It depends. I’m not familiar with the Herbie’s Mat. How thick is the washer? Does it rise above the level of the mat?
By far the most effective way to clamp with a washer is with a threaded spindle and a tapped concave bottom clamp. This allows sufficient force to flatten a record against the platter and effectively create a vacuum between the platter and record. However, if you don’t have a threaded spindle, you can try something like the Record Doctor clamp and see if that works It has the right kind of bottom, but has a tightening mechanism that uses friction in order to hold the spindle. You would have to exert some degree of downward force while tightening it to get the same effect, if you can even do that.
VPI clamp: https://cdn.shopify.com/s/files/1/0105/4542/products/vpi-deluxeclamp-3_1800x.jpg?v=1571265214
Record Doctor Clamp: https://www.audioadvisor.com/images/RDRC_BLK_BTTM.jpg
Edit: I believe also the Sota Reflex clamp does something similar with friction, but as you snap the lever down, it grabs the spindle and moves the weight downward to clamp the record tight. I can't find a picture of the bottom, but you can add a rubber ring around the periphery if it doesn't have a concave base.
By far the most effective way to clamp with a washer is with a threaded spindle and a tapped concave bottom clamp. This allows sufficient force to flatten a record against the platter and effectively create a vacuum between the platter and record. However, if you don’t have a threaded spindle, you can try something like the Record Doctor clamp and see if that works It has the right kind of bottom, but has a tightening mechanism that uses friction in order to hold the spindle. You would have to exert some degree of downward force while tightening it to get the same effect, if you can even do that.
VPI clamp: https://cdn.shopify.com/s/files/1/0105/4542/products/vpi-deluxeclamp-3_1800x.jpg?v=1571265214
Record Doctor Clamp: https://www.audioadvisor.com/images/RDRC_BLK_BTTM.jpg
Edit: I believe also the Sota Reflex clamp does something similar with friction, but as you snap the lever down, it grabs the spindle and moves the weight downward to clamp the record tight. I can't find a picture of the bottom, but you can add a rubber ring around the periphery if it doesn't have a concave base.