Surface Treatment adding weight to assemblies

Question: I have some assemblies in my model that have surface treatment for "no paint" applied. Depending on how i apply the surface treatment it might add to the weight or remove weight depending on the grade that is used. Why is this happening?

Answer: The following examples will explain why and how the weight is affected differently when surface treatments are applied.

First of all, Surface Treatment is "Zero_density" in general, which means that any part of the object that the surface treatment exists on has that volume of the part removed.
Let's look at the example below.

This piece is a beam with no added parts or surface treatment. Its weight and assembly weight are both 401.6 lbf.

In the next image, surface treatment is added for fireproofing the beam. Both the assembly weight and the weight remain at 401.6 lbf.
In the blow up view you can see that this is because the blue surface treatment is outside the material of the beam. In other words, the beam and the surface treatment are separate parts in the model. This is how surface treatments are added correctly, because the surface treatment should not be inside the beam.




However, if the surface treatment has the value of "Zero_density", it means that all density values are 0. In this case, surface treatment can be added inside the material but the assembly weight remains the same.

In the image below, the value was changed to A992, which can be used for Steel I beam.The surface treatment is applied inside the material but the assembly weight stays the same. 


The problem with this method is the fact that if the surface treatment is now pushed outside the beam the weight of the surface treatment is added.