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One of the primary necessities of welding is that the weld area should be free from paint or any other type of substance that could contaminate the weld. This is the purpose of weld thru primer, to help prevent weld failure.

One of the biggest contaminants of metal is rust and corrosion. When you are planning a piping or structural job it is only natural to order the metal parts or pipe ahead of time. This means the job is not held up waiting for the metal parts or pipe to come in.

But while the metal is in storage, there is a big risk that there will be exposure to moisture, dirt or other contaminants that could corrode the metal.

Additionally, after you have completed a weld, it is imperative that you protect the welded area from rust.

How can you prevent that from happening? By utilizing one of the most powerful set up tools in the industry.

By Gregory Sanders: This article has been updated to reflect the most accurate information regarding weld through primers available for those who are interested in after welding cleaning. The best 3 available have changed, and information has been added to assist individuals in finding the best weld through primers currently available on the market. The FAQ has also been updated.

Reviews of Some Top Weld-Through Primers

There are several brands of Weld Thru Primer on the market, but we have researched and reviewed the top three here.

#1 - Dupli-Color DPP108 Prime

Dupli-Color DPP108 Prime Pros

This is a durable primer that is fairly quick drying and completely seals the metal surface to provide superior corrosion resistance.

Durable zinc coating that can be applied to dry metal or galvanized surfaces and it's fairly easy to apply.

Gray color blends with most metals and it's surprisingly corrosion resistant. Dry times vary from 15-30 mins.

Dupli-Color DPP108 Prime Cons

This weld thru primer can be a little tricky to work with, so it requires the use of high heat to get it working well.

It also has a tendency to produce a little bit of splatter when used.

Final Thoughts

Dupli-Color is a trademark of the Sherwin Williams Company, which has been making paints and coatings for over 60 years and is a trusted manufacturing name.  It's easily Cromweld's current top pick and a favorite brand.

It has a 30-day replacement warranty.

#2 - 3M 05917 Weld-Thru Coating II

3M 05917 Weld-Thru Coating II Pros

With this 3M product, you’ll get effective corrosion prevention, based on the zinc powder formula.

The Weld-Thru features a Durable zinc coating that can be applied to dry metal easily with good consistency thanks to the aerosol spray. 

The gray color blends well with most metals. Corrosion resistant it has a drying time from 10 to 20 minutes.

3M 05917 Weld-Thru Coating II Cons

There are occasional issues with the spray clogging and not spraying properly.

An issue that's easily resolved, on the other hand while they do claim the product is weld splatter resistant it's not immune to the issue and it still appears to happen.

Final Thoughts

The 3M Company has been making adherents and coatings for over 40 years and is a trusted manufacturing name.  In general, you can't go wrong with this option.

They offer a 1-year limited warranty on this primer.

#3 - U-Pol Products 0768 Zinc/Copper WELD#2 Weld Through Primer

U-Pol Products 0768 Zinc/Copper Weld#2 Weld Through Primer Pros

This weld thru-primer is offered in a rich formula that offers excellent rust protection. There are 2 formulations available Zinc or Copper.

Can be applied pretty much to any weld surface be it metal, aluminum or galvanized surfaces.

Both formulations provide excellent adhesion and conductivity and are also rust resistant. The dry time is between 10 and 20 minutes. 

U-Pol Products 0768 Zinc/Copper Weld#2 Weld Through Primer Cons

All this comes at a cost, while it does provide excelent features the price is equally high and technically you could buy several other primers for the price of this one.

Final Thoughts

Excellent quality comes at an equal cost, U-POL is a well know manufacturer of automotive refinishing products and is a must have for any car or vehicle shop. This product has a 30-day replacement warranty.

What’s the Purpose of Weld-Thru Primer?

Weld-Thru Primer is a uniquely-designed primer that is applied directly to metal surfaces that you intend to weld. This type of primer goes on just before the welding process, making it easy to have clean welds without a flux core welder and ideal for plug welding.

The purpose of a Weld-Thru-Primer is to prevent corrosion and rusting of the metal joints where two metal pieces are welded together and the use is a requirement for some products' guidelines.

It also helps provide permanent rust protection on the inner edges of the welded metal pieces.

When you’re welding metal parts together there are certain areas such as plugs, overlapping parts and joints where it is not easy to properly apply primer, coating or finishing substances.

For these areas, you need to spray or brush on a primer that can survive the welding process over the metal surfaces. You can then perform  welding and again spray the primer over the surface after you have completed the weld.

What Is Weld-Thru Primer?

Weld-Thru Primer is usually made with zinc although copper may also be used. You use it to form a seal on bare metal to prevent corrosion, but is different from etch primer.

It is generally applied by spraying or brushing it onto bare metals before welding occurs. When the welding is in process, the weld-thru primer becomes liquid-like and flows into the weld pool to help protect the metal from corrosion.

The use of Weld-Thru-Primer originated with manufacturers of steel-constructed products and shipbuilders who would order metal plate, sheet or rods from the steel mill.

