NOCALSAILOR

3M VHB tape or Dow 795 to afix acrylic windows?

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I am replacing 3/8" acrylic windows on my dodger/ pilot house. The frame is 2" square alum. tubing. The last windows were afixed with 795 and 1/4" bolts. I don't want to use the bolts this time. I am leaning towards the 3M Tape as the window is secure instantly not using bolts. I can then seal with 795.

 

Any pros or cons?

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Any plans to head for the tropics? VHB doesn't perform well here; none of 3M's double-sided tape products do, in my experience (and yes, I have prepped properly using alcohol or acetone, abrasion etc.). Maybe they are good in temperate climes. Sorry, no experience with 795 yet.

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I've only used GE Silpruf 2000 (a similar long elongation silicone to 795). Bonded 2m x 1m x 10mm thick acrylic windows to fiberglass cabin of my catamaran. Due to their size they were essentially structural components of the cabin.

Held well with no leaks for 1 circumnavigation. No bolts either :)

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795 was created specifically to bond curtain wall glazing on high rises - I think it can stick down some scraps of acrylic on a boat.

Has always worked great for me in that function as well as when I re-glazed my house (glass units bonded to wood frames).

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I've recently completed an experiment with VHB and must give it a resounding thumbs down.  :angry:

Somewhat different application, but the "Railblaza Ribport" comes with a piece of VHB already cut to shape.  "Just slap it on, no fuss no muss (after prepping as per the fine print.):unsure: I was highly dubious, and glued the first one on with good old polymarine two-part adhesive instead.  But then I started thinking, these 3M engineers are pretty smart guys, I guess, and the manufacturer supplies it for this exact application...   So I fell for it.  Even weighted it down with a couple of olympic weights while it cured.  Yeah, it lasted about three days before the edges started peeling back.  The conventionally-glued one is doing fine.  

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Depending on the size of the window, you may need an offset of something like 1/2” (IIRC, the instructions on the tube specify) which precludes use of VHB. If this isn’t the case, then it should work.

if the link works, there is a series of pix of my salon window reinstallation:

https://m.facebook.com/AvighnaCatana40S/photos/a.922151851191256.1073741832.850398005033308/1404382889634814/?type=3&source=54

 

A useful video 

 

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16 hours ago, NOCALSAILOR said:I am replacing 3/8" acrylic windows on my dodger/ pilot house. The frame is 2" square alum. tubing. The last windows were afixed with 795 and 1/4" bolts. I don't want to use the bolts this time. I am leaning towards the 3M Tape as the window is secure instantly not using bolts. I can then seal with 795.

 

Any pros or cons?

The 3m tape requires clamping pressure to a hieve full surface contact 

this is why its not used in the shipyard 

stick with sika products.  Primer, adhesive and perimeter caulking 

remember..the adhesive needs a 2mm bondline.

this 2 mm is generated with 3 mm square foam tape around  the inside perimeter  edge ot the frame.

the tape...on the inside edge,  will also prevent adhesive bleed out on the inside of the frame...very tedious to clean up.

the keep the window centered in the frame you need plastic spacers around the perimeter . These can be bought or made by cutting up a plastic bog spreader.  Leave them long so that you can pull out after adhesive cure 

 After the window is bonded,  its perimeter is caulked 

 

 

 

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For those on a budget the Sika 295 is about 4x the price of the Dow or GE alternatives. And they don't require the hideously expensive primer either.

I used 20 tubes of caulking for all the big windows on my catamaran. @$25 for Sika 295 and $7 for GE Silpruf I was a bit happier with that alternative.

To position the windows (which were stuck on, not in a recess/rebate): I taped some blue masking tape to cabin side below window locations. Hot melt glued some wood scraps to the tape. This held the weight of the windows and prevented slumping.

I also used rubber spacers to keep the window from overly compressing the caulking. This thick bondline is key. Can't emphasize it enough. Read Sika's window bonding brochure and see what they recommend. For a 1m long window you get to 8mm thick caulking or so.

I used black foam weatherstripping on the inside edge of the recess to prevent caulking bleed through. Looks very tidy.

