"Water-based varnish cupped my 38mm pine slab. Help!"
Hi everyone. Beginner from Russia here, working on a very tight budget. I made a classic mistake and now my thick pine slab is cupped.
The Setup:
Pine butcher block (800x800mm, 38mm thick). I used an 800W electric spray gun to apply 2 heavy coats of water-based acrylic varnish to the bottom side only. I thinned the varnish with about 30% water to get a "mirror" finish.
The Problem:
2 days later, the slab cupped 10mm (0.4") in the center. I disrupted the moisture balance by soaking one side with water-based finish while the top stayed dry.
Current Situation (Photo attached):
I placed the slab face-up on a flat table.
Put a layer of paper and plywood on top.
Added 20kg (44 lbs) of gym weights in the center.
Increased room humidity to 65%.
I just started this "press" and I'm not sure if 20kg is even close to enough for 38mm thick wood.
The "Print Shop" Advantage:
I work in a printing house. I have access to:
Two sheets of plywood (size of the table).
Massive stacks of paper (hundreds of kilograms). I can use these as a heavy press if my gym weights fail.
The Base (Photo attached):
I’m using a central pedestal base. The top mounting cross is only 500x500mm (20x20"). It’s not strong enough to "pull" the edges of an 800x800mm slab flat with screws. I MUST get it flat before mounting.
Questions:
Is 40kg enough for a 38mm thick slab, or should I go straight to the 300kg paper stacks?
Should I wipe the bare top side with a damp cloth now to speed up the counter-bending, or will it raise the grain too much before varnishing?
If I spray the top side with the same water-based varnish now, will the moisture "pull" it back naturally, or will it just lock the cup in place?
I have zero budget for clamps or new tools. Any "poor man's" advice from pro woodworkers would be life-saving!
