If I use contact paper on bathroom counter, do I seal with a poly coat

Short answer is "no". Poly won't stick. Here's an instruction for using contact paper on your counter:

http://www.makedoanddiy.com/2015/10/contact-paper-counter-faux-marble-diy.html

Not needed! Contact paper is vinyl so it already is waterproof. Also it's easier to remove if you ever need to.

no......

If you feel you need a protector to make it more durable & less likely the colored designs on the contact paper will wear off or that something is accidentally spilled on it that would affect the design, you can cover it with a layer of clear contact paper that will act as a sealer. Do not paint it.

To apply the clear contact paper, cut the pieces & apply so that seams are not on top of each other with the 2 different vinyl papers. This will make it more durable & less likely to separate & peel up later.

When you apply the clear, it helps to use the back of the countertop as your straight edge. That way, you can trim off any bits of overhang on front edges & ends so as to have them exact fit one on top of the other. To avoid & be able to work out any bubbles, creases, or areas that don't want to lay perfectly flat, it's much easier to work in small areas peeling the paper backing so as not to "stretch" the vinyl. Remember, this is vinyl you are working with & vinyls will stretch slightly. Once countertop is done, then, do your backsplash same way. If protector is desired on it. Backsplashes don't usually get the abuse & beating for lack of better words that counter-tops get.

When your clear applications are complete & you're happy with them, you CAN seal the edges where countertop & backsplash meet as well as outside edges. Squeeze a small bead of clear acrylic/silicone caulking where you need it & smooth with your finger. Cleanup with damp rag as you normally would. Let cure undisturbed over night.

I hope this helps & gives you some piece of mind that your contact paper will be durable & last a long time.

i did that and it turned out so good! and more durable

Contact paper.... not a good idea... and it will look terrible if installed badly. Consider replacing it with a formica top or butcher block and then using a Spar Varnish type of sealer to water proof it

Use Perspex if you need too or Toughened Glass. Better still Tile it!

Hi Robin: Not sure if you'd be happy with it on your counter. The backsplash may be o.k., and no need to seal it. For the counter, try some linoleum remnants or some stick on flooring tiles. Also waterproof, and they won't tear as easily as contact paper will.

You can but as Ken pointed out, it’s not going to be a permanent fix, just a temporary one. Sealing it will make it very tough to remove when it gets damaged so I wouldn’t recommend that.

No, it doesn't need to be sealed.

If you think you will ever want to change the contact paper, I would not seal it with poly. If you do, it will be nearly impossible to remove later.