Moving to low VOC

Well the time has come. I have to do something to reduce the "friction" when working on rockets in/around the house. My wife, after experiencing full blown Lyme's Disease a couple years back, now has extreme sensitivity to odors, especially those related to the typical volatile solvents we utilize in finish work of our rockets. The result is I have been evaluating options that reduce VOC emissions and, in turn, tend to significantly reduce outgassing odors. First, I want to say this is not a scientific and/or exhaustive search, it is just a quick evaluation and determination based on past experiences with products and some initial testing on a couple of builds. I have used a wide variety laminate and finish systems both branded and generic. My current "go to" combo is as follows:

1. US Composites 635 for lamination
2. SuperFil (from PolyFiber) for major/first fill
3. Rust-Oleum Automotive Filler-Primer spray
4. Bondo Spot Putty for minor/subsequent fill rounds
5. Rust-Oleum 2X White Primer as base coat
6. Rust-Oleum 2X, Rust-Oleum Metallic or Dupli-Color auto for final coat
7. Future Finish acrylic clear coat

US Composites and SuperFil, as most non-polyester epoxy resins/hardeners, are fairly benign with respect to odor/outgassing. In addition, although there are issues with final coats, unless there are problems with the application, the time spent on final coat is minimal and can be confined to one 24 hour period. Also on the clear coat, long-ago I moved away from Rust-Oleum enamel clear spray and also stopped applying Future with an airbrush. So now application of the clear coat is only via foam brushing with only minimal, and a somewhat pleasant odor coming from the Future. The real issue with successive/extended exposure are the rounds of Primer and Spot Putty applications (steps 3 thru 5 above). My priority is to replace these first and then later to retire spray cans all together by potentially going to a water-based airbrush system for final coat(s).

I have been experimenting with the following with fairly good results. My low-VOC choice for primer is now a brush on Rust-Oleum product under the sub-brand Zinsser, called Bondz. This is specially formulated with high solids and some type of acrylic resin/bonding agent to provide superior adhesion. In fact, it has worked so well, I have stopped using Dupli-Color Adhesion Promoter (another extreme odor product) on my nosecones. I usually do two application rounds with a chip brush to a FG laminate base. I then sand to near full exposure and do one more "spot" application to fill more stubborn weave areas. In the past I had tried Kilz products--this is far better and more like a two-part primer such as PolyFiber EP-420. The other advantage to Bondz is that it bright white, so I no longer do a base coat and have been able to achieve good results with flat, gloss, and metallic final coats after final primer sanding with 320 grit paper. But above all, the Bondz product has very little, to no odor.

The other "nut to crack" is my reliance on Bondo Spot Putty. As most know, the odor from this product is extremely strong and pungent. It is also extremely convenient. No mixing and great application compatibility with Rust-Oleum automotive products for fixing minor imperfections. It is also easy to sand/feather making sanding rounds reasonably fast and successful. The one drawback is that it is soft and can nick and be damaged fairly easy if hit in the right spot. There is a wonderful product on the market that fits all the requirements in this area and, in fact, is a bridge between PolyFiber SuperFil and Bondo Spot Putty, it is AeroPoxy Light. This product even more important for this application, is zero VOC. Saying that, and although I have trialed it, I'm not quite ready to jump completely to AeroPoxy Light due to the cost especially considering the many successive final rounds of filler/sanding. So my current plan is to retire both the PolyFiber SuperFil and the Bondo Spot Putty by using US Composites 635 with Fast Hardener along with their SM Fairing Filler and Q-cells (micro-balloons). This combination works extremely well and reasonably mimics AeroPoxy Light at a much lower cost. Also, given the epoxy base, it is more durable than the Bondo Spot Putty. The downside is that you use a lot of filler. Ratios here are 1:2 epoxy vs filler by volume (and for the 2-parts I use an equal amount of SM Fairing and micro-balloons). The saving grace is that the filler material is cheap averaging ~$10 for 5 quarts of product.

OK, so that's where I'm at with my first step in reducing VOC/odor. I don't know if any others have run into this problem and are addressing it, if so, I'd love to hear of options you are considering.

