Candle Wicking, Lamp Wick, and Old-Man Plumbing

Back in the ’90s when I was still a lowly drain man and hadn’t ascended to the honored status of “plumber,” a co-worker whose father had been a plumber before him told me about candle wicking. It could be used, he said, to make gaskets or packing, and I’d find it handy to keep in a tool box somewhere.

I took his advice and dutifully bought a roll and kept it in a tool box. I’m sure that I used it some, but not much. Eventually it went away, probably lost in a theft in one place or another. (Thieves would steal a tool box, not a roll of cotton string.) I didn’t think much more of it after that.

Candle wicking is “old-man plumbing,” a term I learned from a different plumber back in the ’90s. I had asked him about some technique I’d found in an old plumbing book. As years pass, better materials are developed which make plumbing easier to do, and some practices and techniques fall out of use because they’re just no longer necessary.

This week I checked the plumbing supply houses, looking for candle wicking or lamp wick, a thinner form of the same material. The stores hardly carry it any more. The clerks, who hadn’t even been born when I bought my last roll, didn’t know what it was. I finally found some candle wicking at Hugo.

Candle wicking is made up of five thin strands of cotton string loosely wound together. Back in the day, I heard of plumbers who had used mop strings when they didn’t have any candle wicking. The material would be wrapped around waste tubing (e.g., p-traps) to make the joint under a slip nut water tight. I often encountered such joints in the ’90s and usually had to break the slip nut with a chisel to get it off, the joint had been made so well.

One of the five strands would be about the size of lamp wick if it were bought separately. That brings me to the reason for this post.

I was called to a facility where some fire safety equipment had been plumbed with valves and other doo-dads I’d never seen before, and a threaded joint was leaking slightly. The fire safety inspector had demanded that it be fixed. The leak was where a 1″ pipe was threaded into the female end of a weird and surely expensive valve, which would have been very difficult to replace.

Shortening the story quite a bit, I got the joint disassembled and replaced the pipe going into the valve; but when I turned the water back on, I still had a slight drip, just as the original plumber had. I arranged to come back in a couple of days to re-do the job.

This was a revolting development because I had made that joint very carefully, using proven techniques and materials. Why was it leaking? Modern brass, thanks to government regulations, isn’t as hardy as it used to be and I suspect that the original plumber overtightened his joint and distorted the valve ever so slightly.

I checked the Plumbing Zone forums for advice and learned of an “old-man plumbing” technique called “wicking.” Then I found a YouTube video where a guy actually showed how to use lamp wick.

When I returned to the job, I wrapped a strand of lamp wick from one end of the male threads to the other, keeping it in the grooves. Then I applied some True Blu thread sealant and made up the joint. No leaks.