You can use the Select brush to 'mask' a portion of the mesh so that only the desired area will be affected by the subsequent tool operations. Select the faces with the select brush, right-click and choose 'Make Group and Edit' to sculpt only the masked area. (Be sure Lock Boundary is enabled)
You can remove the mask by using the SketchUp Explode feature.
Performance and Frame Rate
Artisan sculpting may be limited by the inherent slowness of SketchUp and the API relative to other 3D modeling applications.
- Use slower strokes and use less detail where possible to maintain a useable refresh rate.
- Temporarily hide objects and geometry (or turn off tags) that are not being edited as SketchUp tends to be faster with less geometry visible.
- Use Sculpt Shading Mode and turn off 'Display Edges' for better performance.
- Use the Reducer Brush on flatter areas to reduce your polycount.
- Disabling 'Optimize Mesh' and 'Add Detail' will also help to increase the frame rate.
Optimum Strength Value
You can achieve better control of your sculpting by using a small strength value and multiple strokes as opposed to using a high strength value with fewer strokes.
It is recommended to keep your strength value in the range of 5% - 30%.