Sealing PVC Ductwork Question

[Mark Duksta]

Hello Everyone,

I'm in the process of installing some 6" S&D ductwork for the new cyclone. I intend on piecing the system together without cement. I only want to use caulk.

My question is do I put the caulk in the joint as I would the cement, then push the two parts together, or do I only seal the joint where the two parts meet?

Mark

[Todd Franks]

Mark,

When installing my pipe, I too did not want to use cement. I wasn't confident that caulk alone would hold everything together. So I chose to use #6 x 3/8 sheetmetal screws to hold the joints together. I sealed most joints with aluminum foil duct tape and caulk where tape wasn't practical.

-Todd

[Matt Meiser]

I used screws as well. I used small self-drilling auto trim screws that I got from a surplus hardware dealer at a local flea market. Make sure the screws you use are short enough that they don't stick too far into the pipe to prevent snags. I found that 1-2 screws at each joint created a strong mechanical connection. For sealing, definitely caulk after you are done. I caulked my first system as I assembled it, when we moved, it was, shall we say challenging, to get everything apart. I ususally ended up having to cut the pipe near the fitting, then chisel the pipe stub out of the fitting. At the new house, I caulked after everything was assembled. In one or two places, I decided to make changes and it was much easier to disassemble.

One other tip: If you use clear caulk it won't look messy.

[John Miliunas]

Mark, on my last system (4" PVC), it was almost a duplicate of what Todd shows. Worked quite well. I envision that Matt's method would work equally as well and I echo what they say about NOT putting caulk on the joints prior to assembly. Even caulk will act like glue once set up, giving you a royal pain if any changes or disassembly is required.

[Mark Duksta]

Thank you gentlemen. The Creek and all the members here have saved me from so many mistakes. I has going to put caulk in the joints. I'm glad I asked first. I'm off to the Borg for some screws and tape.

Mark

[Norman Hitt]

If the joints are pressed together snugly, I would not use any screws, as they are not necessary. You will only need to use tub & tile caulk (which will stay flexible) around the OUTSIDE of the joints, and then use a wet cloth to remove Almost All of the caulk, leaving only a VERY THIN line of caulk at the joint. This very thin line will not only seal any leakage, but will also hold the joints together, yet be very easy to remove by running an exacto knife around the joint, should you need to open up the joints.

Screws pose two potential problems; 1. if they extend inside the pipe, there is a possibility of "Catching" material & possibly causing a jam, and 2. with age and vibration, they can contribute to Cracking of the "Collar and or pipe".

the other option is to just wrap the heavy duty aluminum foil tape around the joint (one layer), and that will both seal it and hold the joints in place.

You will get a more snug fit of the joint pieces if you rotate one piece you are pushing them together.

[John Miliunas]

Thank you gentlemen.
Mark

"Gentlemen"???? Nuts! Todd & Matt, looks like he's talking to YOU guys!

[Ken Garlock]

Hi Mark. When I "hung" my PVC pipe, I pushed the joints together and used ONE small sheet metal screw though the joint to give some mechanical strength to the joint. I then dressed each joint with PL brand window and door urethane caulking. The white color blends in with the color of the PVC. To clean up the joint, just use a shop towel with a little mineral spirits on it. It does a great job. After about a week, the caulk is cured. It is strong, but retains some elasticity. The "PL" company are the same people who market the PL-300 construction adhesive, good stuff.

BTW, for PVC pipe hanger, I cut up Rubber maid shelf standards into one foot lengths. I screwed them to the wall, and put a single 8" shelf support on the standard. No need to tie the pipe down, it is heavy enough to stay in place by itself. I ran all my piping along the wall, up high, or in my floor "ditch."

[Jim Becker]

Plastic or metal, foil tape is the way to go, IMHO. Works great and even adds strength to the joint. I only have pop rivets in my system at high-stress points...everything else is purely the tape.

[Mark Duksta]

We'll now that I'm back from the Borg with the screws I think I just go with the tape only method. Maybe one or two at the high stress areas. Thanks again gentlemen and John.

Mark

[John Miliunas]

We'll now that I'm back from the Borg with the screws I think I just go with the tape only method. Maybe one or two at the high stress areas. Thanks again gentlemen and John.

Mark

Mark, you may find yourself using the screws mainly on the transitional joints, like between the PVC and blast gates or stepdown adapters. As long as they're not sticking way into the airway, you should be fine. I ran the 4" with a fair amount of screws and no problems for close to two years. Good luck and enjoy your cleaner/healthier environment!

[Jeff Sudmeier]

Mark, on my last system (4" PVC), it was almost a duplicate of what Todd shows. Worked quite well. I envision that Matt's method would work equally as well and I echo what they say about NOT putting caulk on the joints prior to assembly. Even caulk will act like glue once set up, giving you a royal pain if any changes or disassembly is required.

Even the foil tape is a royal pain to disassemble and clean up! No matter what you use to seal up the joints that does a good job, it will be work to disassemble them. John gave me some of his 4 inch set up. I think it took me longer to get the foil tape off, than it did to run the pipes! It was all worth it though!