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Apply Flux

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How to Solder Copper Pipes for a Permanent, Watertight Joint · Step 5 of 9

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Flux is a chemical cleaning agent that facilitates soldering. Use a small brush to apply a thin, even layer of flux all around the cleaned exterior of the pipe. Avoid getting flux inside the pipe, as it is acidic and can cause corrosion. Insert the flux-coated pipe into the cleaned fitting and give it a twist to ensure the flux is evenly distributed within the joint. Wipe off any excess flux from the outside of the fitting with a cloth.

Goal: Coat the joint surfaces with flux to prevent oxidation during heating and aid solder flow.

  • Flux is acidic. Avoid getting it in your eyes.
  • Do not apply flux inside the fitting or pipe, as it can lead to long-term corrosion if not burned off completely.

Used in this video

  • Flux BrushApplying flux to the pipe.
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FAQs

What type of torch is best for soldering copper pipes, and how do I know I'm applying enough heat?

The K Tool International Self Igniting Propane Torch Head is sufficient for most residential copper pipe soldering. You'll know you're applying enough heat when the pipe and fitting are hot enough to melt the Oatey Safe Flo Lead-Free Solder *by touching the pipe*, not the flame. The solder should then be drawn into the joint by capillary action.

What are the critical safety precautions I must take when soldering pipes indoors?

Always have a fire extinguisher nearby and remove any flammable materials from the work area, especially when using a torch. Ensure good ventilation to disperse solder fumes, and wear safety glasses to protect your eyes from splashes or heat. It's also crucial to turn off the main water supply before starting to avoid accidents and ensure pipes are dry.

Is it really necessary to deburr, ream, and thoroughly clean the pipes before soldering?

Absolutely. Deburring and reaming with a tool like the Husky 1-5/8 in. Inner/Outer Reamer ensures a smooth pipe interior for optimal water flow and prevents solder from being blocked. Thorough cleaning with sandpaper and applying Oatey H-20 Flux are critical to remove oxidation, allowing the solder to properly bond and create a strong, watertight seal.

What are the most common reasons a soldered joint might leak, and how can I avoid them?

Leaks often occur due to insufficient cleaning, inadequate heat application, or not using enough solder. Ensure pipes are shiny clean before applying Oatey H-20 Flux, heat the joint evenly until it can melt the solder, and feed enough solder to completely fill the joint. If a joint leaks, it must be desoldered, thoroughly cleaned, and resoldered.

Transcript
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I thought we were friends just get some flux on there like so do not get flux on the inside of the pipe because flux is an acid and it can stay in the pipe and over years can burn through it and cause a pinhole but when we do our flaming on here we heat it up so much it burns off and it isn't there after we've done the soldering the other thing as well don't I mean some people would say put flux on the inside of the fitting don't really think that's a great idea what you want to do is just pop it on like so and twist it around a bit and then you know that the flux is all over another little sort of mini

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