Used Kiln Shelves - Safe or Replace?

[Ja.Sc.]

I purchased a used kiln from a rural area school, they were downsizing to a smaller kiln requiring less power and to be able to fire more frequently.  There are some nasty looking pits in the a couple shelves from melted, clay/glaze/something that make me wonder if I should even use them.   They definitely didn't fire past cone 6, which is all I intend to go to, but can this leftover fused gunk further compromise the shelf?  I haven't fired the kiln yet, but I'm getting close to the first bisque load.  Should I get a replacement?

There are also a few shelves with large patches of run glaze.  I've been working on chipping that off,  how thorough do I need to be?  If there is a pin head spot of glaze under the kiln wash, should I take that out?

These are the worst of them. 

[neilestrick]

I wouldn't mess with the one with the big black pits. The others you can grind smooth and then coat them with kiln wash. Any small amount of remaining glaze will absorb the kiln wash and stiffen up, and can then be re-ground and re-coated if needed.

[Potterbabe]

I use a 6” carbide stone rubbing brick used to grind down concrete marks from molds.  It cleans up shelves quickly and costs about $16.  They are available in the concrete section of big box hardware stores.  Not sure about the black icky shelf but Im always up for a challenge because I fired kilns in a community center for years and have seen all sorts of stuff stuck to shelves.  If you want to toss it break it up in small pieces and use the clean bits as post spacers or under uncertain-maybe-might-run glazed work.

[Denice]

If you have an area that you can't get clean you can always avoid setting a piece in that area.   I have a shelf that has some impurities in the shelf material that has come to the surface,  I can't grind it out so I just avoid that area.   Denice

[Ja.Sc.]

Thanks for the recommendations everyone! You saved me a bunch of time!  

I picked up a rubbing brick and it worked like a charm.  There's still some spots on the shelves that would require chiseling, but those are flush and I'll cover with kiln wash.