To determine the approximate proportion of dry cement mortar required for brickwork, we need to consider the size of the bricks, the extra percentage for frog filling, and the wastage.

Given:
Nominal size of bricks: 19 cm x 9 cm x 9 cm
Extra percentage for frog filling: 18%
Wet mortar to dry mortar ratio: 1 m3 wet mortar = 1.3 m3 dry mortar

Let's calculate the volume of one brick first:
Volume of one brick = Length x Width x Height
= 19 cm x 9 cm x 9 cm
= 1539 cm3

Now, let's calculate the volume of bricks for 1 m3 of brickwork:
Volume of bricks for 1 m3 of brickwork = 1 m3 / volume of one brick
= 1000000 cm3 / 1539 cm3
≈ 650.68 bricks

Since we need to consider 18% extra for frog filling, the total volume of bricks required will increase. Let's calculate the total volume of bricks required:
Total volume of bricks required = volume of bricks for 1 m3 of brickwork + (18/100) x volume of bricks for 1 m3 of brickwork
= 650.68 bricks + (18/100) x 650.68 bricks
= 650.68 bricks + 117.12 bricks
= 767.8 bricks

Next, let's calculate the volume of wet mortar required for 1 m3 of brickwork:
Volume of wet mortar required = total volume of bricks required x volume of one brick
= 767.8 bricks x 1539 cm3
≈ 1181548.2 cm3

Now, let's calculate the volume of dry mortar required for 1 m3 of brickwork:
Volume of dry mortar required = volume of wet mortar required / 1.3
= 1181548.2 cm3 / 1.3
≈ 908113.23 cm3

Finally, let's calculate the proportion of dry cement mortar required for brickwork:
Proportion of dry cement mortar = volume of dry mortar required / 1 m3
= 908113.23 cm3 / 1000000 cm3
= 0.90811323

Converting to percentage:
Approximate proportion of dry cement mortar = 0.90811323 x 100
≈ 90.81%

Therefore, the approximate proportion of dry cement mortar required for brickwork is approximately 90.81%.

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