Can this product be fused together at the seams? And if so, is it waterproof?

You can seam to 3/8" Heavy Duty Rubber Rolls together with our seam sealer glue. Our rubber flooring is not waterproof, but it is water-resistant. To make these floors more water-resistant, you can apply our Rubber Floor Finish and Sealer, which will fill in the small pores that are found in our rubber flooring. This, in conjunction with the seam sealer, will help to create a floor that is as close to waterproof as they come.