Grinding overworked concrete

[wmc-wood]

I am about 70% finished grinding 900 sqft garage floor. The slab is 7 years old and never had any finish on it, area was used for storage. The Edco was doing well and occasionaly took a bit to longer to cut the darker top layer. once past the top 1/32, grinding is easy again. The last part is killing me! A new cutter will work well for about 7 minutes then it barely cuts and almost floats on top. I tried a 7" diamond cup on my grinder and that works slightly better but you still got to work at it. I spent atleast 16 hours so far and both the Edco and I slowed drasticaly at the end of today. I wanted to do a acid stain and clear, so i need to cut through the top layer or the last 30% will look nothing like the first part.
Any suggestions?
Thanks

 

[Edger]

That last part is definitely harder. You will have success if you use water and grind with a constant wet mud around the head. This helps to keep the diamonds exposed because hard concrete closes up the diamond segments and they polish instead of cut.

The slurry is a pain, but it can be washed out (don't stain your drive) or vacuum sucked up.

 

[Ultimate Floors by Rhino]

Post a picture of the blade your using on the edco.

 

[Edger]

If you want to know more about grinding hard concrete go to http://www.situp.com.au/Grinding Hard Concrete.html

 

[wmc-wood]

Edger, I did get a minute to try water with the diamond cup and it did appear to help. i will probably grind the top that way and continue with the EDCO over everything. Thanks
AJ, i called it a cutter but i guess it is a stone. basic Edco or nortan.
One rental shop recomended a Scarifier but i dont want the last part done to look differnt from the rest
Thank you for the replies
~Bill

 

[Edger]

Sorry wmc-wood, I know the webpage suggests water with the cupwheel, but I meant water with the Edco which runs slower and will create a slurry.

 

[tlmartin84]

How about spraying it down with muriatic acid, then allowing it to set until you see foaming and then grinding. Thats how we clean and etch all concrete for epoxy coating on abutments (we use a wire brush on a grinder though instead of a cutter).....