Bake normal map

I created a simple stairs with a little bit beveled edges and some damage at some of those edges.
I want to bake the bevel and the damage to much more low poly model which i did and i have the baked normal map for those details.

Now my problem is that i have already a normal map for the concrete texture i want to use for this model, how can i combine those two normal maps ( The one i baked for the bevel and the damaged sections and the normal for the concrete texture ) into one map?
Is it possible to texture the high poly model and bake the bevel and the damage and the texture details at once inside blender? Or i need external image editor for this?

Anyone?? ?

Maybe experiment with using the compositor to mix them together with a mix node(assuming they are the same size and the uv map is the same) and try different settings to see what kind of effect you get. I haven’t tried using separate normal maps before, so I don’t have much insight to offer.

Thanks for your help but i don’t know anything about composting, and i want a way that is simple, fast and get the job done.
Anybody can share his knowledge?

http://www.rodgreen.com/?p=4
Photoshop technique, I guess you could use something like it in Gimp.

I am not sure of the idea of baking the two together, since they might nullify the affect of effect of each other in parts.

Absolutely. Use the concrete texture as a normal or displacement map for the high-poly model, then bake from high-poly to low-poly as usual.

Best wishes,
Matthew

Thanks MCollett, but can you please explain how to use the texture as a normal map? I am a real noob here.