Quick Comparison Table
| Factor | Caulk | Joint Compound |
|---|---|---|
| Flexibility | Stays flexible indefinitely | Rigid when cured |
| Sandability | Cannot sand smooth | Sands perfectly |
| Paintability | Paintable (use latex) | Fully paintable |
| Shrinkage | Minimal with quality caulk | Can shrink, may need multiple coats |
| Texture matching | Poor | Excellent |
| Cost | $4-8 per tube | $8-15 per bucket |
| Best for | Movement-prone gaps | Flat seams and patches |
When to Use Caulk
Caulk works best in joints that move. These include:
- Where walls meet ceilings
- Inside corners between walls (especially in older homes)
- Around door and window frames
- Where drywall meets dissimilar materials like brick or wood trim
- Gaps around bathtub or shower surrounds
The common thread is movement. Anywhere two surfaces can shift independently needs a flexible filler.
Choosing the Right Caulk
For interior drywall work, use paintable latex caulk. DAP Alex Plus and similar products run about $5 per tube and accept paint well. Avoid silicone caulk for areas you plan to paint. Silicone does not hold paint and will peel.
For bathrooms, use a mildew-resistant formula. The few extra dollars prevent black mold lines developing along your caulk seams.
When to Use Joint Compound
Joint compound, or mud, works best on surfaces that stay put:
- Seams between drywall sheets
- Screw and nail dimples
- Small holes and dents
- Skim coating textured walls
- Building up outside corners
If the repair needs to be perfectly flat and sandable, mud is the answer. If it needs to flex, mud will fail.
Compound Types for Gap Filling
Lightweight all-purpose compound works for most gap filling between drywall sheets. For larger gaps over a quarter inch, use setting-type compound (like Durabond) that does not shrink as much. Apply it in layers, letting each cure before adding more.
The Hybrid Approach
Sometimes you need both products on the same repair. Here is an example from my kitchen renovation.
I had a gap where the drywall met an old plaster wall. The plaster side moved. The drywall side did not. I filled the bulk of the gap with joint compound to build it up flat. After it dried, I applied a thin bead of caulk right at the junction line. The mud gave me the flat surface. The caulk handled the movement.
This technique works anywhere rigid meets flexible.
Common Mistakes I Have Made
Using mud in ceiling corners is my most repeated mistake. It always cracks. Every single time. I finally stopped trying after the fourth repaint.
Another mistake: using caulk to fill screw holes. Caulk shrinks slightly and does not sand, so you end up with visible dimples. Always use spackle or joint compound for screw holes.
Third mistake: cheap caulk. The dollar-store tubes shrink badly and turn yellow. Spend the extra $3 for a quality brand. It saves repainting later.
Final Recommendation
When in doubt, think about movement. Will this joint shift over time? Use caulk. Will it stay rigid? Use mud. If you are unsure, caulk is the safer choice. A slightly imperfect caulk line beats a cracked mud joint that needs repeated repairs.