Caulk is the cheapest part of a job and the first part to fail. It fails because it is the wrong type for the joint, or because it went over the old caulk. Pick by what the joint does, then prep it properly.
Check this first
Three questions, answered by the joint:
- Is it wet? Tub and shower joints.
- Does it move? Where two materials meet, a floor and a wall, a counter and a wall, or the outside of the house.
- Will it be painted?
Which caulk for which joint
| Joint | Caulk | From |
|---|---|---|
| Interior trim, casing, baseboard, painted | Latex, which fills the gap and is paintable | Tom Silva |
| Exterior gaps that will be painted | Acrylic caulk with silicone added | Tom Silva |
| Shower wall to tub | 100% silicone. Pricey, many colours, can’t really be painted | Tom Silva |
| Joining metal, such as gutters; long tile expansion joints | Butyl, a rubber sealant that stays soft for a long time. Can be messy | Tom Silva |
| Cracked grout at wall or counter transitions | Colour-matched siliconised acrylic caulk, sanded for sanded grout, unsanded for smooth grout | TileCoach |
| Inside corners of tile that will be painted above | Siliconised acrylic, since silicone does not hold paint | Lowe’s |
| Wide gaps by a sink or wall | Paintable latex over foam backer rod | Vancouver Carpenter |
The Home RenoVision DIY comparison disagrees on the best all-rounder: he rates silicone the most versatile, permanently flexible and mould resistant, and picks a premium grade. He says latex is only for indoors and failed a freeze test, solvent-based does not return to shape, and polyurethane collects dirt unless painted. Read the tube, because both approaches work where the product is made for the joint.
Safety
- Read the tube’s ventilation advice. Solvent-based caulk is the one the Home RenoVision DIY contractor says never to use inside to seal a shower, since the owners couldn’t use their bathroom for a month.
- Lacquer thinner or denatured alcohol for cleaning is flammable. Ventilate, and keep the work away from flame. Use gloves.
- Use a razor blade or knife with a steady hand and your other hand clear.
Step 1: Remove the old caulk
Tom Silva says you cannot caulk over a failed joint: new silicone “will look good for about an hour” but will not stick. Scrape it off completely with a razor blade, clean with a cleaner, lacquer thinner or denatured alcohol, and let the joint dry before the new bead goes in. For cracked grout, cut away loose grout with a razor knife until it is clean.
Step 2: Fill big gaps with backer rod
For wide gaps, push foam backer rod in first. It stops the caulk shrinking so much and keeps the depth even. It should fit fairly snug and sit about 1/8 in. below the surface. In the video the caulk shrank about two millimetres after four or five days, and a second coat with the tape left on gives a flush finish.
Step 3: Tape and cut the tip
Tape the edges you want clean. Cut the tube tip at a 45 degree angle, about 3/16 in. off the tip. A small hole is easier to control. For a thicker advanced silicone, the contractor suggests a gun with a low and a high torque setting.
Step 4: Apply and tool
Tom Silva always pulls the bead; pushing drives caulk into a crack. Go slowly so the joint fills completely, because going too fast can leave air gaps, and the more caulk in the joint, the longer it lasts (TileCoach). Tool with a damp finger and clean with a damp sponge for acrylic and siliconised acrylic. Repairs101 smooths bath and tile caulk with a gloved finger dipped in paint thinner. Follow the label for your product.
Step 5: Keep the tube
TileCoach leaves the tube at the job for touch-ups, with the opening covered with masking or duct tape so it stays airtight.
Mistakes to avoid
- Caulking over old caulk or over a damp joint.
- Using latex where water sits.
- Skipping the backer rod on wide gaps.
- Painting over silicone.
Put it on the calendar
- Check sealants every year, says the Home RenoVision DIY contractor, because you don’t know when they will give up.
- Maintenance joints: where there is continuing movement, clean it out and redo it every 6 months to a year (TileCoach).
- Silicone grades last through a limited number of freeze-thaw cycles; the premium grade lasts longest.
See also
- Tools: caulk gun, utility knife, putty knife
- Caulk a tub or shower, Caulk large gaps, the Large gaps that shrink and Cracked grout problems
- Tiling Basics and Planning a Bathroom Remodel
- The Bathroom and Kitchen rooms
Sources
- Shown on this site, source of the joint-by-joint advice from Tom Silva. Latex, Silicone or Butyl? Matching Caulk to the Joint (video, Ask This Old House) Source
- Shown on this site, source of the four-type comparison and freeze tests. Latex, Solvent, Polyurethane or Silicone: Choosing the Caulk (video, Home RenoVision DIY) Source
- Shown on this site, source of the backer rod method. Filling Big Gaps with Backer Rod and Paintable Latex Caulk (video, Vancouver Carpenter) Source
- Shown on this site, source of the grout-colour caulk advice and maintenance interval. Fix Cracked Grout at Wall Transitions With Matching Caulk (video, TileCoach) Source
- Shown on this site, source of the recaulk step. Regrouting a Shower Surround: Rake, Apply, Cure and Recaulk (video, Repairs101) Source
Watch
The videos and projects this guide mentions.
- Latex, Silicone or Butyl? Matching Caulk to the Joint Video
- Latex, Solvent, Polyurethane or Silicone: Choosing the Caulk Video
- Filling Big Gaps with Backer Rod and Paintable Latex Caulk Video
- Fix Cracked Grout at Wall Transitions With Matching Caulk Video
- Regrouting a Shower Surround: Rake, Apply, Cure and Recaulk Video