Manavashrautasutra 6.2.3

He places the Mahāvrata [sāman bricks]: with three gāyatrī verses, “Come, for you have been pressed,” on the head; the Rathaṃtara on the [right] wing, making two [verses] into three with “To you, hero, we shout,” in the southern half, in the middle, and at the junction; the Bṛhat on the northern [wing], making two [verses] into three with “You indeed we call upon,” in the northern half, in the middle, and at the junction; on the body, the Vāmadevya with three [verses], “In what wonderful way did he become ours,” in the middle; the Yajñāyajñiya on the tail, making two [verses] into three with “At every sacrifice to your Agni,” in the western half, in the middle, and at the junction.

With [the formulas beginning with] “Barley, non-barley,” [he places] seven in the eastern half.

With [the formulas] beginning with “You are earth by birth,” [he places] two in each junction.

With [the formulas] beginning with “Which goddess you are, O brick, young girl, lying beside,” [he places] three in each junction; with “Which goddess you are, O brick, granting life,” he attaches [it] to the nine; with “Lying beside,” above; with “Which goddesses you are, O bricks, very gracious,” [he places] three together in the middle.

With [the formulas] beginning with “To you of equal strength,” [he places] three in each junction.

With [the formulas] beginning with “You are an enhancer,” he places five in each junction, five clockwise, five facing each other.

With [the formulas] beginning with “I place you, full of light,” [he places] three in each junction and two in the middle.

With [the formulas] beginning with “Kṛttikās the lunar mansion, Agni the deity,” he places the nakṣatreṣṭakā bricks in the east facing west. He attaches “You are the lights of Agni” to all of them. In front of the two Viśākhās,

“Full behind and full in front, / up from the middle the full moon has conquered.”

"in which the gods assemble together, / revel here in the highest heaven!"

[with this mantra he sets down] the Full-Moon brick above the Bharaṇīs;

"The share that the gods assigned to you, / O New Moon, entering together in your greatness,

make that our offspring, full of heroes; / bestow wealth upon us, fortunate one, rich in heroic sons!"

[with this] the New-Moon brick.

With [the mantras] beginning with "The golden embryo…" [he sets down] two [bricks] each at the joints.

Having placed the former golden brick and the bull with "Light you are, grant me light", he completes the layer with the lokaṃpṛṇā [bricks].

Having made the horse sniff the naturally perforated pebble, he addresses it with "Light!"

He endows it with a yajus-mantra with: "I place you in the seat of vital strength."

He sets it down in succession with: "May Parameṣṭhin set you down."

No ignorant person [may do this] here, nor is there a bestowing of wishes.

Having breathed in and breathed out, he offers upon the naturally perforated [pebble] with: "I offer the layer."

The sacrificer mutters: "May I ascend to heaven."

The pratiprasthātṛ simultaneously sets down the northern vikarṇī pebble dedicated to Vāyu in the middle of the space of the naturally perforated brick with: "Snorting like a horse in pasture…"

What applies to every layer has been explained.

He completes the layer with loose earth, except for the naturally perforated brick.

The rule: "One piling [the fire-altar] for the first time should pile [it] knee-high" has been explained.