Lotus Elan

Bonded windscreen - applying the mastic safelyasking off

PostPost by: dick+2130/5 » Fri Apr 28, 2017 9:13 pm

Help/advice needed please. I have read a lot of very helpful posts on the forum about fitting the screen and by following them have got to the stage of having the unbonded screen in place on the car (photo attached)

I have read the very good step by step guide by Innes but do not understand the bit about masking off the screen from measurements taken with the bare glass fitted as a trial - can anybody explain please ?

Attached also is drawing showing the screen positions Top, Bottom, & RHS as they are on the car. It looks to me as though the mastic should finish ast the inner edge of the plastic surround otherwise it will be visible from outside the car. Any comments ? + does anyone have a photo of a screen please showing where the mastic goes ?
Final point is that from my drawing it looks like at the sides of the screen sides you need to bond to the windscreen opening trim because trim and screen surround overlap - I seek advice on how to make a neat job of that.

Lot of questions , any help gratefully received.
Thanks,
Dick
Attachments
p1210324.jpg and
p1210320.jpg and
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PostPost by: Sea Ranch » Fri Apr 28, 2017 11:56 pm

Awesome drawings, Dick! Thanks for the accurate views!

Personally, I think the molding shape/profile means the bonding is designed to fail. No way they have allowed enough contact area between glass and window frame/aperture. I have been contemplating cutting/grinding back the final return on the molding profile - the part which wraps around the inside of the glass. Would give a little more area for glue/mastic/bonding agent to adhere to both glass and painted fiberglass.

That said, I don't have any advice. Sorry. :oops: My car had lots of silicone added after the fact and it was very difficult to see what was what. So I just removed it, cleaned it and am hoping (like you) to gain some wisdom/insight before attempting installation.

What product will you use? You refer to "mastic". Where/what? Or will you use silicone or urethane sealants?

Thanks, keep us posted . . . :mrgreen:

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PostPost by: dougal9887 » Sat Apr 29, 2017 8:48 am

Dick,
Re. marking off the screen from measurements/marks, this refers to where you wish the black primer border to end up. I've seen some with a wide border, similar to a modern car. I chose to make the border discreet leaving the inner opening trim as the visual reference as shown in the photo I took for this write up which you may have seen. lotus-chassis-f36/bonded-windscreen-t35507.html
Re. the sides of the screen, the relationship of the outer trim, screen and inner trim shown in your drawing is not the relationship on my install. If you examine the above photo you will see that almost the entire inner trim protrudes beyond the inner edge of the outer trim and there was a reasonable gap for a direct glass to body bond, the inner trim is just tapped into place. Note though that the outer trim IS bonded to the screen. If your install is as per your drawing, I think I would try to trim the inner trim outer edge, if that makes sense, to increase the glass to body contact, since it's only function is to provide a neat finish to the headlining.
When I applied the mastic, I just followed the edge of the inner trim applying more generously where I had noted wider gaps. (This part is a bit heart in mouth and is when some experience would not go amiss!) However you have to work quickly at this stage so there's not too much time to worry about it. You want plenty of mastic along the bottom of the opening which can be smoothed off, on the inside, to a nice finish once the screen has been compressed in place. I found that the single cartridge of mastic just and no more did the job.
Re. support blocks, I don't think you'll want these at the top of the screen. I superglued the bottom blocks to the body so as not to displace them in the panic of screen fitting.
Good luck!
Dougal.
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PostPost by: dick+2130/5 » Tue May 02, 2017 11:07 am

Hi Dougal and Randy,
First to Dougal - an apology and an acknowledgement - it is YOUR seminal write up that i have been working from all the time ! - so how I managed to mis-reference it i do not know.

I found you new comments very helpful Dougal, and went back and had a look at the old trims and windscreen to to check where black mastic lines were. Answer - 11-12 mm from screen edge at the top and 17-18 at the bottom - so i am following you advice and going for a discreet border with minimum visible black line, No problems at the top - the blue band hides it all.

How did you trim the gap between the crashpad and windscreen? I removed a Tee section moulding from the car but not reusable, and Woolies etc have nothing similar.

At the sides the old windscreen opening trim has mastic at least 1/3 the way across from the back edge all round - so my current position is similar to the original fit. Concluded that i will just bond to the windscreen surround and not try to reach the glass. Should be waterproof even if not ideal for strength..

Randy - your question about mastic- I am using the Dinitrol 500 product shown in Dougal's write up. Not Dinitrol 5500 as i gather that it cures more rapidly. Talked to a screen fitter who said Dinitrol was good, but he prefered Sikaflex as it gave a longer working time. I have bought 2 tubes on eBay - i for practice and one to apply ! Hope this helps.
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PostPost by: Craig Elliott » Tue May 02, 2017 5:29 pm

One thing regarding neatness of finish - tar remover seems is very good for getting rid of any excess screen bonding mastic (I used Autoglym intensive tar remover, other stuff may also work)
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PostPost by: dougal9887 » Wed May 03, 2017 2:47 pm

My car never had trim in the gap so maybe Lotus had difficulty also in 1972!
The bit of glass fibre seen between the crash pad and the screen was painted black and a neat finish made to the mastic.
I covered this bit in black leathercloth before fitting the screen and just amoothed the mastic.
20170503_153310.jpg and
Screen mastic.

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PostPost by: 10kph » Sat May 13, 2017 10:14 am

Bonded Plus 2 windscreens have proved to be a problem over years leading to leaks and deterioration in the plastic chrome trim.
I heard that Spyder have altered the screen aperature by possibly securing a filler to the fibreglass lip and then bonding onto that. The screen will then be level with the fibreglass body and the side gap between the glass and pillars/roof filled with a modern black insert or chrome T section if available.
Has anyone seen this done and what comments are available.
Thanks Tony
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