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Thread: reason for using primer on PVC joints

  1. #1
    Home Handyman kskier's Avatar
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    Default reason for using primer on PVC joints

    Why is it necessary to use primer when gluing PVC joints? Wouldn't glue alone be enough?

  2. #2
    DIY scratch-pad engineer leejosepho's Avatar
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    Cleaning -- my can says "Cleaner" -- is essential for removing dirt, dust, oils and so on just like using a surface cleaner and tack rag before spraying paint so it will stick. Beyond that, however, I believe cleaner/primer actually removes some kind of protective surface coating that has been intentionally applied to the pipe during manufacturing. I think it is the black ABS pipe that does not actually need a cleaner prior to cementing, and I vaguely recall the arguments that took place when people were first told PVC is different.

  3. #3
    Plumber Cass's Avatar
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    Joining PVC is considered call solvent welding.

    You are making 2 pieces of PVC 1.

    The job of the primer is to soften the PVC so when you apply the "glue" it will cause the 2 pieces to combine on a molecular level so the 2 are now 1.

    Years back we used to do whole houses not using any primer, then we started using it, then the purple primer was required. The purple primer was a disaster as it would not allow the joints to set right and they would pull apart minutes later sometimes. Then they went away from that and back to regular primer.

    Joints made with out primer could be easily taken apart with a hammer and flat head screw driver

  4. #4
    Plumber jimbo's Avatar
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    Cass is exactly right. Primer presoftens the surface. If you "feel" a piece of pipe after the primer, you feel that it is different. Not mushy soft, but different. It then allows the cement itself to penetrate deeper. A joint will weld without primer, but will be less strong.

    The reason ABS pipe is glues without primer is that most ABS is cellular core. The solid outer layer is very thin. This is the reason that we can change a toilet flange on ABS easily, because you can slice and pry it off. This is much dicier on PBC.

    The so-called "hot" PVC cements probably have a stronger solvent. They are quite useful in irrigation work. Not sure if the inspectors allow them inside the house.

  5. #5

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    thanks,,,,,,,,,,,,I guess like in all things,,,,,,,doing it half way,,,,,,,,maybe faster,,,,,but in the long run the right way is better............

  6. #6

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    The difference is easily observable in sprinkler systems done with PVC. I've often seen glued-only joints come apart underground, especially a tee with a sprinkler riser on it.

  7. #7

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    I think Lee was right. The cleaner and primer are the same thing. They call it it a primer, because they know most of us are too lazy to use a cleaner. They have the same ingredients. They add the purple dye so the inspectors know the PVC was cleaned (primed).

    Furthermore, If you look at the ingredients in the cement, you'll find that the solvents in the cement are exactly the same as the solvents in the primer. Therefore, any softening of the PVC will occur when just using the cement. Perhaps the primer is needed because the code-enforcers don't trust us to put the cement on correctly, and therefore the surface wouldn't be primed correctly. So, the extra step was needed (or 2 extra steps if you clean then prime then glue).
    Last edited by Verdeboy; 12-08-2007 at 10:07 AM.

  8. #8
    Master Plumber master plumber mark's Avatar
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    Talking Primer vs glue.....which one gives the better buzz???

    I only use primer on the pressure cpvc water systems...

    I never use primer on my sch 40 pvc. drains
    its really not necessary..
    only when I have to....

    the primer is just too nasty to keep around on
    many jobs and willl eat through a vinyl
    floor in seconds....

    The primer is much nastier to deal with as far as inhaleing it all day long....

    you dont realize just how messed up you can get on that stuff if you are not careful




    .

  9. #9
    Moderator & Master Plumber hj's Avatar
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    Default pvc

    Primer/cleaner cuts through the glaze on the pipe's surface and creates a "matte/rough" finish that the glue can adhere to better.

  10. #10

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    We all agree with that. But given the fact that the primer and the cement are in the same can, why do you think it is necessary to prime twice, or 3 times if you use the cleaner?

  11. #11
    Consultant cwhyu2's Avatar
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    Because it is requiered in some jurisdictions.

  12. #12

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    A cynical person might think that there's a conspiracy between the manufacturers and the code-enforcers to simply sell more product. The flooring companies may even be in on it, since MPM has proven that the cleaner/primer ruins floors, as well.

  13. #13
    Plumber Cass's Avatar
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    The concentration of the primer when applied to the pipe is 100% and it quickly and deeply penetrates and softens the PVC.

    The solvent, although in the glue will not penetrate as deeply as the primer, thus not giving as strong of a weld as it would be if you used the primer first.

  14. #14
    Forum Admin, Expert Plumber Terry's Avatar
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    A cynical person might think that there's a conspiracy between the manufacturers and the code-enforcers to simply sell more product.
    When gluing pressure joints, the last thing you want to do is go back and dig the joint up.

    Someone is always paying for my time to do it right the first time.
    Nobody pays me to go back and fix a mistake.
    Last edited by Terry; 12-08-2007 at 11:42 AM.

  15. #15
    DIY Senior Member construct30's Avatar
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    They make the purple primer, required in some areas so inspectors know you used it.

    We have some heating guys that don't like to use primer and I have fixed a lot of their leaks on direct vents and furnace drains. I always use primer and never have leaks, Terry is totally right, why ask for trouble.

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