Originally Posted by granite-girl
So Nestor- Are you saying that a cast iron sink is more likely to let water seep under it to the laminate ?
No, I'm not saying that any sink would be more likely to leak water than any other.
Or just while it's apart & he has an empty hole, take care of that then ?
After the sink (and faucet holes, if any) have been cut, but before the top is installed, it's best to protect against water by painting any areas that are likely to get wet with an oil based paint. (Ideally, painting with boiled linseed oil would be best because it penetrates into wood more than modern alkyd paints, but any protection is better than no protection. Boiled linseed oil is gonna take days to dry versus a few hours for alkyd paints.)
Protecting the back side of the front bullnose (in my opinion) is something that everyone SHOULD do. Water dripping off the top in one area repeatedly or condensation on the underside or back of the front bullnose from repeatedly opening a hot dishwasher is gonna cause the particle board in that area to absorb water and swell. Since the plastic laminate doesn't swell, then somethin's gotta give, and the result is usually the glued bond between the laminate and particle board breaking.
That post-formed laminate used to make counter tops is darn near paper thin, and as soon as it's no longer glued down solid to something solid then it becomes extremely susceptible to breaking. And, that's usually the beginning of the end for plastic laminate counter tops.
I've painted every laminate top I've installed in my own building cuz I know it won't do any harm, but I can see that it will maximize the lifespan of the top by keeping the wood dry and the laminate well supported so it doesn't break. I call that doing what makes sense rather than asking a pro how it's supposed to be done cuz no pro will ever take the time to do this cuz the customer will never notice. And, most customers will figure that the cost of doing this should be included in their quote and scream bloody blue murder if it's not done.
PS: If I had a prefab laminate top that was already installed by a pro, I'd either caulk the joint between the front bullnose and the cabinet if it's tight (with even a latex caulk or something that was easy to remove) or try to sneak some paint or other sealant in there with a Q-tip or something if there's room. You don't have to seal the whole back of the front bullnose, just the bottom portion where water drops would collect. I'd seal the whole area behind the front bullnose over/infrontof the dish washer, tho.