I guess you are referring to the corner of the part facing you in the first figure, and the sliced corner on the left in the second figure and not the white lines on the wall facing you. This latter effect is called Moiré or moiré pattern which is an optical illusion created by interference.

This appears to be a slicer error or a rendering error, the walls are not finished. Furthermore from your sparse question it is noteworthy to say that you have sliced the model on a raft.

Why not print the model, it will start a raft and when you come to the part it will clearly show whether it is a slicing or a rendering problem!

If it is a rendering problem, keep continuing printing, if not stop the print and download a most recent version of any other free available slicer tool. The most commonly used free slicer tools are Ultimaker Cura and Slic3r. Setup a printer profile and select and modify material and slicing properties to create a new G-code file for you to print. You can now compare the rendering of used new tool to your current rendering and print the model to see if the part now prints well.

I guess you are referring to the corner of the part facing you in the first figure, and the sliced corner on the left in the second figure and not the white lines on the wall facing you. This latter effect is called Moiré or moiré pattern which is an optical illusion created by interference.

This appears to be a slicer error or a rendering error, the walls are not finished. Furthermore from your sparse question it is noteworthy to say that you have sliced the model on a raft.

Why not print the model, it will start a raft and when you come to the part it will clearly show whether it is a slicing or a rendering problem!

If it is a rendering problem, keep continuing printing, if not, stop the print and download a most recent version of any other free available slicer tool. The most commonly used free slicer tools are Ultimaker Cura and Slic3r. Setup a printer profile and select and modify material and slicing properties to create a new G-code file for you to print. You can now compare the rendering of used new tool to your current rendering and print the model to see if the part now prints well.

I guess you are referring to the corner of the part facing you in the first figure, and the sliced corner on the left in the second figure.

This appears to be a slicer error or a rendering error, the walls are not finished. Furthermore from your sparse question it is noteworthy to say that you have sliced the model on a raft.

Why not print the model, it will start a raft and when you come to the part it will clearly show whether it is a slicing or a rendering problem!

If it is a rendering problem, keep continuing printing, if not stop the print and download a most recent version of any other free available slicer tool. The most commonly used free slicer tools are Ultimaker Cura and Slic3r. Setup a printer profile and select and modify material and slicing properties to create a new G-code file for you to print. You can now compare the rendering of used new tool to your current rendering and print the model to see if the part now prints well.

I guess you are referring to the corner of the part facing you in the first figure, and the sliced corner on the left in the second figure and not the white lines on the wall facing you. This latter effect is called Moiré or moiré pattern which is an optical illusion created by interference.

This appears to be a slicer error or a rendering error, the walls are not finished. Furthermore from your sparse question it is noteworthy to say that you have sliced the model on a raft.

Why not print the model, it will start a raft and when you come to the part it will clearly show whether it is a slicing or a rendering problem!

If it is a rendering problem, keep continuing printing, if not stop the print and download a most recent version of any other free available slicer tool. The most commonly used free slicer tools are Ultimaker Cura and Slic3r. Setup a printer profile and select and modify material and slicing properties to create a new G-code file for you to print. You can now compare the rendering of used new tool to your current rendering and print the model to see if the part now prints well.