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Recently refurbished and reglazed my two Bomar hatches.  Used Sika 295 the first time and they both leaked.  Probably user error.  Re-sealed wth Sika 295 and one of them leaked a second time.  Probably still user error, but now I'm pissed.  Scraped off all the old goop and re-bedded them both with Dow 795.  No more leaks.  That was two rainy winters ago...

IMG_5299.jpg

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Nice job.

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I’ve rebedded, without fasteners, four ‘lights’ and two big salon windows with 795. Have also used 795 to rebed two hatches. Nothing leaks. I’m aboard full time, and was in the Everglades for IRMA so I think that’s probably a good test 

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I found this article helpful

using tape to attach windows

All VHB are not created equal.  Use the right one for your substrates and use the adhesion promoting primer for best results.

I found reasonably priced VHB in small quantities on eBay.

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1 hour ago, thereefgeek said:

Recently refurbished and reglazed my two Bomar hatches.  Used Sika 295 the first time and they both leaked.  Probably user error.  Re-sealed wth Sika 295 and one of them leaked a second time.  Probably still user error, but now I'm pissed.  Scraped off all the old goop and re-bedded them both with Dow 795.  No more leaks.  That was two rainy winters ago...

IMG_5299.jpg

Did you refinish the frame? If so what did you use? Looks great. Is that lexan still in there? I am thinking of using something else because of the scratching.

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6 hours ago, Zonker said:

For those on a budget the Sika 295 is about 4x the price of the Dow or GE alternatives. And they don't require the hideously expensive primer either.

I used 20 tubes of caulking for all the big windows on my catamaran. @$25 for Sika 295 and $7 for GE Silpruf I was a bit happier with that alternative.

 

I have a lot of surface area as well. The silpruf is a bit more than the 795 at Mcmaster. 

My windows now have a 2mm deep trough around the perimeter to keep the caulking thicker.

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54 minutes ago, NOCALSAILOR said:

Did you refinish the frame? If so what did you use? Looks great. Is that lexan still in there? I am thinking of using something else because of the scratching.

Don't use Lexan, use acrylic - cast acrylic if you are the nervous type.

http://www.hydrosight.com/acrylic-vs-polycarbonate-a-quantitative-and-qualitative-comparison/

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Tempered glass in a deck hatch? Never - one good whack with a pole or a pointed bit of hardware and you've only got crumbs.

Laminated glass would be good but heavy and why bother? Acrylic works great, easy to fit, cheap, strong, lasts for years - what's not to like?

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All my windows are held in with VHB.  The only issue I have had is a small spot where the frame was uneven.  The tape initially stuck to both the window and the frame, but subsequently pulled away leading to a minor leak.  What I like about the VHB is that if it screws up it is super easy to remove unlike the glues which are a bitch to remove.  What I don't like is that your frame must be very flat and straight for it to work well, and mine isn't. Note that installing the windows you get only one chance with VHB so you must get it lined up properly before putting it on.  

Having said all that I might try the 795 next time on the one side based on the recommendations here.  I tried the Sikka, butyl, and several other glues and they were all terrible, especially the butyl which leaked out of the joints when the windows expanded in the sun and got on everyone's foulies.

I'll use the VHB again for the other side, no leaks, no mess.  I used the 3M original tape, I wouldn't consider any substitutes.

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6 minutes ago, dash34 said:

.  I tried the Sikka, butyl, and several other glues and they were all terrible, especially the butyl which leaked out of the joints when the windows expanded in the sun and got on everyone's foulies.

Sounds like you got the butyl tape from Lordco or an RV Place.  Was it black?  I bought some of that stuff and it was useless.  Very soft and gummy stuff that tends to more of a semi-liquid state in the summer heat,

The only butyl tape you should use on a boat is the grey stuff Mainesail sells.  It's also available from Marine Outfitters in Ontario.  The yellow stuff available from places like Fibertek is good for vacuum bagging.

But butyl tape probably isn't the right sealant for the type of port lights on the Dash since there isn't a lot of pressure supplied by the acrylic windows and screws.

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11 hours ago, NOCALSAILOR said:

Did you refinish the frame? If so what did you use? Looks great. Is that lexan still in there? I am thinking of using something else because of the scratching.

