Mu Wei didn't let them wait for long as he called them forward one by one, placing the day's wage into their hand and watching them leave with high spirits. They packed and made their way back home.
The addition of a new person made the house a bit cramped. Su Xiao checked on the unconscious Yan Huai and changed his dressing. Wiping off the sweat and blood before administering a new dose of pain relief pills. That night, everyone slept deeply exhausted by the day's work.
The morning air was already alive with the sound of cracking stone and orders across the camp. Outside the perimeter, right where the dormant terracotta pipe protruded from the foundation, Su Xiao supervised the Furnace construction. She had the laborers collect dense heavy river rocks and a specific mix of high iron clay from the valley. This served as a primitive refractory brick that won't crack or melt under intense heat.
Then a double-chamber furnace was slowly built. The bottom chamber is the ash-trap and air-intake. The top chamber is the combustion site where the logs burn. The back of the combustion chamber is molded directly around the terracotta pipe to ensure a tight seal. The workers stacked the heavy stones into a massive, dual-chamber firebox, sealing the interior with a thick paste of clay.
She had them angle the intake vents directly into the path of the mountain wind. Above the furnace, a small vertical stone flue that shoots up outside the house perimeters. A safety valve which ensures the toxic carbon monoxide rush straight up to the chimney into the sky, while the clean, pressurized heat draft gets sucked down into the under-floor pipe network.
This created a natural stoking pump by forcing oxygen into the bottom chamber, stoking an efficient blaze. Meanwhile, Mu Wei was managing the rise of the walls between the four colossal ironwood pillars. He didn't let the men build standard single-layer barriers. Following his wife's strict geometric parameters, the laborers raised a double-layered defense.
On the outside, it was a thick barrier of heavy, fit stone. On the inside, it was smooth mud bricks mixed with straw and charcoal dust. Mud bricks has a high thermal mass. It acts like a sponge, absorbing the radiant heat rising from the slate floors and slowly and slowly radiating it back into the rooms. Between the stone and mud bricks, she leaves a two-inch gap.
It was to be filled with dry straw and packed ash and act as insulation barrier to stop the heat from bleeding out through the stone exterior. She looked at the gaps before turning to Mu Wei. Calling him aside, she whispered,
"We need to change the the insulation matrix for the interior. If we use plain straw, every shout from the courtyard, every sound from Yan's workshop or the howling from the mountain will echo through the walls like a drum"
Mu Wei wiped a sweat from his forehead as his attention remained on her.
"What do you have in mind?"
"A dampening layer"
She explained pointing out towards the damp, sticky ledges of the mountain where thick blankets of wild mountain moss grew.
"Have some of the men harvest the thick, dried moss from the slopes. Some shred it, mix it with the coarse charcoal dust and hemp fibers, and the rest pack the mixture tight into the two-inch gaps".
He immediately turned to the workers and had Shi Dong lead them to get all the moss they could find. As they came back, Su Xiao supervised the process till it was done. After it was done, they moved to the next phase. Mu Wei with some of the men were led to the land's perimeter where they dug around the already marked lane.
With rhythmic, earth shaking strikes, their pickaxes slammed into the frozen dirt, clearing the deep trenches. It was mid afternoon when they finished the work. The other batch rotated to the dining area while the others moved to the next phase which was layering the roof. They didn't just lay tiles over open wood.
First, they pinned down interlocking cedar watch boards to seal the ceiling. Over this wooden deck, the workers slathered a thick, dense layer of rigid waterproofing marl. A primitive concrete mixed from lime plaster, fine clay and charcoal dust. Into this wet bed of ash, the men pressed the fired clay tiles, interlocking the carved pieces into tight, overlapping channels. The geometry of the roof was a marvel.
A steep, sixty-degree pitch at the ridge to prevent heavy winter snow from accumulating and crushing the frame, tapering down to a shallow thirty-degree curve at the eaves. Even during rainy periods, the water builds momentum on the steep slope and literally shoots off the edge of the roof so the foundation never gets damp.
By the time twilight painted the sky, the transformation was staggering. The building was completely enclosed, roofed and insulated. The boundary trenches were neatly laid. The workers packed away their tools and washed off the dark charcoal and moss residue from their hands using the water placed in a bucket in the courtyard. Their chatter was light as they collected their pay and disappeared into the dusk.
The camp soon fell quiet except the steady breathing of the kids and the couple washing the dishes. Lu Dan and Lu Tui were cleaning the surroundings. Mu Wei struck a flint outside, feeding the external firebox. Going back inside, Su Xiao knelt pressing her bare palm to the slate. Ten minutes later, it seemed nothing happened then slowly she felt it.
A warmth pulsing up through the stone to her hands. Then the room slowly dispersing the chill and turning warmer till it was completely warm. The howling sound of wind outside was completely muted as the stayed inside confirming it worked. Mu Wei looked at her, his dark eyes ablaze with utmost pride and awe.
"It works!"
The breathlessness in his voice showed how completely thrown off balance he was. Su Xiao smiled and gave him a triumphant nod. They stayed like that for twenty minutes before shutting it off and making their way back to the camp.