Skinning your TTT in epoxy and fiberglass

[StPatron]

In a continuation of this thread, how does everyone measure your epoxy components prior to mixing? Do you use the graduated mixing cups or pumps?

Pumps... until the level in the jugs is low and then I use a plastic "Solo cup" (either solid or clear) with markings in Sharpie on the side. I don't shake, tip or jiggle the jugs... have never had an air burp. I have to occasionally wipe off the spout on the hardener jug. I stir with a plastic spoon and do a one-thousand one, one-thousand two count while mixing.

I started out using Raka, have also used MAS. Now, using products from Aeromarine. I think I've probably kept them in business for years now..

http://www.aeromarineproducts.com/

[Corwin C]

I make many small batches instead of a couple of large ones, I use the pumps, but verify quantities with a scale. I've never had a problem with the pumps, but sometimes my count has been off and the scale caught my mistake and I was able to correct it. I also enlist a helper to stir very very thoroughly (in my opinion this is one of the most important steps). Scrape the sides, bottom, and corners of your mixing cup, but don't get so vigorous to cause any air bubbles.

In my experience, practically everyone who has worked with epoxy has a favorite method. As long as you follow manufacturer's directions, are accurate when mixing, and spread it out evenly and smoothly within its pot life, you'll do fine. The rest is honestly a matter of trial and error and little tricks from experience. Also, having an experienced person there to help the first time or two can help with the nervousness.

[Larry C]

I guess I should clarify for those that don't know what we are referring to with pumps, measured cups or weight scales.

Pumps are nothing more than plastic mustard pumps used at hot dog stands to dispense mustard. They thread onto the plastic jugs and protrude into resin and hardener. Some companies like Wests System, the pumps are metered so one pump of resin gets one pump of hardener even though the mix ratio is 3 to one.

Other companies such as Raka use the same pump metering for each part of the mix so it takes 2 pumps of resin and one pump of hardener for their 2 to one ratio.

For many years, I just used the pumps and trusted they were accurate. However, I always ended up with extra resin or hardener when everything should have been used up. I always attributed it to they just didn't measure what they sent me, accurately.

I started not trusting the pumps accuracy and I started pumping the resin and hardener into a cup with accurately measured lines on it. Actually it's double cup, one with lines one for the mix. Low and behold the amount left after all should be equally gone from the original jugs was much closer to what it should be.

Then I started using a gram scale to measure by weight rather than volume. Again I still use the pumps, but now I pump into a cup exactly the amount I need of the resin, and pump correct amount of the hardener by weight. This method has proved so accurate that I now expend the same amount of resin and hardener at the end of the jugs so there is little or nothing left in either container.

The bottom line at least for me is being able to use the pumps to dispense the product is great. However, I don't trust the pumps to accurately deliver the correct amount every time. When the pumps set for awhile, the first pump is a primer pump, and tends to burp air which is not giving an accurate measurement. Epoxy that is not measured accurately will either be soft or brittle. At dollars per once and the risk of ruining a project, I needed to find a solution.

Pumping into a measured double cup is very accurate, but you are limited to pre-set amounts marked on the cup.

The Gram scale gives me the ability to measure the tiniest amount to any amount I need with the greatest accuracy. I routinely mix 1/4 oz. or less for different projects.

If your just doing one project such as a TTT the so called metered pumps are probably all you need, but if you frequently use epoxy for many different projects, from big to tiny, you might consider weighing your epoxy with an inexpensive gram scale.

$.02

Larry

[Larry C]

Well Becky...
Are we going to see and hear how your weekend lay-up went?

[NathanL]

I use pumps but I use the metered set of pumps that West sells but it's beyond the scope for most teardrop builders. You just push a button and it measures out how much you set.

The drawback to solo cups is if you put too much you can really melt them down if you are using a fast harderner or like here where it's 100F a lot. I use these little steel cups that are sloped about 30 degrees from vertical. I don't know where I got them but I've had a bunch of them a long time. When the epoxy starts drying you can turn it upside down and whack it hard on the bench and the rest of the epoxy pops out leaving it clean as a whistle.

[aggie79]

Thanks everyone for elaborating on your measuring technique. Your comments are helping to "de-mystify" epoxy construction.

This fall I plan to start a second build and am working on three different designs at this time - traditional breadloaf design, an expanding angular military-appearance design, and a lifting/tilting roof streamliner design. My very patient and understanding wife has requested an internal bathroom and shower, so this build will be bigger than my teardrop. I want to keep the weight down - and minimize the frontal area for drag - so whichever design route I go, my construction method will make substantial use of epoxy and fiberglass.