Yes, took the aluminum frames to a shop and had them sandblasted and sprayed with an aluminum primer (forget what it was, but it was a yellow/green color).  Then I sprayed 4 or 5 coats of 2-part Interlux Perfection+.  The lenses are cast acrylic like Sloop JB said.

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7 hours ago, dash34 said:

All my windows are held in with VHB.  The only issue I have had is a small spot where the frame was uneven.  The tape initially stuck to both the window and the frame, but subsequently pulled away leading to a minor leak.  What I like about the VHB is that if it screws up it is super easy to remove unlike the glues which are a bitch to remove.  What I don't like is that your frame must be very flat and straight for it to work well, and mine isn't. Note that installing the windows you get only one chance with VHB so you must get it lined up properly before putting it on.  

Having said all that I might try the 795 next time on the one side based on the recommendations here.  I tried the Sikka, butyl, and several other glues and they were all terrible, especially the butyl which leaked out of the joints when the windows expanded in the sun and got on everyone's foulies.

I'll use the VHB again for the other side, no leaks, no mess.  I used the 3M original tape, I wouldn't consider any substitutes.

dash, my columbia had a problem with the port window and based on what I read in these very pages, I ended up going with the vhb tape as well as the primary adhesive, followed by a bead of DC 795 around the edges. Two seasons in and that window has been flawless. My frame wasn't 100% even but the VHB seemed to take up some of that fairly easily. Like you said, it requires that you are careful with the initial application. I used a roller around the edge to get proper adhesion, and it's been great. I wasn't aware that it might fail if I drag the boat to Florida, but that's not likely and so far neither the vhb nor the 795 have shown any signs of deterioration in the few weeks of hot weather for the past two seasons. I'll keep an eye on it though. It worked so well I thought about popping the other window out and re-doing it, but decided I'll just wait until it becomes a problem. I felt lucky the port window came out in one piece and didn't want to press my luck.

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3 hours ago, thereefgeek said:

Yes, took the aluminum frames to a shop and had them sandblasted and sprayed with an aluminum primer (forget what it was, but it was a yellow/green color).  Then I sprayed 4 or 5 coats of 2-part Interlux Perfection+.  The lenses are cast acrylic like Sloop JB said.

That chartreuse coloured primer is Zinc Chromate - it's the best tie-coat / primer for aluminium. It's what they use on aircraft so.......

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This was a very informative thread...

 

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Good deal. My father in law used to be in the glazing business so he had an account with the local wholesaler.

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Best price I've found in Vancouver area for 795 is Cascade Aqua Tech at 3215 Norland in Burnaby.

It's been a while but IIRC I paid about $16 CDN for 2 X 10 Oz. tubes.

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UV penetrates the glass and burns the adhesive bonding surface 

 When you look at an auto mobile window you can see that  UV protection is applied to the widow bonding surfave and that this black  UV protection   extendeds several mm past the frame window joint  

Pro  marine window fitters also extend this uv shield ..perhaps 3mm

avoid any clear primers...use black 

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1 hour ago, slug zitski said:

UV penetrates the glass and burns the adhesive bonding surface 

 When you look at an auto mobile window you can see that  UV protection is applied to the widow bonding surfave and that this black  UV protection   extendeds several mm past the frame window joint  

Pro  marine window fitters also extend this uv shield ..perhaps 3mm

avoid any clear primers...use black 

Or for the cheapskates(or cause you just learned about this and you already put your windows in) paint the outside after, extend a littler farther because of the thickness of the acrylic.  Sikaflex even specs this as acceptable, and though uglier it does work.  

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The inside is coated...the coating acts as the primer, uv block 

There are several manufacturers of window bedding supplies.

is see bostik , saba, siki used 

consult the technical description for product use and names. 

The key to a good bond is the substrate preparation  and following the directions 

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On 3/14/2018 at 12:05 AM, 12 metre said:

Sounds like you got the butyl tape from Lordco or an RV Place.  Was it black?  I bought some of that stuff and it was useless.  Very soft and gummy stuff that tends to more of a semi-liquid state in the summer heat,

The only butyl tape you should use on a boat is the grey stuff Mainesail sells.  It's also available from Marine Outfitters in Ontario.  The yellow stuff available from places like Fibertek is good for vacuum bagging.

