Not well. DAP, GE, Henkel, Red Devil, Sashco, Sherwin-Williams and the tile makers we read all say to take the old caulk out first, and no data sheet we read recommends caulking over silicone. Sashco says nothing sticks to it, not even more silicone.
What each maker says
| Maker | Over old silicone | Over old caulk |
|---|---|---|
| DAP | ALEX PLUS, ALEX FLEX and DYNAFLEX ULTRA won’t adhere over 100% silicone | Free of all old caulk; a second bead of KWIK SEAL or KWIK SEAL PLUS may go over the first |
| GE | “You can, but it rarely holds” | Removing old caulk completely is a must |
| Red Devil | Its 100% Silicone won’t adhere to itself or other sealants | Remove old caulking or sealant |
| Sashco | Won’t stick; not even silicone sticks to itself | Remove any old caulk, especially silicone; says its own sealants stick to themselves |
| Henkel (Loctite, OSI) | Loctite PL Concrete: no contact with silicone | Surfaces free of old caulking |
| Sika | Not stated; Sika says not to cure its sealant in the presence of curing silicone | Not stated |
| Custom Building Products, LATICRETE | Remove old sealants | Remove old caulk or other sealants |
From each maker’s data sheet, FAQ or how-to. DAP’s second bead is a fresh bead of the same product, not a cover for old, failed caulk.
Why new caulk won’t hold on silicone
Sashco’s explanation is the oil: silicone has oils in it, and they migrate out of the old bead. GE adds that even after the bead is gone, a thin film of cured silicone often remains, and it will block adhesion if left in place.
One Loctite sink article suggests simply applying a new layer on the existing silicone, but Loctite’s own POLYSEAMSEAL data sheet says it will not adhere well to surfaces previously sealed with silicone.
If the silicone can’t come out, Sashco describes a fallback: run the new bead wider than the old one, so it sticks to clean, silicone-free surface, and test a small area first. Sashco says even then you’re hoping the oils don’t spoil the bond later, and to remove the silicone if it fails.
Getting the old caulk out
- Score along both edges with a utility knife or razor blade, as GE suggests, and pull the bead out. For hardened sealant, GE says gentle heat from a hair dryer can soften it.
- Latex caulk: DAP’s CAULK-BE-GONE softens it in 2 to 6 hours per application. DAP says it doesn’t work on silicone, polyurethane or other non-latex sealants, and not to use it on refinished porcelain, soft plastics, vinyl or ABS tubs and shower enclosures.
- Silicone: Sashco suggests a silicone remover. GE’s data sheets say no substance will dissolve silicone, and GE’s remodel guide names isopropyl alcohol for the film left on many non-porous surfaces, and mineral spirits on some metals.
- Wipe the joint with rubbing alcohol, as DAP and GE both say, and let it dry before the new bead.
Removers and solvents carry their own warnings. We’d read the label or safety data sheet first, keep the room ventilated, and test on a hidden spot.
Removing silicone?
Silicone