couldn't spray polysurfacer quick enough
It set up in my gun after spraying a hood, rear valance, taillight panel and a front nose. Sprayed one light coat using a hvlp with a 2.3 tip. Tried cleaning my gun and by the time I went back to spray the same batch it got hard. Mixed another batch and I must not have done a good job cleaning the gun as it sprayed thinner just fine but with the new batch of polysurfacer it started spitting. So I wasted about 3/4 of a quart total. I figure I tried spraying too much at once. Question is now that I have one coat and I should have about 3-5, if I go back to spray the additional coats tomorrow after I get a new gun, do I have to sand everything all over again with 180 grit paper? I plan on using colorbuild primer next.
The answer should be somewhere in the P-sheets.
But, barring that, I'd say most likely YES to sanding (after all, it's basically sprayable body filler, and you wouldn't build multiple layers of that w/out putting some mechanical tooth into things), after a few minutes the recoat window has expired.
The obvious solution, is to mix smaller batches at a time...basically, when you confine a thermoset resin like that in a large quantity in a confined space, it exotherms (and when it gives off that heat it accelerates the reaction of what's there...as you have discovered).
If you were to mix up more than you could quickly shoot, the trick would be to store the unused portion in a flat pan or mixing cup w/ a wide flat bottom (not always the most practical, but that's how to slow the chemical reaction and minimize the heat build up that kicks things off...once it get's going, there's no slowing it).
Messing w/ catalyst (MEKP) ratios might get you a little leeway, but I wouldn't deviate too much from specs (laying on something that doesn't cure properly would probably be more hassle to the project than digging gum out of the paint cup).
Look at it as an opportunity to do some agressive blocking...for that matter, starting w/ something a bit more coarse (like 120) would aid in the plight to get things flat (by the time you move to 180 you're riding the highs and lows)...granted, if you don't have enough material in place to support agressive blocking, then go w/ the tooth that'll ensure the mechanical adhesion of the next layer.
Thanks for the response. I now understand that I need to use smaller batches..but if you are going to spray multiple panels how do you keep it from hardening in the gun. Seems like I will need to spray a gun full then break it down, clean it then start all over again by mixing a new batch? I am going over this with color build primer so I guess if these panels block well I could just go straight to the colorbuild, you think?? thx for the help!!
what you can do is mix up a bunch of it and keep it in the fridge until you are ready for it. It should slow down the reaction that causes it to harden
Isocyanites in the fridge??? don't drink the milk................
There's absolutely something wrong.
Originally Posted by Mikec35
It could be...
1. The ratio of hardener to primer is incorrect.
2. The type of hardener is incorrect.
3. The temperature demands a slower hardener.
If the products that you're using are meant to be sprayed then they will need at least a 30 minute window (minimum) working time. Most products of this nature will give you an hour or more. Check with the information available from the manufacturer or call your supplier for technical info on that particular product.
What brand of filler primer are you using?
I am using sikkens polysurfacer. The mix ratio is 100 to 5. I was spraying in a 70 degree garage. Each time I spray this stuff it sets up in the gun in about 30 min or less. I feel pretty confident that my mix ratio is correct. I strained the poly and there is a strainer in the gun. The tech says to use a 2.2 tip and I am using a 2.3 tip. I am also spraying at the upper end of the air pressure recommendation. I just looked at my gun and have realized 2 things. I was using the air pressure setting for a gravity feed and not hvlp, was using about 50 psi and the tech sheet says 10 psi. Also just realized that the screw behind the trigger had backed out of the gun and looks like a gasket blew out. I am sure this contributed to my problems.
Just talked to my Sikkens rep...
Sikkens polysurfacer comes with tube of hardener for each quart of surfacer. If you mix half a quart you use half a tube of hardener. This mix should give you time to spray and clean.
I'd say ditch the in-the-gun filter (generally causes more problems, especially w/ more viscous materials like high build primers...if the material has been run through a strainer, any debris should shoot through a 2.3...and redundancy w/ the primer isn't so critical, and you'll be sanding things anyway).
PSI settings are done w/ the air flowing, and gun trigger pulled (and all you can really do unless you have fancy equipment, is read the gauge on the gun or at the wall)...that 10 PSI would be measured at the air cap (i.e. coming out of the gun, and generally not measured by the user...go by the gauge)...also, bottom line, is fiddle w/ PSI's till you get the result you want (spraying at higher PSI may make for more over spray and put it out of the range of working w/in HVLP guidelines, but you can get better atomization and lay the droplets down more finely = flatter).
Still say, mix what you need at the time of spray (and only you can gauge that)...since it's primer, and the downside is a gummed up gun, probably better in this case to mix as you need even if you run short (it is primer, and you will be sanding it) so less chance of waste. If you can shoot it out before things get to viscous, you can back-flush some thinner through the gun to open things back up (again, scrap that filter in the gun, one things thicken from the exotherm, they'll glue right up to the fine openings in the filter).
As far as refrigerated storage, can't hurt if it's convenient (also, in adressing the other post...polyesters are catalyzed w/ MEKP, there are no isocyantes in poly...ISO's are in the hardener component of urethanes)...still don't think either would taste good on a sandwich, but sealed up from the elements it's probably less harmful than some of the stuff that grows in the dark in the back of the veggie drawer.
Also...in terms of what's meant by the gun types...(gravity feed is w/ cup on top vs. a siphon feed w/ cup on the bottom and a pickup tube)...(HVLP is high volume low pressure vs. compliant and conventional...the latter two in increasing air consumption and decreasing transfer efficiency)...double check the specs...and adding air w/in reason can help.
Gaskets falling out of the gun definately wont help spraying finicky materials...the fluid needle packing should be snugged up to accomodate the needle sliding, but not let any fluid out (also wouldn't hurt to put a drop of lube on there).
Best of luck.
Just incase you were interested in saving some money. I've used the sikkens polysurfacer and ive also used the evercoat slicksand.
I like the slicksand better. I use it all the time and i produce flawless results with it. Its a hell of alot cheaper too. The slicksand is only about 56 bucks or so for the gallon with the 4 tubes of mekp hardener. And again with that..its one tube per quart.
Thanks for all the great responses! I only have a couple more panels to do then I am done with the polysurfacer on this car. I Have a new gun, am right on my mix ratio, and will mix a smaller batch next time. I'll be glad to be past the filler primer stage!! I will try slicksand next time..seem's like a good alternative. Thx again.