Originally Posted by 69 widetrack
Yes if it's a 2 part putty, If it's use straight out of the container that means it's a lacquer putty, very prone to shrinking after solvents hit it. If the cracks are extremely fine you could get away with the lacquer putty but again that technology dates back to Henry Ford. I would, sand the area with 180, squeeze the 2 part glaze into the cracks, and block them out, re prime, block and paint. Those cracks are usually in the paint, if the bumper was deteriorating it would look like a web, not straight lines. Make sure you get the glaze right into the cracks.
When fixing cracks in bumper covers be absolutly sure to use a wax & grease remover a few times and blow the excess out of the cracks with an air bolwer before doing anything,wax gets caught in those cracks and they will reapear later on as the filler looses adheasion maybe a couple weeks...two part putty like ez sand will work well but break if the bumper hits something ,theres another one called flexible putty made for bumpers ...What I would do is prep the bumper for epoxy and really lay it down on the cracks so it'll flow down into them and fill them, then do my filler work with the flexible puttyand prime again...Putty seems to just sit on top and not really fill the cracks...epoxy primer is the most flexible primer out there....
Unfortunately your using Sumit materials which I know nothing about with the exception of they target DIY's just like duplicolor and Eastwood does so I have little faith in it ,even though summit may or may not be good stuff I dont know what it can do BUT normaly with Spi I'll start blocking (after priming the metal) with dry block with180 finding all dings and imperfections then doing the filler work and using a few more coats of epoxy I'll then wet block with 400theres really no need for any build prime rspi sands easy and builds...2k or build primer tends to chip easilybut after making the (epoxy sandwitch) Thats when you would want to use the build primer if thats what you want to use