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How to Use Zinc Weld-Through Primer

The Application and Uses of Zinc Weld Through Primer

 Difficulty: Easy

What Is Zinc Weld Through Primer and What Does It Do?

Weld-through primer is a zinc-based product that protects welds from corrosion. It should be used between welded metal panels. Unlike most primers, weld-through primers don’t promote adhesion, but instead provide sacrificial corrosion. This means that when the zinc corrodes, it forms zinc oxide, which protects the steel underneath.


It should be noted that weld-through primer is not designed to be used on the area you will be welding. You should only weld clean, bare metal. The area to be welded should either be masked off beforehand or cleaned after applying the primer.



Anything in an aerosol can may do damage to your health, so you must be prepared before using spray-on etch primer. A ventilator mask is the best way to protect your respiratory system, and you should also only ever apply the primer in a ventilated area. You should also use goggles and gloves. We have a complete range of suitable PPE in our shop.


You should always keep the primer away from fire as it is highly flammable, and the can may explode if it gets too hot.


Step 1: Preparing Your Surface

All surfaces need to be clean and unpainted. If any surface is dirty or greasy, your product will not stay on your surface. Use a good car cleaner and a microfibre cloth to make sure the area you'll be priming is washed properly.


Next, wrap a sheet of 400-grit 'wet or dry' paper around a sanding block and scuff the surface, while using a generous amount of water. This step will help greatly with adhesion. Make sure to wear a mask while sanding. Wipe any sanding particles away with a clean, dry cloth.


Your surface should now be clean, dry and ready to be primed.


Step 2: Using Zinc Weld-Through Primer       

Shake the can and hold it about 15cm (6 inches) above the surface to coat it. Move the can back and forth, in smooth motions, continuing to spray until you have left the area of painting to ensure an even coat.


Depending on the product, you may need more than one coat. In between coats, you should wait 10-20 minutes to allow the paint to dry. This will ensure correct thickness and optimum corrosion protection.


You should also wait for the final layer to dry before welding.


If there’s any primer on the area you’re welding, you should sand away the primer.


Products Used In This Tutorial

Zinc Weld-Through Primer

3M Weld Thru II Coating, 377 ml Aerosol


Microfibre Cloth

Farecla Finishing Cloth (Pack of 3)


3M Microfibre Detailing Cloth



3M Maintenance Free Half Mask Respirator, FFAP3R D Filters



Sealey Safety Goggles with Direct Ventilation


Protective gloves

Colad Black Nitrile Gloves Large (Box of 60)

Car Cleaner

Concept Go Foam Aerosol 450ml


Wetordry Paper

3M P400, 230mm x 280mm, Wetordry Sheet 734, Qty of 25

Sanding Block

3M 70 x 125mm Soft Hookit Sanding Hand Block


Water Sprayer

Concept Mini Water Spray Bottle 600ml