Tinning Flux Vs. Paste Flux: Pros and Cons of Both

Tinning flux and paste flux are essential agents that are widely used in soldering. Perhaps, you are wondering how one compares over the other. Let’s find out the pros and cons of each.

Tinning flux and paste flux have many uses in the world of plumbing. They are used to help prevent oxidation of metal pipes and fittings by removing impurities that degrade the metal surfaces. More importantly, they prevent further oxidation by blocking the entry of air during the wetting process.

The two types of flux may have similar functions but have significant differences in their characteristics. Many professional plumbers prefer the tinning flux over the paste flux. Some prefer otherwise. If you want to learn more about the properties and characteristics of the two, you should read along further. 

What is Tinning Flux?

A tinning flux is a greenish-gray paste consisting of metals like copper, bismuth, tin, ammonium chloride, and sometimes lead that is used to polish, tin, and flux specific metals. 

What is Tinning Flux Used for?

A tinning flux can have several uses but it is mainly used to solder soldered metals. The metals are:

  • Most ideal for copper and copper-coated pipes
  • Iron
  • Brass
  • Zinc

Specifically, a tinning flux can have other functions:

  • Cleaning of metal surfaces. It washes out residual flux out and also cleans the surfaces to achieve an even distribution of solder. 
  • Pre-tinning of surface. Tinning holds the pipes together and makes fittings flow and conform more easily. Think of this as some sort of a “lubricant”.
  • Prevents oxidation of the pipe. When a tinning flux is applied, it acts as a barrier that keeps air from getting in which slows down the natural process of oxidation in metal pieces.

What Surfaces Should You Not Use Tinning Flux On?

You cannot use tinning flux on the following metals or surfaces:

  • Stainless steel
  • Magnesium
  • Aluminum
  • Electrical parts (for water-soluble fluxes)

Attempting to use tinning flux on these surfaces will either cause the flux to fail, or, on electronics, potential damage to the circuits.

Pros of Using Tinning Flux

Many plumbers prefer to use tinning flux because of the following reasons:

  • Ideal on larger pipes: Most pipes are of decent size. And because of its ease of use, tinning flux is often a better choice for many professional plumbers. While it’s ideal on larger pipes, it can still be used on smaller pipes.
  • Wipes better than regular paste: There are several tinning fluxes in the market which makes it easier to remove or wipe after you have finished soldering. Although not proven, many plumbers believe that putting the right amount of flux is the key to better results.
  • Can withstand more heat: A tinning flux when heated is active up to 700oF. This means that it can bear more heat and will not overburn easily.

In general, tinning flux is the top choice for any plumbing job.

Cons of Using Tinning Flux

As useful as tinning flux is, there are scenarios where it’s use may not be ideal.

  • More expensive compared to paste flux: If you have a plumbing business and you use fluxes multiple times a day, then tinning flux could be more expensive to purchase. This could seriously factor into business costs.
  • Shelf life is short: Tinning fluxes tend to last for up to a year from the date of manufacture. If you don’t end up using much tinning flux on a regular basis, you could potentially waste both product and money.

Both of the negatives are simply about the price—make sure to buy only in the amounts you need so you don’t waste too much money.

What is Paste Flux?

A soldering paste flux is a light-yellow past used commonly to clean and flux metals. The common ingredients are similar to tinning fluxes but with the addition of fillers, surfactant blends, and triethanolamine hydrochloride.

What is Paste Flux Used for?

Just like tinning fluxes, it is ideal for copper-based materials or alloys. It can be used for fire sprinklers and potable water pipes. 

What Surfaces Should You Not Use Paste Flux On?

Just like tinning fluxes, you cannot use paste fluxes on the following metals or surfaces:

  • Stainless steel
  • Magnesium
  • Aluminum
  • Electrical parts (for water-soluble paste flux)

Soldering on those materials requires a different flux approach.

What Are the Chemical Properties of Paste Flux?

