The right way to apply coats of polyurethane is to sand the layer before applying the next one. It is a common practice.
The question is, why so?
There are two reasons for the same. We will cover both of them below. Once you know these reasons, it will become easier for you to apply polyurethane coats properly.
Why Sand Between Coats Of Polyurethane?
The sanding between coats of polyurethane is done to increase the adhesion power of polyurethane. Another reason is to ensure that the surface on which you are applying the polyurethane coat is devoid of any flaws. We will explain both of these reasons below.
1. Great adhesion power:
Sanding the layer before applying another coat of polyurethane ensures that the adhesion power of polyurethane increases significantly.
The reason for the same is that when you sand, it becomes easier for polyurethane to create a mechanical bond with the layer beneath. Once such a mechanical bond is created, the polyurethane coat can last for a more extended period.
If the adhesion power is on the lower side, it will certainly not stand the test of time. Especially when it is exposed to water, it can wash away as well. In that case, you will have to apply the layer of polyurethane once again.
The outer layer will not serve its purpose. Applying the polyurethane layer, again and again, can be both expensive and time-consuming.
To avoid this problem, it is a good idea to sand between coats of polyurethane.
2. Surface flaw elimination:
Only when the surface below is devoid of flaws can the polyurethane layer on top remain in place. That is another reason why sanding is necessary in-between coats of polyurethane.
When you’re applying a polyurethane layer, it can get contaminated by dust particles and so on. It can be cracked as well.
If you’re applying a layer of polyurethane on such a layer, the surface area will reduce due to unevenness. In that case, the polyurethane layer will not be stable. It will not dry well. The upper layer might develop cracks, as well. In that case, the life span of the polyurethane layer will decrease considerably.
When you’re sanding it in between, you can provide a smooth surface for the next layer. Sanding will also remove the dust. It ensures that the lower layer is not contaminated.
When you apply the next coat of polyurethane on such a layer, the surface area increases significantly. The higher surface area means that the upper coat can stick to it quite easily. Moreover, the smooth surface ensures that the bond between the 2 layers is excellent.
Not only that, the smooth layer means that the airflow will be restricted. In that case, the polyurethane material does not undergo significant wear and tear. Such a coating can easily stand the test of time.
As you can see, sanding in between coats of polyurethane has numerous benefits. In a nutshell, it significantly increases the efficiency of polyurethane coats. That is why, if you do not want to apply polyurethane coats, again and again, sanding between different layers is a necessity rather than a myth.