MDF for table top ??

[Fred LeBail]

Now it's not as bad as it sounds. A client has designed her own dining table for her new home.There is a single pedestal and the top is 52" x 48" , with a couple of corners 45'd on one side giving seating for 5 with approx 24 " of more for each. ( clear as mud,eh). She is going to put tile on the top and I am wondering if 3/4" MDF would be good as a top under the tile ( substrate)? There will be a edging of Walnut around it that will be Dadooed to fit over the MDF.
The reason I am considering the MDF is that it seems to be flatter than 3/4 ply is. Will it be strong enough to be attached to the top of the pedestal with 4/4 hardwood on edge ?

[Jim Becker]

Fred, to avoid deflection (read: sagging) you'll want to consider two layers of MDF and a good support structure between it and the pedestal. With the tile and folk's elbows (yea, you're not supposed to put them on the table, but we ALL do... ;) ) there is quite a bit of weight to support out and away from the central point. You likely would need to do the same with plywood, too. There is a lot of stress over time on a table top.

[Jack A Entrekin]

if i understand you, i would not use MDF as a backer for the tile (the thin set has water in it MDF+water=bad) i would use conrete backer board on top of plywood.

[Tom Veatch]

...The reason I am considering the MDF is that it seems to be flatter than 3/4 ply is. Will it be strong enough to be attached to the top of the pedestal with 4/4 hardwood on edge ?

With the edge 24 to 26 inches from the center of the single pedestal support? In a word, no way! I'm not sure I'd consider a double layer sufficient for that cantilever either. Especially if you're going to increase the dead weight with a layer of tile that adds weight but no effective bending strength.

If you're going to use a hardwood edging, extend it vertically to make a skirt then use a grid side to side and end to end, like a torsion box grid, tied to the skirt to provide some depth and support for the top. A couple of equally spaced stringers and longerons should be sufficient. If the design appearance requires a thin edge, offset the skirt to the inside a short distance to retain the thin edged appearance. But give that MDF some support.

[Fred LeBail]

I probably should have explained that the pedestal that I will be using is recommended for a 48" to 50" table.The distance between the feet is 38". This may help with some of the overhang.


I am a little concerned about the mastic or grout that may be used for the tile.