polish on MDF

[Just George]

I have 4 sheets of MDF( 2400x1200x25) that I want to make into a bookcase. Has anyone had experience in sealing and polishing MDF?

[Chief Tiff]

You need to use a quick drying and fairly thick finish so it doesn't get sucked into the "end grain". I wouldn't use anything water based either.

The flat faces can erupt into tiny pinholes if not sealed too. I've had success with Feast Watson sanding sealer used neat and wiped on with a cloth. Two coats and she was ready for painting.

How are you supporting the shelves, as MDF is notorious for sagging under it's own weight, let alone with a load of books on top! On a painted childrens bookcase I saw the shelves were edged with a solid wood lipping that extended below the shelf, sort of like a torsion box.

[RossM]

Hi JG -

I did an office fit-out in MDF some time back - 8 desks with shelves over the top. All were finished with clear satin Estapol. The overall look was fine - it will end up a honey colour, and it goes on easily. Use a minimum of 3 coats. I think I used 4 coats. End "grain" will be fine after the first thirsty coat, and may need one more coat than the other surfaces - also it will be much darker than the flat surfaces, so take that into account with your design.

Comment about sag is wise. We had reference books stacked on our desk shelving with no sagging problem. The shelves were 750mm long 25mm MDF and secured to the carcase on three sides. Any longer and I would have used a 50mm hardwood edge across the front of each shelf.

Any single pack polyurethane finish should do the same job, but don't use water based products. Remember to sand between coats, and make sure you get rid of any marks before you start. Scratches and other defects will absorb more finish & really stand out.

[Just George]

How are you supporting the shelves, as MDF is notorious for sagging under it's own weight, let alone with a load of books on top! On a painted childrens bookcase I saw the shelves were edged with a solid wood lipping that extended below the shelf, sort of like a torsion box.

Any cabinets over 600mm automatically get a shelf support at the back of the cabinet as well as the two at the sides of the shelf.