bedding polycarbinate deadlights.

[feetup]

I did a site search but didn't find an answer.

I think I read somewhere that you must not use "X" to bed polycarbinate, but I can't remember what "X" was. Or maybe it was acrylic that must not be used with "Y". I can't remember.

They say that the bladder goes next now that the memory is gone.

I need to bed some Polycarbinate deadlights, and the bedding is all that holds them in place. What would you use?

Tim AKA feetup

[Tim]

"X" = polysulfide: products like 3M 101 and Boatlife LifeCalk. (Yes, that's how it's spelled.)

Supposedly polysulfide attacks the plasticizers in acrylics, polycarbonates, and other plastic types, which can change the properties of the plastic over time. I don't understand, nor care about, the chemistry behind it: it is what it is, and one simply shouldn't use polysulfide when bedding plastic.

I often use butyl rubber caulk to seal plastic ports, but this is a sealant only, not an adhesive. I hate the stuff, but it does work well.

If the bedding is all that's holding your polycarbonate in place, you need an adhesive sealant. I'd suggest 3M 4200, a polyurethane similar to 5200 but with less adhesion, meaning it's not permanent and can be removed (with care). Or use one of the Sika polyurethane products; there are several different types, each with its own properties. Just avoid the strongest polyurethanes (5200, etc.) which are essentially permanent and not the right choice for anything that is likely to be removed, like ports.

Dave (Hirilondë) mentioned in a post the other day about a helpful chart in the Jamestown Distributors catalog. Since it doesn't seem to be available online, I've posted it permanently right here for future reference. Link: Sealant Comparison Chart

[Hirilondë]

If you reference the manufacturers of polycarbonate and acrylics (most make both) you will find that the only recommended beddings are butyl and (prepare yourself for this) silicone. I have searched high and low for a good explanation why, and why no others. I have found neither. I have spoken with the general manager of a large plastics supplier, and he says silicone is the best choice (butyl is too messy). Sabre Yachts use butyl tape and silicone together for their framed deadlights (they sent me a diagram and directions). That has to be messy. I use Sikaflex 291-LOT.

Thanks for posting the charts Tim. Looks like a slightly different version than I have at work, even has the TS strength of Silaflex 291-LOT as 200 vs 250. Minor detail, it has some very useful info people often don't consider when choosing a product.