There are two main types of primer; oil-based and water-based. So what’s the difference between these two undercoats?
The main difference is that oil-based primer uses natural or synthetic oil as its solvent, while water-based primer uses water as its solvent. The difference in solvents, makes both undercoats have different qualities.
Since water-based primers use water, it dries faster since water evaporates faster from the coating. They are also more suited to water-based paints since they use the same solvent.
Water-based or latex primer is an undercoat that is used for prepping surfaces before applying water-based paints. It uses water as its solvent, so it dried super fast since water evaporates fast. When dry, it forms a dry textured layer over the surface.
It is commonly used for areas that require prep work before painting. This is because it can be easily sanded or shaped to bring out the desired finish. Its water-based nature means that you can use it for indoor surfaces.
However, the water-based primer has a flaw. It isn’t good at sealing materials and as such is more suited to non-porous material.
You should use water-based primer:
- For Indoor Surfaces – If you are painting indoor surfaces, such as furniture or walls, use this primer.
- Water-based Paint – If you are applying to use water-based paint, use a water-based primer first.
- Fast Protect – Since it dries fast, you can use it if you need a quick fix.
Oil-based primer is an undercoat that contains a high volume of oils. It is used to seal surfaces and block stains from bleeding through before applying an oil-based paint or sealer.
Because of its oil-based nature, this undercoat has a thick flow and good coverage. It also has a slow dry time, since the oils take longer to evaporate from the coating. However, a slow dry time also means the particles have more time to harden and compact, so this primer offers better protection/durability.
You can use an oil-based primer:
- To Seal Stains – If the surface to be painted is defected, stained, or damaged by moisture, you need a stain-blocking primer. This undercoat will seal (cover) the surface and prevent the stains or dirt from bleeding through and affecting the finish.
- For Oil-based Paint – If you are planning to use oil-based paint, then you need an oil-based undercoat.
- Water-resistant Features– If you are painting over a wet surface, you need to apply an oil-based primer to prevent water from affecting the finish quality.
Oil-Based vs Water-Based Paint Primer
To compare both undercoats, let’s compare similar qualities and see which one is better
Water-based primer uses water as its solvent and is made of solvent, colorants, and a binder. On the other hand, oil-based primer uses oil (natural or synthetic) as its solvent and is formulated with chemicals that prevent stains from bleeding-through.
Dry and Cure Time
Water-based primer dries enough for a re-coat within 30 minutes. It has a fast drying time because its solvent (water) evaporates from the coating hast.
On the other hand, the oil-based primer dried enough for a re-coat within 2 hours. It has a slower dry time because oils take longer to evaporate from the coating.
However, their dry time is also determined by room temperature, the number of coats, and surface type.
In terms of adhesion or bonding, oil-based primers are better and stronger. However, in terms of material adhesion, water-based primers will bind (stick) to more types of materials (surfaces).
The Type of Paint Used For
You can use any type of paint over a water-based primer because it doesn’t have any additives that repel paint. On the other hand, you can only use oil-based paints over oil-based primers.
However, the water-based primer doesn’t stick well over an oil-based finish, so you must sand it first.
Oil-based primers last longer than water-based primers because they have additives that preserve their coating. Also, they are moisture-resistant, meaning they won’t get damaged or washed off from water.
On the other hand, bare water-based primers aren’t as durable and since they use water as their solvent, they are also water-soluble.
Indoor or Outdoor Use
It’s recommended to use water-based primers for indoor surfaces only. That’s because the undercoat isn’t durable enough to withstand outdoor weather elements and can get washed off before you paint over it. If you want to use it outdoors, you must paint over it immediately after it dries.
On the other hand, you can use oil-based primers outdoors since they are formulated with additives that make them withstand weather elements. However, you shouldn’t use an oil-based primer as the final coating on a surface as it will get washed off within 2 days. So, you must paint over it, and then seal the finish for outdoor surfaces.
Water-based primers are easier to clean because you can clean them with a rag and warm water. For tough stains, you can use soapy water. On the other hand, to clean oil-based primers, you need to use a solvent, such as turpentine or mineral spirits.
Sealing and Blocking
If the material is damaged by water, stains, or oil, you need to prime first to seal the stains so they don’t bleed through the finish.
Oil-based primers do a better job of sealing and covering stains and dirt. That’s because they have a thicker coating and their formula is suited for blocking stains and moisture.
On the other hand, water-based primers don’t seal stains as well and their coating is water-soluble and porous. So, they won’t prevent bleed-through.
Oil-based primers have a harder coating when dry. The hard texture is gotten from chemicals and binders in the coating. Because of the hard texture, sanding is more difficult. It’s also less likely to be able to shape its coating once it has dried.
On the other hand, water-based primers have a flexible texture. Its coating is not as hard given the absence of chemicals in the formula. As such, it’s easier to sand, distress, or shape it.
Use on Wood
For wood, an oil-based primer is better especially if it’s porous wood. The Oil-based primer is better at sealing the wood grain and preventing over-absorption of the paint.
On the other hand, water-based primers are suited to sealed and non-porous surfaces.
Here’s a table that highlights their differences:
|Water-based primer||Oil-based primer|
|Clean-Up||Easy||You’ll need a solvent|
|Dry-Time||30 minutes to 1 hour||About 2 hours|
|Type of Paint Used For||All types of paint||Oil-based paints|
|Stain-blocking and Sealing||Poor||Great|
In summary, oil-based and water-based primers are both great undercoats, and the one you choose depends on the task and project.
Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,