If you install a concrete countertop you are going to have to add a sealant to protect it from heat, stains, UV rays, and scratches. Not to mention bacteria production.
Step 1 - Choose Your Sealant
If your counter has been polished with a grit finer than 200, it is too smooth for topical sealers; when polished to a gloss you can only use penetrating sealers.
Step 2 - Clean the Countertop
Wash the countertop really well with vinegar so that you can get all the grit and excess cement powder off it. Make sure you saturate it thoroughly. Then rinse and squeegee it off and get ready to apply the sealant.
Step 3 - Apply the Sealant
Regardless of which sealant you are using, it is applied the same way. Just brush it on with a paintbrush or you can spray it on. Make sure that you get a good coat of it on and then wipe off the excess with a soft cloth. Once dried these are the best sealants to cover all the areas you need covered. There are none that are completely stain proof that will leave the concrete looking like concrete. So any stains on this need to wiped off before they set.