Alternate Window Install Process

Here is my current thinking of how I am going to install my windows and I'm wondering if I am missing something or am perhaps crazy for thinking this will work. This description applies to the side transparancies only, it will be modified for the front windshield.

The intent is to avoid the process of micro and glass to fill the gap with the window. I do not care if the main paint color "bridges" onto the window transparency. The tendency to crack, the asthetics and the work involved have me thinking differently.

I am using Lord Epoxy 7585 A/E as recommended by a trusted Fiberglass person - Geoff Combs.

1) Window opening flage scuffed and 3/4 flange around inside of window transparency also scuffed

2) Window installed using Lord Epoxy

3) Fillet is created on inside edge using Lord Epoxy mixed with Epoxy black tint (test was successful to do this). Epoxy is cleaned up with PPG DTG870 which does not affect plexi window (test also confirmed this).

4) Once aircraft is painted, painter will paint 1" border around transparency edge to cover epoxy adhesion area with black paint.

5) Transition from transparency to canopy on exterior will be filled and filleted with matching black polyeurathane rubber/flexible automotive grade sealant.

This should result in the windows have a defined border around the window, no glass to crack with age and an easy to repair exterior fillet if it should ever need maintenance. In addition, the polyeurathane will allow the plexi/canopy expansion/contraction needed.

Any comments? Ideas? Anyone else follow a similar process?

Mark,
I just sent you a pm. Ignore it, I did not see your post. I started out doing exactly what you plan. I chose the Sika adhesive because it uses a black primer adhesion promoter on the inside of the glass. This left a real nice black border. I was never able to come up with a way to fill the transition area. I tried proseal and a couple of other products, but I was never happy with the results. Below it the door window after installation with the Sika. The Cirrus mechanics use proseal when they form the bead. When I changed back to painting the window, I laid a single layer of 6 oz. cloth around the windows and did the body work to smooth out the transition. I not found that the Sika expands when heated. I left one of the painted doors in the hot van, which probably was 110+ degrees. When I removed it I could clearly see the transition from glass to fiberglass in a couple of the corners. After it cooled down the seam disappeared. I am sure that over time this will develop a crack in the paint along the seam.

I'll try to grab some details of the polyeurathane product. I saw it at my local car finish shop (Industrial Finishes). I'll post details when I can.

Mark,
Any more details on that polyeurathane product you were going to use to fill in the exterior window to fuse gap? Have you used it yet?

The problem I see is 2-fold. Firstly, you are going to find it very difficult to cut and position the window so as to get an even gap for your fillet. Secondly, you will get some of the adhesive squeezing out and filling all or some of the gap that you want to fill with sealant. Hence, trying to get a good-looking, even fillet on the outside is going to be very difficult.

It seems that trying to prevent the cracking is problematic. I have gone with the standard WeldOn adhesive. I have smoothed and levelled the outside margins and the next step is to cover the joins with 2 or 3 layers of fine glass cloth, fill and blend to the bodywork. We shall see.......

I found it very difficult to get a tidy fillet inside with the WeldOn so I intend to tidy it up with some automotive rubber extrusion and then paint the outside to the same edge.

I haven't completed the urethane around the window as I am planning to wait until the fuselage is painted. With the window being painted, I'm not worried about a smaller edge around the window. It's also possible I might just use some more lord epoxy on the exterior which is dyed like I did on the interior and just use that as a fillet between the window and the fuselage. So I think there are a few options for finishing the exterior of the window without risk the cracking issues others have seen.

Charlie
Geoff here the Lord adhesive I recommend is the 7545 A/E it is
a urethane adhesive not Epoxy
Just FYI
Geoff

Geoff,
What are your thoughts on glassing over the window-fuse gap vs. just filling in with something (Lord, micro, etc.)?

Thanks Geoff, just lazy typing. Thanks for the clarification.

I would recommend glassing over the joint with 2 layers of 4 oz cloth.
run your cloth weave 90 degrees to each other. Make the first piece of cloth
slightly smaller then the last piece. The last piece should totally cover the first piece edges. Overlap at least 1/4" if possible. I would leave about 1/32"
to 1/16" gap between the window and fiberglass. Let yuor adhesive Lord
7545 come almost to flush with window and fiberglass top. Leave about 1/32" to 1/16" low if possible. When putting the 2 layers of glass on mix some epoxy with 1/32" chopped glass fibers and apply into remaining gap then apply the 2 layers of glass cloth.
Sand and feather into glass top. Be careful not to sand thru both layers of cloth.
Just filling it in will probablly crack (not recommended).

Geoff

I'm doing the windows at the moment - been doing them and the doors for some weeks actually - by far the favourite part of the build so far

I've gone for layers of light glass over the join but, having read lots of posts, I'm pretty much resigned to cracks eventually. As others have done, I plan to put a black border around the windows. That way, they can be repaired without spoiling the paint job.

Right, back to some more filling and rubbing down