Fixed portlight install—foam tape spacers?

[britinusa]

I'm planning on replacing my plexi windows also. As Noah says it's the crazing!

When I replace mine, which also have screws, I'm going to use Snaps on the screws so that I can sew an external cover for the windows to prevent SoFla Sun Damage.

Paul

[Stu Jackson]

Paul,

You might want to reconsider that idea.  When you pull on snaps, they, well. uhm, pull.  You really don't want to be yanking on the screws that hold your fixed portlights in place. 

Everyone I've ever seen with sun covers over their fixed portlights has installed separate snaps above and below their portlights.

Please think about it.

[britinusa]

Good point Stu.

I could do that, and that raises the question: Are the screws really necessary?

Paul

[KWKloeber]

Paul

The screws aren't recommended by CTY due to issues of cracking around them.  You CERTAINLY don't need fasteners to hold the plexi on when using 795. 

There's a C30-er who went to elaborate measures to use screws and not have them put stress on the plexi.  D'oh.  Why?  If you use them to temporarily hold the plexi while the 795 cures, then CTY recommends you remove them/fill the holes w/ 795.

As far as using them for snaps -- the screws don't hold the windows -- the 795 holds them.  If you overdrill the holes to assure there's no stress on the plexi, and after the 795 cures back out the screws and put in your snap heads, assuring they don't compress the plexi, then there should be no interference.  But that means can't be tightened down to secure them.  You'd probably need to dap epoxy on the threads so they don't loosen up (not being tightened down against the coachroof.)

Possibly Lift-The-Dot fasteners would put less pull on the screw threads? 
There's some other newer snap-type fasteners that require less "pull."  My bro does canvas work - I could pass it by him if you like.

ken

[WTunnessen]

Noah - I've replaced all fixed light ports with replacement lenses from Catalina and using the Dow Corning 795.

Using the foam spacers is not that problematic. Just make sure there is space around them for the glazing caulk to flow  AND don't hold back with caulk.  Better to put it on too think than too thin.  Be sure to blue tape all areas around the window frame inside and out.  Lastly I did not use screws and have not had any problems.

[DaveBMusik]

I initially rebed two using the Catalina technique.
Last year, I purchased four new lites (since the old ones were crazed so badly and cracked around the screw holes) and did the other two using Andy's technique.
I found using the VHB tape to be much easier, cleaner and professional looking. I'm going to rebed the other two new ones this year with VHB.
One benefit of using the VHB tape was there was no need to use screws or a complicated clamping device.
I did find that the new lites I purchased (I think from Catalina Direct) were just a bit too big and needed to be sanded.

[Jon W]

Do you recall if the VHB tape was #5952, and where did you buy it? Did you use 1/2", 3/4", or 1" wide? Thanks.

[sailr4]

I ordered 3M VHB #4991 (0.5") from amazon.


Rob

[DaveBMusik]

Do you recall if the VHB tape was #5952, and where did you buy it? Did you use 1/2", 3/4", or 1" wide? Thanks.

I used 5952 in 1" and trimmed the excess on the interior of the frame. 1/2" might be ok and would leave more room for the sealant between the lite and hull.
I believe the 4991 is thicker but does not come in black.
On both aft windows, there is a solid section where the bulkheads are. I framed the VHB around the edges and then spread some black adhesive in the middle just so the color would look uniform.

[KWKloeber]

On doing the c30 replacements I've seen talk about painting some (all?) of the surface(s?) black beforehand. I have a mk-I so don't am not familiar with the particulars but it seems to be the instructions.  Maybe from CTY?

[Noah]

To close the loop: i just completed my fixed portlight replacement project. Not something I ever want to do again. I followed the factory instructions using Dow 795 sealant, and foam tape spacers. however I did reuse the screws. I placed the spacers slightly back from the edge of the window to allow the sealant to flow around to the edges of the windows. The sealant is a messy process. Lessons learned.
1. Be careful applying sealant. I used a caulking gun and then spread around with a putty knife.
2. Pull tape and masking paper right after applying. I opted to wait and tool/carve it with razor blade the next day. Very tricky and painstaking job to get correct, especially in compound corners.
3. Watch out for air bubbles and voids in sealant. I had a few that I discovered when I tooled joint flush with razor blade. These may have been caused by my putty knife technique. None of the bubbles/voids went all the way through and I considered them to be mainly cosmetic. But  I (hopefully) fixed them by applying another dab/patch of sealant over these 4-5 small areas. Time will tell if it will bond to itself. The cure time is listed as 7-21 days so I am hoping against the old adage/warning that "new" silicone won't bond to "old" does NOT apply here to Dow 795 over itself, one day later.
4. Screws. I cleaned and reused the original screws. Not an easy job. But I like the shiny "bling" and they help hold the window while sealant cured. I later reinstalled them with minimally tightened, in affect gluing them back in with 795. It was a messy job to keep clean. If you opt for screws I would go with two sets—one to install and then remove when sealant sets and duplicate  clean set to go in for final finished job. Still messy to neatly dab 795 on these tiny screws but at least you won't have to clean the goop off the first set, just toss them.

[Noah]

Last pic is view through new head window looking out at my neighbor's C36.

[Phil Spicer]

   Nice job. Your hard work shows. A real labor of love

[Noah]

Thx! I forgot to mention. The install is better to do as a two-man job. Thankfully, Jon W. assisted me down below. He is responsible for the clean edges inside! We used my boat as a warm-up/test platform. When it comes time to do his windows, we will be practiced and it should go smoother!

[Noah]

Whew! Some comfort on patching divots/voids in Dow 795 sealant. Thx to Jsail's research, it is confirmed that Dow 795 can be patched (i.e. "new over old"). Unlike other silicone, Dow 795 silicone adhesive will stick to itself.  See pg. 51 of loooong instructions doc.

https://consumer.dow.com/en-us/document-viewer.html?ramdomVar=7547043403372662019&docPath=/documents/en-us/app-tech-guide/63/63-61/63-6132-01-structural-sealant-glazing-manual-asia.pdf