Protecting blogs from editing

I plan to have two types of articles written on my xwiki (turmerictalks). One will be a wiki type, consisting of collaboratively written/edited articles. The other will be blogs. Blogs do not normally allow editing except by the blogger, but allow comments. I have created two different space for these two types. Configuring the access levels for the wiki type is straightforward. The blog type however poses problems. If I denied edit rights for an authenticated group of bloggers, the current service prevents writing too. Any suggestions? Thanks.