I just looked up my McMaster-Carr order, and I used 5952 series 3M VHB tape. I updated the “new portlights” on the Johanna Rose blog to reflect this along with the McMaster-Carr part numbers.
The 5952 series is black and is 3/16” think. In my case, with the 1/4” polycarbonate, this thickness was perfect. It provided enough of a gap for the Dow 795 with the portlight ending up slightly proud of cabin surface. I would not try to double up the thickness. I think it is more important to put a good bevel on the inner edge to help the sealant flow underneath and around the edge to form a good beaded adhesive seal. I looked into using Sika with the VHB tape, but after researching, I found that there were many good reports of long-term success using the Dow 795. To add to this track record, Dow 795 is much easier to work with and costs about $8 per 10.3oz cartridge (both big pluses for the DIY-er). http://svjohannarose.blogspot.com/2015/07/new-fixed-ports.html <http://svjohannarose.blogspot.com/2015/07/new-fixed-ports.html> - Paul E. 1981 C&C 38 Landfall S/V Johanna Rose Carrabelle, FL http://svjohannarose.blogspot.com/ > On Nov 10, 2015, at 11:27 AM, cnc-list-requ...@cnc-list.com wrote: > > From: Josh Muckley <muckl...@gmail.com <mailto:muckl...@gmail.com>> > To: "C&C List" <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> > Subject: Re: Stus-List Fwd: Replacing Windows > Message-ID: > <CA+zaCRDtZT+=cNs_9SqJMjRuzEeo9cPw-qDFY=qhjzcv8fg...@mail.gmail.com > <mailto:CA+zaCRDtZT+=cNs_9SqJMjRuzEeo9cPw-qDFY=qhjzcv8fg...@mail.gmail.com>> > Content-Type: text/plain; charset="utf-8" > > The attached PDF had pretty good guidance. I would choose the thickest > tape which can still fit under the windows. Maybe even double layers. I > have a friend who used the 4941 series. After looking at the PDF it looks > like the 5952 series has better adhesive qualities and possibly higher > adhesion for the fiberglass and polycarbonate that we're using. The 5958FR > has the highest PSI to thickness ratio. I suggest thicker to allow the > tape to press into any irregularities. Thicker also allows for more > differential expansion of the glass and frame. > > As much as I like the VHB tape I still can't help but think to the auto > industry. They use a urethane made by Sika for windshields. It has to be > primed and heated. It cures in about an hour. I wonder if a combination > of VHB tape and sika-flex might be smart. VHB to get a nice interior > finish and sika for a permanent weatherproof bond and glazing. > > Josh Muckley > S/V Sea Hawk > 1989 C&C 37+ > Solomons, MD
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