Buffering Writes The Serial Port?

Im trying to buffer data being written to a device on a com port. The equipment attached to it does not use any form of flow contol and if you write to much information to quickly it falls over. So I have had the following thoughts.

I would create a list of strings and when I wanted to write data to the com Port I would just add the string to the list. I would then have a Sub running its own thread to step through the list, write the string to the com port ,pause a fixed amount of time, remove string from list and repeat until the list is empty. Then keep looping the above.

Code I have so far is below

Private MsgList as new List (of string)
Private sub MsgPump ()
Do

[Code]....

THis does work but If I add strings to MsgList to quickly it throws an exception.