Ogre Club armour modifier question

Hello all,

I'm relitively new to OK and WHFB so i'm sorry if this seems like a daft question

From reading the OK armies book I think I understand that I gain a -1 armour modifier if I use the ogre club on it's own, but does this stack with the modifier for unit being strength 4.

Or is the club modifier representing the units S4 modifier?

I hope I haven't confused too many of you trying to explain myself  

It does stack.

An ogre using the club inflicts an extra -1 on top of any modifier for strength.

From reading the OK armies book I think I understand that I gain a -1 armour modifier if I use the ogre club on it's own, but does this stack with the modifier for unit being strength 4.

It's in addition to any modifiers for Strength.

Not all club-wielders are S4 (they can actually go up to S7 under the right circumstances), so putting in -1 would be misleading.

Yes as said in the army book, you benefit of the armour piercing if your ogre is armed with a club only. So yes, strength 4 + armour piercing gives your opponent a -2 to armour save if wounded.