Is it feasible to replace that chip board with 1/2 inch drywall?
Because of the swelling and shrinking of the wood with changes in it's
moisture content, you're always going to get a hairline crack opening up
over the joint between the two materials.
However, if I were to do this, I'd:
1. Apply self adhesive fiberglass mesh drywall joint tape to the joint
between the drywall and the chip board.
2. Dilute some white wood glue to a paintable consistancy and paint the
chipboard with that diluted glue. Also paint the fiberglass mesh tape
on both sides of the joint. As the glue dries, it'll help bond the
fiberglass mesh tape to both the chip board and the drywall. There's no
problem letting the glue dry because white wood glue re-emulsifies when
it gets wet, so the wet drywall joint compound you put on the dried glue
will reactivate the glue and it'll help bond the joint compound to the
3. I would use a "curved trowel" to apply joint compound over the tape.
A curved trowel looks like an ordinary plastering trowel until you set
it down on a flat surface or sight along it's edge and notice that it
arches upward in the middle about 1/8 of an inch.
':: WALLBOARD Trim & Tool :: Curved Blade Drywall Trowel'
Because you hold the trowel at a confortable angle to the wall when
using it, a curved trowel allows you to spread a perfectly symmetric
"mound" of drywall joint compound over the fiberglass mesh tape that's
only about 5/64ths inches thick in the middle. That's too thin to show
as a "bump" on the wall, but it's plenty thick enough to cover
fiberglass mesh tape.
The curved trowel will make it easier to deal with the chipboard and
drywall not being perfectly flush at the joint as well. That's because
it's only the corners of the curved trowel that contact the wall, so
things don't have to be flush in between. If the chipboard is wider
than a few inches, I'd just use a regular trowel everywhere except over
4. Sand smooth while holding a bright light close to the wall. The
sharp angle at which the light hits the wall exagerates the roughness of
the joint compound making it easy to see bumps that need to be sanded
down and dips that need to be filled in with more joint compound.
5. Prime and paint.