Krylon Grey Primer fouls the sandpaper?

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Tom

Tom

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I painted a rocket with Krylon "Color Master" Grey primer and let it dry overnight.

The next day I went to sand it down and it keeps gumming up the sandpaper as if it was not really dry. I let it dry another day and it still gums up the paper and does not really sand 'right'.

What am I doing wrong?
 
Tom said:
I painted a rocket with Krylon "Color Master" Grey primer and let it dry overnight.

The next day I went to sand it down and it keeps gumming up the sandpaper as if it was not really dry. I let it dry another day and it still gums up the paper and does not really sand 'right'.

What am I doing wrong?
Click to expand...
Using Krylon Grey Primer is probably the issue. Most of us use some type of automotive primers as they are sandable and fill better than the regular primers (which are meant really for already smooth surfaces and to give better adhesion for color coats). Krylon, Rustoleum, Duplicolor and some other brands are commonly used automotive primers for rocketry.
 
Just this past week I've used the Krylon grey primer you have on three cones for my son ... second set of three go round too ...lol

Three light coats instead of a couple of heavies ... hair dryer between coats
600 grit over sink with running water ... two or three stokes ... wash out , flex paper, wash out... re-wet and two or three strokes again....repeat

Paper loads up real quick so running water and kind of wringing out the paper as you go...did I say running water?

I actually prefer Rusto' paints and primers but my son "insisted" on this one color only Krylon has .... so now he has 6 all the same color ... don't ask! lol
 
Tom said:
Yes wet sanding would be a good solution, but not so good for paper body tubes :)
Click to expand...

Wet sanding works just fine on paper body tubes. The sandpaper is wet, not the tube. If the paint/primer was applied properly, there's no issues whatsoever. The paper need only be moist enough to prevent loading, and gets rinsed out often. Wipe the tube dry each time that you clean off the paper and you'll have zero problems. Also, don't sand through the primer layer, either.

The REAL issue is that usually only the automotive fill primers are suitable for sanding. The mass produced and marketed 'hobby' paints like krylon and rustoleum are meant for spray and pray and go hobby projects. Most normal humans just want to spray it and have done with it in one or two easy steps and coats. We're wanting perfect surfaces and demand a little more performance and perfection from our projects in general. Rattle cans are notorious for taking DAYS to cure enough to sand.

If you're wanting to sand, etc, then pick a product that's MOST suited to what you're wanting to do. Automotive primers are usually lacquer based, which go on smooth, flash off quick, and are fully compatible with any top coat. Krylon/Rusto are enamels, which go on smooth, take quite a while to actually finish drying, and are hard and smooth and glossy.
 
I used to use PlastiKote 466 spot filler/primer. Purchased a bunch back in 2015 but had to throw away 3 cans because the nozzles would clog. They changed the nozzle design from the "standard" nozzle on a stem. I never had a problem with the primer/filler before they changed the design. I now use Dupli-Color primer filler and tape the can to an old sawzall blade, insert it into the reciprocating saw, and shake it.
 
I got me a can of Rustoleum "All Purpose" sandible primer. We will see how that works out. It even came in off white

Great ide with the recip saw for mixing! Points for creativity!
 
I use the Rustoleum 2X sandable primer/filler and it clogs up the paper too if I don't wet sand. It doesn't have to be dripping wet to make a huge difference. Just don't sand thru the primer.

-Bob
 
I’ve had great success with SEM 42013 and U-Pol High #5 high build primers. Both paints dry-sand well if given a few days to dry. I will add that I keep the workshop at 65 degrees, and run a dehumidifier during cold rainy weather. When I sand, I only dry-sand to 600 grit prior to applying the first finish coat. The only issue I found was when using the U-Pol when the can was cool, ~45 degrees, in a workspace that was heated to around 72 degrees. Under those conditions the combination of pressure and temperature changes caused the paint to momentarily boil when it hit the surface, creating pinholes. Note to self - Warm up the paint can also...
 
Krylon Colormaster primer is not sandable primer so it's going to gum up sandpaper. For best results I recommend using sandable filler primer like Duplicolor and wetsand it with 400 or 600 grit sandpaper.
 
when are you guys going to learn?

Well after some experience, and after someone more knowledgeable teaches me.

I still haven't had a chance to try the Rustolium sandable. It has been raining ever since. I will wait till the RH is a little less than 85% :D
 
Tom said:
when are you guys going to learn?

Well after some experience, and after someone more knowledgeable teaches me.

I still haven't had a chance to try the Rustolium sandable. It has been raining ever since. I will wait till the RH is a little less than 85% :D
Click to expand...

