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 Spraying the Wattyl EP universal epoxy primer in preparation for applying the fairing compound to get rid of all the little pits.

  Outgassing….

 

So… what was your first clue Sherlock? The frustration of thinking you have a problem licked and then… back it comes.

I attacked the inboard sheer panel with the "proper tool" and did a beaut of a job applying the kilo and a half lot of bogg. Back to the bench to mix another load and spread out on a table to keep the batch from going off with 'exothermic' heat. Resin and hardener in compact mass creates its own heat which hastens cure which creates more heat until you have a useless smoking mass. I use the black plastic made for concrete work as a disposable surface and spread the mix out on the table to slow it down. When I turned around with my first trowel load of new stuff I was amazed to see a minefield of pits in the previously applied surface! What to do? I knew from experience with the first hull that covering with the 'skim coat' wasn't going to work so I turned to with the trowel on the firming surface to see if I could persuade it to 'fill'. It wasn't going to work…. Shit! Scrape the lot off, but not before taking a quick close-up pic to look at later. See photo below.

 

 By this time the second batch on the table had cooked. Not a good day so far. I mixed up a batch of resin without filler and rolled it on the surfaces I intended to do that day. The idea being to let it fill the weave, go sticky and provide a substrate that might finally work.

The penny dropped when I saw the bubbles… bubbles?!? On the resin I had just rolled was a perfect little bubble, and another... and another. That and a look at the close-up photo I had taken earlier confirmed. I had been proceeding under the assumption that the problem was the trapped air in a surface depression of the laminate was not being successfully displaced by the resin and surface tension caused the pit to remain, more a mechanical issue. But the size of the bubbles indicated that idea wrong. Where was the gas coming from? Was it evacuating from the core itself? And if so, can't water go in the same way the gas comes out? Or was it gas that had been trapped in the laminate? Possibly, but wouldn't all that gas have been evacuated by the second coat of bogg on this last application? Outgassing through screw holes or cut edges.. yes, but out of the panel surface? How? So back to the instruction booklet that came from ATL with the panels. I could find no mention of outgasing at all and no reference to them being waterproof. The closest relevant information I could find was from page 2; "The panels are designed to provide a fair surface on the hull exterior, and while the builder may choose to add laminate for aesthetic or other reasons (authors emphasis), it's not required structurally."

So it may be that the panels are intended as a structural unit only? I shot off an email; "are the glass fibre and epoxy skins on either side of Duflex panels waterproof?" My question must have got lost, no response. That was the last I ever heard from ATL composites where I had always received a timely response with any technical enquiry prior to that question.

An update to this question as of Nov 1st 2011; I have reports from two credible sources of failure of the surface on bridge decks of two boats from well known designers using duflex panels that resulted in absorption of water into the balsa core. One boat was bought cheap and the new owners stripped the deck underside of outer laminate and balsa core. They replaced the core with foam, glued in place by vacuum bagging and then relaminating. The other craft was also reported to have been sold very cheap and it's repair is pending.

Also; an apparent astro-turfer (spruiker) for the panel producers reported to have claimed on the web that duflex panels are indeed structural only, not intended to be waterproof and "everybody knows that". They do now but in context the inference is that has always been the case. The author of this article challenges that and would like to see a widely published account where that is stated that can be verified to have been made public prior to this published article.

And more.. just got a email from a would be builder who reports he has just taken his duflex panel kit to the tip... no joke. The stuff was so bad he couldn't work it and and no one was willing to give even a fraction of his cost for the partially assembled boat. Approx $50,000 thrown away. Besides the porosity, delamination had occurred that prevented faith in the finished product regardless of effort in build so he cut his losses.

To add to the confusion, I asked a reputable builder specialising in other core material about the problem and he felt the same as I, that balsa by itself should outgass like crazy but was surprised it might go through a layer of heavy glass and epoxy. I have asked two other builders who have worked with Duflex panels and they said they didn't have any outgas issue at all, they never took it into account, and then another builder who said it was a common occurrence but he figured it was the gas trapped in the laminate expanding from the heat of the exothermic reaction. hmmm?

The portion or work that I had done that was good and I attributed to the tooling was done at night, under lights when the panels would have been absorbing gas rather than expelling it. The panels have to be worked on a downward temperature curve to beat the problem. Even late afternoon wasn't cool enough to prevent it for me. All bogging from now on will be on the night shift. Hate the night shift!

