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Retired Moderator
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Discussion Starter · #1 ·
on any plastic fittings do you use pipe dope or tape? I have always been told not to use pipe dope on plastic as this lubricated the threads and will cause the fitting to go too far and crack.
 

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You are right, however, I always apply pipe dope on top of tape, even on plastic threads, never had a leak.
 

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You will find using the thicker of the tapes will give you a knowing feeling you won't have a leak. That white thin crap, is just that, crap.
 

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Discussion Starter · #6 ·
so you never had a problem with the pipe dope acting as a lubricant to the threads on plastic? I had one that cracked, could had been me tightening too tight. Or a bad fitting. I thought maybe the dope made it hard for me to feel just how much pressure i was applying. Noe any metal threads, yes, I use both. Just not on plastic, tape only.
 

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You don't want to use just dope on plastic alone, threads get to slick and will cause you to over tighten and not know it, I use very little dope on top of the tape with plastic threads. You can use just tape and it will seal just as good, I have just cone accustom to use both no matter with.
 

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Professional Bullshioter
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Megaloc gets hard as concrete after about a week. Any vibration and I think you will have problems. I use the white permatex teflon dope. Good stuff and stays pliable. My teacher forever ago told me NOT to use tape on plastic threads due to the fact it goes in so easy , it's easy to overtighten. I look more at the number of threads showing instead of the feel on plastic. I had an engineer one time that made us have 3 threads showing when it was made up or redo it.:blink:

I have had superb luck letting the dope set a while before putting the pressure test on it. That and getting every bit of cutting oil off the pipe after threading. I use PVC primer to clean my steel pipe cut threads. Dope sticks much better.
 

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waterheaterzone.com
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Megaloc gets hard as concrete after about a week.
No it doesn't. It is a soft compound like teflon paste, You must be thinking of something else.

Multi-purpose thread sealant made with DuPontTMKEVLAR®for use on
metals including steel, stainless steel, brass, copper, aluminum, and on
plastics including PVC, CPVC and ABS.Leak-free joints can be tested
and put into service at once.MEGALOC wipes clean from hands and
tools with a dry rag, is odor-free, grit-free, and will not separate or
settle.MEGALOC does not harden, crack or become brittle;joints can
be disassembled without damage to pipe, fittings, or threads years
after the joint was made.

MEGALOC is applied easily with a natural bristle brush even at
temperatures as low as -25°F, and performs over a temperature range
of -50°F to +400°F.It provides leak-proof hydraulic resistance to 12,000
psi and withstands gas pressure up to 2,600 psi.MEGALOCis
non-toxic, non-hazardous, and non-flammable.It contains no lead,
heavy metals, or volatile solvents.
You are thinking of BLUE BLOCK maybe? I hate that stuff, is gets hard as rock.
 

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I use only megaloc
 

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J. McCabe Plumbing Inc.
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"so you never had a problem with the pipe dope acting as a lubricant to the threads on plastic?"

Sorry, I didn't read that you were asking about pipe dope on plastic.

Rectorseal #5 says never to use it on plastic, it breaks down the polymers in the plastic and makes it brittle.

You need to read the label, or have you wife read it to you (jus kiddin), on all pipe dope to find out what it "should never" be used on.

Teflon pipe dopes, like rectorseal #100, are ok for plastics.
 

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Professional Bullshioter
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No it doesn't. It is a soft compound like teflon paste, You must be thinking of something else.

You are thinking of BLUE BLOCK maybe? I hate that stuff, is gets hard as rock.
Yup, that's the stuff. Bout 5 yeaars ago I used it for a year. Had trouble with it. And it did get uber hard. Maybe they changed the make up of it since. I love how the can says easy clean up:laughing: I got pants with that crap still on em.
 

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I use rector-seal for my gas work.Sometimes I just use the thick yellow gas tape[if new pipe and fittings].
I avoid pipe-dope on plastic threads though tape makes it easier to cross thread.I think now though there are plenty of pastes that won't break down plastics or nylons.
For other NPT type threads,white or blue paste with teflon seems fine.
 
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