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Old 05-07-2020, 13:08   #1
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Major project ! First a hatch reseal

Hi

First question on my immediate project, front hatch.

It was leaking and upon opening to clean the Perspex fell out. No wonder it was leaking! Iíve cleaned it up like new but wondered what people recommend to seal the Perspex back in again. I donít want to skimp on product.

Thanks in advance

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Old 06-07-2020, 04:30   #2
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Re: Major project ! First a hatch reseal

Well I know what NOT to recommend!


Sikaflexģ-291 must not be used to seal plastics that are prone to stress cracking (e.g. Perspex, polycarbonate, etc.). Once cured, Sikaflexģ-291 can easily be .


https://www.bunnings.com.au/sika-310...alant_p1210247
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Old 06-07-2020, 04:39   #3
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Re: Major project ! First a hatch reseal

Is the lens Acrylic or Polycarbonate the glue is different for each. FWIW if the lens is out anyway replace now and it will be good for many years to come. BUT check the rubber seals as together with a new lens it may be cheaper and more practical to replace the whole thing.
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Old 06-07-2020, 05:34   #4
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Re: Major project ! First a hatch reseal

Quote:
Originally Posted by Tupaia View Post
Is the lens Acrylic or Polycarbonate the glue is different for each. FWIW if the lens is out anyway replace now and it will be good for many years to come. BUT check the rubber seals as together with a new lens it may be cheaper and more practical to replace the whole thing.


Iím not sure, yes the lens has like a crack effect all over is you know what I mean. Iím on a budget so not worried 100% about looks. The rest of the hatch has cleaned up like new and the seals donít seem to be brittle or in bad condition.
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Old 06-07-2020, 06:06   #5
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Re: Major project ! First a hatch reseal

I am also interested in hearing peoples opinions, as I am preparing to tackle this. One recommendation was to use Dow 795, which is a very strong structural glazing sealant that holds windows in skyscrapers. It is also silicone, which I have been told to avoid, though this isn't run of the mill silicone.

I have also been told Sikaflex 295, but that it is important to use the hard to find primer, and that the preparation and application is an involved process that must be done correctly.

I made a temporary repair with Sika 291 because that is what was available when I was cruising a remote location. The bond failed and it leaked after a few weeks, and a few weeks later I was able to pull the acrylic off it by hand.
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Old 06-07-2020, 08:12   #6
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Re: Major project ! First a hatch reseal

I did this job for couple times, the hatch youíre intended to seal look like a Atkins & Hoyle. The best way I found to do this is , after removing the acrylic window as you did, you need to clean both parts well to remove completely the old caulking and adhesive.
Thereafter, I found that two steps seals gave me the best results. I used butyl rubber sealant tape on the horizontal parts of the aluminum frame were the acrylic windows seat. Butyl tape is really inexpensive and easily available at Home Depot or at any window installers shop.
This really sticky material maintains elasticity and adhesion in all weather conditions.
After placing the lens in the window frame, you need to well press it on the adhesive tape. the final step would be to seal the gap between the aluminum frame and the acrylic window with black silicone caulking. Dow 795 is the best but any marine or outdoors silicone can also be used.
Take note that butyl tapes is available in grey and black colour. This product can also be used on deck hardware. One thing to know is that butyl always stay soft and sticky.
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Old 06-07-2020, 08:31   #7
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Re: Major project ! First a hatch reseal

Replacement takes minutes, from your picture you have more labor intensive projects than time.
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Old 06-07-2020, 08:58   #8
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Re: Major project ! First a hatch reseal

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Originally Posted by Northbound44 View Post
I did this job for couple times, the hatch youíre intended to seal look like a Atkins & Hoyle. The best way I found to do this is , after removing the acrylic window as you did, you need to clean both parts well to remove completely the old caulking and adhesive.
Thereafter, I found that two steps seals gave me the best results. I used butyl rubber sealant tape on the horizontal parts of the aluminum frame were the acrylic windows seat. Butyl tape is really inexpensive and easily available at Home Depot or at any window installers shop.
This really sticky material maintains elasticity and adhesion in all weather conditions.
After placing the lens in the window frame, you need to well press it on the adhesive tape. the final step would be to seal the gap between the aluminum frame and the acrylic window with black silicone caulking. Dow 795 is the best but any marine or outdoors silicone can also be used.
Take note that butyl tapes is available in grey and black colour. This product can also be used on deck hardware. One thing to know is that butyl always stay soft and sticky.


It seems to be solid polystyrene or plastic of some sort. Iíve already cleaned with paint thinners itís just the bedding of the window now ! Thanks for the advice
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Old 06-07-2020, 08:59   #9
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Re: Major project ! First a hatch reseal

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Originally Posted by Calif.Ted View Post
Replacement takes minutes, from your picture you have more labor intensive projects than time.


