Thermofoil cabinets are made from a laminate substance that is fused over the top of particle board. Thermofoil is made to be easy to clean, resistant to stains and difficult to damage. As a result, thermofoil is also very difficult to paint. But it is not impossible. Paint is an inexpensive alternative to replacing your cabinets and you should absolutely try to paint the thermofoil before going to the expense of ripping out your cabinets. You will love the results as long as you prep the surface well before you get started.
Prepping the Surface
Clean the cabinets thoroughly to remove all grease and residue. Kitchen cabinets in particular are coated with cooking oils and the oils from your fingers. Use an ammonia-based cleaner to completely clean the cabinets. Let them dry completely. You also need to sand the cabinets well before you begin painting. Use a fine grit sandpaper to lightly rough up the surface. A palm sander will make the job go a lot quicker. The vibration from a palm sander makes the sanding job smoother and more thorough than hand sanding. Focus on creating texture on the cabinets, not on removing the finish. You don't want to sand so much that you sand through the laminate coating. Wipe away all of the sanding dust with a damp rag.
Primer and Paint
The primer is a crucial component when you are attempting to paint a slick surface like Thermofoil. Choose a good bonding primer like Zinsser B-I-N. Zinsser has shellac in it and will stick like glue to the surface of the cabinets. Use a foam roller to apply the primer. A foam roller will apply the paint in a smooth and even coat. You can choose to use any water-based latex paint for the cabinets. Enamel paints are also a good choice because they are extremely durable and will last a long time without chipping and scratching. Enamel is typically very glossy. Choose a satin finish latex paint if you aren't interested in a high gloss finish. Paint the cabinets with multiple thin coats of paint. A foam roller will give you the smoothest finish. Lightly sand the cabinets with fine grit sandpaper between coats. Allow each coat to dry completely before sanding and applying the next coat.
Sealing the Cabinets
For extra protection, add a coat of water-based polyurethane once your cabinets have dried completely. Use good quality brushes to apply polyurethane. Polyurethane comes in matt, satin and gloss finishes. All three will provide good protection. Choose the finish that you like best. Allow the cabinets to cure for seven to 10 days before you subject them to a lot of abuse. The paint will be soft and will dent and peel easily for the first week.