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People
with boats undergoing blister repairs often write us to say, "My
boat has been drying out for six months now, and it still will not
dry. The moisture meter readings are still as high as ever."
The usual procedure is to just let the boat sit and "dry out"
naturally by a process of evaporation. Still others are erecting
tents and what not and installing heaters or dehumidifiers to try
to accelerate the process. And still they report that it's not "drying."
No, it's not drying. And the reason why is a very
simple one. The wetness you are attempting to dry is not water,
but something else. In many cases, it can sit there forever and
never go away. You can prove this for yourself by performing a simple
test. Collect some fluid samples from blisters on any boat. Rupture
the blister with a sharp knife point, then press against it and
let it spray into an empty film canister. Then place droplets of
the sample on a piece of clean metal or glass. Take it home and
put it in a cool, dry place for two weeks.
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| These are samples of blister fluid
after 2 weeks of air drying. The three at top and right are
hardened to the touch and have shown almost no shrinkage due
to evaporation. The large one at the tops is roughly 2mm in
depth. The volume of fluid placed on the plate remained essentially
the same. Water has been added to the sample on the left.
Note that it has dissolved completely, dried up and left the
residue spread around. The one at bottom center developed
those large bubbles when placed in the sun. The one at the
top also developed bubbles, but most of them dissolved after
removal from sunlight. |
When you return to your samples you will find that
it has not evaporated, but has hardened into a droplet of near solid
clear plastic with no detectable loss in volume or size. It may
remain somewhat sticky, or it may fully harden to the touch.
If you now take that sample and put it outside in very damp or humid
weather, you will find that it will soften up again. In other words,
that material is hydroscopic and will absorb water right out of
the atmosphere. Now add a drop of water to the sample. Surprise!
It will dissolve the solidified material very quickly. And if you
take a moisture meter reading of the solidified material on a piece
of glass, you'll get a high reading.
What you will have just demonstrated is the reason
why your hull won't dry, and the answer on how to dry it. What is
migrating out of your exposed hull laminate is a combination of
hydrolyzed polyester resin, salts and other chemicals. These sometimes
migrate to the surface where exposure to air causes the fluid to
naturally cure. But it doesn't go away. It just stays there alternately
curing and softening with the changing atmospheric conditions. On
a rainy day, it will probably become nearly fluid. After a few days
of cool, dry weather it cures again.
Now that you know this gook is water soluble, you
know how to get rid of it. Yep, just take a hose and wash it away!
But while the hull is wet, be sure to give it about 30 minutes to
completely dissolve.
"But won't I just be making my hull wetter
by putting water on it?"
Yes, but only temporarily. We've already discovered
that the fluid weeping out of the hull is NOT water and will NOT
evaporate. As you know, water evaporates very quickly, and the water
you use to rinse the hull down will too. Wet the entire hull down
and keep it wet for about thirty minutes. Then come back with a
hose nozzle and spray it with a bit of pressure to remove the remaining
traces since some of this stuff may take longer to dissolve.
On some boats you will actually see the accumulations
of fluid on the surface, most often in isolated spots that are little
weep holes. This indicates that there is likely a concentration
of fluid under the surface and it is finding its way to the surface
through a capillary. Most likely you will need to wash the hull
down at least three times depending on the condition of the hull.
In any case, this will greatly advance the "drying" process
and your meter readings should begin to drop significantly, only
to start rising again.
Take note of the fact that some hulls actually
do have plain old water saturation with only very small traces of
hydrolyzed resin. In this case, you may find that the hull starts
to dry quickly, but then an odd thing happens. The readings start
to rise again. If that happens, it's because the water is migrating
to the surface, and then leaving deposits of dissolved material
as it evaporates, possibly including salt (which is also hydroscopic),
so that the readings again start to rise. Again, simply wash down
the hull with water to remove it. If you have any doubts about this,
then only try a test area to see if it really works.
Also, if you are located anywhere near the ocean,
make certain that wind-blown salt is not accumulating on your hull.
Salt is hydroscopic and will condense water out of the atmosphere.
If you are anywhere near a shore with surf, keep in mind that salt
can easily be blown inland several miles, and it collects on everything.
It will, for example, accumulate on the topsides of your boat, and
then be washed downwards by rain.
Keep in mind that hydrolyzed resin may or may not
contain other chemicals such as salt. This means that there is no
consistency to how a moisture meter will read the stuff. Plastic
and glass fibers are not conductive, and since moisture meters operate
by metering conductivity, it will all depend on the water and salt
content of the hydrolyzed resin. It may be zero or it may be 30.
But there is one thing you can be sure of, which
is that if the hydrolyzed resin is not removed from the laminate,
it will once again absorb water and start the blistering process
all over again and your expensive blister repair job will fail.
No, despite all the hype about "barrier coats," there
isn't anything that is going to keep water out of the hull laminate
completely.
* * * * * *
If you haven't already started a repair job, but
are thinking about it, we'd strongly suggest you stop to consider
whether it is really possible to cure "boat pox." Shown
below is the disclaimer from a 3M product that is sold as a blister
repair material.
This product is advertised in boating magazines
as a repair for blisters. It does not say so directly, but rather
suggests that it is. Then, in small print on these cans of extremely
expensive materials, we read that the manufacturer is telling us
that the stuff is not intended for ANY particular purpose. It is
up to YOU to decide if this stuff is any good for anything because
3M does not imply or warrant that it is.
So, if you wonder why we tend to be a bit cynical
about the booming business of blister repair, there's graphic reason
why.
Posted June 27, 1999
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