Some stories and questions about using One Shot or other enamels. I have over the past year painted, second coated, and repainted older panels with some One Shot enamels to find lack of adhesion between coats, even when sanded and cleaned properly. I just shot a navy over 400 grit sanded and cleaned with a damp cloth surface.(waited/not a water problem) I did this project on a job that was painted about a year ago. After drying 3 days with 5% hardener and recommended thinner, my paint mask pulls the coats cleanly apart.(doesn't appear to be uncured, just don's adhere well) I have had this problem with coats delaminating 4 months after painting. The coats shot both 30 minutes and 2 days apart (sanded ). It doesn't always happen, but does way to often. It seems that it's characteristics are way to fragile. Another happening was when,I used penetrol in oneshot for a flow enhanser. It seemed to paint out ok, but seperated in the cure on the panel and the gloss peeled off almost like a perfectly clear film to leave a dry flat look on the paint. This after about 6 months of use outdoors. I am getting good looking finishes that don't seem to want to bond together. How does anyone get a hand lettering job to stay on a slick panel surface, if I can't get like coats to bond on sanded and cleaned surfaces??? Jack
p.s. a lot of the probs have been over maroon. I read when it is a drying pain. This last event was over maroon a year old though
Posted by timi NC (Member # 576) on :
Jack,...you don't say what kind of primer you are useing or thinners to spray with,both of which can be determining factors on subsequent coats.Another thing is prep solvents, water won't do the job. Are you painting on mdo or what? Have you tried tack cloths? Do you use any sort of deglossing prep solvent on old coats? A good trick is to scuff till the entire surface is dull on old cured surfaces then prep with prep solvent finally going over the entire suface with a tack cloth before any spraying subsequent coats. Ultimately there are dozens of reasons a sprayed coat of paint won't adhere with paint mask that can cause you problems. Alot of the time it is just too strong a mask adhesive on green(not totally cured) paint that is the culprit.Often as not it can take several days before paint such as one shot cures totally in cold or damp weather.We used to have the same problems with tape on the top & bottom of hand lettered copy back in the days before paint mask.
Posted by Kent Smith (Member # 251) on :
The reducer used for spray appication is deffinately a key factor. The alkyd resin is easily "burned" by hot solvents which weakens or eliminates the bonding altogether. Also even with the hardener added, the cure time of alkyd enamels remains 14 days minimum. If hardener was added to the first coats of enamel then the subsequent coats will not adhere well enough for "tape test" even when scuffed. An enamel which is applied at about 2 mils thick will adhere better than thin coats as it takes more paint to create a cured film. Often spray finishes are little more that 1/2 mil to 1 mil which does not allow for enough resin to be on the surface to migrate into a cured film.
Posted by bronzeo (Member # 1408) on :
The primers are HDU filler primer and Dibond baked enamel scuffed. The one with the most problem is a 1 year old, resanded to 400 Oneshot panel on HDU..... Do you use a primer between the FSC88WB and enamel?
My mix is 5% or less hardener (recommended 10% max) and recommended only low temp reduced by Oneshot............Kent this is a hot reducer, and the only one recommended for use with OS hardner. There was no hardner in the bottom coat, that was applied originally with a brush.
I have tried tack cloths and find that they leave residue from the tack. I can see exactly where I wiped when paint is sprayed on the first coat. .... Timi, what type of prep thinner would you recommend for surface cleaning?
I have to reduce quite a bit to shoot a flat coat. I usually only reduce minimally for an HVLP, but that is a lot of reducer. No real way around that is there?
The peel-offs are not large, and seem well cured. Two of the 3 recent problems I have had have been with or over maroon. I have heard that it takes days for this stuff to dry. This is a repeat but why would the maroon with penetrol (well stirred) seperate and leave the clear finish on the surface to be peeling off like a clearcoat. Do you think this could be caused by a real slow drying and allowing a seperation of the resins and the pigments? I think I will start mixing my own maroon colors and toss my premixed color that I have to alter anyway.
I also had a recent incident where I use a phosphoric acid wash prep on a rust old sign (that was recommended as a paint prep even for autos) It says to paint right over it. Black Oneshot would not dry on it at all. I took it off with putty knife and thinner a week later. I ended up using a lot of Japan drier to get it to even start drying the second time. I would think that a drop of enamel would set up floating in a pan of water.
I'm not badmouthing the Oneshot, and it is nearly all that I use, but what is it with some of these weird characteristics? Thanks for your advice, Jack
[ March 30, 2002, 07:17 AM: Message edited by: bronzeo ]
Posted by warpaint (Member # 2395) on :
Jack, I have not tried this with One-Shot, but it does work well with automotive paints(which I have used with great success when painting door jambs and other hard to sand area) is DuPont's adhesivion promoter. I think it is product no.222. It "softens" the paint so the top coat can bite into it. It might be worth looking into.If I have givien you the wrong product no. let me know and I'll lokk to see exactly what it is and get back to you.
