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Best caulk for fiber cement siding, miratec and fiberglass?

BrunoF | Posted in General Questions on

I am looking for recommendations from experts on what caulk will offer a good balance of durability, cost and ease of application for use on fiber cement siding, Miratech, and fiberglass windows.

the window installers love quad max for window install but all the painters hate it because apparently it is a pain to tool.  So far all of the painters prefer cheap acrylic caulk presumably because they tool easily but I have seen too many houses with poorly caulked siding to want to go that route.

what are some caulks / sealants that I should consider that will tool well and provide good adhesion, flexibility and durability?


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  1. Chris_in_NC | | #1

    Dunno, Quad Max is pretty well loved by siding installers too. Are the painters hung up on wanting to tool, and did the siding installers not caulk the siding to trim?

    OSI specifically states not to tool Quad Max on siding. Their logic is that tooling widens the bead and reduces the depth, making adhesion problems with joint motion, and reducing UV resistance.

    For lap siding to trim, go check out a few videos on Quad Max application and see how you like the bead aesthetics. The siding guys lay it down right out of the gun (no tooling), making sure the tip is cut properly, and it looks really nice with a little practice and some attention to detail.
    I think all of the Hardie colormatch caulk is Quad and more recently Quad Max..?

  2. Ryan_SLC | | #2

    I have done exactly two Hardie areas on my house. I did spread Quad when I did it. Oops. visible consequences 5 years later.

    Actually, looking back, I wish I'd not spread it around and just left it as a clean bead. I'd leave it to the Hardie spec. The caulk should be Quad or on the spec.

  3. aaron_p | | #3

    I've been happy with Sashco Big Stretch for something like that - it shrinks a little bit as it cures, so a straight chamfer tool of the bead ends up with a nice little concave joint. Paints really well and cleans up easily.

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