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Let;'s start over.

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CNKS

05-13-2006 17:51:41




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In the post below I made a comment about VOC's being below a certain level before a charcoal mask was safe. Did not read Rod's response before posting. Rod, you said Iso's are not VOC's. If not what are they? I read a Van Sickle iso label the other day saying that (I think) if the VOC level was less that 10X the minimum acceptable level that a charcoal mask was ok (I know people like us can't measure that and that it's Van Sickles way of selling the stuff to non-professionals). So what are they? Can you really breath iso's by dry sanding? As EX-pro said they would then have to be part of the solids. I may or may not dry sand with 1500 grit, the 3000 has to be wet sanded. Darned if I want to use supplied air for sanding. 3M's system recommends dry sanding with 1500, so I have been told, have not yet read their instructions. Don't see why I couldn't wet sand. I cannot keep the contaminants out of my paint. I may move to NH where the air is cleaner. I think EX-pro or me just opened a can of worms.

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B-maniac

05-19-2006 19:34:51




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 Re: Let;'s start over. in reply to CNKS, 05-13-2006 17:51:41  
Just a comment about wet v/s dry sanding. Wet sanding has proven superior to dry in my 35 yrs. both in finish quallity and speed. The only time I dry sand is if I just have a few minor nibs to take care of. They say uncatylized primers absorb moisture. If it were to stay wet for a week or more,probably. In all the years we had to use that junk, I never had a problem related to wet sanding it. Also do yourself a favor and use hand sanding and block sanding techniques as apposed to power sanders. Again, you get just what you earn. When you wet sand,use a hose or spray bottle as you sand. All residue will be flushed away on each stroke which will increase speed,quallity and paper will last twice as long.Never use a bucket of water.

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CNKS

05-19-2006 19:50:17




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 Re: Let;'s start over. in reply to B-maniac, 05-19-2006 19:34:51  
Wet vs dry -- I'll find out. I have always wet sanded. I bought a variable speed air sander, used it the first time today to color sand with 3M 1500 grit -- dry --. The surface to me looks as good or better as when I wet sanded by hand. I am going to finish it with 3000 grit, wet. These are fenders, I will have the hood that I hand sanded with 1000, 1500, 2000 grit wet to compare it with. I am not satisfied with my buffed out hood, probably because this is only my 2nd time buffing, it has to be learned, and I'm learning.

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Rod (NH)

05-13-2006 19:29:24




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 Re: Let;'s start over. in reply to CNKS, 05-13-2006 17:51:41  
Yes, that's what I said and I may have been incorrect if one looks at it in a precise manner. Isocyanates may technically be one of many, many compounds referred to as VOCs but I don't think they are generally considered to be in the category that is regulated as such. For instance I have never seen isos referred to as harming the ozone layer. But I am not a chemist and can't be sure about this. Perhaps it's because they are not a dominant one among the many. I do know there are unreacted and reacted isocyanates. No expert here, but I think they are a needed constituent for the chemical reaction to take place that results in a urethane or a urethane-like product. It is my understanding (and I may be wrong) that unreacted isos are more hazardous than reacted ones. It is also my understanding that after mixing and before curing, the isos are in diminishing states of reactivity, being the most hazardous while being airborne during spraying. When it comes time for sanding, for instance with 2K surfacers, it is my understanding that the reaction is at least partially if not mostly complete and the hazard is far less. But I am not sure of that. Dust from sanding a 2K surfacer probably has isos in it and should not be inhaled, at least. Of course that is the case with all dusts anyway. Whether 2K surfacer dusts are more hazardous than other dust because of the partially or mostly reacted isos, I don't know. I can't say I have ever seen a specific recommendation to use supplied air for 2k sanding or the "color" sanding that you are referring to. I sand my 2K surfacer dry by hand and only wear a standard dust mask during the process. Unlike my old spraying experience with a cartridge respirator, I have never had a reaction with sanding using just a dust mask. That may be from ignorance however and I may have to re-evaluate the practice. Maybe you two did open a can of worms. I'm not sure. If either of you find any specific recommendation on it, be sure to post it.

Anyway, here's a brief on VOCs, including a listing of the most common ones and a brief on isocyanates from the same source.

BTW, I'm not a proponent of wet sanding but I wouldn't sand 1500 grit dry unless I wanted to buy an awful lot of sandpaper. Maybe 3M has something special going on with that recommendation. If you are alergic to trees, you will need supplied air 24/7 here in NH.

