Look into breathable acrylic sealers.
The other choice would be a silane or siloxane. Totally clear.
Everything you ever wanted to know:
(not meant to be inclusive)
Prosoco http://www.prosoco.com /
W R Meadows http://www.wrmeadows.com/msds-can.html
Dayton Superior http://www.daytonsuperior.com/default.aspx
Keep the whole world singing . . .
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