But butyl tape probably isn't the right sealant for the type of port lights on the Dash since there isn't a lot of pressure supplied by the acrylic windows and screws.

It was from an RV place, but it was grey.  However, just as useless as you describe. 

I am much happier now that the fasteners are gone.  They looked terrible and leaked like crazy.  

dash

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I just used Krylon matt black and sprayed the outside of the pane slightly oversize to protect the caulking from UV. Measure carefully and use the backing paper still on the acrylic to mask off. Cut off excess paper around perimeter with a razor knife.

If you use a glass pane, you can use a glass vendor to apply a ceramic "frit" to the inside of the pane. Much more costly and specialized process than a $6 rattle can.

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Does the 795 need the UV protection as shown in the other thread byy painting the acrylic with black paint on the inside joint edge.

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17 minutes ago, NOCALSAILOR said:

Does the 795 need the UV protection as shown in the other thread byy painting the acrylic with black paint on the inside joint edge.

795 is a silicone and has good UV protection as such. One of the reasons I chose it was because it didn't require a primer. The one thing about painting is that you now have two adhesions to worry about - paint to acrylic and adhesive to paint. I decided to just do the one - adhesive to acrylic. 

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I got my tubes of 795 on Amazon and had them on my front porch within 36 hours...

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I just replaced all my port windows and I used a combination of 3M UHB tape and DOW795.  I cut the tape to allow a bead of the 795 to lay next to it.

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OK - I read most of the stream above and watched the video.  So, my port-light (non framed, non opening) in the head of my J105 has started leaking at the seal.  I think due to heavy feet during a round up.  The Lexan is not broken.  What I am planning on doing is taking the port-light out and then resealing the whole thing.  

Question 1.  Recommendations on removing the old window.

Question 2.  Does a 105 window have enough of a lip to use VHB or do I just go with Dow 795?

Question 3.  Has anyone done this on a 105?

Thanks

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14 hours ago, Old and tall said:

Question 1.  Recommendations on removing the old window.

Question 2.  Does a 105 window have enough of a lip to use VHB or do I just go with Dow 795?

Question 3.  Has anyone done this on a 105?

Thanks

I don’t have experience with your boat make, but I’ve pulled and reinstalled a few windows. This is how I’ve done my salon and side windows (big ones). YMMV

Get a can of DeBond. Get some of those thin wood wedge slats. Get X-acto #18 blade, which is a heavy, flat edged chiseling blade. Get denatured alcohol. 

If you can get next to a professional auto window removal tool (wire between two handles) yer lucky

If you know where the seal break is, begin there. Spray in the DeBond, parse it; don’t need much. let it work.

If you have aforementioned pro tool, get the wire thru at the break and work it round to cut the goo. Ha...ha. 

If not, then gently use Xacto to begin an opening and slide in the wedges, applying some DB as you work your way round the plex. Gently insert wedges, spray DB, and cut the goo with the Xacto, round until you pry the plex off the boat. Don’t be rough; I managed to pull some of my gelcoat off...

Clean the old goo off the plex and the boat. This is where that flat blade xacto really works nicely. Be thorough.

Be also sure to NOT leave the DeBond on for long; apply denatured alcohol which will  neutralize the DB, and the -OH should not fog your plex, as will acetone. DON’T FUCKIN’ USE ACETONE ON YOUR WINDOW, as some moron did on one of mine. You can, though, use acetone on the fibreglass of the boat to help lift the goo. But that said, again, DN -OH is what neutralizes DeBond. 

Prep, and be careful about that, both the window and the substrate, (see elsewhere) and reinstall.

 

Fritting:

I paint the fritting on the outside of the window, me. Then my bond will a. be between plex and glass; and b. be on the outside, so as to block the UV what it’s painted on for.

 

 

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18 hours ago, Old and tall said:

OK - I read most of the stream above and watched the video.  So, my port-light (non framed, non opening) in the head of my J105 has started leaking at the seal.  I think due to heavy feet during a round up.  The Lexan is not broken.  What I am planning on doing is taking the port-light out and then resealing the whole thing.  

Question 1.  Recommendations on removing the old window.

Question 2.  Does a 105 window have enough of a lip to use VHB or do I just go with Dow 795?