Oh I have plenty of time, but still not enough probably ! This is just the outside
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Old 06-07-2020, 10:11   #10
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Re: Major project ! First a hatch reseal

I just resealed my forward hatch. After much research and watching some youtube videos, I settled on Dow 795. Though it should be somewhat easy to find, I couldn't find it at the local Ace, Home Depot or Lowes. I finally ordered it online. My understanding is that it is pretty much the "go to" for sealing the plexiglass into the hatch frame. It is much cheaper than any of the caulks from West Marine and has a very high stretch percentage for changing temps. The result was great. I am getting ready to seal my other two. The most time consuming part is the cleaning, which it looks like you've already done. Be advised the cure time is 14 days. I overlooked that part and had to sail before it was cured, but still no leaks. Guess I got a little lucky there.... Good luck!
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Old 06-07-2020, 13:32   #11
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Re: Major project ! First a hatch reseal

Skip the butyl, Dow 795 is all you need. It is not expensive.

Butyl is very good when an item is bolted to the deck.
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Old 06-07-2020, 13:38   #12
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Re: Major project ! First a hatch reseal

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Originally Posted by mitiempo View Post
Skip the butyl, Dow 795 is all you need. It is not expensive.

Butyl is very good when an item is bolted to the deck.

Trying to find it in the UK, we have DOW products but not that number! Iíll keep looking
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Old 06-07-2020, 13:48   #13
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Re: Major project ! First a hatch reseal

Quote:
Originally Posted by Northbound44 View Post
I did this job for couple times, the hatch youíre intended to seal look like a Atkins & Hoyle. The best way I found to do this is , after removing the acrylic window as you did, you need to clean both parts well to remove completely the old caulking and adhesive.
Thereafter, I found that two steps seals gave me the best results. I used butyl rubber sealant tape on the horizontal parts of the aluminum frame were the acrylic windows seat. Butyl tape is really inexpensive and easily available at Home Depot or at any window installers shop.
This really sticky material maintains elasticity and adhesion in all weather conditions.
After placing the lens in the window frame, you need to well press it on the adhesive tape. the final step would be to seal the gap between the aluminum frame and the acrylic window with black silicone caulking. Dow 795 is the best but any marine or outdoors silicone can also be used.
Take note that butyl tapes is available in grey and black colour. This product can also be used on deck hardware. One thing to know is that butyl always stay soft and sticky.
In hot weather the butyl can run like hot tar, and drip into the interior of the boat.
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Old 06-07-2020, 14:26   #14
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Re: Major project ! First a hatch reseal

Quote:
Originally Posted by The Perfessor View Post
I just resealed my forward hatch. After much research and watching some youtube videos, I settled on Dow 795. Though it should be somewhat easy to find, I couldn't find it at the local Ace, Home Depot or Lowes. I finally ordered it online. My understanding is that it is pretty much the "go to" for sealing the plexiglass into the hatch frame. It is much cheaper than any of the caulks from West Marine and has a very high stretch percentage for changing temps. The result was great. I am getting ready to seal my other two. The most time consuming part is the cleaning, which it looks like you've already done. Be advised the cure time is 14 days. I overlooked that part and had to sail before it was cured, but still no leaks. Guess I got a little lucky there.... Good luck!
Plexiglass is a brand name for Acrylic. Acrylic (and Lexan) lenses are very hard to re bond to the hatch frames because very little sticks to them. Neither acrylic or lexan are specifically listed on Dowseal 795 documentation though "plastic" is mentioned in passing.

Cleaning is essential, particularly the plastic. After cleaning and masking (to protect the parts which will not be in contact with the sealant) light sanding is recommended, followed by cleaning with strong solvent such as acetone.

Next the proper thickness of the sealant bead must be carefully maintained. Acrylic has a very high expansion coefficient (it expands a lot when heated, like in the sun). Smaller hatches have less of a problem with this. But the sealant, Dowseal (795) for example, can expand or contract only up to 50%. Acrylic expands with increasing temperature. An Acrylic lens 30 inches across will expand nearly 1/10 of an inch in a temperature rise of 30 degrees (not hard in direct tropical sunlight) and it will shrink by that in cooling temperatures. A 1/8 bead of 795 can expand or contract 1/16 of an inch so we can see that the adhesion bond of the sealant to the plastic and to the aluminum will be greatly stressed. A thicker bead of sealant is critical. Often professionals will insert spacers to keep the thickness of the bead within specification. A tip: The sealant bead will hold better under compression than tension. Put it on when the temp is low so when it expands on a hot day it will press itself against the frame, rather than pulling away on a cold day.

Mask everything well, apply weight or clamps to hold it in place, and smooth with wet tools or finger.

Remove the masking tape before the sealant cures.
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Old 06-07-2020, 15:27   #15
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Re: Major project ! First a hatch reseal

Here's what I did to refresh my hatches (x 5)

1. removed lens and cleaned frames
2. Took the frames to a local powder coating operation and had them refinished (Bomar Ocean Hatches)
3. Called Select Plastics in CT and had them send me blank lenses cut to size. They rebuild hatches for a business, but we're happy to sell me the raw materials that they use. My recollection was that it was only about $25 per hatch.
4. Rebedded using Sikaflex and the appropriate Sikaflex primer

That was four years ago (with 2.5 of those years in the Caribbean) and they still look brand new. Whole process cost around $50/hatch.
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