How do you replace a built in bathroom counter top and put in a porcelain counter top?
Check underneath the existing countertop to see how it is fastened to the cabinet. Turn off the water to the faucet and remove the faucet, and sink (unless the sink is built-in), and loosen the plumbing. Any trim or tile around the top will have to be removed, then the top can be removed. It should be fastened to the cabinet using screws or clips. then the new countertop can be installed in the same manner. Here is an article that may be of interest. I hope this helps!
The porcelain countertop fabricaters usually remove to measure for install.
It is not clear what you mean by a 'built in' counter top. Are you wanting to replace what I am guessing to be a laminate counter top with a conventional basin, with an integrated porcelain countertop and sink? (picture shown below)
Please post a picture so we can see what you are starting with.
Need to take off sink and the cabinet top the sink is sitting in. It is a built in sink cabinet
One thing to be aware of when replacing existing sinks with a new integrated sink and counter top such as the example in the picture above, is the distance the existing tap/faucet drain pipes project from the wall.
You did not say whether or not you also wanted to purchase new taps/faucet (the example above shows a one hole style suitable for a single lever integrated tap and faucet mechanism.) However, in order that your new set up connects to the existing drain pipes below the countertop, you may have to either purchase new and /or purchase additional plumbing pieces so that the new fits properly on to the the old drain pipe that goes into the wall.
See if these videos may help: