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Technique decking HV urethane esp in colder temps

Hi guys, I am a hobbyist who does a few windshields per year for my own vehicles. I have studied the literature from urethane manufacturers and do my best to follow best practices. I recently started using Sikaflex P2gPlus urethane because lately, it is the easiest high viscosity product for me to get without buying a case. This urethane guns pretty darn stiff. The most recent vehicle I did using the Sika P2GPlus I ended up decking the glass a little higher than I wanted. I am using a Dewalt power gun and I notched my tip to the triangular dimensions provided by the Ford service manual for this vehicle (2014 F150) -- 0.55" tall (same as the pinchweld height at the roof line), 0.30" wide base notch size. It was about 50 degrees in the garage. I two person set and then decked the glass by pushing firmly while working my way around the perimeter. I was trying to deck the glass to sit about 1/16" below the roofline at the top, and to sit down on the depth limiting tab on the factory gravity stops at the bottom, but didn't quite get it set deep enough. I found that once the triangular bead compressed down to about a 5/16" tall rectangular bead, it would not compress any further than this because the urethane was stiff enough that it would support the weight I was applying to the glass.

I am guessing that the only way I was going to be able to deck the glass deeper once the HV urethane started resisting my pushing on it would have been to slap the glass with an open palm while working my way around the perimeter - to break the surface tension of the urethane and let it compress more - is this correct? I am probably going to cut this out and reset it. I am planning on sticking with the HV urethane.

Thanks! Steve

Re: Technique decking HV urethane esp in colder temps

A few factors are getting you, Your using product at 50 degrees which is its low temp application limit area so its going to be stiff. Warm it up to 75 and it will soften up a bit.
Second thing is going to be the moisture draw that it will pull as it is moisture cured so the humidity is going to push your tach free time!!
If your glass is above roof your either going to get wind noise but the safety part is that in a roof crush it is not going to catch that top edge of vehicle body.


Re: Technique decking HV urethane esp in colder temps

Thank you for the reply Clyde. The glass ended up being flush w/ the roof, not above it but not recessed like I have seen looking at other examples of this truck. Which is why I wanted to reset it. I had also read Bob Baranek's article on exposed edge glass where he noted the roof crush support that comes from the glass against the top pinchweld wall.

I measured an uncompressed bead of urethane I had gunned onto a piece of cardboard before starting and I found that the base is much wider than I expected. Although I notched the nozzle to about 0.30" wide at the base, the gunned bead measures more like 0.45"-0.5" at the base. I think the cold, stiff product was flexing the nozzle as it forced out, making the bead wider tan I expected. I am guessing that the bead being so wide at the base probably didn't make decking the glass any easier. I had read on here that technicians know from experience that in colder weather they can notch the nozzle to produce a taller, narrower bead that will deck easier.

I had left the tubes in the house @ 70F before using them but they probably cooled down pretty quickly by the time I got going.

As far as decking the glass, should pushing firmly be enough, or is slapping the glass ever acceptable to get it to deck down on a stiff product? Steve

Re: Technique decking HV urethane esp in colder temps

Please dont slap the glass. the urethane will be compressed quickly but will rise again quickly causing air bubbles.

Re: Technique decking HV urethane esp in colder temps

Thank you, Slappy, I will focus on sizing the bead more accurately for the application and ensuring I am not working in too low of a temperature for the product.

Re: Technique decking HV urethane esp in colder temps

Thanks again for the tips. I cut the glass out without damaging it (what a relief, this was a new OE acoustic shield), triangle notched my nozzle to about 0.3" base x 0.6" high, and decked the glass so that it sits 2-3mm below the roof line now. I used a BMW glass decking template I found online that I printed to scale on card stock to measure how far the glass was set below the roof line. I had to push a lot harder on the glass than I expected to get it to deck down. Not used to working on such a big vehicle w/ more limited reach. Good to go now. -Steve

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