Q.: I have just cast a concrete table using white cement, sand and a superplasticizer. I am looking for a sealer that will protect the smooth concrete surface from oil stains without substantially altering its color or matte finish. So far, all I have found are products that darken the color or give the concrete a sheen or gloss. Do you have any suggestions?
A.: That's a tough one. Water repellents like silicones or stearates do not repel oil. The penetrating sealers we know of would darken the concrete. There are a number of clear coatings but all of them impart gloss. Among these glossy coatings are the acrylics, which have the additional disadvantage that they might soften from oil. Clear urethanes might gradually turn yellow, and clear chlorinated rubber might yellow to some extent. Yellowing would perhaps be less if the table is used indoors and not outdoors. If gloss and some likelihood of yellowing are less objectionable than oil staining, you might apply a clear chlorinated rubber. Otherwise you might have to settle for a tablecloth.