How can I tell whether old caulking is silicone vs latex acrylic?

Mike asked 4 years ago

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?

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