Knauf Soundboard not breaking cleanly

[roofmog]

I've just started my first foray into plaster boarding. I'm adding some soundproofing in an alcove next to my fireplace. However, the Knauf Soundboard that I am working with does not seen the break particularly cleanly. I'm scoring with a straight edge, and then snapping the board as I have seen demonstrated in several online videos. However, I never get a completely clean break, with the edge always ending up pitted. Am I not scoring hard enough, or possibly too hard? Or is there something else I should be doing?

 

[Jadele]

you score it hard, hard as poss really. Bang it hard behind the core, fold it back on itself and cut it up the back
the back

 

[stevethespreader]

When boarding always have a surform handy to trim to size and to straighten up any rough edges

 

[chappers]

^^^This

 

[roofmog]

Thanks for the help. Subsequent boards broke a lot more evenly.

 

[Happyplumber]

The board is a lot more dense then standard PB and also has some fibres added into the chalk material in the construction to give it more strength due to the weight
Like Steve said it's always a good idea to have a Stanley Sure form handy to tidy up the edges where necessary