Solid surface need a special type of adhesive to bond properly it is also best to bridge the crack underneath to prevent expansion and contraction of the joint. Color really doesn’t matter on the bottom so any scrap piece will do. If you have a solid surface countertop builder in your area, they would probably give you scraps to work with. For the glue, it’s best to look up the color of you top and then using that, you can get the exact color match adhesive, check under the dinette table for a sticker with the name and color number. Build your seam up with adhesive and squeegee it down and then leave it bead sticking up. Then it’s just a matter of sanding and polishing with sandpaper and scotch brite pads, white is your final polish. Done with the right color adhesive and the seam should be invisible. I used to make tops in my shop before I retired, really it’s a lot like working with wood only dustier
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