High build over SPI epoxy

bill3337

bill3337

Member
Question about spraying 2 part high build over SPI epoxy. I'm going to spray some doors tomorrow with SPI epoxy and would like to be able to spray the interior face edges of the doors with high build the same day to cover some minor manufacturing stress lines, almost like heavy sanding scratches, but in places hard to apply filler. I'm not using any high build as a primer surfacer on the face of the doors as I'll just use the epoxy for that, they're nice and straight. I've looked in the SPI manual and it tells you flash times to recoat with base, but don't mention flash time to recoat with high build. I'd like to let the epoxy flash for a couple hours, then apply the high build. Any issues there? Thanks, Bill
 
You MUST let the epoxy cure at least 24 hrs (some are more comfortable after 36-48 hrs) at 70 (+) degrees (constant surface temp) before applying your high build primer. Don't rush things especially this time of year if you are in the colder areas.
 
Ok, thanks. I can keep my home booth at 70 degrees, but I'll wait and do the high build next weekend. I just thought it would be nice to do it the same day, but not if it's not recommended.
 
bill3337 said:
Ok, thanks. I can keep my home booth at 70 degrees, but I'll wait and do the high build next weekend. I just thought it would be nice to do it the same day, but not if it's not recommended.
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There is also a second window. Should do it within 7 days for a good chemical bond. If not you will have to scuff the epoxy with 180
 
bill it really boils down to how much epoxy you put on. if you just do 1 single full coat then i would say a couple few hour flash then high build will be fine. if your doing like 3 coats then absolutely overnight. i also would not wait 7 days to get hb on it either. i have always believed that window was way too long. for hb i would not let it go more than 4-5 days. you can get 7 days out of it if you turn the heat off in your shop and let the temp drop to say 50 maybe a day after the epoxy was sprayed. at regular shop temps, every day you wait after the first 24hrs the adhesion will be less and less. at what point that becomes a problems depends on how thick the epoxy is applied and shop temp.
 
Jim C said:
bill it really boils down to how much epoxy you put on. if you just do 1 single full coat then i would say a couple few hour flash then high build will be fine. if your doing like 3 coats then absolutely overnight. i also would not wait 7 days to get hb on it either. i have always believed that window was way too long. for hb i would not let it go more than 4-5 days. you can get 7 days out of it if you turn the heat off in your shop and let the temp drop to say 50 maybe a day after the epoxy was sprayed. at regular shop temps, every day you wait after the first 24hrs the adhesion will be less and less. at what point that becomes a problems depends on how thick the epoxy is applied and shop temp.
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Well damn....lol. I sprayed two full coats on it late Saturday afternoon and was hoping to wait now until this Friday night to shoot the high build, which would be 6 days. I work in my construction business all week and have to push the car on the rotisserie out to be able to spray in my home booth. Instead of sanding everything, which is a big job, I wonder if I scuffed it all with a red scotch brite pad on the 6th day if that would be enough? The shop is about 65 degrees, but I can turn it down to 60.
 
you can simply spray a super reduced coat of epoxy maybe 1hr prior to hb. mix it 1:1:1 and apply like you would an adhesion promoter. this method has always worked really good for me over the years if i was unsure if the epoxy was too cured. with that said if you turn the shop down to 60 then you'll probably be fine @ 6 days. 2k primers are a little less fussy about adhesion to epoxy. basecoat is what you really have to worry about.
 
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