I'm currently on a double entry tourist visa which I can extend for the last time in a few days. I want to change to a non-immigrant B as I have employment in Thailand. The HR department suggested I could change my visa from tourist to non-b but when she looked and saw the tourist visa expired in a few days said there wasn't enough time. I tried in vain to tell her the tourist visa could be extended. She's now preparing the documents to send me off to Laos. Is there any reason why I shouldn't extend the tourist visa and apply for a change in visa status to non-b?

Keeping your employer happy is a probably the best reason. If they give you paperwork to obtain the non immigrant B visa it will save the 1,900 baht extension charge so financially it depends on what, if anything, they will pay for.

I'm currently on a double entry tourist visa which I can extend for the last time in a few days. I want to change to a non-immigrant B as I have employment in Thailand. The HR department suggested I could change my visa from tourist to non-b but when she looked and saw the tourist visa expired in a few days said there wasn't enough time. I tried in vain to tell her the tourist visa could be extended. She's now preparing the documents to send me off to Laos. Is there any reason why I shouldn't extend the tourist visa and apply for a change in visa status to non-b?

Probably you do have a 60 day tourist visa, and you're close to day 60. Right? This means that the original visa will expire in a few days and that you can extend your STAY but not the validity of your visa.

As far as I know there should be at least 21 days left on the original visa in order to change a tourist into a non-B or other non-immigrant-visa.

The 21 day rule is for your permitted to stay stamp - not the visa (which expired on use).

Yes, I'm close to day 60 of my 60 day tourist visa. HR are right then - changing it is a non-starter. Thanks for the help.