Just get some Duplicolor - My thoughts are this, if you spend so much time carefully building your rocket, why skimp on the primer and paint. The primer is the bomb and sands like butter. Yes its almost $7 a can, but there is a reason. Also use it sparingly. Use the CWF or SPG to fill all the imperfections and use the primer as just a final fill and finish process. There's really no need to put super heavy coats on the project you are working on, because you are going to sand most of it off at some point. Also if you are working on the fin can area or nose cone, just spray that particular area. Less waste.
 
It also matters what kind of sandpaper. I've had the best results avoiding clogging with 3M's "Sandblaster" sandpaper. It is clog-resistant.

3460623


Also, I've switched over to using Rustoleum's "2X" line of paints, both for primers and regular colors including white.

I WILL say I never use anything but white primer unless the model is going to be painted darker than "gray". White top coat over gray primer takes too much white paint to get a truly bright white finish, as white paints are NOT as opaque as you'd expect, some degree of the gray shows thru. Worst-ever is black undercoat with white over it, yeesh. Go from brighter to darker, never dark to brighter.

Oh, one more thing. 24 hours is NOT that long for a primer to dry. Best to do a coat a day, and let it dry for 2-3 days after the last coat (some say let it dry till you can't smell the paint anymore, at all). This is part of why I do not do super paint jobs on most of my models, only mostly for scale contest-type models that will be judged.
 
Last edited:
my rule is if you can still smell the paint it is too early to sand. And this is with pressing my nose right up to the rocket
 
Paint clogs sand paper, if not wet sanded or the sandpaper cleaned regularly.
The friction of sanding heats the paint and makes it clog the paper.
the cures are, of course, wet sand but add just a tiny bit of Dawn dish soap to the water and check the paper often rinsing it when it appears to be building up with paint.
If you want to dry sand, sand slowly and check the paper often. remember friction is heat which adheres the paint to the sandpaper. Clean the sand paper by picking off the clogs with your fingernail of use a wire brush to clean the paper. Stainless steel wire brushes work best. Like cleaning a metal file of chips, same concept. Learned that in Metal Shop 10th grade.
 
I take a more telaxed approach and get good results. Not prize winning, but much better than just passing the 30 foot test; it's quite good up close. When I take my time and take care, which I don't always.

First, I've never used filler-primer or used primer as filler. I use filler. Fill-sand-fill-sand until I'm happy. Sanding is with Norton 3X dry. I clean clumps with a finger nail (there aren't many with the filler) and dust by beating the paper against the workbench or my thigh. I've only found the Norton up to 400 grit, so if I get so obsessive as to want 600 then I have to use a different brand.

Then Rusto 2X, usually in the primary finished color directly. Coat lightly. If that leaves bare patches then respray in about a half hour; the can directions say to recoat either within an hour or after 24.

Let the paint dry at least 36 hours in comfortable conditions. I really don't like humid weather, so if I'm comfortable then so is the paint.

Sand if needed with the same method and materials as when sanding the filler, and respray. If the paper is developing lots of clumps to pick out then put the rocket down for another day.l Repeat until happy, which has rarely taken more than three coats, and more often only two.

Take your time, relax, take your time, check your progress often, and take your time. It doesn't meed to be rocket science.
 
Thanks all good advice and ideas!

I got a chance to paint the primer on the Nike-X yesterday. Today I set it out in the warm dry day sun for a couple of hours turning it on occasion.

It actually worked quite well, for a change I saw some 'sawdust' and one piece of ordinary wet/dry 400 grit did most of the airframe. Decent gloss. I will post pics later.
 
georgegassaway said:
It also matters what kind of sandpaper. I've had the best results avoiding clogging with 3M's "Sandblaster" sandpaper. It is clog-resistant.

3460623


Also, I've switched over to using Rustoleum's "2X" line of paints, both for primers and regular colors including white.

I WILL say I never use anything but white primer unless the model is going to be painted darker than "gray". White top coat over gray primer takes too much white paint to get a truly bright white finish, as white paints are NOT as opaque as you'd expect, some degree of the gray shows thru. Worst-ever is black undercoat with white over it, yeesh. Go from brighter to darker, never dark to brighter.

Oh, one more thing. 24 hours is NOT that long for a primer to dry. Best to do a coat a day, and let it dry for 2-3 days after the last coat (some say let it dry till you can't smell the paint anymore, at all). This is part of why I do not do super paint jobs on most of my models, only mostly for scale contest-type models that will be judged.
Click to expand...

How does this compare to the blue and red versions?
 
