I'm not entirely sure what you are talking about. Do you mean the seams of concrete that come out between the boards on forms? If so I would, I use pieces of styrene cut to the sizes between seams. I would think you could then use a solvent type glue and press the pieces together until the softened styrene pushes out like the seams of concrete. In ho scale the seams would be very small. Remember that 1/16th of an inch is very close to 6 inches, so the seams would protrude no more than 1/32 or even 1/64th of an inch.