Flux is inert or inactive at room temperature (15-30oC) but becomes active as it is subjected to heat. Solder paste flux has more active ingredients compared to a liquid flux. A solder paste flux can have as much as 60 to 80% active ingredients compared to the 2 to 25% of the liquid version.

What are the Types of Paste Flux?

There are several types of paste flux; we will discuss the three most common.

Water-soluble Paste Flux

It is glycol based and is often used to excessively clean and oxidize your metal surface because of its high reactive properties. However, because it is a very effective cleaner and oxidizer, water-soluble paste flux can easily corrode your metal surface if incompletely removed. Thus, it’s very important to wipe your pipe clean. 

Rosin Paste Flux

Rosin paste flux is used for surfaces that are easy to solder and clean. It is mild compared to the water-soluble paste flux. Thus, it is less corrosive. Because of this characteristic, rosin paste fluxes do not have to be removed.

Rosin paste flux can be used on large wirings such as electrical parts.

No-Clean Paste Flux

Just like the rosin paste flux, No-clean paste flux are for surfaces that are easy to solder. Its reactivity is similar to a rosin paste. Thus, it is less corrosive or conductive. From the name itself, this type of flux does not need to be wiped clean or removed after soldering.

Pros of Using Paste Flux

Paste flux has several benefits:

  • Acts as a temporary adhesive: Because of its tacky nature, it may be used to temporarily hold two parts together until the heat melts the solder and fuses the two parts together.
  • Prevents oxidation of metal pipe: Just like a tinning flux, a paste flux covers areas where air can pass through. This process prevents oxidation and makes it ideal for metals that are prone to such chemical reaction.

The “pasty” nature of paste flux can be a great help when attempting to apply at odd angles or in tight quarters.

Cons of Using Paste Flux

Paste flux also has two major downsides, however:

  • Not all types of paste flux works: The different types of paste flux may not be suitable for all kinds of metals. Thus, it’s important to be knowledgeable about the different types of fluxes in the market to determine the right one for your project.
  • Toxic when ingested or inhaled: Because of the ingredients present in paste flux, vapors when inhaled can cause irritation. Read along further if you want to know what ingredients causes toxicity and what to do to prevent extreme exposure.

In short, know that the type of paste flux is suited for the metal you will be soldering and practice good PPE and safety practices when working with it.

More About the Fluxes

Many professional plumbers believe that interchanging tinning flux and paste flux makes no huge difference. What matters most is the application or technique, and the type of flux that are more important.

How Do You Apply Tinning Flux?

It’s important to refer to the manufacturer’s instructions on the proper application of your newly purchased tinning flux. However, most tinning fluxes are applied the same way.

Here are the steps on how to properly apply tinning flux:

  • Clean or wipe all surfaces.
  • Apply a pea-sized amount of flux inside and outside the fitting. 
  • Start heating the fitting or near the joint from 400oF to 700oF. It’s important not to overheat the pipe by moving the heat source around the joint to achieve even distribution of solder flow.
  • Allow to cool.
  • Dampen a cloth and wipe any residual tinning flux. 
  • Check for any leaks by letting water run through the pipe.

If you do find a leak, you will unfortunately need to wait for the pipe to dry once more and attempt to seal the gap.

How Do You Apply Paste Flux?

Remember to refer to the manufacturer’s directions first. Otherwise, you can refer to the steps below for a general idea on how to properly apply or use paste flux.

  • Thoroughly clean and smoothen the joint.
  • By using a brush, apply the paste flux to the top of the joint.
  • Turn on the torch and start heating the joint evenly. Do not directly heat the paste.
  • The flux will then start to spread around the solder. At this point, you should cautiously move the torch from side to side.
  • Once the solder starts to flow, remove the torch away from the joint. 

Once again, remember not to directly heat the paste. This will only result in a large mess. Let the heat conduct through the metal to melt the paste and it will work itself into the joint.

