Window Rebedding Compound to use?

[s/v Jedi]

There’s a lot of good information here but it’s not complete in a single post yet so I’ll give it a try:

There are 3 different points to consider: inside edge, outside edge and adhesion.

Inside edge is what you see from the inside. As there needs to be a thickness to what goes between frame and window, this leaves a gap there which is not just ugly, it also accumulates dirt and moisture.
This is dealt with using a self adhesive, foam based weatherstripping. After cleaning the frame and wiping with alcohol, attach this foam around the perimeter of the opening.

Outside edge has two things to consider: the cut edge of the window material and the gap behind it. If replacing the window, use a black one-component urethane paint like EasyPoxy to paint the cut edge of the window black. This prevents UV from entering the material there, which extends the lifespan by multiples. UV that enters the edge goes through the whole sheet of material as the surfaces keep bouncing it back in like light in a glass fiber.
Next is the gap behind it: yes, Dow Corning 795. Order from McMaster Carr etc. You fill the space behind the window material, not the outside edge, which is painted. This provides a watertight seal as well as adhesion for that edge.

Last but not least the adhesion. 3M VHB is great and easy to use. If the max thickness available (3mm?) isn’t enough, which I think it is but check specs for size of window, then you can put two layers in.
If Dow Corning 795 is used, you need spacers to keep the window away from the frame. Pro’s make these spacers from the 795 itself, letting a thick enough bead on a scrap board cure, then cut it to right size and into little pieces which are then glued into place by sticking them into the bead just before the window goes on. The thick bead of 795 on the frame needs to have a V-shape with the pointy end facing out towards to the window. If the thickness needs to become 3mm then that bead must be much higher, like 6mm. It is created by cutting a V into the spout. After seeing this done by pro’s I decided the little extra expense for VHB tape was warranted for diy

For mounting it is easiest to mount a temporary batten beneath it that you can use to support the window. You stick it on with double sided tape but do not use the 3M VHB tape! Best is tape used to hold carpet in place which is easy to remove. First stick it to the batten using a lot of pressure so that it comes off with the batten for minimum cleanup.

[marcjsmith]

SV jedi. you can use the vhb tape to hold the batten. to support the window. just put blue painters tape anywthere you DONT want the vhb to permanelty stick to.. or use a hot glue gun to tack it in place.

[s/v Jedi]

Originally Posted by marcjsmith

SV jedi. you can use the vhb tape to hold the batten. to support the window. just put blue painters tape anywthere you DONT want the vhb to permanelty stick to.. or use a hot glue gun to tack it in place.

Yes, I keep forgetting that trick. With blue tape on hull and batten, you can even use superglue

[Spot]

I have a similar bedding/sealing question.

1/4" (6.4mm) thick hull and glazing , glazing sits loosely in holes in hull.
1" wide (25mm) plastic frames inside and out, bolted together through hull. Not planning on remaking or replacing frames this season. Boat is a daysailor/weekender, cushions were just redone so trying to repair all leaks to keep interior dry. Outside is pretty good white gelcoat, inside is painted CSM.

Is this a Dow 795 situation or am I better off with something that is less tenacious and perhaps water clean-up due to the fact that it will probably 'get messy' trying to goo and bolt all together and that I will be redoing it in a season or two? VHB sounds interesting too but I would need to cut, drill, and fit to match frames and holes.

[s/v Jedi]

Originally Posted by Spot

I have a similar bedding/sealing question.

1/4" (6.4mm) thick hull and glazing , glazing sits loosely in holes in hull.
1" wide (25mm) plastic frames inside and out, bolted together through hull. Not planning on remaking or replacing frames this season. Boat is a daysailor/weekender, cushions were just redone so trying to repair all leaks to keep interior dry. Outside is pretty good white gelcoat, inside is painted CSM.

Is this a Dow 795 situation or am I better off with something that is less tenacious and perhaps water clean-up due to the fact that it will probably 'get messy' trying to goo and bolt all together and that I will be redoing it in a season or two? VHB sounds interesting too but I would need to cut, drill, and fit to match frames and holes.

You can simply use the butyl tape as sold by Compass Marine. Don’t get it from the hardware store as that keeps making a mess for years. I actually used both and the difference is enormous.

[Spot]

Originally Posted by s/v Jedi

You can simply use the butyl tape as sold by Compass Marine. Don’t get it from the hardware store as that keeps making a mess for years. I actually used both and the difference is enormous.

