Remove all water from the birdbath.
Clean the birdbath with the water and dish soap mixed in to remove all dirt and debris. Use the bristle brush to scrub clean the surfaces. Use fresh water to get rid of the soap scum.
Move the birdbath to a dry area, preferably a garden shed, garage or other clean place. Let the surfaces dry thoroughly.
Prepare the two-part concrete epoxy by using a popsicle stick to thoroughly mix together the resin and the hardener in a small glass jar with a wide mouth. Follow the manufacturer's exact guidelines when preparing the epoxy.
Smear some of the epoxy on a putty knife, then work the epoxy into the cracks in your birdbath. Fill all cracks evenly, making sure no cracks show when finished. Let the epoxy dry at least 10 to 15 minutes.
Hold pieces of concrete together with the epoxy if you need to fix broken chunks of concrete. Wait for a few minutes until the pieces form a bond before removing your hands.
Move your birdbath back outside after waiting 24 hours for the epoxy to fully cure. Then, fill the basin with fresh water, and let your birds enjoy their newly repaired bath.