I have serious leakage under a wall of windows. The windows are at least 5 feet above ground. I have removed the inside drywall on the underside of the windows as well as the vapor barrier and insulation to find the problem areas. The outside is aluminum siding, on the inside I am now looking at OSB sheathing. From the inside, I can see that water is coming through at the window ledge level, I can't make out exactly where. I have filled all the holes I can see with Mono Ultra caulk but I still have leakage.

I have now bought a product called "Exterior only - Mulco - Supra Expert - Thermoplastic sealant". Do I have to remove the old caulk?

I don't know for sure what all caulk has been used on this, it was built some 15 years ago and has been caulked several times by different people. How can I tell if silicone was used?

Click here to receive email notifications when answers are posted to this question.

Answers

Answered by Karl Crowder, Crowder Painting from Colorado Springs, Colorado

Distinguishing between pure silicone caulk and regular paintable caulking isn't easy to describe, I will do my best.

1) Silicone caulking is very rubbery and a little spongy. Regular caulking is harder (less spongy) and will harden more over time.

2) Water beads off silicone. Try wiping the caulk with a rag and water. Make sure to wipe off any dust and observe if the water separates from the caulking.

3) Silicone isn't paintable. If the caulking is painted, try scraping it with your fingernail. The paint will be easily removed.

Beyond the feel of the caulking there isn't any test that I no of. Re-caulking the windows over all the existing caulking's could be a little risky. You can't tell for sure what has been used over the years. I recommend removing as much of the old caulk as possible then re-caulk.