Help salvage a large tabletop

[Justin Freund]

So I have a predicament I’ve gotten myself into with a large conference table. I’m in the process of redoing a 4x8 conference table. The table is melamine covered particle board that is 1 1/4” with another 3/4” to build the edges. The customer wanted to salvage the top and reuse it by putting a large vinyl decal over the top and using epoxy over that. No big deal. The issue is that after putting a straightedge on top, there is about a 3/8” bow in the center. The entire table is shaped like a bowl so I can’t shim it out when attaching the top to the base.

I’ve already put too much into the existing top to make a new one I think. I could use more epoxy on top but it would probably double the amount I need and the Ecopoxy is expensive to begin with on a budget build. And I don’t really want the decal to look like it’s in a lake. I’m thinking my best option is to fill the bowl with something before the decal goes on but I don’t know what to fill it with.

I could use a cheaper epoxy to level the table but it’ll all get covered by the decal and might be overkill. I was thinking a vinyl floor leveler might work but I’m afraid of it delaminating under the decal if the table is moved and the top flexes at all.

Any other ideas?

[Peter Christensen]

Was it flat to begin with? If it was and the decal pulled it into a cup you could try putting a sheet of it on the underside to see if it will pull it flat again.If it does epoxy both sides.

I reread and realize the decal isn't on yet. On the bottom saw grooves about an inch deep along the length and across the width (the number determined by what it takes to flatten) like kerf bending. Clamp it flat with cauls and fill the grooves with epoxy. Remove the cauls when set and put a thin coat over the bottom to seal it. Then you can turn it over and finish the top.

[Bill Space]

First thing that came to mind was auto body filler. A gallon is relatively cheap and it seems to stick well to everything.

You could mix it up light on the hardener and gain more working time. I suppose you could also do sections at a time...

Bill

[Wayne Lomman]

Do the saw grooves underneath but screw fix stiffeners under it. You have 3/4" to hide them. Machine some 6x1 hardwood with a 3/8" convex face length wise so that when you screw them on it applies pressure to the underside of the sag. No waiting for epoxy to cure and hoping it stays straight. Cheers

[john lawson]

Not sure if I completely understand how you want to proceed but below are two pictures of the largest table I ever completed, 24x8. The center is made of mdf covered in veneer. The outside 24" or so was granite. It was all cut CNC so I felt confident of the "lines" you would see, but I knew there would be a problem matching the height of the veneered middle to the granite on the edge, and it did have to align perfectly.

Our solution was to put the threaded inserts in the underlayment. When the installation was complete my partner got under the table and used a driver to turn the screws while I used a straight edge and called out "more" or "less" to him. It took us about 30-40 minutes to adjust the table to perfect alignment. Oh yes, and we designed the whole veneer field to sit 1/32" below the granite, knowing that the eye would not pick up on the slight bow we put in it.

So, the idea of our approach was to accept that it would be warped or bowed and to adjust it out on installation. That table went into a brand new bank board room and we never had a single issue with it, it's been almost 10 years.

[john lawson]

Here is a couple of pics finished.

[William Young]

I think the ideas of the grooves and the stiffeners are good. Both together is probably better. However, if you make stiffeners, don't just make them 3/4" thick. At that thickness, they will hardly be effective, if at all. Use a strong, stiff, hardwood and make the vertical dimension as great as possible; maybe 3" min. Then taper 6-8" of the ends down to match the 3/4" table edge. As mentioned, cut these stiffeners so they have a slight curve. Some experimentation may be needed to determine the amount of curve needed to get the top flat. I think that one stiffener every 16-18" over the 8' length of the table would be appropriate.

[Justin Freund]

Thanks for the suggestions guys. Honestly the more I think about trying to salvage the top, the more it sounds like a lot of work to band aid a particle board top. I expect this table to get abused and moved by the top frequently.

I think the best option at this point is to replace the top entirely. I can make it stronger, dead flat, and less likely to have issues later on.

Any suggestions as to order of plywood if I was to laminate layers? The top is 4x8 and needs to be less than 2” thick. I was thinking 2 layers of 3/4” veneer core cabinet ply with a 1/2” MDF core. Or all plywood but I thought the MDF would hold stability. The base is 24”x 60” so the sides will have an approximately 12” overhang and the ends about 18”.

[William Young]

You are there and know your situation better than we do. However, my inclination would be to try the suggestions above and use the re-make idea as a backup plan. Turning the top upside down on the floor (for example) and adding stiffeners seems like it ought to work and would be less work (and few new materials) than starting from scratch. If it doesn't work you will not have much invested and you can start over. If it does work you have accomplished the end result desired and your done.

[Tom Bender]

William is on the right track. You may want to make the stiffeners straight and add shims as needed.

A new 2" thick top with an MDF core and plywood faces sounds really heavy. You could make a torsion box instead.

[Robert Engel]

Thanks for the suggestions guys. Honestly the more I think about trying to salvage the top, the more it sounds like a lot of work to band aid a particle board top. I expect this table to get abused and moved by the top frequently.

I think the best option at this point is to replace the top entirely. I can make it stronger, dead flat, and less likely to have issues later on.

Any suggestions as to order of plywood if I was to laminate layers? The top is 4x8 and needs to be less than 2” thick. I was thinking 2 layers of 3/4” veneer core cabinet ply with a 1/2” MDF core. Or all plywood but I thought the MDF would hold stability. The base is 24”x 60” so the sides will have an approximately 12” overhang and the ends about 18”.

That's what I would do. Just tell the customer it will cost more to fix than the top is worth.

The MDF will add more weight and stability as opposed to 1/2" ply.