Fitting and Installing the Membrane

Plot out the dimensions of the patio and transfer them to the membrane, curl facing down (unlike what is shown in the photo). Use a 3-4-5 folding square and a marker.

Cut the membrane sheet to size using a pair of sharp scissors.

Work in small, manageable areas.

In this case, the membrane was marked with the curl facing up, so the author left the sheet out in the warm sun for 15 minutes to let it relax.

After dampening the mortar bed and aligning the sheet in place, weigh it down with a couple of bags of thinset to keep it from moving.

Carefully pull the front edge of the sheet about halfway back to expose the dampened mortar bed.

Carefully kneel on the folded sheet and using a 1/4-inch square-notched trowel held at a very low angle, comb out latex-modified thinset from the membrane fold to about 18 inches away. Flop the sheet back down, and embed it in the mortar. Pull back the sheet again, to expose bare setting bed. Repeat.

Once the first half of the sheet is fully embedded, smooth, and flat, lay protective boards on it, and fold back the other half of the sheet. Repeat the same steps as for the first half.

Once the entire sheet is adhered, embed the membrane firmly in the thinset using a magnesium float. Push excess mortar to the edge of the sheet.

Remove excess mortar before fitting the adjacent sheet.

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