That takes care of future work but what should I do to insure the first hull won't absorb moisture through the pitted surface? I have to settle the question of whether it's the core or laminate that is the source of the gas. So I unpacked my microscope, (doesn't everyone have one?) and grabbed the first piece of scrap that could be cut to fit the instrument without waste. I took a couple pics with my scope camera and they are displayed here. It does show the gaps in the surface from shortage of resin go about half way through the laminate though no obvious portals into the core are visible to me on this sample. Though interesting, this is inconclusive.
I post the pics for reader interest. I wished I had spread a light coating of resin over every panel prior to assembly, when they were flat. (and cool!) I notice that the laminate on my 19mm panels for my bridgedeck floor are fully covered in resin and smooth.

Before I proceed with the first hull I will conduct an experiment to find out conclusively where the gas came from and how to approach the problem from there. I'll post it to the web site building log after publication.

So… taping on the inside of the hull panels, the first step, can be done with virtual impunity. Any outgassing would vent freely out the back side. Taping the outside joints should be monitored closely as they set. Watch the screw holes! Bogging should be done at night in summer or at least late afternoon in cooler seasons. Makes me wonder how pro operations do that with a normal work shift?

Final fairing will be done when the sections are assembled and sheer finalised but I plan to go as far as I can in units and stall assembly as long as I can.

It is frustrating having to interrupt the process for publication, it always seems to be at the worst time, just as a rhythm is developing

The Update! The experiment to answer the question... is it outgassing from the core???

 
 
Will the paint cover and seal the pits? question asked and answered... no!
Back to hull # 2 while I think about the first hull. I was surprised I didn't have a fight to get syringes from the local chemist. I couldn't get big needles though.. just the wee little ones that Diabetics or junkies would use! No matter, just the open end was good enough for what I wanted to do....
  Notice the arm protection? Those are long socks from the op shop. Cut off the ends and cut a small slot near the end. Then put on with your thumb in the little slot to hole in place and put on the rubber gloves. I find this kind of arm protection essential. Also protection from the fumes is important. Epoxy is not overwhelming in stench like other resins but far more harmful than any other.
 So.. before glassing the bum.. fill all those little holes from screws with the syringe.
Then the night shift.. I put two layers of glass on the keel panel and two layers of bogg over the lot but this is all you get for pics. Kay was not allowed in much as the fumes were very strong except when she was wearing a mask herself. Kay helped consolidate the layers of glass. 
Then back to old hull # 1.. Mixing fairing compound and applying. The visor is a jewelers eyewear. But no matter how careful I was... I couldn't see them all.
 After the fairing compound set then sand with the new Rupes brand orbital sander... great tool!
I picked up some aluminium angle and some long pieces of hardwood strips to use as fairing batons. I found little error in the surface. The worst spot was about 2mm off over a length of about 4 feet (1.2metre).  This should be easy to correct when the final fairing is done later.
 This gives an idea of how extensive and localised the pitting was. The Fairing compound near the chines is there for smoothing not sealing. The pitting was limited to where there was no tape covering the duflex panels.
 Then back to hull number 2 in the tent. Feeling pretty confident because of my success in the big job I did at night.. which turned out so good, no pits anywhere... and then this absolute shit done mid-day later...
 Then these little buggars... finally figuring it all out. After the first bogging attempts failed I thought I would roll on some plain resin to fill the rough surface of the Duflex panels, blaming the air trapped in the low spots for the trouble. But then the whole surface I was 'painting' with resin started blowing bubbles.... and the penny dropped. This appeared to be outgassing, but how?? Aren't these panels sealed??
 And this is where I dropped the project in disgust. I should have scraped off this bogg but it was hard to plan well at the time.. was too pissed off. I had a paper to build anyway...

So what is going on with these things....

I pulled out my microscope and had a look at a randomly selected scrap of panel. This shows the open nature of the weave of the glass cloth. The cloth at far left is peel ply. This is magnified 10X

 This is 30X magnification. The pattern you see in the surface is left from the peel ply after removal.
 A look at the edge.
Another angle of the side view
 This is just a macro shot with the camera of the surface of my 19mm panels. I wished the 13mm panels that are the bulk of my order, had this much resin. It would take a lot of guess work and additional resin work out of it.
I have since used the 19mm panels and can verify they are much better to work than the 13 panels have been with their impoverished resin coating. Thought the 19mm panels can still outgas and they must also be watched, it is much less than the 13mm parcel. I believe that heat is either created and/or introduced into the manufacturing process and that heat causes tremendous outgassing when they are being made. Especially with the thin resin this allowed the formation of thousands or pores in the surface that remained after curing.