Caulk alone won’t fi x door leak
Q: There's a moisture problem in the basement directly under the sliding patio door on the back of my home. The gutters are clear and the patio is level. I plan to seal between the bottom aluminum threshold and the concrete curb and caulk the gap between the side trim and brick. I know I need to install a concrete overlay to get my patio to drain. How would you repair this? — Doug T., Windsor, Ontario
A: You're suffering water problems along with many other homeowners, judging by my mail. When I look at the photos sent to me, it's clear that many builders and remodelers are clueless about flashing exterior doors.
I regret to say that your plan of attack may not solve the problem. What's more, caulk is not a permanent solution, no matter what the label states.
Your photos show that you've got a brick exterior with raked mortar joints. This method of dressing the mortar creates a shelf on top of each row of brick, and it's the least waterproof joint.
The most weatherresistant joint is a convex one created with a rounded tool. Water hitting the wall during rainstorms is automatically forced down the wall by the concave joints. With your raked joint, water can collect to a slight degree on the small shelf. If a brick, or two or three, has a backwards tilt, the water can seep behind the brick.
Your photos also scream that your builder didn't put a proper flashing under the door threshold. This would shed water to the outside of the concrete step beneath.
Think for a moment how overlapping shingles, even feathers, work. Each successive shingle or feather overlaps the one below, and gravity pulls the water over each one. Thus the water never gets into the core of the building, or the bird.
In the case of your door, water can get behind the concrete curb under the threshold. While there might be a hidden flashing behind the curb, how is it possible for the water to get back out on top of the patio and drain away from the house? The concrete curb is acting like a dam.
My advice is to carefully remove the aluminum trim covering the wood trim that surrounds the patio door. Then remove any wood trim. You need to determine whether the top and sides of the door have proper flashing.
As drastic as it sounds, you also need to remove the concrete curb that's under the door threshold. I'm sure it's only going to take an hour using a 4-pound hammer, or even less time if you rent an electric demolition hammer. Be sure to tape thin sheets of plywood over the door's glass to protect it from flying pieces of concrete.
Once you've exposed the top, sides and bottom of the door, you can assess what needs to be done to make the door waterproof. I'm hoping that you discover the builder or carpenter installed a proper flashing pan under the entire door threshold. That's the first step that should have been taken even before the door was lifted into the rough opening.
If there's no flashing pan under the door, you need to remove the entire door and start the installation process from scratch. There are pre-formed plastic flashing pans that you can use under the door, or you can create one with thin sheets of lead or rubberized-asphaltbased flashing tape. There are videos online that show you how to install these flashings.
The ultimate goal is to create a series of overlapping layers so that any water that gets behind the door trim is captured and redirected back out, below the door threshold.