When windows are newly installed, they should fit perfectly in the space allotted for them. After a few years, however, it is possible that a house may settle, and the window frame may shift slightly, causing cracks between the frame and the wall. If cracking around a window frame appears after an earthquake or another major event, have your home inspected for structural damage. If the crack appears slowly over time, it probably is a natural shift, and you can fix the cracking space yourself.
Clean around the cracked area with a clean wet rag, wiping dirt and dust from around the crack. Allow the area to dry completely.
Use frame sealant for cracks between the window frame and wall that are below 10mm in width. Prepare the sealant by placing the sealant tube into a caulk gun and cutting the tip of the tube to create an opening that is roughly the same size as the cracking space you need to fill.
Hold the tip of the sealant container up to the crack at one end. Lightly depress the trigger on the caulk gun to push the sealant out the tip. Keep steady pressure on the trigger and move the tip down the length of the cracking space, squeezing sealant into the space.
Stop pressing the trigger at each corner of the window, then begin a new line of sealant across the next crack. If large globs of sealant sit anywhere along the line, wet your finger and smooth the sealant down against the surface.
Clean the area with a wet rag, removing dirt from the crack. Allow the area to fully dry.
Use mortar to fill cracking spaces between a window frame and wall if they are wider than 10 millimetres. Mix the mortar according to the directions on the packaging to get the proper consistency.
Spray water into the cracked space to moisten, and apply mortar to the crack with a putty knife. Spread the mortar over the crack; use the tip of the putty knife to force the mortar into the cracking space. Continue adding mortar until the crack is filled and even with the wall.
Use the edge of the putty knife to remove mortar that gets on the surrounding wall. Wipe off any spots of mortar that remain on the wall while the mortar still is wet.
Go over the new mortar work with sealant after three or more days when the mortar is fully set. Apply the sealant over the new mortar and smooth it down with a wet finger so it sits flat against the surface.