What happens if you paint bare wood without primer?

If you paint bare wood without primer, several problems can occur that affect appearance, adhesion, and durability. Bare wood is porous and absorbs paint unevenly, so paint will soak into grain, resulting in uneven color, blotchy finish, and requiring many more coats to get coverage, wasting paint and money. Without primer, wood tannins and knots can bleed through paint, causing yellow or brown stains that show through, especially with light colors. Paint adhesion will be poor, so paint may peel, crack, or flake sooner because primer creates bonding layer that sticks to wood and gives topcoat something to grip. Bare wood also has moisture and natural oils that can cause paint to bubble or not cure properly. Knots may expand and cause paint to crack. Finish will not be smooth, grain will raise, and you will see wood texture unevenly. Long term, unprimed wood is not sealed, so moisture can penetrate and cause wood to swell, rot, and paint to fail faster, reducing paint job life from 7 to 10 years to 2 to 3 years. So you can paint bare wood without primer, but result will be blotchy, poor adhesion, tannin bleed, and short lived, so primer is strongly recommended to seal wood and ensure even durable finish.