“Caulk” is the general word for a joint sealant, and silicone is one type of it. The practical choice is usually between paintable acrylic latex caulk and nonpaintable 100% silicone. Use acrylic latex, often sold with added silicone, on trim, baseboards and other joints you will paint. Use 100% silicone on joints you won’t paint that face water or weather, such as around a tub, sink or exterior flashing, as long as the label approves those surfaces.
How the two common types compare
| Point | Acrylic latex (example: DAP Alex Plus) | 100% silicone (example: DAP All Purpose RTV) |
|---|---|---|
| Paintable | Yes. DAP says Alex Plus can be painted in 30 minutes with latex or oil paint | No. DAP says to paint the surface before applying it |
| Cleanup | Water | Not water-based; follow the label |
| Moisture | DAP lists kitchens, baths and basements; check the label for wet-area limits | DAP describes a waterproof, weatherproof seal |
| Flexibility | Silicone additive improves flexibility; rated to ASTM C834 | DAP says it handles expansion and contraction without cracking |
| Cure | Paint-ready time is listed separately from full cure | DAP: allow 24 hours to fully cure |
Sources: DAP’s Alex Plus and All Purpose RTV 100% Silicone product pages. Other brands and hybrid formulas vary, so read the label. A tube that says “siliconized” is not the same as 100% silicone.
Pick by joint
- Painted trim, baseboards and crown: paintable acrylic latex.
- Tub, shower, sink and backsplash joints: a formula approved for wet areas and for both surfaces. Check any limits on natural stone, acrylic tubs or plastics.
- Exterior windows, doors and flashing: a formula rated for exterior use, the substrates involved and the expected movement. Never seal a weep hole or a designed drainage gap.
- Tile movement joints and changes of plane: flexible sealant rather than grout. See grout vs caulk .
Prep matters more than the brand
New sealant won’t bond well to old caulk, soap film or a damp joint. Remove the failed bead, clean and dry the joint as the label says, and use backer rod in deep or wide gaps instead of filling the void (wide-joint guidance ). Because silicone can’t be painted, remove an old silicone bead completely before switching to a paintable caulk.
If the joint keeps cracking or water keeps returning, find the movement or leak first. Sealant finishes a sound joint. It can’t replace waterproofing, flashing or a structural repair.