I'm *very* interested in a brush-on low-voc primer that I could do in my basement. Looking at the Bondz product pages, it doesn't say anything about high solids content. Is it really a substitute for filler/primer? How does it sand?

neil_w said:

I'm *very* interested in a brush-on low-voc primer that I could do in my basement. Looking at the Bondz product pages, it doesn't say anything about high solids content. Is it really a substitute for filler/primer? How does it sand?

Click to expand...

I would say it is a matter of degree. The high-hide/stain-block offerings probably have higher solids and are thus marketed as such. I will say that this stuff is extremely thick which is probably a combination of titanium dioxide/solids and the acrylic adhesive base. It takes a good while to mix before use. Once mixed though the solids stay suspended for some time. There are probably other offerings in the Zinsser (or even Kilz) line up that have higher solids and in fact, I was looking at one oil-based offering, but in the end, I opted for the water base and lower odor offering while the adhesive characteristics and white color were just a plus. Regarding sanding, it is harder to sand than Rust-Oleum Automotive Filler-Primer. With Rusto Filler-Primer that gray "dust" almost falls off the rocket when sanding. With the Bondz you do have to pay more attention to sanding the drips/runs to get an even surface (again, other Zinsser products may behave differently).

Note: Taking a closer look, the Bondz is ~33% solids by volume, whereas the high-block offerings are quite a bit higher at 57%. It looks like you could bump this up by adding calcium carbonate and talc to the Bondz although it may change the adhesive characteristics. Interestingly Rust-Oleum Automotive Filler Primer is labeled high-build (not high solids) and no solids content is given for that product that I can see, they just say "proprietary."

Well I have been doing more extensive testing and using a particular primer mix that I feel shows great promise. Over the last 90 days I have used it on one typical 3" cardboard, a 2.6" fiberglass builds; I also have done two larger cardboard airframes wrapped with fiberglass. These last two were important to test to see just how successful the primer would be on pinholes. One of these two 5.5" rockets was from Polecat, which as most know, uses some fairly heavyweight fiberglass with prominent fabric weave. In the past I have had to fill Polecat rockets with SuperFil to effectively eliminate the pinholes otherwise you have to spend a fortune on filler-primer. As you will see though, no more!

Original formula
So as I mentioned in the first post, I selected Zinnser Bondz for its advertised adhesive qualities and to meet the overall goal of low to zero-VOC and low-odor. After first use on the 3” cardboard frame I was pleasantly surprised. First, almost no odor; you can stick your nose down into the can and it kind of smells like chalk (the kind used on the old blackboards for you young’uns), but even that smell is not so strong. When it settles in the can the product definitely separates. The liquid that rises to the top actually looks like epoxy, I’m sure it isn’t, but there is some type of adhesive involved because after the first application on the 3” airframe, I can tell you, that stuff is stuck and stuck well. So what does that mean. Well one good, and one kind of bad thing. Good is you probably will never get a better base material to apply your color coat to. If there is ever any chipping on your rocket, it is highly unlikely it will be at the primer level. It’s not going anywhere. Now the bad thing… Although you could try to hand sand this stuff, I would not recommend it. As a coating it is tough. Yes, it does sand nice and even, but it does take some work. I highly recommend using a power sander.

Although I was extremely happy with the adhesion, as thick as the product goes on, I was surprised that there was still some evidence of spirals on the cardboard airframe. This wasn’t evident after initial brushing (applied with a cheap chip brush), but as the Bondz dries out and the adhesive cures it tightens on the substrate and in some places you could see parts of the spirals. So after seeing this, it reminded me of the question in the second post above from neil_w. As it turns out, there are many fillers that have higher solids content than the standard Bondz product.

Refinements
So in an effort to get the best of both worlds, high adhesion and high fill, I decided to source the two most common paint fillers, 1) calcium carbonate, i.e., limestone powder, and 2) talc, or powdered chalk. Both these fillers are cheap and readily available at most composite sourcing companies. I have never used either of these, but did some research on percentages on the range of fill in some of the high-fill primers and decided to start slow at the lower end. Now I know liquid ounces are not the same as dry ounces, but I just used that equivalency and came up with the combo of 6 oz. of talc and 4 oz. of calcium carbonate per gallon of Bondz. I was worried about some comments on painting (like professional painting) forums regarding the drying/thickening of adding these two fillers. As it turns out, although slightly thicker, I really did not notice a difference in application or drying effects with the amount of filler I added as outlined above.

