Polyester Primer

D

Dwg86

Anyone have experience with polyester primer (slick sand)? I’m working on a hood , and trying to get it straight. I’ve had someone tell me not to use. They said it was to brittle and would crack out. I’m a little concerned about using to much 2k primer. I’ve though about putting filler on the whole hood, but I’m. It sure how sanding would go. If I press too hard the moves in. It’s not oil canning, there just are some places where there isn’t any support.
 
how much filling are we talking here? polyester primer is used every day and it works great but there are limits for any product. i would normally do 4 good coats then block it all down leaving it fairly thin. if you need to fill some good size dings that are 1/16"-1/8" then that should be done with regular filler. polyester primer should go on once you have gotten the body as close as you possible can with filler first. polyprimer should be applied to really fine tune the surface, nothing more.
 
Less than a 1/16. I had a guy at a body shop say not to use it.
I don’t think it’s enough to skim the whole hood in filler, but I think it’s more that can be filled with 2k primer. So I though about slick sand or feather fill. I’ve just never used it.
 
Its probably the pressure you are putting on the block. I know you said it moves easy, but to have a 1/16" dip, you won't even see it move. Some hoods are very soft.
 
With some hoods you may want to start with a coarser than normal sandpaper at a much lighter pressure, otherwise you could end up starting over more than once on chasing out dips. How you sand can be as important as what you sand.
Also may be possible on some older hoods to wipe down the inside & reapply a urethane caulk between the steel inner support & upper surface to stiffen it somewhat where old adhesives have worn out.
 
Can I apply polyester primer on top of SPI epoxy within the 7 day window, or do I need to sand the SPI epoxy?
 
I think polyester primer is fine for what you are doing. I use it quite a bit. Friend of mine calls it bodyman in a can. LOL....

My personal favorite is Z-Chrome Rust Defender.

Don
 
Thanks for all the info. My hood has some minor imperfections (less than a 1/16 inch). But when I sand the hood it dips in pretty easy in the center.
I think I’ll try the polyester primer. I’ll grab some slick sand.
 
I saw on another forum someone promoting Duratec Poly Primer. It appears to be mainly for use with molds and I couldn't find where it was stated for use on automotive applications. Anyone heard of it?
 
yeah duratec make alot of polyester primers and other products for the fiberglass and composites industry. they make very good stuff. i had about a dozen gallons given to me some years back. the problem with it is, its really hard and sands like a rock. when i say its hard i mean really hard. nothing like what we are used to in the autobody world. you will be block sanding until your arms fall off lol. i used it on one automotive project and i swore never again. i ended up using the stuff to coat the plywood tops on my work tables in the shop. unless its something you can use a da on then dont use it.
 
Dwg86 said:
Thanks for all the info. My hood has some minor imperfections (less than a 1/16 inch). But when I sand the hood it dips in pretty easy in the center.
I think I’ll try the polyester primer. I’ll grab some slick sand.
Click to expand...
The harder it is to sand the more pressure you will use, and there may be plenty of material on there already, since you may have been sanding more out of the center of the hood.
 
I just checked the support on the center of the hood and it’s not touching the sheet metal. Does anyone know what to put in there? If I close up the gap it will help support the sheet metal, and I won’t have as much of a problem with the hood while I sand.
 
I tried to get a picture but it didn’t come out so good. It’s about 1/8 inch.
 

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I see Rust defender & Evercoat superbuild mentioned. What's the favorite/best ???
Haven't used any in awhile. I think the last I tried was Feather fill G2, it was alright.
Could have used some last week on a job, would have saved some time.
 
I figured you might find a spot that could benefit from some urethane caulk. I didn't mention a brand because some of the products I have access to at my day job are sold at commercial building industry supply places. Commercial caulks are far different now than home crap most are used to seeing. One we recently started using, Dymonic 100 is similar to windshield urethane in strength. I have used actual windshield urethane caulk for similar use before. You may get this much cheaper from a glass shop than the 20 something bucks I've seen it at in auto parts stores. Anything I've ever used seemed way better than the cheap crap factories used years ago.
You just want some flexibility along with strength. Not sure what products the auto paint stores may have, I've always used what I have available if possible. You could even use the orange fire retardant spray foams to stiffen between braces & metal, trim back after a few hours & run a seam over it. I have the professional guns for the large cans, which are controllable & tightening the flow knob will keep unused portion good for months.

Sanding hoods flat, or to the proper curvatures should I say, is one of the most difficult areas in some cases to bodywork to perfection. If you can easily get some more support from the inner structure, it will save you some grief, particularly on a large hood without many defined body lines.
By the way, what hood are you working on? More details as to what you're working on can improve what answers you get on a forum. Sometimes the best answer you get may not be exactly what you asked for.
 
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