If you’re building a house: waterproof the structure correctly. This will protect most of your rebar, and it will protect your walls, your finishes, and keep mo

If you’re building a house: waterproof the structure correctly. This will protect most of your rebar, and it will protect your walls, your finishes, and keep mold from growing. The lifespan of ordinary rebar in competently cast concrete that is kept dry is very, very long. Maybe if you live right next to the ocean you will have somewhat different considerations, but a quality waterproofing membrane on the outside of your foundation is worthwhile anyway and will help control salt spray as a side benefit. If you visit, say, an 20 year old, incompetently built structure in a place with real weather (ski lodges are often like this), you can see that the concrete will be in perfectly fine condition, but the structure may smell moldy and interior finishes will be failing.