Sand over ABS Plastic

Hello,I have a 40 gallon frag tank (used as a display) and it is only about 1 month old, at first i decided to go BB and had black ABS cut out for the bottom of the tank. Now, from more research I believe I want to use a shallow sand bed, my question is can i just slowly put the sand over the ABS plastic or should i take it out first? Also if you have any suggestions for the best type of sand i would love to hear them.