[Highland Park] Shop vac

We are trying to clean our basement floor of the white plaster-type stuff that is flaking off the walls lo these many years. I rented a shop vac from Home Depot (only $5/day) and although it was clean inside and they showed me the filter which looked clean (which someone had warned me about), it does not have very much suction at all. I may take it back and see if I am doing something wrong. I thought I'd see if anyone in the neighborhood has a shop vac (dry use) that I could borrow or rent. I know it is a lot to ask but I thought I'd try. I would need it for 1/2 a day probably. Or if you have any tips for improving the suction, I would appreciate it. Many thanks, Susan --