Gray water holding tank leaks through crack

Here's what I ended up doing. ABS cement is 70% MEK and 30% acetone and ABS plastic. I swabbed the whole center rib with MEK. It cleaned it up well and my thought was that the MEK would seep into the crack and bond the crack. Then I put 1 layer of ABS cement over in along the whole valley. Remember ABS cement is ABS disolved in solvent. My tests showed that it builds up a permanently bonded layer when applied to ABS plastic. I then split a piece of the drywall reinforcement mesh in 2. This was exactly the right width to cover the valley where the crack was. I then applied 2 layers of ABS cement waiting 12 hours or more between layers. I put on another layer of mesh and then 3 more layers of ABS cement. My thought is that the mesh was not needed for strenght but I needed it to ensure that I was getting an even thickness of the ABS and no thin spots. Working upside down, gravity is not on our side here.

I just filled the tank with water and no leaks. It does go through a lot of flexing in the process. I will definately update this post if I run into any problems with this process. I'm sure it would work on bigger cracks than mine and even open gaps. The mesh allows you to bridge gaps.

BTW, I discovered that there is a potential problem using the 2 part epoxy puddy to seal the tank. The epoxy will expand differently than the ABS Tank across temperature changes and eventually create a leak. ABS on ABS seems to be the answer.

[Brightsu]

My husband just repaired a crack in our clear water tank, it did great he went to advance
auto and purchased a fiberglass kit, he said the important thing is to drill 3/16 hole on each side of the crack to keep it from cracking more, it was messy but did a beautiful job.

[Wavery]

Originally Posted by Brightsu

My husband just repaired a crack in our clear water tank, it did great he went to advance
auto and purchased a fiberglass kit, he said the important thing is to drill 3/16 hole on each side of the crack to keep it from cracking more, it was messy but did a beautiful job.

The fresh water tank is a whole different issue. That tank is made of Polyethylene plastic. I have found no product that will successfully stick to Polyethylene plastic over time (although some products make this claim). It's sorta like trying to glue something to a wax candle.

The proper repair for Polyethylene plastic is plastic welding, using Polyethylene plastic welding rod.

There is a very good chance that the F/G patch that you put on that tank will fail. If you can grab a corner of the F/G patch and pull on it, it will probably pull right off.

If I were you, I would not tow with water in that tank. The water pressure and sloshing will increase the stress on the patch and cause it to fail sooner.

I wanted to follow up with an update on my original problem and repair using ABS cement layered with fiberglass strip. This held for a while. Eventually I tested it with a full tank including a few inches of water in the tub. This caused it to fail due to the extensive sagging in the tank when it was full. So, I put on another 5 layers of ABS with 3 layers of fiberglass mesh strips in between. I added a U-bracket brace that extend from one side of the frame to the other to prevent the tank from sagging when full. On the one side, you have to bend it around the tank to get to the frame. This system has been worked well including testing it with full tank.

BTW on the polyethylene tank. Or, it might be polypropylene... There is a way to get adhesives to stick. Ever wonder how those labels stick so well to plastic shampoo and detergent bottles? The plastic is flame treated. This changes the surface chemistry. You actually pass a propane torch flame over the plastic. Just don't leave it there too long. It's the flame that changes it, not the heat. You can see the change if you put some water on the surface. Before flame treatment, it will bead up. After, it will stick and wet the surface. Try it on an old frisbee before trying on a freshwater tank. Although, plastic welding would be best and is more a more conventional repair.

[Bill]

Well I'll be darned! Flame-treating polyethylene to aid adhesion? I never heard of that! But Google brings up a huge number of seemingly-reliable sources (as opposed to "my brother-in-law's-cousin-says" anecdotes ...) that seem to confirm this.

Several years ago, our member BobRederick tried plastic welding, with some, but limited, success. Flame treating sounds like it might be a good alternative.

Thanks

Bill