To apply caulk make sure that the surface is clean and dry.

Also raise the lower sash and apply caulk where the upper surface of the sill meets the other parts of the window frame and trim.

To apply caulk, first make sure the surface to be caulked is clean, free of old caulk and dry (if specified on the product label).

Applying caulk in a smooth ribbon, or bead, takes practice.

Inexpensive guns available at hardware and department stores are fine for latex, silicone and siliconized caulk; for applying stiff caulk like neoprene or butyl, and for large jobs, a professional gun that delivers more thrust makes squeezing the trigger easier.

Where neatness counts, apply masking tape to the surfaces on both sides of the seam before applying caulk.

To apply caulk, first make sure the surface is clean, dry (if the instructions on the cartridge specify) and free of old caulk and flaking paint.

Step 3: Apply caulk to joint.

Modify the existing threshold as specified in the instructions; then apply caulk to the surface that beneath the threshold of the prehung door.

Inside, test for leaks where fireplace masonry meets walls and ceilings, and if necessary, apply caulk.