Small texture error.

I think this kind of thing first showed up when garrys mod changed to source 2

(look at the walls for the problem.)

I just installed garrys mod on my new laptop which has this spec:
(it can also run oblivion so I don’t think it is the graphics card)
intel pentium dual-core 2.0ghz
up to 1244mb mobile intel graphics
4gb ddr2 ram
I’m on Vista home basic.

How do I fix this issue?

Try changing the texture quality from Very High to High.