Rolled Mastic Duct Sealants Foils 3'' X100

This has to be the world‘s stickiest tape. This very heavy, thick and durable foil tape sticks to everything and is very permanent once supplied. If you accidentally fold it upon itself, fuggeddaboudit, you won’t get it apart. This is perfect for sealing duct board or other items such as flex duct to a takeoff boot or similar such applications. This is a large roll also. 100 linear feet, so it might be expensive at first glance, but it really isn’t. It goes a long way.

Last summer was hot in Central Texas, and my utility bill was sky high during the hottest months. This year I renewed the electric service contract and prices are naturally much higher, so I decided to do some deep investigation into why the HVAC wasn't performing as well as I expected it to. A couple of rooms at the end of the duct runs were always far hotter than the rest, even though the air temperature was the right temp coming out of the register. Fast-forward and what I discovered was the mastic on the downstairs evaporator coil box (both furnace units in the attic) had become separated from the supply and return boxes/plenum, who knows for how long. It was essentially blowing a significant amount of cold air into the attic instead of the house. This made the upstairs unit stay on 24/7 during hot months since it was essentially trying to cool the entire home. I cleaned the surfaces (well enough...I won't claim to have made it as clean as recommended) and slapped this rolled mastic tape on all affected areas. Also re-arranged some of the duct work that had sagged out of spec due to the home builders not properly stretching the flexduct when installing. Then I used more of this mastic tape on the upstairs furnace and sealed things up nice and tight. A/C issues solved! Rooms at the end of the runs are the same temps as the rest now, and my A/C runs about 40% less on those super hot days! Every homeowner should own a roll of this mastic tape and understand how such an inexpensive item can affect such an expensive system.

Hardcast mastic tape is the best because the backing comes off easily and doesn’t slow you down struggling to remove it like SureTape does. And it’s super sticky, strong, durable.

The mastic adheres well to the ductwork and seals completely. It's a bit of a chore getting the backing to start to peel, but otherwise I highly recommend.

**Edit - First, some have complained that they received 2" rolls. I've bought this on three separate occasions, the latest delivered on 11/1/2023, and all have been 3" rolls. Not saying the others didn't get what they claim, but I have gotten exactly what I ordered.** This tape works well for metal HVAC ducts, but here's a tip on how to avoid a king-sized struggle getting the release liner off: Don't cut the tape with scissors or a utility knife! If you do this, you'll have a hard time picking away at the corner of the tape to get the release liner started so you can pull it off. Instead of cutting with scissors or knife, grip the tape and tear it. It tears very easily, and the tearing action will get the release liner started for you. If you don't like the torn edge, you can trim it with an old pair of scissors after the release liner is started. Once you get the liner started, I recommend not removing it all at once on longer pieces of tape. This mastic tape is *extremely* sticky. It's best to take the liner off bit at a time as you go along placing the strip in place on the duct seam. This avoids the nasty problem of the tape sticking to something you didn't intent it to stick to. If you don't believe this, you will after your first try with this stuff. I wipe down the surface (galvanized sheet steel ducts in my case) with lacquer thinner or acetone (whatever I have on hand) and a paper towel. Your ducts may look clean, but if you give them a quick wipe-off and look at the paper tower you'll see that they most likely are not very clean. Both acetone and lacquer thinner dry super quickly, but neither is very healthy so take precautions. Be sure to squeegee the tape down after its in place with a fairly stiff squeegee. I use the 3M squeegees designed for this, and they work great. A bondo spreader is too thin in my opinion. Even a scrap of lumber will work in a pinch as long as there's no sharp edge to tear the tape. But this is not a good place to skimp. Get a proper squeegee for a few bucks. As with all tapes of any kind, it's a good idea to avoid placing the tape so that the edge of a strip falls on a sharp bend. This has such great adhesion that it might not matter but better safe than sorry - taping your ducts is not something you want to do again if you can avoid it. Finally, some HVAC pros do this and some think it's a waste, but I believe it's a good idea to paint the edges of the tape with HVAC duct sealing mastic. When tape gets old, the edges generally fail first and the mastic will help prevent this. I use Red Devil HVAC duct mastic, which works well and is one of the more reasonably priced brands.