Sealants for a cracked black tank made of LLDPE

[dwdanby]

I got this response from Forest River for my 2004 FR Cardinal 32ft fifth wheel:

"Our fresh water tanks and holding tanks are composed of “linear low density” polyethylene (LLDPE) material. The “linear” term refers to the polymerization of ethylene with longer-chain olefins. LLDPE is a thermoplastic resin, so it can be melted down and recycled."

I've got many answers here and elsewhere about sealants. So far the best / easiest looks to be FlexSeal paste. However, FlexSeal won't answer me about whether the paste will work on LLDPE. This is what they said:

"Please keep in mind that some rubber or plasticized materials can contain anywhere from 10% to 90% poly-olefins. A Poly-olefin is a type of polymer which by its very nature constantly releases chemicals that are designed to resist proper adhesion. Unfortunately, there is no way of knowing how much of this polymer is in a particular piece of rubber or plastic since manufacturers do not have to disclose this information."

The FR comment above mentions "longer-chain olefins."

Basically I'm very limited as to how I can fix the crack - I'm in no condition to work on it myself and have to rely on a handyman who's never worked on RVs. (The dealer says they won't touch it.) The FlexSeal paste plus wire mesh is something the handyman says he can do; drilling holes or widening the crack to apply sealant isn't an option.

Any suggestions welcome.

 

[NY_Dutch]

I would still recommend end drilling the crack to keep it from spreading before applying the sealer.

 

[Larry N.]

I would still recommend end drilling the crack to keep it from spreading before applying the sealer.

I'll agree with that. Stop Drilling cracks is standard practice, whether it be fiberglass, plexiglass or other plastic or composite material. The round shape of the drill hole (one at each end of the crack) relieves the stresses that cause the crack to spread further. It doesn't have to be a very big drill bit -- usually just slightly larger than the crack itself (width, not length), so 1/8" might be plenty.

 

[crawford 111]

yes drill to stop crack and before you seal it what ever you use ruff it up it wont stick to a smooth surface don't ask how I know LOL

 

[JayArr]

If you can't do this yourself and need to hire a handyman then I recommend that you replace the tank.

Patching things up with glue and stuff you bought at the hardware store is a good bet when there is no labour fee involved. A Saturday morning at Home Depot followed by a couple of hours working on your trailer or RV is not a lot to lose if it fails but when you start adding in paid labour it becomes a bad bet IMHO. What if you pay this guy for two hours and it doesn't work, what if it only seals for a few months or the crack reappears after a big bump on the road or what if he makes it worse?

Replaceing the whole tank would be about a four hour job on my trailer, cut the vent pipe, remove the toilet, disconnect from the dumping pipes and undo the clamp that holds it in the frame. If you have to pay for two hours to patch it then why not pay for four hours and get it done right.

 

[Isaac-1]

You may want to investigate plastic welding as fix for this problem

 

[boatbuilder]

There are companies that specialize in ultrasonic welding plastic tanks. You might do a search for one in your area. If you are near a marina you might ask them. Many kayaks and dinghies are made from the same type of material.

 

[Cameodon]

Drill it, put the flex seal to it, see what happens. If it doesn't hold you won't be out a great deal.

 

[Isaac-1]

I don't know about that if you intent to try plastic welding etc, cleaning off the failed flex seal could be a BIG pain

 

[IBTripping]

I don't trust any of the Flex products to last very long. No matter what glue or welding you decide to use, I'd suggest also covering it with Eternabond tape. It's awesome stuff.

 

[dabrooks]

Most black tanks are ABS. My friend had a crack in his black tank. His was ABS. We drilled both ends of the crack and made a paste up of shaving from cutting ABS pipe and ABS pipe sealant. We put a thin coat over the crack an put fiberglass mesh in the thin coat. After it set up we put 2 more coats of the paste over it, Four years later no leaks.

 

[NY_Dutch]

Most black tanks are ABS. My friend had a crack in his black tank. His was ABS. We drilled both ends of the crack and made a paste up of shaving from cutting ABS pipe and ABS pipe sealant. We put a thin coat over the crack an put fiberglass mesh in the thin coat. After it set up we put 2 more coats of the paste over it, Four years later no leaks.

According to Forest River, his black tank is made of linear low density polyethylene (LLDPE), not ABS.

 

[Cameodon]

I don't know about that if you intent to try plastic welding etc, cleaning off the failed flex seal could be a BIG pain

If the flex seal didn’t work I’d then replace the tank…it seems plastic weld must be pretty expensive. Don’t you have to remove the tank?
I’ve used flex seal and it’s pretty darn durably, I know others that have too.

 

[jubileee]

I’ve repaired many cracked abs, polyethylene, plastic, pvc metal tanks, totes, troughs, pipes and ect this way:
Drill holes each end of crack. Pop rivet holes shut. Screws will rust. I use aluminum or plastic pop rivets. Don’t pull until they pop, just pull snug and cut off.
Fiberglass the area with at least three layers of matting. Patch should be at least 3” from each side and end of crack if possible.
Wait 24 hours and fiberglass again with at least three layers of matting.
Wait a couple hours, cut off any whiskers, sand if needed, then paint area with fiberglass resin getting the resin an inch or so outside of matting if possible.

 

[Rene T]

I wonder if using a standard soldering gun would weld the crack shut that’s after drilling holes on the ends. Carefully melting the tank material and moving it over the crack.

 

[Isaac-1]

You generally need far more thermal control to properly weld plastic than is possibly with a soldering iron. The key is to get the plastic warm enough to melt and bond to itself, but not so hot as to burn and chemically change its properties. Unfortunately with many plastics this is a fairly narrow temperature range.

 

[Cameodon]

You generally need far more thermal control to properly weld plastic than is possibly with a soldering iron. The key is to get the plastic warm enough to melt and bond to itself, but not so hot as to burn and chemically change its properties. Unfortunately with many plastics this is a fairly narrow temperature range.

This is what I was wondering. Ive done a considerable amount of metal welding and same deal, temperatures is a very fine line. I used JB WELD on my tank on a very small hole

 

[whiteva]

I was successful using the following. Drill small relief holes on each end of crack. Sand area using 80 grit to rough up. Cut an aliminum patch 4 times the size of the crack. Use eternabond rolled (hand pressure roller) on the tank the same size as the aluminum patch (don't forget to remove the film after rolling) then drill and install patch using aluminum pop rivets or SS screws. This was only a two beer job 5 years ago. Just for grins, I checked it this morning because the tank needed dumping, still no sign of leaking.

Cheers

 

[Carbonation]

A new 49 gallon black tank is 220.
Maybe 3 hours of labor to drop and replace.
One and done.
I think you'll fight this over and over until just replacing the tank becomes the only option.

 

[dabrooks]

Most black tanks are ABS. My friend had a crack in his black tank. His was ABS. We drilled both ends of the crack and made a paste up of shaving from cutting ABS pipe and ABS pipe sealant. We put a thin coat over the crack an put fiberglass mesh in the thin coat. After it set up we put 2 more coats of the paste over it, Four years later no leaks.

I did find that I misspoke most black tanks are polyethylene not ABS.