How can I fix range hood mounting holes in an MDF cabinet?

Question

Had an installer come out a few weeks ago to do a range hood. He messed up some of the mounts for underneath the cabinet and many of the holes are stripped now. I need to take it down to adjust it but I'm worried the surviving screws won't go back in when I reattach it since the cabinets are made of MDF.

• Would it be reasonable to put some wood blocks inside the cabinets and use longer screws to mount into them?
• Use a different fastener?
• Patch the holes in the MDF?

Open to ideas.

More information:

This is the hood: https://www.homedepot.com/p/Cosmo-30-in-Ducted-Under-Cabinet-Range-Hood-in-Stainless-Steel-with-LED-Lighting-and-Permanent-Filters-UC30/206686542

Per the instructions, the unit is meant to be hung from the wall and screwed into the cabinet above.

Cabinet looks similar to these, with a recessed bottom about half an inch: https://www.cabinetdistribution.com/cabinets/rta-kitchen-cabinets/dove-gray.html

Looking at it again it looks like the included screws were barely long enough to penetrate the bottom of the cabinet to begin with.

Answer 1

Adding a real wood or plywood block inside the cabinet and driving the screws through the MDF into that would work. Of course, you'd also need to securely glue these wood blocks to the cabinet itself.

Using a different fastener, such as a nut & bolt with washers at each end would certainly work. Use a large fender washer to spread the clamping force across as much MDF as possible and don't over tighten.

Patching holes in MDF doesn't really work all that well. MDF is saw dust and resin, cured under heat and high pressure. Filling the hole with a good quality epoxy might work, then you could drill a pilot hole in the epoxy for the screws. But the epoxy plug might just pop right back out of the MDF, depending on the shape and texture of the hole that was plugged. Also, plugging the hole up to ensure the epoxy doesn't leak out may or may not work well.

Patching MDF with the traditional "glue and match sticks" probably won't work all that well, either, again due to the way MDF is made, more than the patching method.

Answer 2

Threaded inserts should work well with MDF, you need to drill an over-sized hole then screw the insert in with a hex driver and a suitable machine screw can be screwed into the insert.

Tee nuts could work too, but they can be hard to seat in MDF and will show on the other side. Same sort of deal drill the hole over-size and "nail" the tee nut into the hole from the back side (optionally first cutting a recess using a spade bit to allow the nut to fit flush) , the tee nut accepts matching machine screws.

Oversize wood screws are another option - just use fatter screws.