Do this before trying to fill the crack with any kind of filler.
How to fix cracked window sill.
Resist the urge to keep touching and fiddling with the look of the smoothed caulking you will probably make it look worse.
It is important to prevent water moisture from getting under your window this is a short video to show how easy it is to seal up the cracks in your concret.
Sand the surface with a 100 grit sanding sponge.
Scrape the sill with a metal scraper to remove chipped or peeling paint.
Step 1 use a putty knife or a paint scraper to remove the peeling and cracked paint.
Sand the sill with 100 grit paper to smooth the surface for priming.
How to repair weathered wood sills.
Rub the surface of any and all damaged areas with a stiff brush.
How to repair a concrete window sill preparation.
If there is not one there you may want to push up the cracked sill and install a skirting board to help support the sill.
Check for sill movement such as a crack where one side has settled or is down farther than the other side causing a crown and a crack.
Fit the narrow tip.
Using a small putty knife starting at the window smooth the caulking flush to the sill.
Dig out damaged wood image copyright.
Step 1 clean the surface.
We pulled out the rest of the nails that were left behind.
Switch to a 220 grit sanding sponge to finish off with a very smooth surface.
Then we used a hammer and banged popped the sill upwards being careful to avoid any further damage.
Remove any existing paint and dirt first from the area by scraping and wiping the area down with a rag moistened with tsp.
You will need to raise one side or the other with plastic.
Remove the excess material build up on the putty knife.
Step 2 remove loose wood.
First we ran a cutting blade this is my favorite caulk removing tool around all the edges including between the underneath trim and the window sill.
With any luck this re work may keep the crack closed up.
Sometimes a skirting trim or board is installed under a sill like this to help support the sill.
Fix any small or medium cracks in your concrete window sill with caulk.
Finishing the mortar joint.