How much water do you add to 3.5 lbs of portland cement?

The general guideline for mixing Portland cement is to use a water-to-cement ratio of approximately 0.4 to 0.6, depending on the desired strength and workability. For 3.5 lbs of Portland cement, this translates to adding about 1.4 to 2.1 lbs (or roughly 0.17 to 0.25 gallons) of water. It's essential to adjust the amount based on specific project requirements and environmental conditions. Always follow the manufacturer's recommendations for the best results.