The Egyptians could only get stone for building from the far south of the country. In the north, where the Hebrews lived, they used stone only for the most important state and religious buildings.
They built other structures with mortar and bricks made from durable clay. They mixed in seashells or straw to bind it together. After sun-drying in a mold, these materials were surprisingly strong. This was especially true in Egypt, where there was little rain or humidity.