The most important item in Gruharambham is laying the foundation stone or 'Adisthanashila'. It is called the 'Shilasthapanam'. So, it should be done exactly at the prescribed time for Gruharambham. Many people do a 'Bhoomipooja', before laying the foundation stone. Some are seen getting that stone blessed from their 'Ishta Devatha' Temple. Arranging a small pooja on the spot is very welcome, seeking the blessings of Lord Ganapathy and other Devathas, including Vastu. The excavation for foundation can be done little earlier to laying the first stone. But, it is a custom and almost a belief that at the time of the excavation for foundation, Bhoomi pooja can be done. The excavation should be started from the North-East corner (Eshana cone) of the plot and the Bhoomi pooja also should be arranged to be done at that part. Before starting excavation, usually a fresh stump from a jackfruit tree or from a tree having sap, is fixed first exactly at the NE corner. It is from that stump, string is connected to those at the other corners, to ear mark the area for excavation for the proposed house. Some people use the Muhurtha for Gruharambham for fixing this stump. It is not correct. The Muhurtha should be used for laying the foundation stone. Of course you can use a good time for fixing the stump also, just before laying the stone. You need avoid Rahukalam, Gulikakalam and Yamakandakalam, which are readily available in every Calendar.