Tinning Flux and Paste Flux Health Hazards and Shelf Life

If you want to know more about the two kinds of flux in the market, you should continue reading as we will be discussing the health hazards, uses on electrical components, and even some alternatives that you can use in place of these manufactured products.

Is Tinning Flux Harmful to Health?

Because of its ingredients, it’s important to apply the tinning flux using a brush and not with your fingers. Tinning flux is considered an eye and skin irritant. Thus, it’s important to wear face shields before application to prevent excessive inhalation of vapors. Always read the fine print before using any chemicals.

Is Tinning Flux Toxic?

Paste flux can be harmful to the body just like tinning fluxes. Some of the ingredients that can cause harm are:

  • Ammonium chloride is often associated with asthma attacks described as wheezing, coughing, and shortness of breath. Long term exposure can affect the kidneys. 
  • Hydrochloric acid, or the household name muriatic acid, has a pungent smell that is strongly acidic and can react when in contact with your skin. This is why it’s important not to use your fingers to apply paste flux.
  • Zinc chloride is considered a respiratory irritant when inhaled and can cause blindness.
  • Rosin produced from pines and some types of conifers is also known to cause asthma. It has been associated to permanently clog lung tissues. 

To avoid as much exposure to these harmful ingredients, always wear a mask or shield when working. If possible, try working in an area where there is adequate ventilation so that fumes can disperse easily compared to confined spaces.

Can You Use Tinning Flux for Electronics?

Not all kinds of tinning flux will work on electronics. Certain products can be too corrosive and can damage electrical parts. Thus, it’s important to read the label and look for anything that says it is safe to use on electrical parts.  

Generally speaking, tinning fluxes that are water-based are not suitable for electronics.

Just be warned that manufacturers often list what their products can be used for and not what it can’t be used for. If you’re unsure because the label does not indicate it, try finding the specifications online. Most online stores have specification documents attached, which will bear all the information including ingredients, indications, uses, properties, and health hazards.

Can You Use Paste Flux for Electronics?

The answer is the same when it comes to paste flux. A lot of times fluxes for plumbing are different for electronics. Thus, it is best to shop for fluxes specific to your needs. In general, paste flux made of rosin or No-clean types are more suitable for electronics because it contains fewer active ingredients.

What Happens If I Forget to Remove Flux Residue in Electronics?

If you used a No-clean paste flux, then you don’t really have to worry as it is designed not to remove the residue after soldering. However, if you used a water-based paste flux, your electrical component could be damaged.

Is it Safe to Use Expired Tinning Flux or Paste Flux?

No. If you use tinning flux or paste flux past their expiration date, expect that their reactivity and performance will not deliver well. The ability to remove oxides on the metal surfaces will greatly decrease and may result in poor output.

The reason for this is that solder paste contains activators that are responsible for removing oxides when subjected to extreme heat. Often times, manufacturers would recommend refrigerating flux after opening to preserve these activators. It is best to keep these fluxes in refrigerated temperature and only take them out to thaw at room temperature when needed.

How Do You Know If Tinning Flux or Paste Flux Is Still Usable?

There are signs that you need to look out for to determine if your flux is no longer usable.

  • More viscous. Observe the consistency of your flux. Notice any difference in viscosity.
  • Poor fusion. You can observe this when you add paste on to a surface. See if the paste will form into a ball surrounded by a puddle. If it only forms a puddle and does not reflow into a ball, that could mean your flux has degraded.

If either of these problems appear, just get some new flux. Attempting to use old, expired flux, even if it works, will result in a weaker joint that could cause issues later.

Alternatives to Tinning Flux or Paste Flux

If the health hazards are too extreme for you, there are certain alternatives that you can opt to use.

Vaseline Works as an Alternative to Tinning Flux or Paste Flux

Vaseline, or petroleum jelly, can be an effective alternative to your tinning flux or paste flux. Yes! It’s possible. Not only is it cheap and effective, it is less toxic compared to a tinning flux or paste flux. It can even be used on any electrical parts unlike the tinning flux or paste flux. Moreover, petroleum jelly can even act as a cleaner.

