The ceiling may be sprayed and look professional if the stippled effect is very light. A ceiling with very heavy peaks and valleys may not look so good once additional plaster is applied. Ensure the ceiling texture is adhering to the wall well. There should not be signs of peeling or loose texture.
Attempt to mimic the current stippled look on a few pieces of cardboard. Stippled paint is often rolled on joint compound. You may also look for paintable wallpapers mimicking this effect. Spray on additional texture to understand what the final, plastered ceiling may look like. Practice several times to see if you like the look for your home's ceiling.
If you decide to spray your ceiling with additional texture, a few preparation tips are key. Lightly wash the ceiling with a damp sponge or rag. Use a vacuum to suction away any dust, cobwebs or grime. Paint the ceiling with a bonding primer to ensure the textures stick and bind together. You do not want the textures to begin separating or peeling apart in the future.
If your stippled ceiling is loose, peeling or damaged and you feel the second layer of texture will not bond with the plaster, you may need to remove the plaster. Only do this if you are absolutely sure you want a new look as it is very messy and tedious. The texture must be sanded, moistened and scrapped off with a putty knife. To save money, hire a professional drywall professional to perform this task. You can then complete the project by respraying the texture yourself and saving money.