All Replies on Redoing my dust collection pipes

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View scottfl's profile

Redoing my dust collection pipes

by scottfl
posted 08-16-2017 10:48 PM

19 replies so far

View Redoak49's profile


4867 posts in 2836 days

#1 posted 08-16-2017 11:48 PM

I can not help you but that is the reason I used Gorilla Tape.

View fivecodys's profile


1647 posts in 2483 days

#2 posted 08-16-2017 11:52 PM

Maybe a heat gun to soften the joint?
That is really a tough one.

-- A bad day woodworking is still better than a good day working.

View jmos's profile


917 posts in 3217 days

#3 posted 08-17-2017 12:14 AM

I wish I had a solution for you, but I think cutting my be your only bet. I’ll second Chem, heat may work.

My system is thin walled 6” PVC (ASTM-2729?) and I put in a couple of self tapping screws at each joint. The joints are really tight and it’s easy to reconfigure when needed. Just a thought for the reassembly.

Good luck!

-- John

View JBrow's profile


1368 posts in 1767 days

#4 posted 08-17-2017 12:41 AM


Since I have not dealt with the problem of disabling a joint held together with silicone caulk, I can only guess as to how to disengage the fitting from the pipe. But it would probably be faster and easier to cut out the section(s) of pipe that have to be relocated. A few straight couplings could then be bought to patch things back together.

When re-assembling the duct work, using tape as suggested by Redoak49, would provide an effective yet reversible seal. I used HVAC metal foil tape on my system and it continues doing a good job.

If committed to dissembling the joints, here are the approaches I could come up with:

There appear to be commercial solvents that claim to render silicone removable, but before buying any of these solvent, experimenting with some vinegar might work. From the odor given off when applying silicone caulk, I suspect that acetic acid (vinegar) is the carrier solvent. I have observed that silicone caulk is cured when no odor of vinegar remains. Perhaps allowing the vinegar to soak into the silicone would re-soften the silicone.

Some commercial silicone caulk removing chemicals are available. I suspect these are designed for tube and tile applications, although a couple of products may work for your application. I am not sure what, if any, affect these commercial solvents would have on PVC. These are found solvents at…

One problem with the chemical approach is ensuring the solvent is in constant contact with the silicone. Pipe in the horizontal position mounted to a ceiling makes this a challenge. Perhaps loading a glue syringe with solvent and the directing the syringe into the joint would work. Once injected, a dam of some sort may be needed to keep the solvent from flowing out of the joint. Some plumbers putty might work for this.

If the joint is secured with a single bead of silicone, perhaps the silicone bond could be broken mechanically. A hack saw blade may be thin enough to work into the joint and then a sawing action could break the bond. If the joint is too tight to work a hack saw blade into the joint, then the perhaps the PVC pipe could be soften with a heat gun so that the hack saw blade can make entry. However, the PVC connection will likely need to remain warm as the silicone is cut.

View Fred Hargis's profile

Fred Hargis

6415 posts in 3340 days

#5 posted 08-17-2017 11:38 AM

I’ve always used silicone to seal my joints (2729), and I’ve completely removed and reinstalled my system twice…and it’s currently completely disassembled waiting for my shop to be finished (we moved again) so I can re-install it there. But I’ve never put the silicone internal to the joint, it was always around the seam on the OD. That said, I’ve always been able to separate the joints with maybe a few exceptions. But then I always had the parts dismounted and laying on the floor. I think you need to flex the joint back and forth slightly to break the adhesion of the silicone, then pull them apart. It’s not always easy, but (in my experience) it’s usually works. Then I use a razor scraper to remove the left over caulk from the pipe before reassembly. On the shorter sub assemblies, it helps to have something to secure one end, like a workmate. Strap wrenches are also good for rotating the parts to break the adhesion.

-- Our village hasn't lost it's idiot, he was elected to congress.

View Blindhog's profile


163 posts in 1896 days

#6 posted 08-17-2017 12:31 PM

I have the same system and did not use any tape/adhesive on the joints. Testing each joint with smoke and no leaks. The system has been in place for nearly three years without any problems. I know this does not help your current situation, but a thought for your future retrofit.

-- Don't let perfection get in the way of plenty good enough

View Robert's profile


3932 posts in 2328 days

#7 posted 08-17-2017 01:20 PM

I think you can break it loose.

I would try a band wrench and see if you can break it loose by rotation. A piece of rubber or sandpaper will improve grip.

-- Everything is a prototype thats why its one of a kind!!

View GR8HUNTER's profile


7780 posts in 1560 days

#8 posted 08-17-2017 01:36 PM

Fred and rwe have the answer for you FORCE them apart….. GOOD LUCK :<))

-- Tony---- Reinholds,Pa.------ REMEMBER TO ALWAYS HAVE FUN

View Redsoxfan's profile


38 posts in 2473 days

#9 posted 08-17-2017 02:09 PM

get yourself two strap wrenches and apply opposing torque. you’ll bust the caulk seal.

then, as indicated above, either use tape (my method) or caulk the outer end of the fitting.

