Calling caulk experts!

[Scott T-Bird]

This is not related to my sailboat, but I think this forum is a good source of information. I had Sikaflex 15LM polyurethane caulk used with fiberglass-framed window installations in a pool enclosure. Caulk surrounding the jambs and at the head of every window is perfectly clean. Black mildew stains the caulk under the sill of just about every window where there is standing water on the stool. Mildew stains only the caulk, not the window frame or the stool (which is a composite product). Obviously, this is a very high humidity, high temperature interior environment. Exterior caulk is fine and the exterior environment is harsh ... down to below 0.
I don't want to compromise high strength, elasticity and durability qualities, but manager is complaining about mildew. My research indicates that mildew is largely unavoidable where there is free water in this environment and products that advertise mildew resistance are lesser products meant for interior environments like bathroom and shower enclosures. The Sika rep says Sika doesn't make a mildew resistant formulation. I don't think replacement is called for, just better cleaning ... where am I going wrong?

 

[Rich Stidger]

I have a similar issue in a bath enclosure at home. Where a bottle of shampoo is set in the corner of the tub, the caulk behind the bottle gets mildew. I clean with a home-made mix of water and bleach. What I have found is that if the bottle is moved out of the corner so that there is space and free air behind the bottle, I get much less mildew. The space and air circulation (I presume) reduces the mildew.

Sorry I don't have a better cleaning solution, but I have found that just water and bleach works as well as the high-priced cleaners.

 

[Scott T-Bird]

I was reading that the soap actually attracts mildew, so a soapy bottle doesn't help. Actually, cleaning isn't my job. I just have a pissed-off manager because he thinks I was supposed to spec a caulk that doesn't require that attention.

 

[woodster]

Well you manager is an uninformed person that needs a class in caulking ....there is no mildew free product out there..... Even gillies in New Zealand doesn't make one and if they ....they couldn't ship it stateside

 

[JamesG161]

I build homes. My Benjamin-Moore paint dealer can make color matched caulking. On their counter was a small pack of Mildew killer powder they added , on request, to all their paints and caulking. I have added it with no apparent problems with the paint or caulking using that powder (I only add it on request by a client, exterior mild pressure washing does the job better). You might check them!
Jim...

 

[Scott T-Bird]

Thanks Woodster & Jim,
I wrote a letter explaining that the caulk is paintable, so one option could be to apply a coating with a mildew-resistant formula. I won't offer any guarantee because I think the bigger problem is they don't manage humidity properly - which is a common problem in pool enclosures. But my suggestion was met with hostility. The guy won't be satisfied until the caulk is removed and replaced with something else. I'm not ready to concede, yet. Aside from that, the building was emptied when the windows were installed. Now, with the pool in use, I won't concede to applying or replacing anything while condensation is dripping from the walls. That will just add fuel to the flames if I ever have to tell him that.
I also spec'd the paint application to protect the steel structure of the building with this renovation. I can just image the call I'm going to get the first time a spec of corrosion appears ... even if it is 5 years from now. (Maybe I'll be retired by then!).