Caulking compounds vary in strength and properties. Caulk is a substance that can emit VOCs and luckily there are many caulk options available that do not adversely affect indoor air quality. See our Artricle Indoor Air Quality -- Identifying Sources and Making Renovation Choices that Eliminate Contamination for an in-depth review of air qality considerations.

The Department of Energy has prepared the following useful guide to caulks:

 Caulking Compound  Recommended Uses  Cleanup  Shrinkage Adhesion   Notes
 Household Silicone  Joints between bath and kitchen fixtures and tile,  metal joints such as gutters.   Dry cloth immediately or mineral spirits.  Little or none.  Good to excellent.  Flexible:  cured silicone stretches up to 3x its width and compresses to one-half the width.
 Construction Silicone  Seals disimilar building materilas like wood to stone, metal flashing to brick, and will adhere to painted surfaces.   Dry cloth immediately or mineral spirits.  Little or none  Good to excellent.  Flexible (stretches and compresses).
 Polyurethane, expandable spray foam  Expands when curing; good for larger cracks indoors or outdoors. Use in nonfriction areas, as rubber becomes dry and powdery over time.  Solvent such as lacquer thinner, if immediate.  None.  Good to excellent.  Expands a lot to fit large, irregular gaps.  Flexible. Can be used at varyng temperaturers. Must be painted for exterior use.  Manufacturing process produces greenhouse gases.
 Water-based foam sealant  Around window and door frames in new construction (will not overexpand and bend new windows); smaller cracks.  Water.  None; expands only 25%.  Good to excellent.  Takes 24 hours to cure and must be exposed to air. Cures to soft consistency. Production does not produce greenhouse gases.
 Butyl rubber  Seals most dissimilar materials (glass, metal, plastic, wood, and concrete.) Seals around windows and flashing, bonds loose shingles.  Mineral spirits.  From 5% to 30%.  Good.  Durable 10 or more years; resilient, not brittle. Can be painted after one week curing. Variable shrinkage; may require two applications. Does not adhere well to painted surfaces. Toxic; follow label precautions.
 Latex  Seals joints around tub and shower. Fills cracks in tile, plaster, glass, and plastic; fills nail holes.  Water.  From 5% to 10%.  Good to excellent.  Easy to use. Seams can be trimmed or smoothed with moist finger or tool. Water resistant when dry. Can be sanded and painted. Less elastic than above materials. Varied durability, 2–10 years. Will not adhere to metal. Little flexibility once cured. Needs to be painted when used on exteriors.
 Oil or resin-based  Seals exterior seams and joints on building materials.  Mineral spirits.  From 10% to 20%.  Good.  Readily available. Least expensive of the four types. Rope and tube form available. Oils dry out and become brittle, material may fall out. Low durability, 1–4 years. Poor adhesion to porous surfaces like masonry. Should be painted. Can be toxic (check label). Limited temperature range.

Caulking can be tricky. Read and follow the instructions on the compound cartridge, and follow these tips:

  • Clean all areas to be caulked or you may not get good adhesion. This means remove any old caulk and paint, and make sure the area is dry so you won't seal in moisture.  The best time to apply caulk is during dry weather when the outdoor temperature is above 45°F (7.2°C) and the humidity level is low to prevent cracks from swelling with moisture.
  • Apply caulk to all joints in a window frame and the joint between the frame and the wall.
  • Hold the gun at a consistent, forty-five degree angle to enable the caulk to get deep into the crack. You know you've got the right angle when the caulk is immediately forced into the crack as it comes out of the tube.
  • Caulk in one straight continuous stream, if possible. Avoid stops and starts.
  • Send caulk to the bottom of an opening to avoid bubbles.
  • Make sure the caulk sticks to both sides of a crack or seam.
  • Release the trigger before pulling the gun away to avoid applying too much caulking compound. A caulking gun with an automatic release makes this much easier.
  • If caulk oozes out of a crack, use a putty knife to push it back in.
  • Don't be stingy. If the caulk shrinks, reapply it to form a smooth bead that will seal the crack completely.