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Old 09-17-2009, 07:09 PM   #1
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How-To: ABS Tank Crack Repair

This is the method I used to repair several large cracks in the black tank and dump pipe on my 2363. It has been approximately 18 months and 2,000 miles since the repair with no signs of trouble.

I did not take pictures of the process when I repaired the tank as it was very tight under there. To write this, I recreated the process with a small piece of ABS sheet material.

As long as you can reach and work in the area of the crack, you will not need to drop the tank.

The first thing to do is throughly clean the tank. I filled and dumped the tank several times to help clear any large "particles." I then used a wand through the toilet to flush the tank clean (exactly like many do when dumping). The tank was flushed until the water ran clear with absolutely no particles appearing (viewed through one of those clearview pipe extensions).

With the tank clean, I filled the tank with a mixture of bleach and water and left it sit several hours. The mixture of bleach and water used was about 2-3 times stronger than what is used to sanitize the fresh water system. Bleach is rough on the seals in the blade valve, so it is a good idea to replace the valve when the repair is complete. Since I was going to be laying under the tank working on it, I felt the $12 valve was better than a face full of unpleasant liquid. After draining the bleach mixture, I filled the tank with water and dumped it. At this point, I felt the tank was as clean as it was going to get.

With the tank clean, the next step is to dry it out completely. You do not want to have water running into the area of the repair, as this may prevent the repair from being sucessful. I found the best way to dry the tank was to open the drain gate valve with the cap off and leave it that way. Then I went inside, opened the toilet flush valve, and inserted a pipe fitting in the opening to keep the valve open. Obviously this should be done with the water off! I then placed a small fan on the toilet seat, blowing "up" to draw air through the tank and help it dry. There was NO foul odor due to the thorough cleaning with bleach. I found it took about a good 24 hours to get the tank dry in springtime conditions. This time will vary with temperature and humidity.

With the tank clean and dry we can move onto the repair itself. First, you need to identify the crack in the tank. To make things easier to see in pictures, I "drew" a crack onto a small piece of ABS sheet with a silver marker:

Once the crack has been identified, you want to "stop drill" the ends of the crack. You drill small holes at the ends of the crack(s), this relieves stress in the material and will prevent the crack from spreading. I also like to drill at the intersection where cracks meet or split:

The next step is to create a vee groove along the length of the crack and around the holes you just drilled. I do this using a dremel tool and a round grinding bit:

You want to create a V-shaped groove, approximately 3/16-1/4 wide along the length of the crack and around the holes you drilled. This increases surface area for the repair material to bond to, resulting in a strong repair. You do not want to penetrate the material when grooving it, aim for a groove about 75% of the depth of the material. When you are done, it should look something like this:

Next you will make your repair material. First you need to obtain BLACK ABS Cement. It MUST be the black cement. Black ABS cement is abs shavings dissolved in a solvent. This is the can you want, I purchased mine at Lowes in the plumbing department:

To make the repair material we will dissolve additional ABS into the cement. To do this, we need to create some ABS shavings to dissolve in the cement. I purchased an ABS pipe fitting ($1) from Lowes in the plumbing department to make shavings from. You want to make relatively fine shavings, so a file or rasp is a good tool to use. I use a rotary rasp and catch the shavings in a small plastic container.

This is the rasp I use:

and here's what the shavings should look like:

Raid the kitchen and obtain a small clean glass jar with a re-sealable lid. Find something with a nice wide mouth. A pickle jar works just perfect. Pour some of the Black ABS cement into the bottom of the jar, and slowly stir in some of the shavings you made. I use a paint stirring stick to mix it, something metal is also fine. Do NOT use anything plastic to mix this, as the solvent in the cement will dissolve it as well.

As you add the shavings, keep stirring. You will notice that they quickly dissolve into the liquid cement, causing it to thicken. We are shooting for something around the consistency of pancake batter. You don't want to go for a "paste" as that would be too light on solvent and would not flow into the nooks and crannies. At the same time, you do not want to go too thin, as it will lack the ability to "fill" the repair area, and it will not stay where you put it. That's really bad when you are working upside-down.

When you have the consistency of pancake batter, you are good to go. You should have a nice bottle of goop that looks something like this (I used a very small jar for this example):

Now grab some Acetone:

Fold up a paper towel and wet it with the acetone. You want to clean the area to be repaired with the acetone. As you clean, you will see the plastic start to "melt" a little bit. The paper towel will turn black and the "sheen" of the plastic will change:

With the area cleaned, you can now begin applying your repair material. I use a flux brush (some people call this an acid brush):

Using the brush, "dab" the repair material into the groove you created earlier. Do not try to "brush" it on as that will just create plastic strings and will not give you an adequate fill. You want to apply several thin coats the entire length of the crack, giving about 24 hours of cure time between coats. Each day, before applying an additonal coat, check thre previous coat to ensure it has cured. It should be fairly hard. Before applying another coat, re-clean the area with the acetone on a paper towel.

You do not want to try to fill the entire depth of the groove in one shot! Shallow coats allows the solvent to evaporate, leaving you with a hard ABS repair.

With the repair material applied and still "wet", it will look something like this:

I needed three thin "coats" to fill the repair on my tank. The last coat should be applied a little wider than the groove, and a little higher than the surrounding area. Be sure to cap your repair material when it's not in use, it dries out quickly. I throw out the flux brush after each application, it's not worth trying to clean them.

When you are done filling, give the repair a few days to cure nice and hard before putting water in the tank.

That's all there is to it. Good luck!

- Frank

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Old 09-17-2009, 07:28 PM   #2
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Awesome pics and description! Thank you for sharing this!

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Old 09-17-2009, 08:09 PM   #3
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Very impressive Frank.

Thank you so much for putting this together. This method seems sound. Your directions were very clear. I do believe I am going to try this as soon as I can get the camper rolling again to drain it at the dump staion.

Great Job
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Old 09-17-2009, 08:14 PM   #4
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Very nicely done, Frank! This is a keeper!

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Old 09-17-2009, 09:35 PM   #5
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Happy to be of assistance. Hopefully this will help somebody out of a jam.

It's not a difficult job, it's just creepy laying under that tank when you know what was in it...
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Old 09-17-2009, 10:31 PM   #6
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GREAT job! These how to posts with pics go a long way.


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Old 06-13-2016, 06:32 PM   #7
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Thank you sir! I will be making a repair using these directions within the next week or so!
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Old 06-14-2016, 06:10 AM   #8
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Nice job I would like to add a couple of things. The method of supporting the pipes at least on mine left a lot to be desired it was a multi hole strap that some where over the years had rotted away so the pipes basically on their own. Some one had repaired the small leak with bondo (body filler) so the mess is stuff I did not bother to grind off as it had no relation to the leak. The wood blocks are pressure treated deck board I really did not want that stuff to move around I'm sure that is what broke it in the first place as both valves were just hanging from the black tank. One other suggestion tilt the camper to one side so the water runs to the back of the tank either with the jacks or driving it up on blocks.
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Old 06-14-2016, 05:14 PM   #9
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Might try this. My new 1984 camper has a crack where black tank drains. Previous owner put some black leak sealer.
I've done something similar with repairing my Apache hard sides Popup. Except we use bits of abs and MEK. Mek melts the abs and you paint some MEK on like you did with the acetone soften it. Could I do a tan repair have some left in a jar
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Old 06-18-2016, 11:07 AM   #10
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My strap is broken so I need to otherwise support it too like mainah was saying.

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