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Outgassing from the core?.. Yes or No

 A note! I was passed a message from a builder that saw some bullshit on a forum that said everyone knows about this and wonders why I made the big effort to answer the question... utter rot. Be careful as the forums are seeded with partisans... with undisclosed interests to protect.

Builders who have ordered duflex and received the lovely pamphlet that comes with the stuff with explicate instructions and how too's will note that the word "outgas" is not found in their literature. A phone call made to ATL asking about this important question was not responded to. Why?? And I know for fact there are many boats out there made of duflex that have hundreds or thousands of pits filled with car finishing putty because that's all they knew. When I asked the wattel paint rep about this problem, that's what he came up with too. They all think the pits are just in the bogg but it's not nessearily so, they often penetrate to the balsa core. There are a lot of people out there trying hard to hide the faults this stuff has. If I had known, there is no way I would have spent the money when going foam would have been so much less expensive and more reliable.


The short answer is YES. At least the set of panels I have show that Duflex panels can outgas from the core readily.

As I mentioned in the previous installment, Bogged Down in Assumptions, I had asked builders if they had problems with outgassing and some said no and one said yes but he figured it was air trapped in the weave rather than from the core that was outgassing. So, now I know I was asking the wrong question. Going back and getting more information I have learned that before this article was published, many professional builders did not know what the cause is of the pits and holes that often occur in the bogg applied over the Duflex. Not that pits can't occur in the Bogg otherwise but if my hulls are any indication, the vast majority are from outgassing. In the article linked above, I noted that a large section of bogg that I did at night was absolutely pit free. This was further evidensed by more sanding done since the article linked above was written and still... not one detectable hole or pit whereas all bogg I've done before or since (that was all done during daytime, warmer hours) has pits.... lots of them!

So what does it all mean? Every one of those pits from outgassing is a path from the water to the balsa core and all that is preventing ingress of water is the means of sealing those holes/pits. Puty? Paint? Resin coat? Keeping in mind that if the resin coat is applied during warmer hours, it too will be subject to gassing. Will this be a problem some day for boats built without taking this all into account? It could be. Even if a seal is obtained on the surface with the means listed above, all it would take would be a scratch under the water line (rock, floating debris etc) to reveal a pathway into the core.

 EDIT September 09... I have recently talked with a builder working for a comapny assembling a popular style of cat made with Duflex panels. According to him, the designer now calls for the panels to have two coats of resin applied late in the day before further assembly. Word is now getting around.

Anyway.. have a look at the proceedure and come to your own conclusion.

I sawed off one side of the fibreglass from a scrap piece big enough to fit under my acrylic bell jar to test under vacume. I left as much of the core as possible with the test piece.
On the other side I traced the outline of my vacume chamber.
 To provide a seal I used some cheap polyurethane and...
 a piece of plastic sheet ..

 then pressed the jar in place to form it all to smooth. I then let set and later cut away the excess plastic inside the circle.

This is when I noticed how poor the visibility was through the jar and cleaned that up before the fianl experiment.

 After the sealant was firm I placed the panel in a tray that I poured some water with red food colouring into. Within a few minutes the red water was already 'wicking up' through the panel skin. This was unexpected. I was just letting the balsa core absorb some red water in preperation for running under vacume. This shot taken at 2:13 PM
Then more occuring.. this shot one minute later at 2:14 PM
 Then at 2:21 PM the first bunch of red water toward the centre of the panel was noted as I put the jar on. The piece of plastic pipe was there to reinforce the panel as under vacume I wasn't sure it would withstand the atmospheric pressure. It would be a messy implosion.
 Now ready to vacume noting the location of the red water.
 Within seconds and well before the chamber should have been at maximum vacume, the insides were being sprayed with red mist. The pump was turned off prematurely. It wasn't necessary to go further.

 I felt that the cause of the permeability was the lack of resin in the fibreglass cloth. Besides the finishing work required because of the rough surface, could it be that the shortage of resin was an actual mechanical shortcoming?

Another scrap of similar type to the one tested, this one I will coat with resin and try the same test with it.

Spread with a rubber "squeedgy"..
 and covered with a few pieces of 'peel ply'..
 to be as close to factory finish as possible.
Next day, build a gasket as before... this is 4:20 PM.
 This is 4:48 PM and still no sign of 'wicking' through the panel though red water is creeping up the sides. When it comes through the panel it shows an intense red dot at the point of entry. This 'cloudy looking' film around the edges appears to not be related to the balsa.
This is 4:58
This is shot with a flash at 7:10 PM. I didn't see the little speck of red at the time. It was days later when processing the photos that I noticed it where indicated by the arrow.
 This is at 7:09 AM the next morning. That is when I first spotted the red water
 This is a closer look. Notice the air bubbles trapped in the weave? From the factory some of the weave is open (see the "assumptions" article again for microscope shots) and some is covered but leaving an air bubble trapped under the skin.

 This shot, 7:38 AM.

The Vacume test is really superfluous at this point but might as well continue for the sake of entertainment! The arrow indicates the position of the red water mark. I have to hold down the jar because the panel has swollen and warped from the absorbsion of water in the balsa.

 As the vacume comes up a few other marks start to show.
 And then near max vacume, about 28 inches of mercury for this pump and current weather conditions. I release my hands which were holding the jar down to flatten the other wise warped panel.
 This is with the vacume running at max.

Conclusion? Spreading resin over panels that have been delivered impoverished of resin from the factory benefits the panels as far as I can tell. Because of the trapped air in the lean panel resin, I would suggest the best result would have been to have the panels fully resined in the beginning., but doing them up post delivery is better than nothing. If I had it to do over again, I would deffinately have spent a few days and a few hundred $$ worth of resin to be able to do it on a flat, horizontal surface.

Since doing this experiment I have ground off a lot of previous work on my first hull to expose panel surface that I will cover with a thin bogg, resin mix (will only be using bogg in the mix to help keep the mix from sagging out of the weave where the surface is verticle) to try to fill as much as I can below or near the water line. Then start over with the bogg. This will all be done in evening hours of course.

If you have Duflex panels and are curious about this aspect of them, you don't need the vacume pump and bell jar. Simply using the tray and coloured water will indicate if you have reason for concern. Just cut off one side of the glass on any reasonable size piece of scrap and watch for an hour.

Not all Duflex panels from ATL composits have this resin shortage issue that I attribute to this kind of permeability problem. My 19mm panels were filled beautifully. Again.. see the "assumptions" article, microscope shots. Heat used in the manufactoring to speed curing may have a part to play in this problem as well.

Having resin rich panels will make them heavier but the resin you have to install after the fact puts any weight saved right back on.