Sanding Epoxy Primer Before Base Coat – Any Rules to Know?

Epoxy primer is a friendly solution for preventing metal surfaces from rusting and covering the walls of a water tank to increase its quality, durability, versatility, and capacity. In addition, epoxy primer allows an object to withstand a wide range of chemicals, temperatures, and liquids.

Most professionals use a double coat because Epoxy primer does not have color, and applying Epoxy primer is much easier than painting the surface. In addition, the molecules of primers bond fast, making Epoxy primer easy to coat, paint, or spray.

The amount of primer used could affect the product. If the layer of primer is too thick, it becomes unbalanced due to vertical layering. While Epoxy primer provides a nice finish for the product, it becomes difficult when the layer is thick because it must be sanded out.

You will also have to sand the layer of Epoxy if you want to mix in a material that does not bond with primers to improve bonding and adhesion. However, it should be noted that Epoxy needs to be properly cured before sanding without making the coat uneven. We will see the rules you should know when sanding Epoxy primer before a base coat in this article,

What is Epoxy Primer?

Epoxy primer is also known as a sealer that produces a smooth finish to applied coats. It is a semi-specific term used for sealers in the market. It leaves a non-porous finish that prevents oxidation from occurring hence recommended as the first base coat for steel.

It is also used on fiberglass, plastic, black iron phosphate, and other materials due to its mechanical ability, strong adhesion, and chemical resistance to toxic liquids, humidity, and high temperature. In addition, it provides woodworkers and painters with excellent bonding capacity and can be used to waterproof materials.

What Is Base Coat?

A base coat is the first layer of coating material or paints applied before the finishing coat. A base coat is made with fillers, pigments, and plasticizers to cover the small surface imperfections and improve the overall appearance of the top coating and product.

Rules to be Taken into Consideration When Sanding Epoxy Primer Before a Base Coat

When preparing for the sanding of an Epoxy primer surface, the first thing to do is apply the ‘guide coat.’ The guide coat allows the woodworker or painter to see minor imperfections or defects in sanding the primer surface.

After applying the guide coat, use ‘block sand’ on the defects with a P320 grit until the guide coat is removed. Then reapply the guide coat. The Epoxy primer must be hard and dry before sanding to prevent the solvent from penetrating the wood surface, and then the final preparation is carried out.

The final sanding before applying the base coat is performed with wet sanding with a fine grade of wet or dry abrasive paper. Sanding after applying primer keeps the surface smooth and flat and eliminates brush marks.

How Do You Prepare Epoxy Primer for Base Coat?

Epoxy primer can clog paper when dry sanding is used, so to prepare Epoxy primer for a base coat, wet sanding is the best way to prep a base coat. Go over your work after with a red or grey scuff pad for a better finish. You can even use the same method as 2K Urethane primer with a 400 to 600 grit wet.

Is Sanding Epoxy Primer Necessary?

Most products can be used over Epoxy primer without sanding. But, to ensure the product you have can be used, we recommend you check the product page or manufacturer’s website.

Suppose the manufacturer of your product says base paint or LPU paint. In that case, it means that the base coat or paint will bond quickly with Epoxy primer before sanding, but if the coat or paint is incompatible, sand the epoxy primer and allow it to dry thoroughly as a non-compatible coat or paint takes time to dry.

Recommended Waiting Period for Sanding Epoxy Primer

The Epoxy needs to be properly cured before sanding to avoid damage to the finished product. However, it is a long wait for Epoxy primer and epoxy resins to cure completely, reducing efficiency.

The wait can be brought down to 2 days by using the standard heat of a coastal state’s daylight or a heater to bring the temperature to 50°F or 85°F before sanding the surface of an Epoxy primer layer.

If none of these methods are used, and you do not wait for the Epoxy primer to dry, the sandpaper will remove the layer of Epoxy primer, and the primer will block its pores, causing you to start over.

Even when the curing methods are used, you cannot sand the Epoxy layer in less than 24 hours to avoid damage.

What Grit Sandpaper You Should Use on Epoxy Primer Before Base Coat

Sandpaper grit is the population of abrasive or tough particles per square inch of a sandpaper sheet. The more abrasive particles present, the more effective and finer the sandpaper is but the less abrasive particles present, the more coarse the sandpaper is. Here are different grit sandpapers that can be used:

– 40 to 80 Grit

This is a coarse sandpaper grit that will leave behind visible marks. Hence, it is not recommended for minor coat scratches. However, it can be used for rough sanding before bodywork and shaping body filler.

– 120 to 180 Grit

This sandpaper is used to flatten out scratches, feather edge of body filler, remove light rust, and spot putty sanding.

– 320 to 400 Grit

This is much more refined than the other two grits and can be used for rough sanding of the primer, fine sanding, and final body filler preparation.

– 600 to 800 Grit

This grit sandpaper is great for surface imperfections in the Epoxy primer before applying paint. It is recommended to start with the low grit and move to 800 grit.

– 1000 to 1200 Grit

This sandpaper grit is used to deal with base coat imperfections and works best with wet sanding techniques.

– 1500 to 2000 Grit

This sandpaper grit works for imperfections and minor scratches before and after applying a clear coat. This grit works best with the wet sanding technique to make sure clogging of the sandpaper doesn’t occur.

Best Practices for Epoxy Primer Sanding

Do not attempt to use just any type of sanding even though the Epoxy primer is completely cured. Instead, you should carefully select a technique and medium of sanding. These practices will help determine the best product and optimal sanding method.

Choosing the Right Grit

If you decide to use coarse sanding paper, the layer of Epoxy primer will be removed, and the underlying surface of the element or working product will be exposed to oxidation and damage.

On the other hand, if the sanding paper is too fine, it will not affect the primer. Therefore, it is crucial that you use 320 grit sandpaper or 400 grit sandpaper. With these grits, a lowers grit will require lower passes, and a higher grit will require more effort.

Only Wet Sand, Do Not Dry Sand

The wet sanding process involves using water to soften the impact of sanding. Dry sanding can remove the epoxy primer entirely and leave deeper abrasions. When wet sanding, you should use water to lubricate the surface for better results in preparing the primer.

Avoid Power Sanders

It is essential to use a sanding block and hand-sand the Epoxy primed surface regardless of the paper grit.

Hand sanding allows you to exercise more control over the depth of impact and the number of passes. But power sanders, on the other hand, can be too harsh on the primer, so it is best to avoid them. The sanding blocks are also cheaper than the power sanding tools.

Topcoats That Are Conducive to Epoxy Primer

There are Topcoats that do not have enough adhesion and require sanding of Epoxy primer, but it is preferable to use Topcoats that bond quickly with primer, so you do not have to worry about sanding. Sanding aids the adhesion process. Two Topcoats that are conducive for Epoxy primer include:

  • Clear sealer – A clear, see-through sealer that is applied over Epoxy primer with no hand sanding.
  • Linear polyurethane (LPU) – Linear polyurethane paints bond quickly with the primer even though it has not been sanded. This could be a good choice for woodworkers.

Epoxy primer can be applied to bare fiberglass, steel, or plastic. It is very flexible, and you can use it as a sealer in wood finishes and products.