-- Brian, Western MA

View splintergroup's profile


3978 posts in 2069 days

#10 posted 08-17-2017 02:16 PM

I’m in the “force” camp. My 6” PVC pipes are (were) siliconed together and it took two band wrenches and some back/forth jiggling to break the seal. Silicon does not stick very well to PVC thankfully.

Be careful of using any solvents as they may also attack the PVC and further “weld” it. Solvents can be useful however as a way to lubricate the joint before applying the band wrenches. I’d consider mineral spirits applied with a syringe around the perimeter of the joint, the capillary action should take care of the rest.

Now I just dry fit the joints and use aluminum tape to seal things up.

View TungOil's profile


1382 posts in 1342 days

#11 posted 08-17-2017 03:44 PM

My metal ductwork is all sealed with silicone inside the joint. It comes apart easily with some twisting when necessary. My old system was PVC and I found the joints to be so tight as to not need any sealant.

I also agree with not using a solvent, but more from a safety perspective. Depending on the solvent used you may inadvertently create an explosion hazard if the fumes are allowed to concentrate in the piping somehow.

-- The optimist says "the glass is half full". The pessimist says "the glass is half empty". The engineer says "the glass is twice as big as it needs to be"

View jonah's profile


2124 posts in 4146 days

#12 posted 08-17-2017 03:50 PM

Side question: why do people use PVC instead of metal ductwork?

View pintodeluxe's profile


6204 posts in 3660 days

#13 posted 08-17-2017 04:35 PM

I did the same thing, although it was duct mastic. At first I was destroying the pipe to get it apart. Then I used a propane forced air heater to warm the joints and they all popped loose. It wasn’t easy, but with heat it may be possible.

Now I use only rivets and aluminum foil tape to assemble my duct work.
Good luck with your project.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View RobS888's profile


2829 posts in 2692 days

#14 posted 08-17-2017 04:42 PM

Side question: why do people use PVC instead of metal ductwork?

- jonah

Ease of use,

-- I always knew gun nuts where afraid of something, just never thought popcorn was on the list.

View Bill Berklich's profile

Bill Berklich

1171 posts in 1235 days

#15 posted 08-17-2017 05:16 PM

If it is on the inside mating surfaces you are pretty much out of luck. Even if it didn’t “glue” it together the adhesion on the surfaces will make separation problematic (think silicone router mat). Once you’ve cut the pipe free of the fittings you can (maybe) recover the fittings by cutting inside longitudinally and then collapsing the female portion. Good luck

-- Bill - Rochester MI

View WoodES's profile


184 posts in 2538 days

#16 posted 08-18-2017 06:00 AM

I have the 6” thin wall PVC piping in the shop ceiling and glued the joints in the rafters, screwed & taped the drop pipes, This allows me to change the drops. I figured if I had to change anything below the rafter, I could easily make the change. Above the rafter the sawzall & new connections would be the way I plan to go.

You could make up a sample from scraps or purchase some parts from your home box store and experiment with the other solutions presented.

I did a google search on dissolving silicone and had several solvents returned as the result. Try searching for products in your area.

Let us know what works.

View Andre's profile


3693 posts in 2653 days

#17 posted 08-18-2017 07:09 AM

Use a Ex acto or other sharp blade to cut through the silicone bead, there is an acid that will break down the silicone but not sure what it would do the the PVC? Meant for porcelain or fiberglass. I used some years ago with very little success. After the bead is cut you should be able to twist it apart? I left a few critical joints loose fit when I assembled my ducting system and glued all the rest with PVC cement so I know they are never coming apart! Always meant to duct tape those loose joints but never got around to it for some reason? Good luck!

-- Lifting one end of the plank.

View tomsteve's profile


1064 posts in 2066 days

#18 posted 08-18-2017 12:48 PM

you could just cut the pipe each side of the joint and use a coupler to reassemble. sure seems a lot simpler to me.

View SirTim's profile


9 posts in 1274 days

#19 posted 08-19-2017 03:24 PM

If none of the ideas people are giving are working or you don’t want to try and you want to save the fittings then what bluenose said will do the trick. I installed this stuff for a living and the fittings are not cheap. A well glued fitting will even come apart. Cut close to flush of the fitting, use a saw blade of some type (I have a holder that holds sawsall blades) to cut along the pipe and cut the pipe just to the fitting. You can usually pry a slotted screw driver down between. It should be very easy to pry. My system has only sheet metal screws. These joints don’t leak and if they do it is so insignificant it is not worth the worry. If you really want to use silicone again, assemble the joint and put a bead on the outside only

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