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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?

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up vote 6 down vote accepted

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.

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mapp gas is a must, never had much luck with propane. Lots of heat is the trick. – shirlock homes Feb 5 '11 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 '11 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 '11 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.

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