[Oldragbaggers]

Well Becky...
Are we going to see and hear how your weekend lay-up went?

I posted an update to my build journal, but didn't get to the layup stage. This weekend I cut the pieces of wall insulation for one wall, glued the skin on one side, and then glued the insulation into the cavities. That's as far as I got. Layup next weekend I hope, if it don't rain.

[Larry C]

Well Becky...
Are we going to see and hear how your weekend lay-up went?

I posted an update to my build journal, but didn't get to the layup stage. This weekend I cut the pieces of wall insulation for one wall, glued the skin on one side, and then glued the insulation into the cavities. That's as far as I got. Layup next weekend I hope, if it don't rain.

Becky...
Looking good! Let me guess the "P" on the foam pieces is for the Port Side of the trailer? Using nautical descriptions me thinks. What glue did you use for the insulation?

Larry

[Oldragbaggers]

Hi Larry. I used (what else) epoxy mixed with High Density Adhesive Filler (West System). I'm getting ready to go outside now and take the weights off and see how stuck it is.

Are we that transparent with our abbreviations?

[Oldragbaggers]

Yep......it's stuck alright. Man, I love this stuff.

[48Rob]

Becky,

Your cut out looks great, very precise and clean!

Why do your cutouts have the shape they do?
What I'm after, is why didn't you take more plywood out, and leave just a few "studs" with maybe a center horizontal support.

I don't mean to sound/be critical, as I am not, I'm trying to understand the reasoning.
Is there a formula?

Rob

[Larry C]

Becky,
I am sure you have this already worked out but, I thought I should mention that your choice of wheel size change may have an effect on the inner wall framing location for your fenders.
I am in a bit of a quandary where to to place my fender framing, so seeing yours caught my eye.




Larry

[Larry C]

[quote="

Are we that transparent with our abbreviations?[/quote]

It just made me laugh, I do the same thing, thinking in boat terms on my trailer.

[Oldragbaggers]

Hi Rob,
First just let me preface my answer by saying that there's probably no understanding the way I think, and I can't give you an answer that is going to have any basis in engineering or architecture or science of any kind. When I originally drew up my openings and cut them in my 1/4" luan template I did cut the openings larger and left much less wood. But, first of all it just looked flimsy to me. I know that's not much of an explanation. I knew I was going to use very thin skins on it and it just seemed like that didn't leave much support. I want, above all things, for this to be a sturdy, strong, long-lasting trailer. And even though leaving as much wood as I did probably accomplished nothing except making it heavier, it made me feel better. Does that make any sense? Probably not. The other thing was that I wanted to leave myself more room for adjustments with my cabinetry and attachments. I don't have everything worked out down to the millimeter. I have a vague idea of how it will be, but a lot of the design of my interior is going to happen after the shell is up and I wanted to be able to adjust things an inch or 2 in either direction and still have wood to screw into.

Larry,
You scared the hell out of me for a minute there. I cut this thing out last fall, so I had to run out to the garage, lift the wall and check it. I cut the template after I had the new wheels on. Whew. But I guess that would have been another instance of that extra wood coming in handy. Room to adjust.


To be honest with you all....I started out with a lot of lofty and high falootin ideas about how this had to be so and so, the trailer had to be so so and the shell had to be so so and the dimensions had to be so so. If I was starting over tomorrow I would get a Harbor Frieght 4x8 frame, throw a floor on it, put up some solid 3/4" walls, fiberglass and paint the whole thing and go camping. And then maybe someday in the future, with that experience under my belt, a teardrop to play with in the meantime, and time to work out every detail of my ideal build in advance, I'd do one that was "just so and so." (Newbies....are you listening?) But I'm committed now (or should be) so I'll just keep moving forward with what I'm doing.

[KCStudly]

I call it, 'that looks about right' engineering. Never underestimate the power of your subconscious experience telling you what makes sense and what doesn't. Some people have it, some people don't. Some times we listen to ourselves, some times we talk ourselves out of it or don't listen.

If your gut tells you something isn't right, at least listen enough to consider the options. Sharpen the pencil and do some real engineering or
hedge your bet with a little safety margin. Bottom line is you considered your options and the ramifications of your choices and found a happy medium that suits the circumstances of the situation. Congratulations, you are officially an engineer!

But seriously, you are doing great. I like the quality of your work and the way you are telling your story. Keep at it and before you know it you will have a camper that you can be proud of ...and something tells me that it won't be your last one, either.