On the interior, caulk is used to fill cracks and voids with the purpose of sealing out water, air, or just for aesthetic reasons. Outside of tubs and windows, the last of the three is most common reason for caulking on the interior.
Interior caulking
Interior caulk is used for aesthetic purposes most often. In new construction or remodeling, new wood trim will be caulked to the wall as well as gaps between and within pieces of trim. For generic painter’s caulking of gaps and cracks a silicone latex or straight latex caulk are used. Most of the time this caulk will be applied after priming the bare or raw wood and new drywall but before painting.
Flat paints over latex caulk
One exception to the caulk before painting rule is if you are going to be painting in a flat paint over the caulk. Interior flat paints are often loaded near the critical pigment volume concentration and will easily crack if applied over a soft substrate or one with little “tooth”. In the case of flat interior paints, you will find that you may need to prime over the caulk (after if has dried) with a oil based primer prior to applying the flat finish paint. This procedure will eliminate “mud cracking” of the flat finish over the caulked joints.
If you are applying caulk over a fresh (but dry) coat of primer, there will be little surface preparation. In the case of a repaint situation, you want to be sure the substrate to be caulked is clean and dust free. If you are replacing caulk as in around a bathtub etc…. You may need to remove the previous caulk.
Once the caulk is out, you want to clean out the joint with a dust brush and do a solvent wipe with rubbing alcohol or Krud Kutter if alcohol will damage the substrate.
Do you need to tear out the old caulk?
If the old caulk has simply become hard and cracked with age but is adhering well, you may be able to put a wider bead of caulk right over the old.
Matching caulks
Many paint stores have caulk that will match a few (or many) of their paint colors. OSI brand caulk has a huge color selection. You can almost always match to a particular paint color with OSI caulk. OSI (Ohio Sealant Inc.) makes both interior and exterior caulk.
Applying the caulk
With most interior caulking you will try to keep the bead of caulk as small (thin) as possible, since most interior caulk is for aesthetics. If caulking for function (as around a tub or countertop) you may want to cut you opening at about ¼”-1/8”. When ding aesthetic caulking you will cut the opening on the spout of the tube about 1/8” wide. Cut the spout with the spout cutter on the caulk gun itself or with a razor knife. The cut should be on an angle (about a 45 degree angle) to aid in laying down a good looking bead. You will need to pierce the inner seal inside the tube with the lance attached to the gun (if there is one), or with a wire or long nail.
Technique
Professionals don’t mask off the caulk joint, it would take too long to do this for many joints. Professionals have learned to apply steady pressure to the caulk gun trigger as they pull the gun down the joint - all the while watching the bead to be sure it is not being “stretched” thin or oozing out the sides of the spout . The key a good caulk bead is steady pressure and movement of the gun. Professionals often don’t wipe or tool the bead (if they laid down a good bead), but on the interior where the beads are small, usually a finger wipe will do. No water or rag is used on the wipe unless the bead got messy.
Mask and wipe / tooling the bead
Tooling is really an outside technique that is hardly every done inside because inside caulk beads are as a rule small. I will refer the reader to the exterior caulking article and the section on “tooling” for further information on tooling.
Masking and wiping: Many DIY’ers since they only caulk from time to time, have not mastered the steady pressure / steady movement of good caulking. So, the nest best thing is to either use a specialty tool made for DIY’ers to wipe a caulk bead smooth or to mask and wipe.
Masking requires the applicator to lay down masking tape at the desired width of the caulk bead, then to lay the caulk bead down within that perimeter. Once the bead is down, a finger or a tool (a spoon can be used for this as a makeshift caulking tool) is used to wipe the bead down and smooth. Once the bead is wiped, the tape is removed from both sides of the joint you should have a perfect caulk bead.
Removing old caulk
A pointed tool like a 5 in 1 painter’s tool, or a razor blade is usually employed for the removal of old caulk. Be careful not to scratch the underlying substrate. Once you have an end up, you may be able to pull the caulk out of the joint. For softer substrates you may need to resort to a wood shim or plastic putty knife (those disposable ones you can find in hardware stores) to avoid scratching the underlying substrate
Caulking New Wood Trim
Removing Old Caulk / Recaulking a Tub
Interior Caulking
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