whatever adhesive you choose.  One trick
I use to aid adhesion is to drill some small holes around the defect.
This lets the adhesive of choice ooze through, form blobs on the other
side and form a mechanical bond.  Even if the adhesion is poor the
mechanical bond will hold it in place.

Another aid is to greatly roughen the surface where the adhesive will
go.  I've developed a technique using an electric engraving pen.  Turn
the pen up on max power and holding it loosely pointing AGAINST the
direction of travel, rake it across the material.  It should chatter
and bounce and leave a row of fairly deep and closely spaced pits.
Sweep the area around the defect as if you were painting with a very
narrow brush. You should end up with a fairly uniform field of pits.

The adhesive forms tiny little mechanical bonds in each pit,
especially the materials that expand slightly upon curing (the Dexter
stuff does.)  This covers a lot of sins of poor adhesion :-)

>
>I now think that the crack is at the edge of a molded in "reinforcing"
>curve in the bottom of the tank. While I like Neon John's technique, I
>don't think it will work going round a corner.

I don't think you'll need to do this since your tank is ABS but..
There is a modified technique for uneven surfaces.  That is, coat the
plywood with Bondo and lay it in place over the uneven surface so that
the highest surface squeezes out the Bondo thinly.  Let it cure.  It
probably won't stick at all but if it does, tap it loose.  Then drill
the holes, apply the marine caulk and screw it down.  The Bondo forms
a contour that perfectly fits the uneven surface.

John