Thanks Jedi. I appreciate the side-by-side comparison of the different butyls. My local butyl tape seems to flow quite a bit and takes extra work to roll out into a nice shape/thickness for most applications. I think it was designed for steel roofing. It does work good for vacuum bagging as a mastic for the cut edges of the bagging film.

[s/v Jedi]

Originally Posted by Spot

Thanks Jedi. I appreciate the side-by-side comparison of the different butyls. My local butyl tape seems to flow quite a bit and takes extra work to roll out into a nice shape/thickness for most applications. I think it was designed for steel roofing. It does work good for vacuum bagging as a mastic for the cut edges of the bagging film.

I still have butyl (the white kind) squeezing out the edges of a porthole 6 years later. When the sun is beating down on it, there’s even some liquid kind of goo running down from it, a complete mess.

A year ago I used Rod’s butyl tape on a hatch and as thin and firm as it seems, a 1/8” bead squeezed out when torquing down the hatch frame and I left that, waiting for more squeeze out. It still looks the exact same today, no additional squeeze out and no other goo.

[Spot]

Thanks again Jedi!

[Windseeker]

Jedi,

Thank you for your comprehensive write-up.

"If the max thickness available (3mm?) isn’t enough, ... then you can put two layers in."

You must be a Master Jedi as you read my mind on my next question. I have a plan now thanks to all the input. Sometimes you know where you want to go, but don't always know how to get there. It's great to have a place to bounce ideas and share experiences.

Mark

[s/v Jedi]

Originally Posted by Windseeker

Jedi,

Thank you for your comprehensive write-up.

"If the max thickness available (3mm?) isn’t enough, ... then you can put two layers in."

You must be a Master Jedi as you read my mind on my next question. I have a plan now thanks to all the input. Sometimes you know where you want to go, but don't always know how to get there. It's great to have a place to bounce ideas and share experiences.

Mark

Thank you I like to think I’m a master Jedi but must confess it’s more a result of having been in the same place as you before

[Windseeker]

I found this PDF on VHB tapes. It was useful in sorting out what to order.

[marcjsmith]

here is what I ordered from mcmaster carr i went with black on black that way there would not be any white glass or different colored tape showing through the windows from the outside.



1Foam Mounting Tape
3M VHB 5952, 1" Wide, 108 Feet Long, Black
8127A251
each120.14
each$120.142


Structural Glass Sealant
Dow Corning Silicone 795, 10.3 oz., Black
7452A212
each9.63
each$19.26

[CHM]

Dow 795.

[bstreep]

Dow 795.

If you have a curve, take the old window, and make a mold. Then flatten the old window with a heat gun. Use it as a pattern for your new window. Use a heat gun to carefully heat the new window, and bend to the mold to fit. Ours actually has a crease in the window. A couple of practice tries bending it, and we got the hang of it. My wife still shakes her head about that project.


Tip on getting the old window out: Drill a 1" hole in the old window, pass a line through it. Knot the line, and then use the line to pull the old window out!

[Windseeker]

HI,

Thank you for all the input, I wrote up my experience and took some pics.


1) Cleaned the site with Denatured Alcohol. The corner is where the old sealant had failed.
2) I bought a few different rolls of the super flexible automotive corner masking tape. The super thin 3mm wide roll was useless, but the 5mm and the 12mm worked well for masking around the corner.
3) Another masking shot. The vertical strip of blue tape was like have an extra hand to keep it into place.
4) Applied the VHB Tape to a paint stir stick and applied it to the bottom as a shelf with the blue tape underneath.
5) This was the most helpful. Since this window sort of "floats" in this frame, I needed to play with it to find the "center" so to speak. I could position it so I had at least enough room for the tape all around. I created an alignment mark for the window and the frame.
6) Applied the VHB tape all around keeping in mind Jedi's comment about the perspective from inside the boat keeping it completely flush. 1/2" wide tape was the widest I could use and had to double up layers along the top mostly.
7) Applied the Dow Silicone around the outside tape edges where needed and heavily into the corner where the leak was prior. Also (kind of hard to see), I used an extra vertical strip of VHB along the edge of the cabin cutout to give that clean appearance from the inside of the window.
8) Used my alignment mark to drop her back in.


The instructions were to remove the masking tape immediately, but that was a gooey mess and took some cleaning up. Maybe I should have waited 30 minutes for it to be a little less gooey.
In all, this was a good repair. I waited for a heavy rain to report back No Leaks!
Not a particular difficult technical repair, but definitely takes thought and planning.

So, THANK YOU so much for the insight and comments. It made a big difference in the outcome.

Mark