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Patio cement blocks are not very hard to cut by because they are not very hard... by concrete standards, anyway! Using a power tool is definitely the method of choice if you want your job to have the most professional appearance! You have a couple of tool choices. The first is to use your own hand-held circular saw. The blade to use is a special fibrous non-metallic blade designed specifically for cutting cement. If you are only cutting a half dozen blocks, just buy one of these blades for your saw and go to town. However, be warned that concrete dust can damage the motor over time.
If you have a lot of block to cut, please don't destroy your own hard-working saw! Instead, visit the local rental store and look over their offerings. There are a number of heavy-duty hand-held and table-type saws available that will make short work of that block and save your own saw for what it does best… cutting wood!