I have a project in a business office where the first level walls are made of old concrete. The tricky and unfortunate dillema is the wall is made up of old coral heads and sand from the near by caribbean sea years ago. On the island i live on this was a common practice back in the day, although today because the salt was never removed, the wall is very brittle at the suface and if brushed up against comes off. I havnt tried anything yet. I would like to try some type off concrete sealer but not sure which type or brand to try. It is a business office so something with the least amount of fumes or harsh smell would be ideal. Any suggestions?