Polymer addition to cement paste was found to decrease the thermal stability and thermal expansion coefficient (CTE). The addition of methylcellulose (0.4% of the cement weight) reduced the mechanical weakening onset temperature from 125 to 42°C, while decreasing the CTE near room temperature from 10 10 - 6 °C - 1 to nearly zero. The addition of latex (20% of the cement weight) reduced the mechanical weakening onset temperature from 125°C to near room temperature, while decreasing the CTE near room temperature from 10 10 - 6 °C - 1 to -4 10 - 6 °C - 1 .