Masonry: Backer Rod

So this video is about backer rods that are used in expansion joints and to fill gaps in buildings. And backer rods are usually squished into a gap. And what happens here is the foam itself does not allow adherence with the caulk. So the caulk cannot stick to the backer rod. but it is squished and it seals the gap between the two pieces of masonry or the two precast members. So they come in all kinds of sizes and lengths, and they come as small as that for small gaps. I'm looking at this drawing, and I'm comparing it to this drawing, And this drawing I have prepared, but it's drawn by hand, and this is a very nice computer drawing. But, as usual, my student has committed some errors here that I'd like to fix with you. Maybe you can learn something from it. First of all, the use of the backer rod is to control the depth of sealant, and it looks like it's really excessive in this drawing. So it has to do with the width of the gap, and it's probably just a little bit less than the width of the gap. The second error I see is my student drew the backer rod as round. Probably that was the markup I gave him, I'm not sure. But it needs to be squished. So maybe that's too much squishing, but it's not round. And it's in contact here and here, and the sealant is going to come in here. and not adhere. Here it is, for example, between two precast double T's of concrete, and there's the backer rod. And then they're going to come back and put caulk in there and around the stem of the double T. Now, backer rods come in a lot of shapes and different types of foam. So a closed cell backer rod, such as this one, would provide a lot more insulation value. So the cells are closed, air cannot leak in through there, versus open cell. Open cell backer rods are used for interior gaps.