New window sealing question.

[Fore and Aft]

I left the bolts in place, thats why I used dome nuts on the inside. The first window I installed was a bit of a sh*t fight as I had it all installed without bolts and then it slowly started to peel away from the frame. So I quickly installed a couple of small bolts to help keep it snug against the frame.
I chose 9mm becuase I felt our windows were fairly large 900mm x 250mm wide maybe? Also our windows were designed for 9mm Perpsex plus the thickness of the sealant tape.
9mm is also a nice thickness to work with, not to floppy. Remember if you are cutting out the windows put some masking tape on the bottom of your jigsaw.
Cheers

[Hoohaa]

Originally Posted by Fore and Aft

I left the bolts in place, thats why I used dome nuts on the inside. The first window I installed was a bit of a sh*t fight as I had it all installed without bolts and then it slowly started to peel away from the frame. So I quickly installed a couple of small bolts to help keep it snug against the frame.
I chose 9mm becuase I felt our windows were fairly large 900mm x 250mm wide maybe? Also our windows were designed for 9mm Perpsex plus the thickness of the sealant tape.
9mm is also a nice thickness to work with, not to floppy. Remember if you are cutting out the windows put some masking tape on the bottom of your jigsaw.
Cheers

Masking tape on the bottom of the jigsaw? A bit confused about this.
Also. If you had a good system of strongbacks to hold the window in place while the glue sets, do you think you could have done away with the bolts all together?
And did you find the 9mm gauge to still be reasonably flexible at 900mm long?
Sorry for the barrage of questions but this info is Gold to me.
Jeff

[Ilina]

Hoohaa,

4952 is typically white and 1.1mm thick.

4991 is dark grey and 2.3mm thick, its also the product of choice for bonding acrylic and polycarb.



The tape needs to be able to expand and contract with your window material, and if its too thin, the tape cant stretch, which will result in adhesion failure.



Same rule applies to the 795. for maximum strength, the sealant needs to be bonding between the back face of the window material and the window rebate / cabin side.

You will find that all the tech data on sealants will be at a minimum of 3 or 4mm thick.

This is mostly to achieve movement ability, but sealant much thinner than 2mm is like playing with fire.



If you are laying down a wide bead of sealant which is beside a line of 4991, you will need to give the sealant at least 7 to 10 days to fully cure and reach full strength. Being moisture cured, it will only cure at a rate of 1mm per 24 hrs ( as a rule of thumb ). Some sealants, get very slow when trying to single side cure beyond 25mm of sealant width, so we have seen sealant still wet inside a joint after 30 days.



If you are going to hold the curve with the tape, then be sure to read up on the minimum time required to reach full bond strength. I dont believe it is advised by 3M to rely on the tape alone to sustain constant peel strength.



Read up on cold forming poly carb.


Avoid using csk fixings !


Good luck :-)

[Fore and Aft]

A Jigsaw is the electric saw you can use to cut Perspex. They normally have a metal base and I like to cover it with masking tape. The Perspex is covered with paper but I like to be 110% sure I am not going to scratch the windows while cutting them out.
I am not sure about leaving the bolts out. Perspex does expand and contract a small amount on hot days.
I felt 9mm was flexible enough for my 12mm bend.
I am not sure about wedging the window against the frame until the sealant dried. It would have be very hard to do with our windows. I would also be annoyed after all that effort if the window then popped out. To be honest I do not even notice the little bolts. I think I actually countersunk them enough that I could then cover the bolt head with black Fixtech and then you do not see them from the outside.
Have you thought about getting the windows pre bent to the curve you require? Not sure how that could be done, but surely someone who works with Perspex or custom windscreens could pre-bend the windows for you.
Good luck Jeff

[er9]

Originally Posted by Fore and Aft

A Jigsaw is the electric saw you can use to cut Perspex. They normally have a metal base and I like to cover it with masking tape. The Perspex is covered with paper but I like to be 110% sure I am not going to scratch the windows while cutting them out.
I am not sure about leaving the bolts out. Perspex does expand and contract a small amount on hot days.
I felt 9mm was flexible enough for my 12mm bend.
I am not sure about wedging the window against the frame until the sealant dried. It would have be very hard to do with our windows. I would also be annoyed after all that effort if the window then popped out. To be honest I do not even notice the little bolts. I think I actually countersunk them enough that I could then cover the bolt head with black Fixtech and then you do not see them from the outside.
Have you thought about getting the windows pre bent to the curve you require? Not sure how that could be done, but surely someone who works with Perspex or custom windscreens could pre-bend the windows for you.
Good luck Jeff

not hard but you would need to find a shop with an oven.

we cover our jigsaws with masking as well. much simpler than making a fancy plexi cover for the bottom of the saw and definately helps prevent scratching.

on a side note. anyone considering using adhesives on plexi wanting the absolute best bond possible should consider having your windows etched with a laser wherever the glue would make contact. similar to how car windows have that black band/border around their edges. you can also mask and sand with #220 sandpaper and acheive similar result. it will considerable increase the bonding strength because you then get mechanical and chemical bonding.

[Hoohaa]

I have picked up an offcut of 10mm acrylic to test on the boat tomorrow. Its pretty stiff, so it should be interesting to see how hard it is to bend around the edge.
I am also having trouble getting Black 3M VHB 4991 in 2.3mm thickness. Its not hard to get light grey but black seems to be an endangered species here in OZ.

