Portland cement is a central material in construction and infrastructure globally. The U.S. alone produces over 80 tonnes of cement yearly, generating millions of tonnes in CO2-eq. Recent developments in architectural biomaterials offer alternatives that reduce emissions and decrease lifecycle energy. Despite their ecologically benign nature, many of these materials underperform in strength and weather durability. Expanding on four years of research in the DumoLab, Terrene 4.0 further develops and analyzes a sand-based composite stabilized with a shellfish-derived polysaccharide binder, referred collectively as ChitoSand. We build upon Terrene 1.0-3.0, which has 2.97 MPa compressive strength and loses structural integrity upon 20 minutes of water exposure. To address strength limitations, a natural cross-linking agent was introduced and evaluated via droplet penetration, water absorption [ASTM C97], contact angle [ASTM D7334], and compressive strength [ASTM C31] measurements. The crosslinking modification extended penetration time by over 150 minutes, reduced early water uptake by ~90%, increased initial contact angle by 26°, and yielded strength gains. Shellac, beeswax, soy wax, tung oil, and linseed oil coatings were investigated to improve ChitoSand’s weather resistance. Performance was assessed using the same droplet penetration, water absorption, and contact angle measurements, as well as UV weathering simulations [ASTM G154]. Additional shellac testing was conducted after thermal crosslinking at high and low temperatures. Shellac and beeswax were most effective, raising the contact angle by 21° and 23°, and extending droplet penetration by 71 and 124 minutes, respectively, while crosslinked shellac extended time by 20 additional minutes.