Fir siding

[hopm]

Took on a project sawing 12"x6"x12' fir beams into exterior siding. Sawed to 7/16" and it sawed out great. I was pleased with the outcome.....but....customer was concerned as to how the sawed finish would take stain evenly. He requested I plane it to 5/16". I put new blades on the planer before I started but I'm having a lot of tear out and breakage. This stuff is like glass. I'm considering sanding. I have access to a commercial belt sander. Any suggestion or guidance would be much appreciated!!!

[ladylake]

  I think 5/16 is way to thin for siding , tell him to spray the stain on, I have rough cedar on my house which covers real nice with a spayer.   Steve

[doc henderson]

I think rough sawn is great and will hold the finish better.  it must not be tapered.  how dry is it?  a drum sander would not give the tear out.  or will it be painted?  I sawed a cedar beam to 4/4 and made about 4 very nice potting benches,  rough sawn.

[beenthere]

Customers concern now wasn't in the deal initially (I presume) so suggest getting paid for the job you "took on". 
Then let customer know that there are options that you can or cannot do (plane or sand), but they will cost more $$ and be up front about it. 
Unless you are just doing this "for the fun of it"