Question 3.  Has anyone done this on a 105?

Thanks

what Max said about removing - mine popped right out with some light screwdriver pressure, but the tape they used (not vhb) was really old and dried out. His is a much safer method to get the window out.

I've never seen the window out of a 105 but it's hard to imagine you don't have enough lip for the 1/4" vhb. I wouldn't do just one. My technique is to lay the vhb on the hull at the inner portion of the frame so you have enough room for the 795 bead. Once the port is in place, bonded, and set up for a day or two go back with the 795. mask the frame AND the window edge, squirt the gunk and use your finger to make a smooth bead, then remove the tape - don't let the 795 set up on the tape before you remove it. So far I'm batting 1.000 (2 for 2) using this technique on the windows.

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Also, do the 795 on a windless day and pull the tape slowly. It tends to form tendrils as you pull the tape and they'll blow around if it's windy. I'd recommend two layers of tape, the lower layer about a millimeter farther away from the 795 bead. When you pull the upper layer, it should leave a clean 795 edge but any tendrils that form and want to get on the window or the gelcoat will hit the lower tape instead. 

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You remove windows with a cheese cutter.   Piece of wire or  thin cord...handle on each side...saw it back and forth around the perimeter of the window..one man inside, one outside .

 

to  initially insert the wire or cord you use a needle or a stiff wire hook .

 

if you  go to a good auto parts store they will sell the needle  and wire or cord  for cutting 

 

The long tool is the needle for inserting the wire ..push it thru the caulk or tape...then insert wirein the needle eye and pull  thru 

 

 

 

 

 

IMG_8628.JPG

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14 hours ago, IStream said:

Also, do the 795 on a windless day and pull the tape slowly. It tends to form tendrils as you pull the tape and they'll blow around if it's windy. I'd recommend two layers of tape, the lower layer about a millimeter farther away from the 795 bead. When you pull the upper layer, it should leave a clean 795 edge but any tendrils that form and want to get on the window or the gelcoat will hit the lower tape instead. 

The following tips are good enough for doing 150lb nearly inch thick glass windows on cruise ships, so it's good enough for a sailboat. 

In an average 10 day refit we might do 50 windows, and use up a pallet of sealant(fireproof and silicone).

 

1. A quick spray with a foaming (ammonia free!) glass cleaner after you fill the gap, but before tooling makes a big difference. 

2. Tool it so there is just a hint of sealant on the tape and you avoid a lot of the tendrils(companies such as CR Lawrence sell a specific rubber block for doing this, it isn't expensive and one will last a lifetime of sticking stuff on boats).

http://www.crlaurence.ca/crlapps/showline/offerpage.aspx?ProductID=45624&GroupID=44861&History=39324:112:2875:3280:2875:3022&ModelID=44861&pom=0

3.  Instead of the exacto blade I use an olfa knife and a coated blade so you can saw through the sealant with the blade fully extended.  A little dish soap and water(or water based sex lube) works wonders, and won't cause later contamination issues like oil based cutting fluids after rinsing.   There's a DOW citrus based de-bonder/sealant cleaner that isn't harmful to plastics, but it's expensive and not really needed unless the window is set in a frame where you have to be careful not to damage the anodizing by cutting through the sealant.

Blade I use:  https://olfa.com/professional/product/18mm-snap-off-speed-blades-10-pack-lfb-10b/

Cruise ship glass companies are too cheap to buy the coated blades so I buy my own, less risk of excessive force on the knife and a snapped blade, worth every penny in reduced stress.

4. ALWAYS, ALWAYS, ALWAYS cut with the handle leading the blade and cut on the pull stroke, relax and push it back in.  It's natural to do the reverse(cuts easier) but if you snap the blade and slam your hand into it instead of pulling away from the blade, you are getting a lot of stitches.  Guess how I know that one?

I don't like the wire type cutters, they can scuff up the frame/hull/edge of the pane, fine on cars though. 

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Those cheese cutters are veristile...

What is important is that when a window is seated into adhesive , the bond line thickness is respected ...2 or 3 mm minimum  for the widows I  have  worked with.

