re-appearing darkness

[Brent Deines]

I for one feel a bit foolish for not mentioning the possibility of this being a moisture problem. Screenman will be so disappointed in me! Frankly it didn't sound like a moisture problem for me, but I agree with you that here in the Northwest we can't afford to take any chances.

[TechEvo]

I agree that you need to always be checking for moisture. But also for Delta Kits users keeping a fresh seal on the tip is very crucial as was mentioned earlier. I was having a similar problem for a bit and it turned out my seal was to worn. Just something to keep in mind.

[screenman]

Bit of a problem here I do not know which of my lines to use so here they both are.

If in doubt dry it out.

Moisture is our biggest enemy.

Whilst I also agree this problem could have many other causes.

I always just work on the idea that every single damage I see has at least some moisture content, dry out to me is as part of every process much as putting resin in the injector is.

[ChampionCHIP,wsr]

i agree with the past post, pressure, wettness,etc. this has happened to me also and somtimes i think it could be soap or possibly salt. it seems to happen more in winter, any opinions on this. i do dry every chip out, try to keep up on worn seals and pressure on tip. i will even re-set and fill again and black mark will show up again. think i read somewhere soap or salt can cause a chemical reaction and make a dark spot.
paul

[doctor ding]

With all due respect, Brent, I disagree with your statement about the injector on a suction cup-mounted bridge needing more pressure against the glass to seat properly than the injector on a vacuum cup-mounted bridge and here's why: That statement contradicts Newton's third law of physics which states that for every action there is an equal and opposite reaction. If we acknowledge that Newton's third law is correct, the proper statement would be that the injector on a suction cup-mounted bridge (suction cups being more flexible hence absorbing more force or energy by flexing) would have to be turned more to achieve the same pressure on the glass than the injector on a vacuum cup-mounted bridge (which is less flexible hence absorbing less force or energy by flexing) but ultimately the same pressure would be able to be achieved with either system and more importantly, it would absolutely not require more pressure to properly seat an injector in a suction cup bridge than a vacuum cup bridge.
As the injector in a suction cup-type bridge is screwed down, the suction cup(s) absorb some of the force exerted against the glass by the injector seal which causes the cup(s) to flex which results in the net force against the glass being diminished which results in having to screw the injector more to achieve a specific net pressure on the glass. The vacuum cup-type bridge which is less resilient will flex less as force is exerted against it resulting in fewer turns of the injector to achieve the same net pressure. Consequently I would submit that the suction cup-type bridge is theoretically more forgiving and hence less dangerous in the hands of a neophyte technician or a part-time semi-professional with limited experience (because it's more difficult to over-tighten) than a vacuum cup-type bridge. I apologize for getting all sciency and logical and everything.

[Brent Deines]

doctor ding,

You are right, or at least partially. I could have stated my point a bit more clearly, but the point is still valid. Having used both vacuum cups and suction cups to hold the bridge to the glass myself, and having sold thousands of each type of tool I can tell you that most technicians use less pressure against the glass when using a vacuum cup, and also experience less leakage. Because of the flex in the suction cup the tendency is to over tighten the injector when using this type of system.

The problem is that due to the flex in the suction cup, even if the same initial pressure is applied against the glass, when the injection process is initiated the suction cup mounted bridge will still lift as the cup flexes, often causing a leak. Because there is little or no flex in the vacuum cup the bridge does not lift when the injection process is initiated. Until you max out the stretch on the suction cup you cannot obtain the same stable environment that the vacuum cup provides, therefore a technician does have to create more pressure against the glass when using a suction cup mounted injector than if using a vacuum cup injector to obtain the same stability.

The original question had to do with re-appearing darkness in the break, and we have found that using too much pressure against the glass can cause this problem. We have also found that problem to be much more prevalent in suction cup mounted bridges because of the reasons stated above, but the problem can be attributed to using too much pressure regardless of the system used.

[simplyweb]

Once the resin as been injected into the repair is it possable to get any moister out that might still be in the repair.

[Brent Deines]

Once the resin as been injected into the repair is it possable to get any moister out that might still be in the repair.

In my opinion, no. I have analyzed some of the claims being made about this recently, and have spoken with an engineer and 2 chemists about it. All agree that the water needs to be removed before the resin is injected.

[screenman]

We have certainly tried and certainly without much success. I think maybe using an awful lot of heat we might have managed to get some out of a bullseye, but would certainly not reccomend trying.

We have carried out some interesting experiments curing resin underwater.

[doctor ding]

Simplyweb;

The short answer to your question would be NO.
The longer answer would be that back in the day when I was a young and foolish newbie at WSR I tried (and sort of succeeded) in removing moisture from a bullseye after resin had been injected into the break by heating the inside of the glass with a BIC lighter until the moisture boiled and I watched it evacuate through the resin. At the time I was using a type of resin which is (hopefully) not made anymore, so I have no idea what the effect would would be on a more modern resin but I liked the result so little that I never repeated the technique. Instead, I taught myself to recognize moisture in a break and err on the side of caution (if in doubt dry it out).