To apply, use the same manner as you would when using tinning flux. The great thing about petroleum jelly is that it cleans your metal surface, it greases your joints for a better fit, and it melts away when subjected to high temperatures of heat. Just so you know, tinning flux or paste flux are mostly petroleum-based, which is why Vaseline works just as fine.

Lemon Juice Can Be Used for Emergency Needs

If for any reason you ran out of tinning flux or paste flux and you’re in dire need to fix an electrical component, then lemon juice or citric acid from your pantry would work. However, be aware that this only works for electronics and not for plumbing.

Alice Godfrey of Our Pastimes has listed the steps to make homemade flux made out of lemons:

  • You will need a paper towel, juice strainer, and six lemons, and 2 bowls or plastic containers.
  • Place the paper towel on top of the bowl or plastic container.
  • Cut the lemons in half. Using the strainer, squeeze the juices and let it run through the strainer and paper towel and into the container.
  • Using a wooden spoon, stir the juice for about half a minute.
  • Pour the juice to the second bowl or container with the use of a strainer.
  • The extracted juice can now be used as a flux.

While a fun project, this doesn’t have much practical value. However, it could still be a good trick to know in a pinch!

Homemade Rosin Flux for a Natural Alternative to Synthetic Tinning Flux or Paste Flux

If you’re up for a little challenge, then here are the ingredients you will need to make your own homemade rosin flux according to Instructables:

  • 15 pine cones
  • 1 quart of denatured ethyl alcohol

Once you have those, you can follow these steps to extract the rosin and make your flux:

  • You will need clean plastic or metal containers with lid
  • Cut all cone leaves and place in a container
  • Submerge the leaves with ethyl alcohol overnight.
  • The next day, mix and then strain the liquid into another container.
  • This time add a white filter paper onto the strainer.
  • Strain the liquid again.
  • Transfer liquid in a spray bottle.

Remember that natural doesn’t meant healthy—rosin is rosin, and this flux can still clog your lungs. You still need to wear all PPE and act safely. While a fun science project, this is again best used in a pinch. Always buy manufactured flux if you are able; homemade fluxes cannot be properly certified or tested. 

Conclusion

Tinning flux and paste flux are not too different from each other. The debate still goes on for seasoned plumbers whether tinning flux is better than paste flux. However, they all agree that the correct application is what matters more to achieve optimal results. 

What’s more important is to use the correct type of flux whether to use water-soluble fluxes or rosin-based fluxes when working on specific projects to prevent the nasty effects of corrosion.

Sources

https://www.homeownershub.com/maintenance/tinning-flux-vs-standard-paste-flux-314641-.htm

Flux with Tin or Not? (plbg.com)

https://www.ridgidforum.com/forum/mechanical-trades/ask-the-plumbing-experts/17076-soldering-paste-vs-tinning-flux

https://images.homedepot-static.com/catalog/pdfImages/7f/7f3875f8-5ef3-449f-bf81-738ecb17470b.pdf

https://www.7pcb.com/blog/bitteles-use-of-flux-in-pcba-no-clean-flux-vs-water-soluble-flux.php#:~:text=Specifically%2C%20the%20goal%20of%20the,is%20thus%20a%20stronger%20cleaner.

http://seattlefindings.com/assets/images/Product%20Instructions%20PDF/How_to_Use_Solder_Paste.pdf

https://www.mountsinai.org/health-library/poison/acid-soldering-flux-poisoning

https://ourpastimes.com/make-citric-acid-flux-soldering-12103849.html

https://www.instructables.com/Make-your-own-Eco-friendly-soldering-flux/

https://www.indium.com/blog/solder-paste-expiration-shelf-life.php

https://www.dfrsolutions.com/blog/why-flux-residue-can-cause-electronics-failures

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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