I came into possession of a huge work table that is not flat and would like to flatten it. It is too much work to rebuild it; it is built into a corner. The top is linoleum covered and is close to flat but not close enough. This was an upholstery shop work table. I was thinking of buttering up a 4x8 3/4" piece of MDF with Great Stuff and plopping on the table with some wieghts. Anybody try this before? Any suggestions are welcome.
Thanks Huck

Your best bet might be to remove the table top and see if the frame is out of square or just wasn't installed properly. Just buttering down 3/4 MDF and hoping it will fix your problem is just asking for more problems. Using a lot of pressure to flatten down a piece of MDF just might crack the MDF.

You say it is not flat but you don't say exactly what is wrong. Is it twisted? Is it bowing up or down in the middle? Is it in the shape of a bowl?

Here is how I made my building board flatter. This assumes I will be placing a new MDF surface on top of the existing surface.
1) 1st level the existing surface as best you can.
2) Using various thicknesses of aircraft ply, 1/32, 1/64th etc … I cut 1" squares of these
3) Then I lay out a grid on the table top say 10"
4) Using a long level place shims on the 2 to 3 low corners till I have level pads, fasten these shims down with CA as needed.
5) If your real picky you can even sand down the leveling shims to perfection, I use a real long sanding bar, the best part here is you only have to sand down the 1" squares.
6) Now I place 1/32" spaces on the corner pads and run a tight string across the corner shims.
7) Now I can place the additional shims at each of the points on the grid, I should have a 1/32 or smaller space between the new shims and the string. Glue down the shims as you go.
7) Again sand down the high spots as needed. When done I should have a set of perfectly level shim pads on a 10" grid.
8) Now I can place the new MDF surface on top and screw it down through the shims, Always place the screws so they go through a shim.
9) Then I place several layers (2) of dry wall as a pinning surface. As the surface gets messed up I just flip over or remove the piece of abused drywall.

Sounds like a "killer" building board !! What is the size , & is it portable?

I think the problem is that your MDF may tend to follow the contour of the existing top and end up just as uneven. I think adding a new top from something like MDF is on the right track but I'd look at using some shims from wood, paper or cardboard to help get it flat.

How about using the non-flat board for laying your building equipment on, or, other non-related building tasks that always come up in a shop and just build yourself a new FLAT building board to use when required?

Soft landings.

Joe

have had good luck with finding a straight hollow core door and plopping it on top of the table,then I apply a layer of Formica to one side. now perfect for plan drawing, other side gets layer of ceiling tile - Celotex sheet, etc - for pinning parts to. don't forget clear plastic sheet when glueing. double duty and can be stood in the corner when not used. mine is 4 years old with quite a few planes built on it and still usable. dick

Thanks for the input. I think I will build a 3x6 table and use the existing table for storage and assembly work. I have space for a new table and would like one that I can walk arround. The existing table is built into a corner of the shop and I can't even reach the wall side of the surface, it is 5' x 10'. I can use the shop for just paying the heat and electric bills so I can't complain. I have about 650 sq ft to play in and a lavatory, and nice overhead lighting.

The original idea was not well thought out. I agree the 3/4" MDF will probably bend a little even with the Great Stuff leveling ability. I most likely could not squirt the Great Stuff on fast enough on such a large surface so that it would expand uniformly and stay soft enough to level it out.

Huck

Huck, if the table will hold liquid, take the linoleum off and scurb down the surface witha stiff steel brush, Vaccum it off. Then get some of the grey putty that the floor guys use and float out the surface. You could even use cement. just lay a couple level screed boards to get it level. once it is levled out, then you can put you mdf down on top. You will have seams though. This would be a lot of trouble and expense, and I think the idea of a new table, one you could take down and move later if needed would be money better spent. I would build a 4x8 table top, 2 sheets of 3/4 ply laminated together and set on six 4x4 legs framed together with 2x4's Use 1/4" lag bolts and counter bore the holes so the heads are below wood surface. For $100, you could have a killer work table and like I said, a few screws and it is a kit waiting for a new home.

Man, I wish I had your problem.

Don