Over the years I've soldered several remodels worth of copper pipe (water and hydronic heat). I'm not great, but I get the job done, until I have to add a brass fitting. For some reason, I can't get the solder to suck into the joint. Does soldering a brass fittings to copper pipe require a special technique?

4 Answers 4


Very Important Make sure the joint is really clean when you solder - so use emery cloth or sandpaper to remove any contaminants in your solder joint and flux the joint prior to heating. I like to wipe the joint with acetone before applying flux but I'm anal retentive like that.

Also you might want to consider using MAPP gas vs propane - those brass fittings take a lot of heat before you will get solder to flow into the joint.

  • 3
    mapp gas is a must, never had much luck with propane. Lots of heat is the trick. Feb 5, 2011 at 6:44
  • Cleaning and MAPP are key. I've never bothered with acetone, nor have I seen anyone do that before. Make sure your flux and brush are clean too: you just spent all that time cleaning the fitting, don't wipe a mixture of flux and dirt onto it.
    – gregmac
    Feb 5, 2011 at 6:57
  • Using solvent to clean the joint area after mechanical abrasion is a holdover from my electronics soldering days (definitely something I've never seen a regular plumber do).
    – kkeilman
    Feb 5, 2011 at 7:07

If the problem is that the solder is not "pulling" into the joint it may not be hot enough (try using MAPP instead of propane in your torch). But I find the biggest help is to use lots of flux (aka soldering paste). Go crazy with it, use it really liberally.


I just had the same experience. What i figured out was, whereas they say to concentrate your heat on one side of the fitting until it is hot enough for the solder to flow for copper, i had to heat all around the fitting for brass. Once I did that it flowed just like copper. Like the pros are saying, it took more heat for it to flow properly with the brass.


I found (after a couple of bad jobs) that if your solder is sitting in a toolbox it oxidizes and gets dirt on the roll you will have problems. It will have major problems sticking, and you will be there for hours, -- even copper to copper. Dirty/oxidized solder will make for a lot of frustration in the field, hold you up on a job, and just plain out make you feel inadequate in your skills (when it has nothing to do with you). I now double-bag my solder and keep it totally clean from now on. The comments on flux, brush, and fitting to be clean are true too. It is a game changer in keeping fresh/clean solder. I learned by being embarrassed on a couple of jobs and somehow figured it out. I had to walk away from one job and told her I did not know what it was (on solder not adhering/sticking to a hose bib change out), and to call another tech/plumber. I felt really bad. Repair is a tough game sometimes.

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