stunthanger.com
Building Tips and technical articles. => Paint and finishing => Topic started by: Paul Taylor on January 21, 2014, 09:39:19 AM
-
I'm asking this question to try and find an answer for my friend. He is not a computer person.
He has painted a plane using certified dope. He said he made real sure the base coat of white paint was clean. Hey put on a mask and painted the color. When removing the mask large patches came up. He is ready to throw the plane away but just set it aside for now.
He has painted several planes in the past few years. First time this has been a real problem.
I thought maybe old dope but he said less then a year old.
Thoughts?
-
Depends on how the mask was pulled off. Almost have to pull it back on it self. Some guys use heat to remove masks on paint jobs.
-
Not enough thinner
-
Did he "scuff" the doped surface before he applied the paint?
-
Its all about getting good adhesion between the various paint layers and using low tack masking materials. Sparky's suggestion about more thinner is probably one of the most common mistakes that leads to a dry coat with poor adhesion. Heating masking when removing can't hurt.
-
Allen I never have dry adhesion. It always has enough thinner to chemically bond to the next coat. Dopes are chemical bond and enamels are mechanical bond.
-
I usually start out with an eyeball mix of about 50:50 thinner for most colors, and will sometimes still add more thinner. That's using Brodak dope and I've yet to have a problem with adhesion.
-
Allen I never have dry adhesion. It always has enough thinner to chemically bond to the next coat. Dopes are chemical bond and enamels are mechanical bond.
Sparky is correct. I have had similar problems when I don't use enough thinner. I had to do a lot of touch ups on my Cutlass because I didn't thin the blue enough. The paint will not make a chemical bond if there is enough thinner.
Derek
-
what you guys are saying is pretty much correct,,
however laucquer does not make a chemical bond , not technically
what it does is reflow the undercoats
a chemical bond is what occurs with urethanes,,
if you spray to dry, or with not enough thinner, or to high of temp, the fresh coat will not melt into the previous coats
that is how lacquer bonds, unlike enamels, or urethanes,, as you spray dope, it needs to have enough thinner( and slow enough thinner) to be able to soften the undercoats
-
what you guys are saying is pretty much correct,,
however laucquer does not make a chemical bond , not technically
what it does is reflow the undercoats
a chemical bond is what occurs with urethanes,,
if you spray to dry, or with not enough thinner, or to high of temp, the fresh coat will not melt into the previous coats
that is how lacquer bonds, unlike enamels, or urethanes,, as you spray dope, it needs to have enough thinner( and slow enough thinner) to be able to soften the undercoats
Thanks mark, you da man! 8)
Derek
-
If the thinner is dissolving, not melting the undercoat, that is a chemical reaction, albeit a slow one. The end result is a melding or mechanical bond, created by a chemical reaction.
Either way, use more thinner and under some circumstances a tad of retarder. D>K
no a chemical reaction is one in which the final states of the original chemicals are not the same as they were originally, and cannot be returned to their original state,,
a mechanical bond is one where there is nothing except the "bite" of the new layer into the old,, as in soaking into pores or scratches,,
Lacquer is neither,, it does not form layers ( when properly applied),, every layer adds to the thickness, but it is in fact, when properly applied,, part of the original layer,, the only way you can peel a layer of color off is if you did not apply it correctly,, that being, you sprayed it to dry, or not enough thinner, or the WRONG thinner,,
now think back to all the times I preach about systems, and using the thinner designed for the product,, you will start to understand my continued repeating of this,, you HAVE to have enough thinner in the material as it lays on the preceding layer to melt in, burn in, flow together, however you want to say it,
bottom line,, if you peel the color off the substrate when you are using lacquer, its because you did not spray the layer that peeled properly
-
Phil Granderson mentions in his article on finishing in "Flying Lines" to spray a coat of clear thinned 80% over the base coat before applying tape to start masking. While I have not tried this, I will on my current legacy build over the white base and give it a go.
I agree on the lack of thinner as RS says.
Here is the link to that article; http://flyinglines.org/ptg.finishing.html
-
Thanks Rob,
Here is some additional info which may help others reduce or avoid this problem.
There is quite a difference between Certified and Brodak or Randolph clear. Certified uses an ingredient to plasticize the clear. Not sure what it is. It takes longer for it to complete dry and when it has dried it is softer than Brodak or Randolph. For that reason I stopped using Certified as a prep or an undercoat.
The final step in preparation for color is very important and will help prevent your base coat from coming off when you remove the masking tape. Clean the entire airplane with Original Windex at least two times. Thin some clear dope 80% and spray on a quick wet coat. The purpose is to lock down everything before color. Don't sand this coat of clear. Do not skip this last thin coat of clear or you could have a mess when you remove the masking tape during the trim. Do this before you spray on a blocking coat (ie. gray) and your base color.
Finally, as others have said thin your blocking coat and base color more.
Oh yeah, Paul, tell your friend NO ONE gets those super finishing with first going through some grief, so hang in there!