Glass block walls can add a great deal of beauty and value to a home, but once installed they require maintenance. One thing that can happen is that the glass block mortar placed around the blocks could dry out, crack, or even chip away. When this happens, leaks can occur which are not only annoying, but can also waste heating or cooling energy. Fortunately, repairing the mortar around a glass block window can be a rather simple process, assuming that the damage is not excessive.
Scrape away all silicone and then all dried and loose glass block mortar with your putty knife. Use caution when scraping and do not twist your knife and place pressure on the edges of the glass block as this could cause chipping of the glass. Take your time and clean away as much of the loose material as possible.
Check the block for stability. If the glass block does not move excessively and remains solidly in place after you have scraped away all silicone and all loose mortar, then use your putty knife to force new glass block mortar into the joint. Fill as much of the joint as possible with the mortar. Glass block mortar is available at most major hardware stores.
Use a damp cloth to wipe any excess mortar off the face of any glass block and then use a finger that has been dipped in water to make a smooth 1/8th-inch deep indentation in the mortar of the joint.
Add a bead of clear or white silicone sealant along the joint after the mortar has fully dried as per the manufacturer's instructions. Allow the silicone sealant to dry as per the manufacturer's instructions.
If glass blocks are excessively loose once the silicone and mortar has been scraped away, reinstall the entire wall as per the original installation instructions. However, unless the original installation was completely botched, this step should be unnecessary.