Randy Charles is the owner of PaintCentric.com, a website dedicated to providing information, tips, tricks, and news about all things paint. With over 10 years...Read more
Sometimes, you might be tempted to use some leftover interior paints on the outside walls of your building. Unfortunately, in as much as it saves you some money, you stand the risk of spending more money anytime soon. This is because the paints will deteriorate badly sooner than you expect, requiring a brand new painting job.
So reconsidering the question, can you use interior paint outside? This is not advisable in most cases. This is because interior paints lack some required chemicals that make them resilient to snow, heat, UV, mildew, rain/cold.
Moreover, while painting, you will notice that the paint finds it difficult to adhere to the surface. This is because the formulation of the paint makes it too thin for outdoor walls, including masonry. In addition, indoor paints most times require several coats even to produce a thin layer. Also, it takes a significantly longer period to dry and is almost impossible to dry in very humid conditions. This article provides the necessary information you need to aid your choice of paint for outdoor application.
- Can You Use Interior Paint Outside?
- What Is The Difference Between Outdoor Paint And Interior Paint?
- Type Of Resins Required
- What To Do If You Already Used Interior Paint Outside?
- How Long Will Interior Paint Last Outside?
Can You Use Interior Paint Outside?
While you might be tempted to use interior paint outside, maybe to reduce cost, we strongly advise that you don’t. Extensively discussed below are the reasons why you should never use interior paint outside.
The most noteworthy difference between interior and outdoor paint is the presence of more additives in outdoor paint. While interior paint is formulated to withstand abrasion, resist wash and counterstaining, outdoor paint is not like that. Also, interior paints lack the special weather-proof additives contained in most outdoor paints. Hence, interior paint gets a big ‘NO’ for outdoor use.
Consumption Of Excess Paints
Compared to outdoor paint, interior paint has a much thinner layer. This creates difficulty while painting, as it requires extra layers of paint to achieve an equal amount of coverage. Even with the several layers of paint, it wouldn’t look as good as outdoor paint.
It would help if you also didn’t use interior paint as a replacement for outdoor paint because it won’t last long. Exterior paint contains additives that keep it intact despite several hours in the sun or rain. On the other hand, interior paint can lose its hue, chalk, or even crack in just a matter of months. Hence, you incur extra spending since you’ll require a repaint sooner than planned.
It Takes A Longer Time To Dry
Interior paints are designed to take a much longer time to dry up compared to outdoor paint. Moreover, it may never get dry in humid weather conditions and can get washed off in the event of rainfall.
What Is The Difference Between Outdoor Paint And Interior Paint?
Outdoor paint differs from interior paint with regards to many distinguishing properties. Such as the type of binder used, VOC level, corrosion resistance, water resistance, heat resistance, type of resin used, type of pigment used, type of additive used.
The differences are treated under the following subheadings:
Keeping corrosion in check is a huge source of concern for most outdoor painters and paint manufacturers. To serve for much longer, manufacturers have designed outdoor paints to be able to withstand harsh, corrosive conditions. Compared to internal paints, corrosion-resistant paints are coated to withstand mechanical stresses, corrosive agents, high humidity, etc. To achieve this, factors that act on the base coat, substrate, and topcoats are taken into consideration.
Interior paints, on the other hand, are much less exposed to corrosive conditions. Hence, the formulation allows for little or no corrosion-resistant content.
External paints have to be highly water-resistant. This is because of their constant exposure to rain, mist, snow, mildew, and the rest. For instance, in acrylic paint, you need to add a sealer over it to make it waterproof.
If water passes through the paint on the external walls, it travels through the concrete and, subsequently, the inner walls. This is bad as the interior paint used is affected, and the walls weaken, endangering the whole building. Hence, exposure to water becomes a very vital factor to put into consideration.
Interior paints, on the other hand, require less water resistance. This is because they are less prone to coming in contact with water. Also, rooms where these commonly occur are your bathrooms and kitchens, but these walls are usually covered with tiles.
However, some folks prefer to have a paint drawing or decoration on their toilet or bathroom walls. If you choose not to have your water-susceptible walls tiled, then you can have them painted. Moreover, your choice of paint must be water-resistant.
Heat-resistant paint is formulated to endure temperatures far exceeding room temperatures. This heat-resistant property is achieved by combining a binder solution and a pigment powder. Also, the binder solution used by most manufacturers is a constituent of polysiliconalkoxide. On a more general term, heat-resistant paints can withstand flame, heat, grease, rust, and smoke.
Exposure to sunlight for long periods can cause your paint to develop bumps and blisters. This gives your walls the appearance of badly-fried yam chips, and you don’t want that. Hence, when considering paint for your outside walls, you should consider heat-resistant paint.
On the contrary, the paint on your interior walls is adequately protected from heat hence, nullifying the need for heat-resistant paints.
Type Of Resins Required
The kind of resin required in outdoor paints is flexible. Due to variations in the temperature and exposure to moisture, the paint contracts and expands accordingly. Hence, the resins used have to be flexible and soft so they won’t be affected.