The metals often traveled great distances and were then stored either on the job site or in a warehouse. They could be in storage for long periods of time before they were actually used and welded into the final structure.

Oftentimes, by the time the metals were actually needed, they would have been rendered unusable due to the buildup of rust and/or corrosion due to dirt and the environmental elements. By coating the bare metal before transport and storage, protection is provided and the investment preserved.

Many people confuse weld-thru primer with paint primer. But paint primer is used for an altogether different purpose.

Weld-thru Primer is to protect bare metal from corrosion. On the other hand, a painting primer is used to cover any flaws on a surface in order for the paint to adhere and coat the metal better.

When Do I Need To Use Weld-Thru Primer

There are several applications in which weld-thru-primer should be used and the metals coded

If you plan to store bare metal for a while before you begin your welding project, spraying or brushing on the bare metal with weld-thru-primer can protect it from corrosion.

  • When you are welding metal parts or panels that are overlapped, the underlapping piece needs to be protected with weld-thru primer.
  • It should also be sprayed or brushed on a metal joint or pinches after you have finished welding in order to protect the weld from dirt and moisture and prevent rust and corrosion.
  • If you are planning to paint the metal after it has been welded, you will want to spray or brush on weld-thru primer in the areas where you might not be able to get the paint into.
  • Auto body repair business to remove any paint so that you can have clean welds for cars, trucks, and other vehicles for your customers
  • If Colors are involved - black, red, or even an adhesive that can introduce impurities

For the best results using a weld-thru-primer, it is best to remove any paint or protective coatings around the area to be welded, clean the surface with a solvent and sand it lightly.

The area to be welded should be thoroughly clean bare metal. You then want to coat the bare metal surface including any overlaps with weld-thru primer.

It is a good idea to apply 2 coats of the weld-thru-primer to all the surfaces being welded and allow 5 to 10 minutes between each coat.

Let the primer cure for at least 30 minutes before you begin the welding process to be sure it is completely dry. Some advertise - and come through on - a shorter drying time, but it’s always better safe than sorry.

Now you are ready to weld the area. After the welding process has been completed, be sure to remove any weld-thru primer that is remaining before you paint or coat the metal to ensure the paint or coating will adhere to the surface.

Drawbacks of Weld-Through Primer

Not everyone agrees about the need for weld-thru primer.  Some feel that adding it is an unnecessary step and others feel that it can actual impede the welding process. Some of the drawbacks often cited are:

  • There are some people that say using it can produce welds that are brittle or very porous. However that may just be attributable to some specific brands of weld-through primer.
  • Others have stated that you have to spray several coats of Weld-through-primer, let each coat dry really well, then scrape the spot that you plan to weld in order to get a good and smooth weld.
  • Zinc weld-through-primer is not actually intended for use with MIG welding. As you weld, the zinc in the Weld-Through-Primer can cause a lot of spatter. As the paint burns off it can leave behind a sooty residue.
  • There was a time when all OEMs required the use of weld-through primer to reinforce the weld; however some don’t require that any longer, as they prefer to leave the OEM coat intact.
  • Weld-through-primer is not suitable for use on aluminum.


While there are some drawbacks to the use of Weld-Thru-Primer, as there are with any product, the benefits still outweigh the drawbacks.  

In order to prevent rust and corrosion on bare metal both before and after the welding process, it is highly recommended that you use this simple, spray-on product.


1. Does weld through primer work?

It contributes to the long-term corrosion protection of the inner edges of the welded metal pieces. Allow the primer to cure completely before welding to ensure that the zinc adheres to the metal properly. Remove any remaining weld-through primer prior to painting to ensure that the paint adheres to the painted surfaces.

2. Can you spot weld through weld through primer?

Tobie stated that weld-through primer was still permitted for resistance spot welding of the squeeze type. However, according to the Body Repair News, "when performing squeeze-type resistance spot welding (STRSW), apply a zinc-rich weld-through primer or spot sealer to the bare steel areas to be welded and wipe away; any excess."

3. What is purpose of weld through primer?

These primers are typically applied before the welding process. The purpose of a weld through primer is to protect metal joints where two metal pieces are welded together against corrosion and rusting and provide permanent corrosion protection on the inner edges of the welded metal pieces.

4. What's the difference between filler primer and self-etching primer?

The critical distinction between etch primer and filler or Bondo is that filler or Bondo must be applied directly to the metal before spraying. On bare metal, the application sequence is as follows:

1) bodywork, which may include the application of filler/Bondo
2) solvent for the preparation of paint
3) primer that etches itself
4) primer with a strong adhesion
5) primer
6) final coat

5. Does self-etching primer need to be sanded?

At some point during any complete restoration or body repair project, you will need to sand primer. However, because self-etching primers contain an acid-base, the majority of manufacturers do not recommend directly sanding them.

About the Author Gregory

Hi, my name is Gregory! I have been welding practically all of my life and love it. As I have gotten older I have started to weld less and less, so in order to continue my love for welding I created this website. I like to write about my experiences and help you all become welders. I hope that you enjoy the site!

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