I decided to do a test application of both the original Bondz and my high-solids Bondz mix on a tough application, the Polecat airframe. I applied both to a 4”x12” section of the airframe (2’ in length total) right in the same area so the pinhole effect would be equal. I was amazed at the difference. The fill version showed only a couple of pinholes after sanding whereas the “straight” Bondz had probably 25% of the area still exhibiting pinholes. Now, I’m sure after a couple applications and sanding rounds the original Bondz would have been OK, but I’m building bigger and bigger rockets so, I’m opting for my “high-solids” version to save time and effort.

Now some people would say, limestone, what?! Yes, you are adding “rock” to your airframe. But of course, in practice most of that filler is removed via sanding. But even if not, I’m wondering which is heavier, an epoxy based filler, or a liquid with 3% to 4% lime powder? I haven’t done the math, but it would be an interesting comparison so I’ll have to do it later. And notice I’m comparing this primer-filler to real filler. In my first post I had mentioned mixing my own fairing compound. I have bought the materials for making it, but haven’t bothered yet as this filler-primer is able to fill most all undulations and imperfections in typical fiberglassing jobs (see pic below). Yes, I had a couple places to fill where there were complex curves, but they were so small, it wasn’t worth mixing even a small amount of fairing compound to try it.

Second question might be on the price of Bondz, which seems fairly high at $28 to $30 per gallon. So my interest in this first test round was on just how expensive was it? Well so far, I have done two coats on four rockets as mentioned above and I have used less approximately 1/8th of the gallon. So four rockets completely primed for under $4. Heck, I would have needed 7 or 8 cans of Rustoleum or Duplicolor filler-primer spending ~$30. I’d say, the Bondz mix is very cheap! Why so little used? Not sure; but guessing it is a combo of, 1) no loss of paint floating in the air, and 2) extreme coverage/cover-up from the thickened Bondz.

What’s next
Well of course, I’m only partway there. I have to see how the whole process works once the rockets are put into service. Time will tell. I’m especially interested now in nosecones. I have both fiberglass (polyester gel and filament wound) and plastic nosecones to test. We’ll see how the long-term results go. Anyway, here are a few pictures…

Kinda going in reverse order. Here is the typical matte finish after two coats and sanding. The last round was using 220 grit using a soft head on my Festool Rotex 90. I can tell you this is baby-butt smooth. I’m not even going to put on a base coat of enamel, I’m just going directly to finish coat. Note that this is the Polecat Skeeter. Took about 10 minutes per coat to apply and probably ½ hour of sanding per coat, which isn’t bad, but look at the airframe—no sign of any of those ugly pinholes. Nothing. Nada!



Here is a picture of a second coat application on my LOC King Viper III. For those that know this rocket, it is particularly challenging in the fin area to get all the surfaces and angles transitioned correctly and looking right. You can see how thick the primer goes on wet, but as mentioned it cures and tightens up nicely on the substrate.



Here is the real test case, a plastic nosecone that has a few layers of fiberglass at the base to align with the seam of the airframe. We’ll see how the long-term performance is starting with my first launch of this rocket coming up at MWP14.



Here is a snapshot after a first coat and a sanding round. This is the airframe of the King Viper III. Now you see how splotchy this looks. I can assure you that this is not a bad fiberglassing job. There is very little undulation in this surface. But what this really illustrates is the value of a highly adhesive primer. Most filler-primers almost dust off the surface when you are sanding them and then in the shallow areas the primer typically just disappears, but in the case of this Bondz mixture, you fill every little “micron in height” dip to end up with a very level surface.



And then finally, one snapshot of the base materials.

Subscribed. op:

Thanks, I needed that! Subscribed..

StanO

I've had good luck with Gesso mixed with airbrush medium for a primer.

https://www.goldenpaints.com/technicalinfo_gesso