Blind Soldering

What's the best way to sweat on a pipe that is so close to the wall, you can't see the other side of the pipe? How do you know the solder is flowing in the part of the joint you can't see?

1) Spray the wall with water. Make sure you have a water bottle nearby.

2) Use a cloth flame shield. About $15 at your local hardware store.

3) Use a $2 extension mirror to see behind the joint.


If you've cleaned, fluxed, and sweated properly then the joint will hold and you really don't need to see behind the joint.

Take the bottom and top off a #10 can and split it so that you have a flat piece of metal. This works pretty well as a cheap way to protect from fire. Do have a spray bottle of water handy just in case. As noted, clean the pipe end and the inside of the fitting well, apply plenty of flux. Bend your solder so that you can reach around to the backside of the joint. Heat the joint until the solder flows, then bring the solder around the joint. Solder will flow into the joint if it's well fluxed and if you can get your solder around most of the fitting. I tend to use a bit more solder than probably necessary on joints like this just to be sure.

Ditto on the 'protect the wall' advice.

Feed from the top. When you see a bead develop on the bottom, you can be fairly certain the joint is evenly filled on both the visible and wall side.

Make sure the line is dry. Fitting and pipe cleaned and fluxed. Direct the flame as best you can away from the wall with the blue tip of the flame touching the copper fitting and keep touching the joint with the solder until it not only melts, but when the solder flows fast, I would consider the joint soldered. Take the flame away and just wipe the joint with a quick move with your finger. It won't hurt you.

You dont have to see the backside of the solder joint.