# Metal to Plastic Connections?



## DemRem (Apr 21, 2012)

Metal to plastic connections (like M Pex fitting to F CPVC threads and vise versa) make me nervous sometimes.

Haven't done many of them and I've always been able to get them sealed eventually, but sometimes it seems like the sealing is too difficult for comfort.

What are you guys using on these?

Currently I wrap with tape then dope it. However, I was thinking I need to go with higher quality sealant. Like rectorseal and blue monster tape. I also thought it would be a good idea to work the dope into both male and female threads since it seems like if you only coat one or the other it leaves air pockets that water can sometimes travel up (hope that makes sense)


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## Inner10 (Mar 12, 2009)

It's an all around bad idea to thread a metal male fitting into a female plastic. IPS fittings with dissimilar materials in general are a bad idea. There are proper pex to CPVC premade fittings you can use.


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## DemRem (Apr 21, 2012)

Inner10 said:


> It's an all around bad idea to thread a metal male fitting into a female plastic. IPS fittings with dissimilar materials in general are a bad idea. There are proper pex to CPVC premade fittings you can use.


That is a much better fitting!

But still curious what is the absolute best way to do it if you have to (was reading something a while ago about some guy working with pool systems that was dealing with metal to plastic fittings and it got me thinking)


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## Inner10 (Mar 12, 2009)

DemRem said:


> That is a much better fitting!
> 
> But still curious what is the absolute best way to do it if you have to (was reading something a while ago about some guy working with pool systems that was dealing with metal to plastic fittings and it got me thinking)


Besides not doing it I'd dope it to lubricate the connection to reduce stress on the plastic as much as possible.


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## rex (Jul 2, 2007)

I'd sharkbite that b!tch.

I won't glue PVC for water in a repair situation. I mean I probably would if I had to but, try not to.


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## MarkJames (Nov 25, 2012)

DemRem said:


> Metal to plastic connections (like M Pex fitting to F CPVC threads and vise versa) make me nervous sometimes.
> 
> Haven't done many of them and I've always been able to get them sealed eventually, but sometimes it seems like the sealing is too difficult for comfort.
> 
> ...


I'm thinking he might be running cpvc to a mixing valve, or something like that. I had a helluva time doing that with all-plastic male fittings, and then I found those combo fittings ( Fergusen had them, I think) with metal male end fused to plastic female end (the glue end for the cpvc). That allows you to crank the heck out of it to get it tight enough. I couldn't do with an all-plastic fitting since I'd usually strip the "nut" before it got tight enough.


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## TimelessQuality (Sep 23, 2007)

??


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## MarkJames (Nov 25, 2012)

Yup, that's the one. Thanks.


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## tyb525 (Feb 26, 2013)

You can't tighten the plastic as much as you think you need to, it's so easy to get it too tight, which deforms the fittings causing a leak. Also pipe dope is better to use than tape on plastic (imo) because it is not as thick and allows you to screw it in farther without deformation., and make sure it is the white stuff compatible with plastic, the gray stuff is not.

It is also a good idea to screw in a metal fitting before the plastic, this can help eliminate burrs that can cut plastic.

All said in my non-plumbing licensed opinion (however my boss is licensed and he taught me...)


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## Oconomowoc (Oct 13, 2011)

You want to transition by first using a Sharkbite, then shove in some PEX followed by a MIP to Pro Press adapter backed up by a galvanized union which is converted in to a lead wiped joint using a McDonald fitting. From here, you want to use a compression coupling FIP.


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## Gary H (Dec 10, 2008)

Oconomowoc said:


> You want to transition by first using a Sharkbite, then shove in some PEX followed by a MIP to Pro Press adapter backed up by a galvanized union which is converted in to a lead wiped joint using a McDonald fitting. From here, you want to use a compression coupling FIP.


Could a Taco Bell fitting be used instead of a McDonald ?


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## Oconomowoc (Oct 13, 2011)

Gary H said:


> Could a Taco Bell fitting be used instead of a McDonald ?


Possibly, but it has to be a left hand fitting.


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## tyb525 (Feb 26, 2013)

Sounds like a few conversations I've overheard at blowes..


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## KillerToiletSpider (May 27, 2007)

Oconomowoc said:


> You want to transition by first using a Sharkbite, then shove in some PEX followed by a MIP to Pro Press adapter backed up by a galvanized union which is converted in to a lead wiped joint using a McDonald fitting. From here, you want to use a compression coupling FIP.


The wiped lead joint has to be before the galvanized union, not after, to prevent galvanic corrosion.


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## plummen (Jan 9, 2010)

Gary H said:


> Could a Taco Bell fitting be used instead of a McDonald ?


I had one of those chicken soft fittings from taco hell last week,It tasted like nasty tuna fish out of a can and gave my stomachthe cpvc's!:laughing:


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