Does Masonry Paint Need a Primer? (Explained)

Priming before applying paint helps it adhere better. But what if you are working on masonry? Does masonry paint need a primer? 

Yes, masonry paints need a primer or undercoat before they are applied. This is because masonry surfaces have increased moisture retention. If you apply masonry paint without sealing or priming the stone surface first, the coating will not dry well.

Also, masonry is usually rough and sometimes riddled with cracks and holes. So, you must apply an undercoat to fill these holes and cracks or the finish won’t come out smooth. 

Can You Paint Directly Over Masonry?

You shouldn’t paint straight onto masonry because its surface isn’t ideal for paint application. If you do, the coating will not stick and the finish will be filled with bumps and slits. Eventually, the whole finish will peel off.

Masonry is one of the toughest finishes in building and construction. The finish is made from a combination of materials like rocks, sand, cement, and the like. All of these materials are mixed to produce a finish with improved moisture retention. This means that it does well to hide and retain water.

So, if you paint without a primer, the coating will be severely affected by moisture. The moisture content of the surface will prevent the coating from having good adhesion to the masonry.

Also, masonry is usually rough. Old masonry surfaces especially are riddled with cracks, holes, and sometimes nail holes. If the paint is applied over such a surface, the finish will be very rough and bumpy. 

Why Do You Need an Undercoat?

Masonry paint needs an undercoat or primer to adhere properly and provide a fine finish. Without an undercoat, the coating when dry will have bumps and eventually peel off.

The undercoat helps to seal the surface to prevent moisture from affecting the coating. It helps to provide a smooth layer that the paint can be applied on.

Also, a primer is needed because masonry surfaces are a bit porous due to cracks.  This means that the surface will require more coatings to be fully covered. But an undercoat seals the surface preventing wastage.

Also, the rough texture of masonry will not allow paint to stick. It will also produce a rough finish when it dries. The undercoat helps to cover this rough surface and when dry, will provide a smooth surface for the coating to bond to.

Sealing

Masonry paints don’t need a top coat or sealant because they are specially designed with solvents to be tough given the type of material and environment they are used in.

Also, when dry they have a thick texture. The thickness of the finish is durable enough and prevents top coats and sealants from adhering well. However, this goes for solvent-based masonry paints only.

Acrylic and latex masonry paints are usually sealed with a top coat to prevent the colors from fading due to the effects of the weather. This is because they are water-based and not as durable. So, they need a sealant.

Since masonry paint is used on concrete, brick, stucco, and cinder blocks, the paint is formulated with extra additives to be strong and durable. This means it will last longer than most types of paints. 

Sandtex Masonry Paint

Sandtex masonry paint needs a primer if applied over rough surfaces. This paint uses micro-seal technology to provide unmatched results on masonry even without using a primer first. However, you can only get a smooth finish on properly prepped surfaces.

If the surface is riddled with holes, cracks, and pores, you must apply a basecoat to fill these imperfections. If you don’t, the imperfection will suck more paint than needed.

If the surface is rough, except for primer you also need Sandtex-ready mixed filler. The filler is used to repair masonry before you apply the paint. The filler can also be used as a primer (basecoat).

However, if the surface is smooth, you can apply it without a primer. You can also know if you need a primer by trying the Sandtex tester pots. The tester pots are small cans that have different paint types for masonry. You can try them on masonry without a primer and check out each finish.

Types of Primers To Use

You need to use an epoxy concrete primer for masonry paint. Epoxy primers will absorb and grip the surface creating a firm and smooth layer. They also treat the masonry material by sealing and covering cracks and holes that can suck paint.

Also, epoxy primer is ideal because oil-based primers are better than water-based primers for concrete. This is because they have chemicals and additives that help them bond well to surfaces.

When you want to prep masonry for paint application, you need to use a primer designed to seal and repair tough surfaces like concrete. You also need a basecoat that has enough resins and additives to adhere to the porous texture of masonry. Oil-based primers have all of these things, while water-based don’t.

This is why using latex primers isn’t recommended. They are water-based and don’t have resins that can improve the paint bonding. 

If You Don’t Prime:

If you don’t prime before painting masonry, the coating(s) will peel off and tear. This is because its rough texture will affect the curing process of the coating. The particles will not bond together while curing.

Instead, the particles will be separated and they will cure in different segments. The separation occurs due to the presence of edges and bumps in the masonry. These edges and bumps poke out of the coating after it is applied. Over time, the finish will appear torn.

This will create gaps in the coating that will make it more susceptible to moisture and friction. The finish will eventually start to peel off the surface.

Sure, you can apply more coats to seal these edges but doing this will just result in wastage and uneven application. Also, the coating will not dry evenly and there will be color variations. The only way out of this is to prime the masonry before the paint is applied.

Things To Know

How Many Coats of Primer?

You need only 1 coat of epoxy primer before applying masonry paint. However, if the surface has a lot of holes and cracks, you might need a second coat.

How Many Coats of Masonry Paint?

If it’s an unfinished masonry surface then you need 2 coats of masonry paint. If there’s an existing finish, you need one coat only (plus the primer coating).

Primer Over Existing Finish

If there’s an existing finish, then priming over it isn’t necessary. However, if the old finish is filled with crack and hold, then you should add a light coat of primer. 

Final Words

In summary, applying a primer before masonry paint is recommended, and sometimes mandatory. You must use an epoxy primer to get the best results. If you don’t, the finish will come out rough and will have bumps. 

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