but maybe one. Does the brick around the oven get warm or hot?
get some silicon/latex white caulk and caulk in all the cracks and imperfections.
Get a three inch brush that will load up alot of paint. then get a gallon of latex primer and a gallon of finish coat. Apply about three coats of primer, allow proper drying time between each coat, then apply your finish coat, go with two coats. The more coats you apply the more the brick and mortar are filled in.