SEALING COAX THE RIGHT WAY
BY THOMAS BROOKS, KG5ZSU
July 2021	

	Yeah, that sort of title will get me strung up by my coax. But let’s face it, most people end up with wet coax at some point in time, so we might as well learn from those who don’t have repeat trouble. I haven't had any trouble so far, although I suppose that some of my coax COULD have goten a little moisture in the shield. But, it hasn't cause any trouble yet.
	Correction: I did get just a little water intrusion where the plugs on my MFJ surge suppressors leaked. I hadn't sealed those.

	There are a few ways to do this right. The methods are as follows, in order of reliability, the top three being very close:

		3M self-vulcanizing tape under a layer of Scotch 88 or Super 33 outdoor rated tape
		
		a layer of Coax-Seal putty under a layer of Scotch 88 or Super 33 outdoor rated tape

		a layer of rubber electrical tape under a layer of Scotch 88 or Super 33 outdoor rated tape

		two alternating layers of Scotch 88 or Super 33 outdoor rated tape


	For each method, I recommend Scotch brand tapes, but you could use any brand. Just make sure what ever one you use for the outermost layer is outdoor rated. Whether you use self-vulcanizing tape, coax putty, or electrical tape, use the following technique:

	Assemble the connectors as needed and tighten snugly. Don’t strip any threads out. Wrap one layer of tape starting from what would be the top of your assembly, roughly 3” inches above the end of the connector, and wrap downhill, overlapping each layer about 50% (or the recomended ammount on the package). Stretch it nice and snugly so it seals well. Continue until you reach the bottom of your assembly, about 3” below the end of the connector. Make 2-3 loose wraps at this point if using vinyl electrical tape so that it can relax and not peel back, then cut it with a sharp knife. Ripping it will make it peel loose.

	Then make another layer of tape, this time wrapping from 1-2” bellow the end of the last layer, wrapping uphill. This is your outer shell. This makes sure the water is shed off of each overlapping layer and doesn’t seep between the layers. I make this set of wraps in the opposite direction as the first one, so in the end they seem to criss-cross like a finger trap over the cable. The first wrap or two need to be snug enough to seal well against the cable, and I overlap it in such a way so that the end of the first wrap does not stick loose; the tail gets covered by the next wrap so you only have one end to unwrap from should you need to remove it. Continue wrapping each layer uphill, overlapping about 50% of the tape’s width, until you reach about 1-2” inches above the first layer of tape, and make 2 or 3 full wraps, loose enough so the tape relaxes a little, but not so loose that it doesn’t hold a seal. These end wraps should overlap about 50%, but it isn’t critical. Cut the tape loose.

	To finish it up, make a turn or two more around the top end to keep the second layer’s tail from coming loose. Again, always cut the ends with the tape relaxed, and don’t stretch the last wrap overly tight.

	If you are doing this on something like an extension cord that gets drug around often, you can use a colored tape as the inner layer so that as the outer wears through, you have a visible indicator that it needs repaired.

	I have heard very good things from several ources on the reliability of the vulcanizing tape combo, and I would trust it completely, along with the tape over putty method. That's has lasted on a repeater antenna I helped install last year with no problems at all. For this, make a layer of Coax-Seal or other putty-type sealant over the connector as the package would indicate. Then make an uphill wrapping layer of tape that presses into the putty firmly, and leave it at that. Or, if you are really paranoid, do the alternating tape technique over the putty; just switch and do a downhill layer followed by an uphil one in the opposite direction. 

	As an added tip, don’t ever, ever, use silicone sealant on coax or other electrical connectors. It releases acetic acid and will corrode the connectors and coax braid, decreasing conductivity and performance.