can anyone tell me how big of an air compressor is needed for shotcrete? contractor has 175 cfm is that big enough? never done shotcrete before so i don't know for sure. 

Everyone I ever spoke to said the same thing. 185cfm.

I have watched but never done one ounce myself.

I dont know what that is but as long as its one of those compressors they use for jack hammers and stuff it should be good. some got a pressure regulator where you hook up the hose, i had to take those off in order to get the pressure we needed.

Oh when you stop pumping make sure you leave the air on just a bit to keep the jets from plugging up.

185 cfm is min. with 1 inch hose i tape it to the 2 inch concrete hose with duct tape.  use safety whips on air hose connections. 

I am not an athority on the subject, but just talked to a friend of mine who does shotcrete full time.  He said 175 cfm is plenty if you are not using the large nozzle which is designed to introduce additives at the tip.  If you are using a regular nozzel, you should be fine with 175 to 185 cfm.  He said that if you want to test it, try hooking it up and then open the valve completely.  If your air hose pressure doesn't drop below 75 psi you should be good to go. 

Hope this was some kind of help.

I went to a lecture @ world of concrete and the guy said use a minimum of 200 cfm. Over time the compressor will become less efficient. The manual for my line pump says to let a little cement come out b4 the nozzle goes on and use a vibrator on the hopper and right b4 the pool or whatever you're building.