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Thread: “Ungluing” PVC held together by silicone caulk

  1. #1

    “Ungluing” PVC held together by silicone caulk

    I recently got a Clearvue cyclone from Craigslist which came with a bunch of 6” PVC pipe fittings that were connected together using silicone caulk. I want to salvage as much as I can. I’ve tried a heat gun, a knife, and 99% isopropyl alcohol but I can’t get the pieces to separate. I can be more aggressive with any of these methods but I thought I’d ask if anyone has had experience with this. My best idea is to cut the internal connecting pieces into quarters and pry them out using alcohol or mineral spirits to get the residual caulk off. I’m open to any/all suggestions. Thanks.
    Larry

  2. #2
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    A quick google search suggests WD40 https://wd40.co.uk/tips-and-tricks/h...move-silicone/

  3. #3
    My first reaction was acetone. It dissolves silicone. But of course it will probably weld the PVC together...

    Tony
    Last edited by Tony Latham; 10-25-2020 at 12:24 PM. Reason: Bad info.

  4. #4
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    For normal pvc glue you heat up the male section until soft enough to drag out with channel locks. Takes a good heat gun. Then before the female end cools, take a new piece and twirl around in it to make it round.

  5. #5
    Sectioning it as you describe is probably the best way to get it to release. Before spending the time with solvents see if sectioning the inside pipe allows you to get a screwdriver or chisel to pop a section. If you are successful in saving some or all and you can scrape out the residue. I think on reassembly I'd use 3 screws per joint and only do a bead of caulk on the face of the joint as a seal. That will give you the greatest flexibility going forward.

  6. #6
    In case anyone comes to this in the future the easiest way I found was to make a single longitudinal cut into the male pvc. This allowed me to curl the male section which peeled it away from the female connection. Neither WD40 nor alcohol would get in far enough to release the silicone that was acting like a glue. I used my multi tool to make the cuts. Took 30-60 seconds for each piece of pvc.

  7. #7
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    That is good advice. I have all PVC piping and when put together have no leaks. I did not see any need for a sealant. I have used either Gorilla Tape or sheet metal screws for a mechanical connection. I find the a couple of #8 x 3/4" sheet metal screws work the best for me.

  8. #8
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    There is no solvent for cured silicone. The heat method mentioned may be your best option that will then be followed by lots of post cleanup. We use to break down solvent welded PVC in a pinch with a torch heating the pipe from inside but its a nasty process because if you heat the pipe slowly enough not to scorch it and catch it on fire the hub/socket its connected to winds up hot enough that its pretty much destroyed in the process. So you have to torch the pipe/fitting stub hard and fast with the torch to break the solvent weld and tear it out quickly trying not to put a ton of heat into the socket.
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  9. #9
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    Quote Originally Posted by Mark Bolton View Post
    There is no solvent for cured silicone. The heat method mentioned may be your best option that will then be followed by lots of post cleanup. We use to break down solvent welded PVC in a pinch with a torch heating the pipe from inside but its a nasty process because if you heat the pipe slowly enough not to scorch it and catch it on fire the hub/socket its connected to winds up hot enough that its pretty much destroyed in the process. So you have to torch the pipe/fitting stub hard and fast with the torch to break the solvent weld and tear it out quickly trying not to put a ton of heat into the socket.
    Well, not that can be handled without the assistance of a full hazmat team. Seriously nasty stuff.

    There are products that work to loosen the bond between cured silicone & the substrate, but they still require lots of scrubbing & don't really work that well.

    WD40 or acetone won't do anything but make a mess.

    I've had to do this more times than I remember & have had good success with cutting off the pipe, cutting a slit to split it within the fitting, and then using a heat gun to gently get things to a flexible stage. At that point it's not too hard to peel the pipe out of the fitting. The trick is to apply enough heat to make the inside pipe flexible enough, but not for the fitting to melt to the point of losing its form. Like Mark said, try to get most of the heat to the stub of pipe in the fitting. A wet rag wrapped around the outside of the fitting help to keep it cooler. This method works for ABS pipe & fittings as well.

    It would be easy to do if it was glued with silicon sealant because it doesn't stick to PVC all that well.

  10. #10
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    Hmmm, I put together all my plastic DC ducting with caulking (don't recall exactly what) but I only used it to seal the joint AFTER putting the pipe/fitting together DRY. The caulk was used to air seal the joint. If necessary, I would then drive a small screw to lock the pipe and fitting together. Taking them apart was simple and pretty easy by backing the screw out and using a utility knife to slice away at the caulk.

    Are you saying that the whole pipe and fitting were 'smeared' with silicone and then joined?
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  11. #11
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    I too was wondering why the joint would be 'glued' with silicone. PVC fittings are a taper fit & will seal well enough for dust collection without sealant or glue. If there is a leak due to a bad fit, then a little bead of caulking around the shoulder of the fitting will fix that.

  12. #12
    Silicone was liberally applied throughout the joint. This was in a pro shop and used for years. My guess is it Wasn’t intended to ever be separated. It was free and those fittings aren’t cheap so I figured why not. I’ve just made small cuts and have scraped off the excess silicone.

  13. #13
    Quote Originally Posted by Larry A Miller View Post
    Silicone was liberally applied throughout the joint. This was in a pro shop and used for years. My guess is it Wasn’t intended to ever be separated. It was free and those fittings aren’t cheap so I figured why not. I’ve just made small cuts and have scraped off the excess silicone.
    Bizarre they would go through so much effort to join the pipes with silicone, which can't be easy to do since the taper in the joint would tend to cause the joint to creep apart over the several hours it takes the silicone to cure, when you can buy actual PVC pipe glue made for gluing PVC pipes that cures in 30 seconds after putting on the fitting.

    I guess it never ceases to amaze me how much effort people will put into doing things incorrectly. Not to mention you would think a pro shop with insurance requirements would use correct metal pipe and fittings made for dust collection, rather than cobbling together DWV pipe and fittings.

  14. #14
    Andrew, if it was DWV fittings it would be easier to separate. If it is normal sch 40 deep well fittings it would be more difficult in both assembly and now for Larry. The original user may have use a bit of silicone as a lubricant to help assemble the joints rather than as a seal. Kind of a twofer. Dry assembly of 6” pipe is difficult if you want full make up.

  15. #15
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    If you have a vise large enough to hold the pipe or fittings, apply heat with a heat gun and wrestle them apart, this WILL NOT be fun but can be done. Also score the outside of the joint with a razor knife will help.

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