Called Wood Scapes would treat the shakes OK, but it would not give one additional ounce of fire protection. You could get this product in clear or any other color you would like.
You would of course have to spray it on. The first coat will just soak in so much that it would not even show. you would need several coats to build up protection.
In Texas we use it all on cedar shake siding. Makes the wood look rich and new. Does great with our heat and sun.
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