The Kyrlon you get at Small*Warts or other mass-crap stores has been reformulated for "EPA" BS. If you want the real deal then you need to get this stuff, it's the real deal like Krylon used to be 35 years ago. Actual Lacquer.
https://www.fullsource.com/krylon-industrial-and-mro-aerosol-paint/

If you prep and sand BEFORE primer you will get the best results. For wood I use sanding sealer made from Nitrocellulose + MEK + Talc. Mix procedure Fill a polyethylene bottle (candy making bottle for example) with loose dried NC, fill with MEK leaving a little room for stirring. Let sit for a day. It will have a thick gel in the bottom, stir it up with a bamboo stick or wood dowel. Let sit for another day. It takes a while for it to totally dissolve. Proper consistency is like thin pancake syrup, and it will be crystal clear. If it is thick like honey it needs more MEK, If too thin add a little more Nitrocellulose. To make some sealer pour out some into a plastic deli cup. must be plastic type 5 PP. add about 20-25% by volume talc, mix it in and use. Do not add talc to the stock bottle, it will just settle out. This stuff even if you get some brush streaks and runs, it sands very well and takes paint very well. You can get Nitrocellulose from Firefox FX (<$20 for 1 LB) Enough for maybe a gallon or more of sealer. If you want to try out a smaller batch get a couple packs of decent quality white ping pong balls. They are nitrocellulose. Do not get the cheap dollar store ones. Bust them up and dissolve in MEK (Acetone works too, but evaporates a bit too fast.) I have not tried the "New" MEK substitute yet, I got the real deal from an industrial supply co. as the good stuff is not available in any main-stream hardware store anymore, unless they got unsold stock left. I tried Home Depot, Lowe's, Ace, True Value and an independent store, none have it.
DO NOT USE this stuff on anything styrene or ABS, it will attack the surface.
 
Well I finished the Nike-X and... launched it this morning. Did not get a shot of it first :(

It flew beautifully straight up on a B6-3, ejection just after apogee a very successful flight... except!

You guessed it, landed on the roof of the only building for miles. A bathroom building. It had a sloped roof but the shrouds evidently hung up on a screw head. I tried throwing some water bottles at it but finally gave up. It's still up there!
 
jqavins said:
First, I've never used filler-primer...
Click to expand...
On reflection, I take it back, sort of. The filler I've been using for a while is A DAP foamed spackle. I recently switched to a 3M product that's a combination of that and primer. It goes on smoother and, yes, makes painting later easier. Still, it goes on like spackle, i.e. filler, not being applied as a liquid.
 
Tom said:
Well I finished the Nike-X and... launched it this morning. Did not get a shot of it first :(

It flew beautifully straight up on a B6-3, ejection just after apogee a very successful flight... except!

You guessed it, landed on the roof of the only building for miles. A bathroom building. It had a sloped roof but the shrouds evidently hung up on a screw head. I tried throwing some water bottles at it but finally gave up. It's still up there!
Click to expand...

Bummer! Unfortunately, that is the way this hobby goes. The Rocket Gods must be satisfied. Some times it's a tree, a building or a CATO, but rest assured, they will get their share. Always take a photo.....
Is the field close enough you can go back with a ladder and a fishing pole? (I would never recommend climbing on a roof, you do so at your own risk)
 
beeblebrox said:
The Kyrlon you get at Small*Warts or other mass-crap stores has been reformulated for "EPA" BS. If you want the real deal then you need to get this stuff, it's the real deal like Krylon used to be 35 years ago. Actual Lacquer.
https://www.fullsource.com/krylon-industrial-and-mro-aerosol-paint/

If you prep and sand BEFORE primer you will get the best results. For wood I use sanding sealer made from Nitrocellulose + MEK + Talc. Mix procedure Fill a polyethylene bottle (candy making bottle for example) with loose dried NC, fill with MEK leaving a little room for stirring. Let sit for a day. It will have a thick gel in the bottom, stir it up with a bamboo stick or wood dowel. Let sit for another day. It takes a while for it to totally dissolve. Proper consistency is like thin pancake syrup, and it will be crystal clear. If it is thick like honey it needs more MEK, If too thin add a little more Nitrocellulose. To make some sealer pour out some into a plastic deli cup. must be plastic type 5 PP. add about 20-25% by volume talc, mix it in and use. Do not add talc to the stock bottle, it will just settle out. This stuff even if you get some brush streaks and runs, it sands very well and takes paint very well. You can get Nitrocellulose from Firefox FX (<$20 for 1 LB) Enough for maybe a gallon or more of sealer. If you want to try out a smaller batch get a couple packs of decent quality white ping pong balls. They are nitrocellulose. Do not get the cheap dollar store ones. Bust them up and dissolve in MEK (Acetone works too, but evaporates a bit too fast.) I have not tried the "New" MEK substitute yet, I got the real deal from an industrial supply co. as the good stuff is not available in any main-stream hardware store anymore, unless they got unsold stock left. I tried Home Depot, Lowe's, Ace, True Value and an independent store, none have it.
DO NOT USE this stuff on anything styrene or ABS, it will attack the surface.
Click to expand...

Most hardware stores have PVC cleaner and PVC primer which are both mostly MEK.
 

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