White no-bond patches

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xantipo

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Sep 2, 2009, 8:48:10 AM9/2/09
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One of the great advantages of this discussion group is its potential
to share information around about building processes, doubts, tips and
tricks that can be of great help to all of us.
In that sense I bring here an issue I feel could be helpful to many
builders.

When I began laminating the first float half I noticed the occurrence
of some white no-bond patches (WNBP) ranging in size from hardly
noticeable spots to some extensive areas clearly identifiable . If
it’s true that in most situations there was no risk regarding the
overall mechanical properties of the laminate in other cases some
grinding down and patching had to be done to insure laminate integrity
( close to the stringers for example).
This situation was not consistent throughout the subsequent laminates
and in most cases the occurrences were minimal. There was also no
particular technical procedure which could be identified as the main
cause for this phenomenon.
Before I got into the lamination of the exterior surfaces I had to get
to the bottom of this problem. Other builders ( Menno in particular)
referred the same situation and some discussion was developed around
this subject. There wasn’t however neither a adequate explanation nor
a solution for WNBP.
I suspected it either had to do with the presence of dust, chemical
bonding problem ( silane), boundary reaction between PVC and epoxy or
most likely , in my view, a combination of these factors. I noticed,
however, that WNBP never took place where putty had been applied. For
some reason it worked as a pore filler ( less dust buildup) and/or a
more efficient interface between foam and resin. If there was little I
could do about the chemical properties of foam and resin, I could
deal with the dust and putty factors.
I decided then to apply a thin coat of resin lightly thickened with
micro balloons , sand it down and do a meticulous vacuum ( 2-3
passes). Additionally I vacuum the floor and wet it out before
lamination.
The result was excellent. In the first half hull I couldn’t find a
single flaw in the whole laminate. It was crystal clear and exhibited
excellent adhesion to the foam. On following laminations there were
some minor flaws of no importance, but no WNBP at all.
So, if you have experienced this sort of problem, you might consider
doing the same. It leads to some extra work but it clearly pays off.
Besides , applying a pre coat of resin with micro balloons will seal
the pvc pores with a layer which is lighter than plain resin. The
extra sanding needed will also work towards the final fairing process.
Although recommended , there’s no need to saturate the whole surface
with the resin/filler coat. I used a roller and tried to spread the
mixture as much as I could but couldn’t help leaving an irregular
distribution with some areas more saturated than others. Maybe you
could improve this method by using a squeegee or some other procedure.

You can check my blog www.matosf22.blogspot.com for additional
information and photos.

Tor

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Sep 2, 2009, 11:42:01 AM9/2/09
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On Sep 2, 2:48 pm, xantipo <xant...@sapo.pt> wrote:


Regarding:

> Besides , applying a pre coat of resin with micro balloons will seal
> the pvc pores with a layer which is lighter than plain resin.

I also formulated this hypothesis, but testing actually showed it
false.


> The extra sanding needed will also work towards the final fairing process.

I found that sanding on single laminated (one side finished only)
panels should be carried out with much precautions as the flex in the
laminate easily leads to an uneven surface, especially if epoxy is
applied, as more pressure on the board is being used.

> You can check my blogwww.matosf22.blogspot.com for additional
> information and photos.

Your laminates looks very good!

jungle jim

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Sep 2, 2009, 12:33:13 PM9/2/09
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We are using West system & corecell & haven't had any bonding or
bubbling issues. We pour resin on the foam & spread it with up to
12" (30cm) plastic spreader on the whole part. Start at one end & roll
out the cloth about 50" at a time. Pull or squeege out any bumps or
wrinkles, this is fairly easy before the glass gets saturated. Carry
on to the next 50" & work your way down the part. Now go back to where
you started & the resin should have wicked into the glass. Apply more
resin to areas where the glass did no go clear, or looks dry. If you
are working in a rising temperature the material (Foam) could be off-
gassing & create those bubbles. Try to work in a steady or falling
temperature as per the Gougeon brothers advice.

xantipo

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Sep 2, 2009, 12:41:33 PM9/2/09
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Tor,
Thanks for the feedback.
About your argument in opposition to resin/filler pre-coat being
lighter than plain resin, I believe some clearing up is needed.
I got that information a few days ago from Ian in response to my
question to him about WNBP.

It wood be very interesting to develop this issue especially taking in
consideration that you ran some tests and found otherwise in a
situation where common sense doesn't match experiment and it could
lead builders in the wrong direction.

Let's see what others have to say. I for one am curious.

Your right about the sanding pressure on a resin hardened surface
leading to distortion. In may case I did most of the fairing on bare
foam first and lightly sanded the resin/filler coat just to prepare
the surface for subsquent bonding and didn't detect any surface
changes as it easy to see when you hitting the foam by controling dull/
shiny appearance.
I would second your advice if hull is poorly faired in which case a
different approach should be considered.
> > You can check my blogwww.matosf22.blogspot.comfor additional

Tor

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Sep 3, 2009, 6:06:43 AM9/3/09
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On Sep 2, 6:41 pm, xantipo <xant...@sapo.pt> wrote:
> Tor,
> Thanks for the feedback.
> About your argument in opposition to resin/filler pre-coat being
> lighter than plain resin, I believe some clearing up is needed.
> I got that information a few days ago from Ian in response to my
> question to him about WNBP.
>

After more thought my result may not be applicable in your situation
and should consequently be disregarded.

The conditions was vacuum resin infusion which leads to a total fill-
up of the foam surface and thus a bit heavier laminate (but of very
high quality) especially when using light fabrics as the foam surface
constitutes a larger proportion of the total laminate.
My hypothesis was: Filling the voids with microballoons will weigh
less than filling with epoxy alone, and if the microballoons was
applied dry in the bag there would not be any secondary bonding
issues.

My testing set up was as follows:
Divinycell H60 foam, three pieces. One layer carbon 200g/m² 2x2
twill. Vacuum resin infusion using SP systems Prime 20 LV epoxy
system.
One piece bare foam. One piece skimmed with epoxy/microballoons, much
as you describe your successful method. One piece had the pores of the
foam filled with dry microballoons.
I don't remember the numbers but I was surprised to find that the bare
foam made the lightest panel and the one with dry microballoons the
heaviest.

I do now not use resin infusion for hull, but wet lay up and vacuum
bagging which works very well for avoiding WNBP.

Tor

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Sep 3, 2009, 6:10:50 AM9/3/09
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I think a thorough wet out of the foam first is a key as well. Dust,
as mentioned earlier will make this more difficult. The bubbles must
come from trapped air expanding under heat, and the epoxy curing
process produce heat so a constant or falling ambient temperature is
not always enough to avoid this. Thus wetting the surface well is
probably the key.

Just my thoughts.
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