how long before applying slick sand?

S

Steves69LS3

i just layed three coats of the new epoxy primer on my trunk lid. its about 80 degrees out.
how long before i can apply slick sand?
 
The longer you wait, the safer it is. I'd wait til the next day at the minimum if there are three fresh coats, even at a nice warm temp I've been bit several times by putting poly primer on epoxy too soon. At this point I just wait several days because the potential for problems is just not worth it. Poly primer is definitely not the same as applying filler, there is something in the poly primer that can soak into the epoxy and re-liquify it if you hit it too soon.
 
The thicker the epoxy is the slower the cure and some spray a lot heavier than others-this all leads to variables. 80* temps are good! On 2-3 coats of epoxy I usually wait 12-24hrs and never have problems. Crash, what polyester primer are you using? Do you reduce it? For better sprayability I've reduced slick sand and feather fill up to 4-1 with acetone and never had any problems.
 
I have used G2 with no reduction, 2 coats with about 15 min. flash through an old Sharpe SGF 1.8.

I'm sure the OP will not have a problem, but I do like to advocate caution just in case. Waiting longer won't hurt anything, but going too fast definitely can.
 
You guys are right but where I like to say min of 24 to 48 hours is if the temp is boarder line.

Problem with the polyesters is they are all Acetone and because they are so thick the acetone will set there like a wick against the epoxy but most shops just wait over night before applying and very few times do we ever have an issue with that, if we do it is always cold related.
 
thanks for the input guys!
i waited until today to spray the poly. its about 80 degrees here. yesterday after the 3 coats of epoxy, i let it sit out in the sun for the rest of the day. today i did the same with the poly. it seems rock hard now.
boy did i have to race to clean my gun lol! i dropped a hockey puck of un used poly out of the cup. thank god it wasnt hard in the gun.
 
yes i have seen many times where the epoxy seems cured enough after 12hrs so i apply polyester over it then when the poly is cured i goto sand it and now the epoxy is gummy underneath. i always wait 24-48 now and dont ever have an issue.
 
Same here. Unless I am spotting in bare metal areas after bodywork before poly. I always do filler work over the epoxy (rare cases over the metal) then apply poly over that. If I am just sealing up some bare metal, 1 even, reduced (20%) coat over the metal then straight to poly after 2-3 hours. (in winter time booth set to 80 to flash.)

But if 2 WET coats of un-reduced epoxy, always next day.
 
Steves69LS3;28611 said:
thanks for the input guys!
i waited until today to spray the poly. its about 80 degrees here. yesterday after the 3 coats of epoxy, i let it sit out in the sun for the rest of the day. today i did the same with the poly. it seems rock hard now.
boy did i have to race to clean my gun lol! i dropped a hockey puck of un used poly out of the cup. thank god it wasnt hard in the gun.
Click to expand...

How long are you leaving it in the gun?? The second I add the hardener, I start the timer. In 30 minutes I have everything dumped back out of my gun and am running lacquer thinner through the gun, never came close to getting even so much as skinning over this way.

I let my epoxy sit at least a day and then sprayed next day or two days later with Slick Sand. Have almost the entire car in slick sand (roof, a door, both quarters, hood, trunk lid) for a year over the epoxy with no problems whatsoever.

There are several observations I've made with the slick sand...Barry likes to say it sands like concrete. Initially, it does and I found for me what works best is breaking the crust down with 120 grit. Once I get through that, I sand with 220, and I know this is going to be a complete sacrilege to say, but I've gone straight from blocking a quarter in slick sand with 220 to my tail light panel in SPI 2k with 220, and the slick sand did sand quite a bit easier without virtually any loading in the sand paper. The 2k sanded a little hard and loads the paper in good time. I blow out my paper and the panel frequently regardless of what I'm sanding, however.

Regardless of that, I'm regretting doing so much of the slick sand on my car as the final block cannot be wet sanded. Barry and I have talked about this before and have gone over several options. The other thing is you get these little bumpy rough pits that never sanded out and those are a pain in the ass. You don't get these with the 2k. Maybe these are just from me sucking :D So now I'm really considering putting a few light coats of 2k over the panels, blocking them down, this will fill in all the imperfections in the slick sand, and then wet sanding.
 
After I'm finished with the body work I spray one coat of unreduced epoxy wait a couple of hours than spray two coats of Slick Sand. I block Slick Sand with 80 first to get it flat than 180 followed by epoxy.
 
I've wetsanded poly primers many many times and never had any problems, it's even recommend in the tech sheets. If there's epoxy under it then there's no worry about corrosion at all. Now, if you've got poly primer sprayed direct to bare metal-this can be a problem wet sanding and you'll have corrosion hotspots in areas that are cut through.
 
Next question. I sprayed my hood with three coats of epoxy last Thursday. I want to shoot poly later today. Should I scuff the epoxy?
 
Won't hurt or help if you do or don't with Poly-type primer.
Personally I would not as I want the mils of epoxy maxed out.

Of course if you reduced the epoxy, then we have to regroup as that does change things.
 
Thanks guys. I'm still in the 7 day window so I guess no scuffing
 
A scuff with a maroon scotchbrite when in doubt but you should be ok at 4 days
 
I'm at 72 hours after 2 wet coats of SPI epoxy, so no scuff needed?

How much do I mix for about 10 square feet? (My estimate of a 65 mustang Fastback deck lid and a stone guard, just one side of each.)
 
No sanding would be needed for either of you in the time frames you stated.
Polyester has very good adhesion and a wicking effect, that is why we ask the epoxy set for 48 hours first.
 
You must log in or register to reply here.
Back
Top