On the other hand, the kind of resin adopted in interior paint formulation is often rigid. This is because they don’t experience the contraction and expansion common with exterior surfaces. They also don’t need protection from ultraviolet radiation as they are shielded from direct sunlight. These resins, however, are formulated to provide protection against factors such as scuffing.
Ultra Violet(UV) Protection
Due to the constant exposure to sunlight, walls start looking faded or completely discoloured. This is caused by a reaction between the powerful UV rays emitted by the sun and the paint’s pigment. Furthermore, by causing the resin to dry out, the UV makes the paint crack as it dries out on itself.
Exterior walls are more prone since they are always exposed to direct sun rays, endangering the paint in the process. To tackle this challenge, some paint-manufacturing companies utilize inorganic compounds for the absorption of ultraviolet radiation. Some compounds commonly used for UV protection are cerium oxide and zinc oxide.
On the other hand, interior paints do not require such protective compounds as they are always shielded.
Kind of Additive Present
You may have come across lines of clay burrowed onto walls or spirogyra growing on walls, usually on external walls. The first is caused by an insect, while the latter by fungal action. These conditions are rarely seen on interior walls. This necessitates the addition of extra additives like pesticides, mildewcides, and fungicides to paint used for external walls.
Interior paint, on the other hand, is not prone to those factors, thereby varying the kind of additives you should apply. Oil stains, for example, are much common in the home, necessitating washing. Hence wash-resistant additives are needed. In general, the purpose for which the surface is meant plays a vital role in determining your choice of additive.
Kind Of Pigments Used
Pigments are substances added to paint to give it the desired color. They could either be organic (from plants or animals) or inorganic (solid minerals). The kind of pigment most ideal for outdoor paint is inorganic. This kind of pigment is known for its durability, with samples found on cave paintings as old as 30,000 years. Furthermore, a higher concentration of it creates more concrete content resulting in deeply rich colors. This creates a higher resistance to the discoloration effect caused by the sunlight.
Interior paints, however, are usually known to contain organic pigments. This kind of pigment is known for the ease with which it fades when used on an external surface. Compared to inorganic pigments, they are known to blend, mix, and disperse better in the base.
Kind of Binders Used
Binders are additives added to a paint formula to bind the pigment together, usually polymers. In addition, it is used to make sure the paint sticks to the painted surface. Outdoor paint is formulated with binders offering adequate resistance against such effects as chalking and cracking.
Interior paint, on the contrary, is more prone to contact and scratches. Hence, the kind of binder used in it is formulated to provide more resilience to abrasion.
VOC (Volatile Organic Compounds) Content Level
These are compounds useful as solvents in the liquid component of paint, known to vaporize at room temperature. They help keep the liquid paint from hardening and evaporating as they dry up on walls. However, health research deems them harmful for long-term exposure to humans.
This is because some health problems have been linked to exposure to these compounds. Some of the related short-term problems are headaches and dizziness, while long-term problems include liver damage and respiratory diseases. They are also found to be related to certain kinds of cancer.
In compliance with safety guidelines, interior water-based paints (latex inclusive) are formulated to contain the lowest VOC levels. While outdoor paint, on the other hand, has a varying level of VOC which more often is slightly high.
In the information tabulated below, we have taken the time to highlight the differences between the two paint types.
|Properties||Interior paint||Outdoor Paint|
|Kind of resin used||Rigid||Flexible|
|Type of Binder used||Resists abrasion||Resists chalking and cracking|
|Type of Pigment used||Usually organic||Usually Inorganic|
|Water Resistance Level||Low||High|
|VOC Level||Relatively Low to Nil||Relatively High|
What To Do If You Already Used Interior Paint Outside?
Using interior paints on your outside wall doesn’t mark the end of it. It simply means you will need a painting job much sooner than you’re supposed to. So, instead of the much convenient 10 to 15 years, you should be anticipating 2 to 5 years.
Interior paints are designed for the more protected indoor wall surfaces. Owing to that, they cannot withstand the more hostile conditions of outside walls. It will discolor much quickly and lacks the additives required to shield it from mildew, herbs, UV, extreme temperatures.
Whether you simply didn’t know the difference or you picked the wrong jar from the store, it’s never too late. You may still want a satisfactory job done once and for all; simply apply outdoor paint over it. You might consider painting over it with a sealer if you have the money, but it is relatively very expensive. Or, buy outdoor paint of good quality in the same base and color and paint over it.
How Long Will Interior Paint Last Outside?
Most interior paint will last outside for 2 to5 years. This is because they are not built to withstand extreme conditions compared to outdoor paints.
But there are many factors that determine how long paint lasts on any surface. The most noteworthy ones are the quality of paint you use and the exposure/condition of the painted surface.
Can you use interior paint outside? We recommend that you do not. This is because interior paint is designed and formulated for indoor use and best serves that purpose. If you insist, however, on using it outdoors, then you stand risking all warranties. That is because it can’t resist extreme weather conditions, and you will need to spruce or repaint sooner than planned.
This article has taken a more detailed approach in helping you understand everything you need to know about internal and exterior paints. It has also covered information on why certain paint types are suitable for the purpose for which they are designated.