I have a bridge outside my home. It is mostly made out of wood. But part of it has some slate. It is is good condition. I have noticed a few cracks in the slate and I want to seal it up so that water can't get in between the wood part of the bridge and the slate part of the bridge. I also want to better protect it so it doesn't crack further. Can you recommend any clear type of waterproof sealant? I should also mention that we drive our car on the bridge to access the garage and we walk over it daily...so I also have to be careful that the sealant isn't slippery.