Our kitchen is made almost entirely from MDF.
We have 1 closet where the hinges have pulled out and several drawers where the screws have pulled out. The MDF around the screws has just been eroded so the screws no longer fix in.
What is the best way to fix these screws so they stay in?
For the hinges, you can try moving them if the have the correct drills to make new mounting wholes, so try a Kitchen Door Hinge Repair Plate
Depending what is on the other side of the MDF, you may be able to use a bolt with a washer.
If the screws go into the end of the MDF, try longer screws.
For holes that are the right shape, but worn, add some wood glue, and screw it back in. For a little extra friction, stick a little piece of one of those plastic coffee stirs in there too.
If chunks of mdf have broken off with your screw, you'll need to cut some more away, and glue a replacement block in place.
It's important to use a clamp when gluing pieces together. Then lightly sand (just to rough the surface), clean, and prime, before repainting.
You can repair them in a way that is likely stronger than the original by gluing in some dowels and then re-drilling the proper sized holes.
Buy some wood dowel at the hardware store, something around 1/4" diameter will probably work. Then drill out the old holes to match the dowel (you should use some scrap material and check the fit before drilling out the holes in the cabinets in case the dowel is slightly undersized). Cut the dowel to just shorter than the hole you drilled out and glue it in. Pound it in flush, otherwise you will have extra work of trimming or sanding it flush. When the glue is dry drill pilot holes for your screws and replace the doors.
+1 for Brian's suggestion on cutting away the damaged area. This will help you get a clean edge to glue a replacement block in place, which will improve adhesion between the old and new surfaces. The less gaps and the tighter the fit, the more securely glue will hold it. That's probably your best bet without investing tons of time and effort.
You could also try filling in the holes with wood putty if it's a small enough area, and then try screwing in the mounting hardware somewhere else along the piece.
But the sturdiest thing is probably to replace each component as it fails.
MDF is a terrible substance to screw into because it doesn't hold mechanical fasteners well, as you've seen. It's usually better backed up by something that can handle higher stresses.
If it's not cost-prohibitive or you have some tools around, you might consider replacing each failed unit with something stronger like plywood. Otherwise you're probably going to keep running into this. The only downside is it's much more involved than a simple repair and it will probably alter the finished look unless you can manage to use the existing material as a surface layer on new construction.
Just jamb a couple of toothpicks into the screw holes, then replace the screws and you should find plenty of bite.
Just another solution from an old magazine I once read:
Take a golf tee, fill the hole with glue, tap the golf tee into the hole. Let dry. Cut off golf tee flush. Screw will now hold again.
