How to Seal a Chalkboard
There are a couple of reasons why you might want to seal a chalkboard. The first reason is to seal a porous surface (such as a painted chalkboard) so that you can easily erase your liquid chalk markers. The second reason is you would like to seal over top of your chalk markers so they can't be erased.
In either case, we recommend using either Krylon Crystal Clear Acrylic Spray or if you prefer a matte finish, then Aleene's Spray Acrylic Sealer Matte Finish will work well. Apply 3 coats of sealer if you are sealing a porous surface so that you can easily erase your chalk markers in the future. A single coat should do if you are sealing over top of your chalk markers so they can't be erased. Be sure to follow the manufacturer's instructions on the spray can.
Of course, please test in a small inconspicuous area first! We'd hate for something to go wrong, so please test first.