How to patch an RV black tank crack

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dwdanby

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Apr 15, 2020
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Hello all! I have a 2004 Forest River Cardinal 32ft fifth wheel with a crack in the black tank, we took off the metal sheeting and we can see it, maybe 5"-6" long or so, and the water is coming through it pretty strong. It's in the side of the tank. The only dealership we can get to doesn't handle hazmat and won't replace it for us. At the moment we've exhausted every avenue and our only option is to try to patch it ourselves. When we asked about what we should use to patch it, the dealer said the tank is made of "some kind of molded plastic." That was all the advice they would give. The best we can think of is Flexseal tape. Does anyone know in more detail what the tank is made of, and what would work best to patch it?
 

donn

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There are a bunch of youtube videos about fixing plastic. But sadly black tanks I believe are made of polyurethane and not repairable. Patching materials dont hold well either. Find a Forest River dealer, they should be able to order a new tank for you. Drop the thermoplastic underbelly and insulation and drop the tank. If its empty is wont be very heavy. A piece of plywood and a floor jack should make it a one person job.
 

Henry J Fate

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If access permits, using some JB Weld on a prepared crack then covered with an oversized plate using original GE silicone over the crack and all under the plate using sheet metal screws that screw into the tank wall will work. Drill clearance holes in the plate and a tiny pilot hole in the tank for each screw to help prevent additional cracking. Offset the end screws off the centerline of the crack. That will work if the workmanship is very good.

The problem with patching tanks is that tanks flex. Especially during a dump. As tanks get older the plastics become brittle and becoming more likely to crack.

Prepping the crack for the apoxy is of a high priority for success. The area covered by the plate should also be prepped well so that the silicone bonds properly.
 
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JayArr

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Jun 13, 2020
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Mission British Columbia Canada
The trick is keeping the crack from re-opening.

Eastwood Tools sells a plastic repair tool that allows you to embed hot metal staples into plastic. You may want to look at that as a way to keep it from re-opening. The tank isn't pressurized so actually sealing the crack isn't a tough job, just keeping it from re-opening.

 

Rene T

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Farmington NH
If access permits, using some JB Weld on a prepared crack then covered with an oversized plate using original GE silicone over the crack and all under the plate using sheet metal screws that screw into the tank wall will work. Drill clearance holes in the plate and a tiny pilot hole in the tank for each screw to help prevent additional cracking. Offset the end screws off the centerline of the crack. That will work if the workmanship is very good.

The problem with patching tanks is that tanks flex. Especially during a dump. As tanks get older the plastics become brittle and becoming more likely to crack.

Prepping the crack for the apoxy is of a high priority for success. The area covered by the plate should also be prepped well so that the silicone bonds properly.
Henry, what do you think about drilling a smal hole at each end of the crack which may help it to not extend any further?
 

Henry J Fate

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Henry, what do you think about drilling a smal hole at each end of the crack which may help it to not extend any further?

Drilling holes at each end and installing staples before the JB Weld are good suggestions.

I would also V groove the crack to give the apoxy some depth.
 
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NY_Dutch

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Where our wheels take us!
I've done a few field repairs on black and grey tank cracks over the years by end drilling the crack, sanding the area around it, stuffing the crack with silicone sealer, and covering the area with Eternabond tape. Some of those repairs were still holding years later.
 

ChasA

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Mar 21, 2009
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There are plastic welding services and supplies. Google is your friend.
 
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