Polystyrene: A Step by Step Manual on Insulating a Building with Polystyrene

Among all the insulation materials for exterior walls, Polystyrene is one of the most popular ones. In the thermal performance game between Vata bazaltica vs polistiren, the competition may be head-to-head, but there are many reasons to lean towards Polystyrene.

If you are looking for building material with good insulating qualities and low thermal conductivity, Polystyrene should be your first choice. The advantages of Polystyrene are it is light and easy to install, can resist compression, and is impermeable to water vapor, making it perfect for exterior walls, low floors, roofs, and rooftops. It can also go strongly up to over 50 years.

Step by Step Manual on Insulating a Building with Polystyrene

Regardless of how well Polystyrene is as an insulating material, it would be useless if it is not insulated properly. To get a sustainable outcome, choosing an insulation system is extremely important. A proper insulation system is elaborated below:

Step 1: Preparing the wall

The surface of the wall you plan to insulate needs to be clean, smooth, and solid. You must fill up all the cracks on the wall, clean the excess mortar pieces, dust, wash and dry the wall. The walls also need to be primed to ensure the stability of the entire system.

Step 2: The starting base layer

In this stage, the base for the first board is applied to ensure the prevention of the cold air between the insulating boards and the wall. This base is known as the starting track. It also creates an obstacle for rodents and insects from nesting within the insulation. It is very important to apply the base evenly, or else it can get problematic later in the system.

Step 3: Installing

The boards need to be installed by placing them by the corner and leaving space for plaster. The plaster must be applied evenly, covering all the edges as well as mounded on the middle of the boards. It is very important to cover the edges for durability and to ensure there are no gaps between the boards and the walls.

Spet 4: Anchoring

Once the plaster dries, which usually takes two days, it is important to anchor. Anchoring may cause the plaster to tear off from the edges. Usually, boards are anchored automatically if there are any exposed parts on the wall.  You may not need to anchor the whole wall, but it is important to anchors around doors, windows, and wall edges.

Step 5: Filling up the cracks and gaps

In this stage, all cracks and gaps between the boards and cracks of any other form should be filled in with Polystyrene. If there are any gaps or cracks left unfilled, it may cause thermal bridges. Also, these exposed cracks and gaps will be visible on the surface of the wall. If there are any additional amounts of protruding polystyrene pieces, you need to carefully cut them off.

Once all the excess foams are cut off, all the uneven flaws need to be scraped with a float polystyrene tool until the surface looks even. If not, these uneven flaws will be visible on the surface.

Step 6: Applying Adhesives and Fiberglass Mesh

The next stage is to apply adhesives on the surface and apply fiberglass mesh to create a strong foundation for the surface tiles and the plaster. It works as a reinforcing coat to strengthen the edges and corners of the insulation. It works to strengthen edges that have more probability of cracking, like near the window, around the door.

Step 7: Priming agent

It is the stage where you have to cover the reinforcing coat of fiberglass mesh with the right priming agent. Proper prime enhances plaster adhesion and its level of absorption.

Usually, these priming agents are offered in various colors. You will get the choice to match it with the color of the plaster. It reduces the chances of discoloration of the surface and stops the wall underneath from being visible.

Step 8: Plastering or painting the wall- finishing touches

This is the last stage of insulating. You can use a thin coat of plaster or surface paint to add appealing value. There are different kinds of plasters available in the market. They are known for their resistance to dirt and permeability to harmful smoke.


As mentioned before, insulating a building with Polystyrene is great if you want low thermal conductivity. Light material that is easy to install. That being said, you can insulate your building with Polystyrene. And still not be happy with the outcome if the process is not properly followed.

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