how much retarder per quart of dope?

I am ordering the dope to finish up my vector and was wondering how much retarder i am going to need per quart of unthinned dope? Can anyone help me out? Thanks, BEN

LAST EDITED ON Jan-18-04 AT 09:14 PM (CDT)
 
Ben,

It sort of depends on the weather. When the humidity is very high (like here in Puget Sound pretty much all the time), I'd use about 5% to 8% by volume. Could use as much as 10% if the weather is really bad. The big thing to remember is that retarder can really stretch out the drying time.

Randy Powell

PS-I'm no expert. This just just waht I've done and had pretty good outcomes.

With the 85% to 90% humidity down here in Dixieland, I have gone as high as 25%, but usually only use 15% retarder. I also use a little more thinner. The drying time is stretched and the dope does level out more, but wait three days before doing any sanding. AND this is not over decals. A light dry coat of clear over them is needed and when you apply the clear with more than 5% retarder, avoid any heavy coating of the decals.

Hi Ben, Bob Smiley here.

I have sprayed three planes now with the Brodak dope system. I have found that trying to weigh out retarder-thinner by percentages usually does not work. If you are spraying you want the paint to spray out looking wet and shiny. The professional that painted my Lancair did not use a scale or measure out the thinner and retarder. He used his experience, trial and error. If it comes out dry then you are:
a. spraying too far away from the surface or using too much pressure.( use enough pressure to get the paint to flow on the part, not blast it on), or
b. the paint is too thick and needs more thinner (especially if it blobs or clogs up) (Sometimes if it sputters, you have moisture in your system and need to purge your compressor and get in line filters and traps to remove moisture from your air supply),or
c. if it dries too quickly and gets a film look add more retarder and/or thinner,

The retarder helps the paint to flow and level out and adds shine and smoothness to the finish by slowing down the drying time. Thinner is the medium to shoot it through the gun and it dries quite quickly thus you get a flash or clouding if not enough retarder is added. It is my understanding that there is a magic relationship between the proper mixture of dope, thinner and retarder coupled with the right distance from the surface and the proper amount of air mixing with the paint as it shoots through the air. How forgiving is this relationship; I do not know but you will know when you are "in the zone". Don't ask me what that is ( some type of mystical chemistry for some paint guru to explain). You have to find it out for yourself after sanding a couple of orange peel paint jobs etc. and making some changes in your technique.

Neat thing about runs in the paint usinglaquer. Let it dry and then sand them out if needed. It is light, especially the clear. Often times lacquer runs shrink up and no extra effort is needed. other times you can spray extra dope on the run area and run it off the painted part. (This will work if your paint is thinnedout properly.) I painted with highly thinned paint thus any mistakes were not monstrous or disastorous as related to weight. Case in point, my Don Stills Stuka weighs 31.4 oZ and only 5 0z of silkspan fillets, dope, color and trim.

Suggestion to reduce the risk of tail heavy planes. Paint control surfaces with the trailing edge up. That way the paint runs to the forward edge of all parts. Do the same for the plane. Paint it tail up. if there is any paint buildup it is towards the CG not the Tail.

Bob Smiley
a Lancair 360 builder/pilot trying to be a modeler.