# Forum Home Renovation Plumbing  Joining PVC into clay pipes

## wattlebloke

Ive read a few threads on this topic, and wanted to run a new idea past the brains trust...Im going to join 90mm pvc into an eartherware collar: Can I just slip it inside and use expanding foam to seal the joint?

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## plum

No.

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## wattlebloke

Oh? My thinking was that waterproof expanding foam takes the place of cement? It’s a downpipe going into the top end of a stormwater drain...

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## commodorenut

There are correct flexi couplings to use. 
One tip my plumber showed me when we redid the sewer from clay to 100mm DWV  (I was his labour) was wrapping some copper wire around the PVC pipe beside the collar - apparently it deters tree roots from trying to get in. 
EDIT: Just saw your new post after I'd written mine.  All my old stormwater is like that - downpipes concreted into clay collars.  This is still an acceptable method for rectangular metal, but not sure about round poly.  Expanding foam isn't though....

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## Bluesrule

Your idea would certainly not be an acceptable way for a plumber to seal the joint.  However, it certainly could work. 
My previous place had been designed so that the downpipe was situated over the clay stormwater pipe but with a grate over the clay pipe.  This meant that any leaves, etc that went into the downpipe did not block the downpipe.  Worked a treat.  Worst case scenario was that some water may miss the pipe in a heavy downpour but that never caused any problems.  Made it very easy to ensure there were no blocked downpipes.  The house also had a "new" extension  with sealed downpipes and they regularly blocked with leaves so I know what connection I prefer.  What this shows, however, is that the sealed connection between downpipe and stormwater pipe isn't all that important in its own right.  All you are really trying to do is seal the connection so that vermin or other items cannot get into the drains. 
Getting back to the use of expanding filler - while it may work it has a number of disadvantages:
-  the filler can expand more than expected and block or partially block the connection.
-  filler is not UV stable and will break down over time.
-  the expanding foam is quite expensive. 
Making a mortar mix is quite easy and very much cheaper than the expanding foam.  Even if you have to buy way more mortar mix ingredients than you need for the job it will still be considerably cheaper than one can of expanding foam.

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## wattlebloke

Thanks for those well-considered replies Bluesrule and Commodorenut. I happen to have a heap of copper wire available to use as a root deterrent! And yes, a box collector drain thing is a far smarter idea than plumbing strait into the stormwater in this situation.

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## bluehorse

Having a bit of a look at this sort of thing and in my travels found flexseal coupling interesting.

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## pharmaboy2

Flexible couplings from your local plumbers supply.  Easier, won’t require redoing, done to a standard

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## Bros

Those flexible couplings look like the ones on my toilet. I have found over time they crack and start to leak.

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## r3nov8or

> Those flexible couplings look like the ones on my toilet. I have found over time they crack and start to leak.

  I think that underground they are fine. Toilet applications get a lifetime of harsh cleaning chemicals, air freshener chemicals and minor levels of UV constantly, affecting the rubber over time

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## commodorenut

Those collars are generally made from EPDM.  That's exactly what my plumber used to connect clay to plastic.  
EPDM is fine underground - and with constant exposure to water.  
Most tap o-rings are EPDM, and commercial water treatment plants specify it too (in a potable water approved material compound).
In fact, EPDM is one of the best synthetic rubber products available for this, as it's also got a good resistance to ozone & UV, so it can be used in exposed outdoor applications too. 
EPDM's nemesis is mineral based oils & solvents, hydrocarbons, and acids.  So if someone uses vinegar as a cleaning agent, it will eventually cause problems with the EPDM.  Some cleaning chemicals are also acidic, or have hydrocarbons in them - so as r3nov8or mentioned, this is another potential cause of failure. 
Plumbing fittings such as sharkbite and the likes use EPDM O-rings an offer a 25 year guarantee - that's how confident they are with the material.  
The military are more conservative - depending on the standard followed, they give it up to a 15 year shelf life (service life is different though, often far longer).

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