I would like to know how to fill a large gap between wood and cement. I have attached some pictures. This is outside on the front covered entry. I am going to try and fill the gap so that rain water does not seep through the gap. Two long boards are nailed to the beams that support the roof over the entry. They are above the cement walk. There is an uneven gap between the boards and the cement. I was going to put closed cell backer rod in the gap and then caulk it with Sika Self-Leveling Sealant which was suggested by an employer at Lowe's. My problem is, what kind of material can I use to make a form so that the sealant doesn't run all over the place on each side of the boards as I am applying it? Thank you so much. Billie
DMoore is right, if you have a grading problem you should get that fixed if you can afford it.
That said, in your other comment you mention that its just water blowing in? If the water drains toward the wood normally and you only flood because of wind blowing it in, I would definitely not plug the gap. Get a piece of plastic trim and screw it to the outside of the wood. Cut out a few notches for drainage.
I am almost positive that this gap was left there to let water OUT. I would not fill it. If you do want to fill it and potentially cause other issues, just use masonry caulk.