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CNKS

05-13-2006 20:23:21




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 Re: Let;'s start over. in reply to Rod (NH), 05-13-2006 19:29:24  
Thanks, I'm only allergic to the dust, dirt, lint, whatever that falls into my paint, and it only affects my sanity. I don't think it is solvent pop or any of the other things on the Sherwin Williams site that we discussed previously, as it occurs in the first coat, in the booth or out, fans off or on, new filters or old filters, two different spray guns, etc, etc. I ruled out the guns when I finally practiced on a piece of sheet metal with different pressures, etc, no change. Took can of IH 2150 spray paint (GOOD paint as far as rattle cans go), and got the same thing. Sometime on a a calm day (never happen here) I'm going to paint some part outside and see if the problem is entirely in my building. Anyway I had forgotten that you dry sand your surfacer, so I'm probably ok. I don't understand the dry sanding with 1500 either, but that's what Len Stuart at Autobodystore told me when I ordered the sander -- I'm going to try it wet and dry. Six inch orbital variable speed with the 3M "hook-it" system. My goal being to have to do as little buffing as possible, because as you know buffing tractor hoods, etc is difficult because of their small size. I almost have the procedure figured out, but have a ways to go yet before I can get the scratches down to an acceptable level, thus the sander. As of now they can't be seen from more than a couple of feet away -- in other words you have to look for them, they don't jump right out, but they are there. Buffing is harder than painting, for me anyway. A science unto itself. There are compounds/polishes that work by abrasive action, others by chemical action. Went to a Meguiar's demo at a local detail shop yesterday. Learned things that I would have never even thought of. Now if I can just apply what I learned. I would like to go to one of PPG's schools sometime, doubt if I ever do, though.

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Rod (NH)

05-13-2006 20:09:43




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 Re: Let;'s start over. in reply to Rod (NH), 05-13-2006 19:29:24  
Jeez, getting tired I guess. My reference to a list of common VOCs is incorrect - ignore that.



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CNKS

05-13-2006 20:27:00




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 Re: Let;'s start over. in reply to Rod (NH), 05-13-2006 20:09:43  
Dunno what you are trying to show -- that one looks ok to me.



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Rod (NH)

05-14-2006 06:12:37




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 Re: Let;'s start over. in reply to CNKS, 05-13-2006 20:27:00  
My error was in not carefully reading the VOC reference that I linked to. The list provided there of a number of compounds were not common VOCs at all. They are compounds that were excluded from the VOC designation. That still leaves us with the fact that isos may technically be a VOC. I don't know and I don't think it's important to know except for any purely academic value.

I did read over again the PPG position paper (FAQ) on isocyanates and found this wording:

Q18. Are there any hazards associated with sanding or machining
isocyanate products?

A. For cured parts or films, it is not expected that isocyanates would be
generated in the dust produced during sanding or machining processes.
It is still recommended that a respirator suitable for preventing inhalation
of dust particulates formed during these operations be worn.

Sanding or machining uncured isocyanate coatings poses a potentially
larger hazard than cured parts since it is possible that airborne
isocyanates can be generated. “Wet” sanding reduces the total amount
of sanding dust generated and should be used whenever possible. Local
exhaust ventilation, such as a vacuum sander, is another control
measure that can be used to minimize potential exposure to airborne
contaminants. PPE should also be used to prevent skin and respiratory
tract exposure to isocyanates when handling or machining uncured
isocyanate products.

This seems to support my stated understanding that the degree of hazard is related to the state of cure. The MP182 tech sheet indicates 2-3 hours after application to sand and topcoat. I tend not to get on it that fast - perhaps a carry over from my past practice of allowing liberal dry times when using lacquer surfacers. I do know the 182 has a short pot life (1 hr), much shorter than the MTK (8 hrs). From that I guess you could say that the curing is faster for the surfacer than the topcoat. I have no idea what the actual cure state is of the 182 at 3 hrs. In any event, my practice of using a standard dust mask for sanding it has not shown to cause me any noticeable reaction. I have never power sanded it so I can't push my experience to include that method, which is likely to produce a higher level of airborne dust than by hand. In any event, I'll continue my present practice until such time that I notice any adverse reaction by doing it or see some agency/manufacturer documented recommendation that is more definitive than what PPG has provided.

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CNKS

05-14-2006 07:06:36




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 Re: Let;'s start over. in reply to Rod (NH), 05-14-2006 06:12:37  
Makes sense -- The MTK that I will be sanding on my fenders will be a week-10 days old. If I decide to redo my hood (best to leave it alone) there is the possiblility, given the hand sanding and buffing I have already done, that I will sand through the top coat. Thus I will have to reapply. Thus it will probably be at least a couple of days old, as I likely will not do it the next day.



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