You are not expected to tip within Laos, however it's up to you. If you are quite happy to pay a bit extra for the quality of their service, then by all means, offer them a tip but not under normal circumstances. In Laos, the best thing to do to show your appreciation for good service is be pleasant and polite to the staff.
Laos is a developing country and most staff in Laos are paid a pittance so they must make up their income to a living wage via tips. Tips aren't expected, but course they're always appreciated.
You'll never find any employees in Laos refusing to finish a job, or threatening to quit, because they weren't tipped or felt that a tip wasn't enough. They will be paid for their work and they're expected to do a good job regardless.
If you want to leave a tip, please be generous and give them kips which is the currency of Laos, or foreign currency with some value. Leaving One Baht or a One Cent Penny as a tip is a deliberate insult to Lao people and is best avoided.