Why Limestone and Sandstone are not used together for construction purposes?

Limestone and sandstone have sufficiently different properties to make them poor substitutes for one another. Situations that call for the hardness and resistance to corrosion/alteration that welded sandstone offers would be bad situations for the softer and acid sensitive limestone. The porous feature of nearly all sandstones would make them problematic in cases where less porous limestone are used. Coarser-grained sandstone makes a less-polished facing or decorative stone than fine-grained limestone. Different tools are used to work the two materials. And each type of stone will weather at different rates and in different ways, making any surface containing both uneven over time.

Also, most regions build primarily with whatever the local rocks happen to be. So you will find more limestone in central Texas and more sandstone in Arizona. If you go to the trouble of importing stone from somewhere else, you are doing it because that is the best stone for the job. You are unlikely to then use inferior local stone for some part of that job.

Marble, granite and sandstone are used for facing work of buildings. Limestone and sandstone are used for general building works. Compact limestone and sandstone are used for Fire-resistant masonry. Granite, quartzite stones are used in foundations of building in places with the high groundwater level. Limestone and sandstone are both well-loved natural stone materials used in landscape construction, primarily as decorative pavers for patios and walkways, as well as wall facing and coping. With their warm, sunny coloring and fine texture, both can be used to achieve a very similar look.