Almost perfect but waves(?) and nibs, nibs, nibs!!!

Chris Martin

Promoted Users
Hi all,

Making some progress in my airplane painting saga. I have been able to go from awfully orange peel application to now fairly smooth spray (Single Stage, Iwata Kiwamy4, 1.4 tip). As Barry told me when I talked to him it did take a while getting used to this compliant paints and new style of spraying compared to last time I sprayed something 24 years ago! but getting there.

The two problems I still have to solve are what I think you guys call "Urethane Waves" (but not sure. It is not orange peel but small waviness in the otherwise almost glass looking finish) and nibs. Last test panel I sprayed the SS reduced to 25% and will try again with 4:1:1 (20%) and no reduction to see if waves get better. Gun pressure is steady at 29-30 psi. The other possibility is that I am asking too much of the SS and what I have today is good enough (I can be a bit of a perfectiones at times, although I am changing my expectations as I age).

The nibs are driving me crazy though and maybe I can get some ideas from the experts. I spent two months restoring a "moveable" spray booth that was given to me and I am disappointed about the large amount of nibs I am getting. I include a picture of my finished DIY booth. It is nice, has two very good fans but not stellar flow. Intake filters are just 4 plain AC ones (probably too restrictive but I don't get overspray cloud). And I put as much lighting as my pocket could tolerate (my 60 yr old eyes are not as good as they used to).

The problem is that my test panel ends up with too many nibs for the effort put. I have tried a deVilbiss filter at the gun and same. I clean the panel with blue paper obtained from auto paint supply store and SPI waterborne W&G. Then Blue Surgical tack rag. Dust with air. And first coat is always full of nibs. I don't think the second coat is the same. I use an electric blower to try to dust off the booth before painting. I turn off the fans as soon as I finish the coat. Nothing seems to work. The nobs are there as soon as I spray the first coat on.

My suspicion is that the booth is made of wood covered with plastic on the outside. The booth was used on multiple projects in the past. I cleaned the wood as well as I could with damp rags but I suspect old overspray in the wood may be finding its way to my test panel. I could varnish the exposed wood to seal the old overspray but here we go with more work on this one time use booth. The booth is not totally sealed but I am surprised about the large amount of nibs even if some dust finds it's way in.

I know there is probably not much I can do other than finding the source of the contamination but maybe I can get a few good pointers here to try.

Chris
 

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Can you explain how your system works? Are you pushing air into the booth or pulling air on the exhaust side? How is the air filtered going in and from where? In the picture it looks like you have the exhaust filters on one end, low close to the floor and a pleated intake filter up high on the left of the picture near the opposite end. If you are pushing on the intake end with significant velocity through a small filter that could be causing some turbulence in the booth.
 
Hi, Thanks for the reply.

Fans are exhaust and bottom as you see in the picture. With overspray arrestors (hopeful that they do something). 4 pleated filters up high at other end (entrance). One on each side (you can see one) and one on each door for a total of four.

I have a wind speed meter I could use to measure the airflow at each filter. They are quite restrictive. If I open the doors with the fans running you can feel a good amount of air coming in.

I could measure the pressure inside.

Quite frustrating since I sprayed SPI epoxy two years ago in this same booth and all (or almost) perfectly nib free. Maybe SS is a nib magnet.

Chris
 
Unless it is the plastic that is treated to hold/bond paint such as used in painters masking plastic the air movement and thus plastic movement is probably knocking off pieces from previous sprays
 
I thought about static. I am sure it is bad in there. but this is Florida so the humidity probably helps that. BTW, the parts are fiberglass, which makes it hard to ground but I could try.

The pressure inside and the restrictive intake filters keep the plastic tight. And I just replaced all the plastic with new so it is fairly clean.

One thing I am doing that I think is in the wrong order is I clean with W&G and let dry. Then tack, then I adjust the gun on that panel you see in the floor on the right side of the picture. I am thinking now that I could be picking up dust when I do that that goes right into the test panel. Next time I will try leaving tack and blow air on part for last right before spraying (duh!).

I am also going to varnish the 2x2s that hold the parts (before I go ahead and varnish all the wood in desperation but hopefully don't need to do that).
 
One thing I need to try is that my test panel is a flat rectangle, taped to a flat wood board covered with plastic to keep clean. but I don't dust and tack that surface. Maybe when i start spraying I get the junk in that panel transferred to the test panel. I need to be more anal but I don't remember being this picky in previous projects.
 
No pics of the nibs but will take one as soon as I can.

I wear a suit and hood when I spray the real parts (can't say it's fresh but I don't do this for a living so it's low use). For the test panel no. Just my jeans and shirt. I do use a fresh air respirator though.

Chris
 
No pics of the nibs but will take one as soon as I can.

I wear a suit and hood when I spray the real parts (can't say it's fresh but I don't do this for a living so it's low use). For the test panel no. Just my jeans and shirt. I do use a fresh air respirator though.

Chris
You'd be surprised the difference a paint suit will make.
If you think about household dust that accumulates so quickly, it is almost completely comprised of clothing fiber and dead skin.
 
No pics of the nibs but will take one as soon as I can.

I wear a suit and hood when I spray the real parts (can't say it's fresh but I don't do this for a living so it's low use). For the test panel no. Just my jeans and shirt. I do use a fresh air respirator though.

Chris
Were you wearing the paint suit when you shot the epoxy with no nibs? Seems like an important data point.
 
just an fyi. a crossflow booth should move air through the booth from 75-125 feet per minute. not at the filters. basically in the middle of the booth. that booth wants to be a big tube moving air at that speed. not saying thats a nib problem. you just mentioned you had an air speed meter and were going to measure at the filters so thought i would throw that in there. if the booth is clean then 90% of all dust nibs come from the painter and or hose.
 
Dirtiest paint job I ever did was when I lined all my walls and ceiling in plastic- wrong plastic! Everything on the plastic from the base coat overspray was “sucked” onto the clear coat from static- never used plastic again
 
This has me wondering if I may be in for some headaches as well. My garage wont work as its full and also full of dust from being a woodshop. I don't want to spray outside for the known reasons. I bought this and have just about finished setting it up and am planning to use for sealer base and clear but I have to split my sessions into body, then fenders and hood. Am I going to run into issues as well if I am just doing this one car?. Nothing has ever been sprayed in it.


I will be pulling air from one side with a fan and have 3 16x25 pleated filters on the opposite side for intake.
 
The plastic sheet issue is a good consideration. However, I spent several weeks replacing all the plastic with the wrong stuff since I didn't think about this which I am learning now. if it becomes an issue so be it :rolleyes:
 
The plastic sheet issue is a good consideration. However, I spent several weeks replacing all the plastic with the wrong stuff since I didn't think about this which I am learning now. if it becomes an issue so be it :rolleyes:
Semi funny story. I've been using the Norton auto painting plastic for a few years now. Great stuff. It is clearly marked on one side "Paint This Side" I've been diligent about checking that, but somehow on one wheel opening I got it backwards.
Sprayed base just fine. Next day was tacking off for clear and bumped the plastic. Massive shower of paint flakes everywhere.
Whoops! Luckily I found it before spraying the clear, that would have been a disaster.
 
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