Red Devil 0841DW F-Seal 181 Fiber Reinforced Water Based Duct Sealant, 1 Gallon, White

Used this to seal various parts of my air conditioning system. I applied to seams and screws on the air handler in the attic and also to all connections of the flex duct from the sheet metal plenum. The goal was to reduce as much air loss as possible.I removed the flex duct that was held on with duct tape and a screw. It was all installed around 35 years ago and I found old instructions that said to use duct tape which of course today you are not supposed to use duct tape for anything HVAC anymore. I used an old 2" paint brush. You really want one with stiff bristles because this stuff is thick maybe closer to joint compound consistency. I spread everywhere around each start collar really pushing the sealant into the cracks and leaving a thick layer. I put a liberal glob over any screwheads and spread across any places air might pass through such as seams.It was dry enough within an hour to not be pliable anymore but full cure says 24-48 hrs. For me, I was able to do the second coat for most except the thicker spots. I poured a little water into the jug which thinned it so I could get a better spread over the thicker parts and feather out the product. I was working in a hot attic and I found having a separate container with just water helped a lot since leaving the lid off obviously dries it out. Adding water back in seemed to restore even the drier bits along the sides of the jug. I used a putty knife to scrape it back in and it mixed back in to the rest of it easily. I assume after a full cure it no longer accepts water and creates a permanent moisture proof barrier. Otherwise what's the point.I also spread some on the neck of the start collar and then inside the duct so that when I slid the flex duct back over there would be a seal. This is what you're supposed to do. I then put a screw back in to secure the two together. You're not supposed to do that though, you're supposed to use a zip tie and tensioning tool but I didn't feel like spending the money on those things was necessary since the screws held fine all this time. I used paper backed, pressure sealing foil tape to wrap the flex duct and seal it to the collar. Using pressure you get a great seal so no air can get in or out. Another coating of this mastic over the taped edges and I was set. Simply pull the fiberglass back over the collar and against the plenum then pull the outer vapor layer over the insulation to the plenum and I was done.I also redid a bunch of the flex connections to the boots. The boots had riveted edges which could easily pass air through so I spread over all corners inside or out.I have a 5 ton system and with everything I did there is still half of the container left. I liked the white color because I was able to use it on the ceiling diffusers to seal any cracks without worry about the color. I don't know what else this stuff can be used on but I'm going to find out.

Liked the first two tubs so much I ordered a third. I used this to help air seal my new duct system located in my crawlspace. After almost two years, there is no cracking, chipping, or peeling. Two coats hides the print of the foil tape underneath. Appears to be very solid and durable.However, the third tub had a shipping issue and arrived with the lid slightly open which then leaked into the box. Amazon's return policy had a replacement on front porch two days later. This time someone completely sealed the lid to the bucket with a tape called " The Gripper" which prevented the same thing from happening again - box arrived upsidedown with the tape split open. Same delivering company both times.

I used this duct sealant to seal seams and joints on approximately 250 feet of spiral pipe and assorted fittings and blast gates on my workshop sawdust collection system. I had a multitude of pipe joints, and size transitions from 8 inch duct down to 4 inches, along with a myriad of bewildering elbows and gates.The item performed as advertised, spreading easily across seams and joints and providing an airtight seal once properly cured.I found the application easiest with a cheap chip brush-aka a worn out paint brush with all but the first 1/2 of bristles brush cut off. Between this and latex gloves, I managed to properly seal every joint (inside and out) on the first try. School of hard knocks tip: keep a bucket of water and an old rag handy-this stuff is capable of coating a rookie installer in a wonderful layer of sealing goodness. However, I found that working cleanly and efficiently drastically reduced the amount of after the fact cleanup necessary.The hardest part of this process for me was waiting 24-48 hours for the duct sealant to cure before testing/usage. I used a few incense sticks to test for leaks, using the smoke to test for drafts/leaks within the vacuum system.Bottom Line Up Front: it works well, cleans up easily, and is relatively inexpensive. I have 3/4 of the large pail left-for future expansion projects.

Very good for sealing ductwork.Would have been bet ter if the co mp any would have put Ta pe to keep l I d on during tra ns Port.

The mastic is easy to apply and quickly seals leaky AC ducts. It works better than tape as it gets into folds and crinkled duct connections where tape can’t form a seal.

Used the Red Devil F-Seal 181 sealant to seal up around some flex duct terminations on a small HVAC project I was working on. Easy to apply, set properly in the indicated time, happy with this product allowing me to finish things out like a pro.

Don't buy this mastic! It shrinks and cracks like crazy, even when applied thin. Completely useless. Worse than useless! It was a smooth consistency out of the tub and went on like normal mastic. It seemed OK at first but was a complete disaster the next day. Nearly every seam has cracks. It even cracked where fiberglass tape was used, just awful performance. Buy Hardcast, Ductmate, or any other reputable brand that you would find at an actual HVAC supplier. Mama says this stuff is the DEVIL!

The product arrived with a slightly open box, and a small amount had leaked out. Thankfully, it still works. Some of the material inside the bucket is hardened, but it's still usable. It seems like this might be a bit of a gamble in terms of condition upon arrival. I couldn't find this at my local store, and ultimately, I'm happy with how well it works.