I used the reverse method to obtain a smooth surface. The first attempt was relegated to the bin. I have done this technique in the past and now remember why I haven't used it lately. It can be a bit of a challenge to apply the mastic in an even coat. I used a baker's knife to spread icing. But even with back buttering, the mastic came thru the spaces between the tesserae. Bigger pieces are better with this technique. Patience and a light touch also help.