[PegasusIX]

For my windows I used 10mm Acrylic with a rebate to the outside for sealant with VHB tape 2-3mm, black. I calculated the differential expansion between fibreglass and acrylic at 50degrees C (hot sun) which indicated this thickness of VHB was required to accomodate. The rebate has a 3mm foam backing tape and black fixtech 2 to 1 ratio across the rebate. With this arrangement if the sealant shows signs of releasing I can cut out and replace a section without removing windows. For my larger widows (800mm long) it seemed they were reluctant to curve to cabin sides. I had the Acrylic supplier hat in an ocean to give a slight curve to reduce pressure to straighten. No leaks after 3 years. Install with double sided tape and then add sealant after. Key installation techniques as advised by 3m tec rep, abrade fibreglass and acrylic with abrading pad, clean with isopropyl alcohol and wipe cloth one way only. Pressure with roller to compress tape on initial installation. The use of 3M VHB tape is simpler and better than all sealant installation and more reliable and leak resistant than bolts and screws. The sealant in my arrangement only keeps the water away from the 3M tape. All strength provided by VHB tape.

[PegasusIX]

Originally Posted by PegasusIX

For my windows I used 10mm Acrylic with a rebate to the outside for sealant with VHB tape 2-3mm, black. I calculated the differential expansion between fibreglass and acrylic at 50degrees C (hot sun) which indicated this thickness of VHB was required to accomodate. The rebate has a 3mm foam backing tape and black fixtech 2 to 1 ratio across the rebate. With this arrangement if the sealant shows signs of releasing I can cut out and replace a section without removing windows. For my larger widows (800mm long) it seemed they were reluctant to curve to cabin sides. I had the Acrylic supplier hat in an ocean to give a slight curve to reduce pressure to straighten. No leaks after 3 years. Install with double sided tape and then add sealant after. Key installation techniques as advised by 3m tec rep, abrade fibreglass and acrylic with abrading pad, clean with isopropyl alcohol and wipe cloth one way only. Pressure with roller to compress tape on initial installation. The use of 3M VHB tape is simpler and better than all sealant installation and more reliable and leak resistant than bolts and screws. The sealant in my arrangement only keeps the water away from the 3M tape. All strength provided by VHB tape.

That was heat in an oven to curve acrylic.

[Captain Bucknut]

Originally Posted by Captain Bucknut

https://youtu.be/MQyjxVUskd8 for the Boatworks video.

What I learned.......

The VHB tape works great and sealing it with DOW 795 was perfect.

As in the video, take the time to tape off when applying the 795, really makes for nice clean edges.

I started out in the shade on the port side and when I moved to starboard....... be careful as the hot sun will cause the lenses to separate if you have a curve. No problem, saw it happening as we were working on the other side and pressed the lenses back in and then threw up some towels to shade. If you have to walk away from the job, use sand bags to hold pressure. Checked em out the next am and all was good.

Sorry no pics but trust me they look great. Old ones had screws and the old selant used to chaulk all over the cabin and was a mess.

[SharkBite]

Originally Posted by Hoohaa

I am also having trouble getting Black 3M VHB 4991 in 2.3mm thickness. Its not hard to get light grey but black seems to be an endangered species here in OZ.

Hi from the UK. I'm new here but following thread with interest.


According to 3M's product data sheet, the 4991 tape is only available in the light grey colour.


The 4947 is available in black, but is only 1.1mm thick so not a suitable substitute. The 4918 is closest at 2.13mm which is clear/colourless for glass bonding.


Is that helpful?

[Hoohaa]

Thanks for great replies and yes Sharkbite that is helpful.
So now I will bight the bullet and buy the grey role of tape.
Also. The supplier of the 3B tape I had already bought by mistake, unexpectedly gave me a full refund yesterday and I still have the roll. I will post it back today. But it's good that there are still trusting people out there.
I took the 10mm acrylic and pushed it up against the curved window yesterday. Turns out it only needs about 10mm of flexing. It did it easily. So 10mm acrylic it is.

[Hoohaa]

Bucknut. Did you apply black paint to the acrylic to hide the grey tape? Thanks for the pics. I will post mine when I get started.

[GRIT]

I just did these today. Grey 4991 and Dow 795. There is a 4991B (black) but I had no luck finding it. The plexi is the darkest available, and the tape doesn't show through.

https://industrialtape.com/catalog/p...-vhb-tape.html

Click "specification" and you'll see the colour is black.

I scuffed, both the window and the paint, with the recommended Red 3m pad.

They're very large windows, and 12mm thick, but still fall within specs for the 4991 to support for long term.

If you're looking for 4991 in Canada, ULINE has it. Their service is fantastic.

I had no luck finding Dow 795 in Canada, without paying a fortune on Amazon. So I got it at a very reasonable price from McMaster and Carr. Shipped via Purolator, and received it in two days. Expiry date is Feb 2019. Better than Amazon.ca, where the expiry date was august 2018 or not shown at all, nor were e-mails answered.


Cheers.
Paul.

PS. Can anyone tell me how to rotate a photo? That last one should be turned clockwise a quarter turn.
Thanks.

[Greg4cocokai]

I used a router bit to cut my 5- 1/2" acrylic lenses for my hatches. Just clamp them together and run the router around. Way easier than cutting with a jig saw. Took me a little over a hour for all 5.

[Hoohaa]

Originally Posted by Greg4cocokai

I used a router bit to cut my 5- 1/2" acrylic lenses for my hatches. Just clamp them together and run the router around. Way easier than cutting with a jig saw. Took me a little over a hour for all 5.Attachment 171519

Sounds good. What was the bit diameter?