Scratchbuilding the Dove part 6

FINISHING HULL MASTER SURFACES

USE OF ISOTHERMIC CURING FILLERS

Applying a smooth finish to the rough surface of the dense foam hull master halves started by filling the open cells of the carved and sanded surfaces with a Bondo like two-part filler. Evercoat produces two of my favorites: Spot-Lite is a fast curing yet easy to sand surfacer. Euro-Soft, on the other hand, cures a bit slower but assumes a much tougher surface after changing state to a solid.

Use of thermosetting Evercoat fillers and air-dry touch up putty to fill the rough surface of the masters.  Also arrayed around the master here are seen the various type of sanding tools I employed on this job.

Each of these fillers is suited for specific jobs. Both achieve a change of state from liquid (actually, a very thick syrup, if you will) to a solid  through a chemical heating of the material, initiated when a 'cream harder' is mixed with the filler. The internal heat (isothermic) causes the polyester molecules to link into long strands taking on the characteristic of a solid. Three things control the rate of this materials change of state: the ambient temperature, amount of material mixed, and the ratio between filler and hardener. It is wise to work only small amounts of  catalyzed filler at a time, particularly so with the fast setting Spot-Lite.

(Those large non-structural gaps between parts you kit assemblers are sometimes presented with can best be addressed with Spot-Lite  filler - not one of those god awful air-dry putties sold at the hobby store!)

With an open cell surface of large area, such as the two hull master halves I'm working here, I prefer to use Euro-Soft filler. Note in the photo that I have laid out the various types of sanding tools used to work the filler once it has cured hard on the surface of the model/master.

SANDING

Most sanding starts with #100 used wet. Yes, it makes a big mess, but the water acts to unclog the sandpaper, making it cut well throughout its use. The water, by carrying away the dust, also permits better control of the cut - you can see the uncluttered surface as its being abraded away by the sandpaper. After the  initial course sanding, I shift to #240 sandpaper and make a second cut on the Euro-Soft surface.

After working the Euro-Soft surface with sand paper (and after the model has been thoroughly dried of water) it is my practice to then brush the entire structure down (a disposable brush, like an 'acid-brush' is the tool of choice here) with a thin coat of Nitro-Stan 9001 air-dry lacquer touch-up putty. You can get this, along with most of the finishing fillers, putty, primer, and tools I'm describing here, at your local automotive refinishing supply store.

 USE OF AIR DRY TOUCH UP PUTTY

An air-dry putty, you have to lay the Nitro-Stan on thin. This type putty is suitable for addressing the small scratches and 'dings' that result from the gross filing and sanding done on the two-part filler used to seal the surface of the hull halves. Once the Nitro-Stan putty had dried hard, the entire surface of my DOVE hull halves were  wet sanded with #400 followed by #600. At that point the surfaces were smooth enough to proceed with the first coat of primer.

By the way: Get rid off your 'hobby' primers and putties. They're crap. Designed by  guy's who are much too worried about a litigation suite from your estate than to producing a consumable with solvents volatile enough to get the job done. Use the 'real stuff' and you'll never go back to that crummy 'Green Stuff' and other slop sold at the hobby shop. Once you start working with automotive grade contouring, filling, and priming systems, you'll never look back.

(Another thing: notice that I don't waste any  breath telling you about the dangers involved with these substances. Don't have to. Everything you buy has a list of warnings and recommended equipment to ware or use to prevent injury. It's like this, boy's and girl's:  if you're too dumb to practice shop safety and to read and follow the more than ample warnings provided with your tools and consumables, then your slow, bloody, and agonizing death is on your head).

I favor the use of DuPont's Fill 'N Sand 131S acrylic primer-surfacer.  This is the perfect primer for just about any type substrate.

PRIMING THE HULL MASTERS

The absolute best universal primer is  DuPont's gray 131S Fill 'n Sand acrylic primer-surfacer.

This stuff can be laid on thick as mud (where do you think 'Mr. Surfacer' comes from, anyway?) or thinned to a wash. When shot with a gun (don't brush on  this stuff!) it will not attack styrene or ABS plastic. I use it on everything: wood, paper, metal, plastic, GRP. EVERYTHING!

You don't have a spray-brush?

Get one!

The primed surface of the DOVE hull masters were inspected and flaws addressed with spot applications of Nitro-Stan Putty. Those few trouble spots were then wet sanded again and primed. The process repeated until a smooth, unblemished surface had  been achieved.

Though a high quality finish in primer is as far as we need to go with the finish of a master, it is the first MOST VITAL step in achieving an attractive paint job. Up to this point, the use of fillers, putty, and primers, as I have discussed here, are as applicable for that simple little ENTERPRISE kit of yours as it is for my type of work.

Remember, regardless of what the substrate of the model is (wood, paper, styrene, GRP, fossilized horse manure, glass, metal, whatever) it is the last coat of opaque paint that we are observing when we examine the finished model/kit. If you do the job of filling the imperfections of the substrate then an excellent finish can be achieved - no mater what is under all that paint

A poorly executed first attempt to fabricate the DOVE's cockpit structure.  Note that I built with a removable access hatch.  More on this attempt, and the more successful unit in later installments of the article.

COCKPIT MASTER

Oops I made one attempt to build a master of the DOVE's canopy, but it had to be discarded after I detected - way into its fabrication, wasting a day - a flaw. The picture illustrates just some of the documentation that went into the construction of this rather  involved shape.

The procedural sketch shows how I put two blanks together to form the piece - the central running seam between them providing the central datum line about which I laid out other measurements. Several of the following installment will outline, in excruciating detail, the many steps that went into the planning, construction, and finishing of a correct DOVE canopy intermittent master, tool, GRP canopy production master and the detailing of that piece.

Coming next... part 7