 With the correct bond line damage to the substrate is avoided when removing , with a cheese cutter or any tool, in future 

if your google the variuos adhesives you will find helpful info such surface prep, primer, the V  shape of the adhesive bead ...

 

https://gbr.sika.com/dms/getdocument.get/5cf9ab56-445c-3635-87a2-a2f80e0443b9/

 

 

 

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1 hour ago, slug zitski said:

Those cheese cutters are veristile...

What is important is that when a window is seated into adhesive , the bond line thickness is respected ...2 or 3 mm minimum  for the widows I  have  worked with.

 With the correct bond line damage to the substrate is avoided when removing , with a cheese cutter or any tool, in future 

if your google the variuos adhesives you will find helpful info such surface prep, primer, the V  shape of the adhesive bead ...

 

https://gbr.sika.com/dms/getdocument.get/5cf9ab56-445c-3635-87a2-a2f80e0443b9/


 

 

Cruise ships and many others use windows set in a flange, these don't work nicely there(tried one once,  didn't like them there either, but I'd try anything once with that many feet of cut to go).   Fine when one side of the bond is glass and the other bare metal though and the joint relatively thick and narrow(car windshields).   Acrylic portlights and no metal frame and a moving wire are just asking for marks to be left behind on something, and an olfa knife is more multi-purpose on a boat.  Side note, Dow makes nice nozzles with the V precut and a small sticking out post from the end that is easily trimmed so you get an exactly uniform bead.  Right up there with the rotating sealant nozzles I like for awkward angles for useful cheap things to throw in your kit. 

 

 

 

 

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Thank you all for the much needed information.  Now to put theory to practice.  I’ll report back when complete.

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Window popped out very easily.  Does not look like it had any tape holding it just black goop.  Now my job is to clean off the goop.  More info to foloow

C027AD17-6F35-4C49-86FB-0994580C53C7.jpeg

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Do you have an oscillating tool?  They make a sealant removal blade that works well as long as it's kept sharp.  Lightly debur the underside after sharpening and it'll leave a scratch free surface.  

 

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So I spent a couple of hours getting the goop off.  Messy but not difficult.   (The water gods did manage to get a couple of my tools)  It's interesting how the inner lining is tabbed to the outer skin of the boat.  Also there is a lip all around the inner lining of the window.  Now waiting on the tape and goop to be delivered.

IMG_1862.JPG

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I'd try to get it a lot cleaner than that. Some Debond or DSR-5 will get that last layer of schmutz off and give the new stuff something to bond to.

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Insufficiently clean.  I don't like the bristle disks for this myself, I find they leave ridges.  The fine or V fine 3m roloc scotchbrite type are ok, but really you just need some more time with a good scraper and then some sandpaper and a solvent wash.  It should look as white as the hull or close to it.  Any old adhesive will screw with your new bond, and you really want a little bit of tooth from some sandpaper on there(I'd probably be happy with 120-180 grit). 

 

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Also quick tip for any sort of spinning abrasive/wire brush.  Get the hex shank ones that'll fit in an impact driver.  They are typically 500-1000 RPM faster than your drill, and smaller and lighter.  500 RPM doesn't sound like much but @ 2500-3000 you're talking a substantial increase in removal rate. 

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I'd look for one of those decal/stripe "erasers" at a tool store or auto body supply place before I went to Worst Marine for it.

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yup, you can save yourself 3 bucks if you order from Grainger or Walmart. The link was more for the product than the vendor.

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Thank you all for the information.

I used some sandpaper and got it a little cleaner, but not as perfect as some of the pictures above.  I reinstalled the window yesterday using Dow 295 and am happy with the outcome.  I was unable to use the VHD tape because of the inside lip the window sits on is too proud and causes a ridge that is higher than the depression for the 295.   I masked all around the outside and on the window itself, then used a tongue depressor to clean the visible seams.  So far so good.  Next time I have to do this I'll purchase Debond - any specific name for that?  

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For cleaning up the fiberglass after removal, I used mineral spirits.  Did a great job of removing the last of the silicon from previous installation.  Still takes a bit of elbow grease to get the last little globs off.

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I bought some "Silicone removal paste" in Australia. Works pretty good. Trowel it on, leave it for 10-15 mins like paint stripper and remove any old silicone.

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