The Task
There are many different techniques to apply epoxy resin
and fiberglass cloth on stripper boats.
The results of each technique can vary greatly depending
on the skill, patience, powers of observation, ability to visualize, experience,
and dumb luck of the person applying that technique. These are a lot of
variables beyond the control of most novices.
However, there are a lot of variables that can be controlled.
This is my experience with fiberglass and epoxy lay-ups.
What works well and not-so-well.
The Problem
Epoxy
Epoxy is a syrup consistency. Lay-up transparency can
be achieved if you can make the epoxy thin enough to totally wet-out the
fiberglass cloth, so all the air is displaced and every fiber is wet. If
your epoxy resin is not nearly as thin as water it will not totally wet-out
your fiberglass cloth. If the glass has a silvery look to it from certain
angles, it has not been totally wet-out.
Some epoxy manufacturers advertise epoxy that will cure
at low temperatures. None of these are intended for fiberglass wet-out!
If you can only raise room temperatures to 70 degrees you may be able to
get a decent wet-out of fiberglass cloth with one of the special very thin
wet-out epoxies, but you will pay extra for these resins and they are not
for weave filling or gluing purposes.
Understanding how to make epoxy thin enough, for a long
enough time, is critical to solving the glass transparency problem.
Fiberglass
Fiberglass cloth can be wet-out in a transparent fashion,
but is not necessarily intended to be used in this way by those selling
it. Many builders of boats other than strippers use epoxy/fiberglass which
will be painted.
Some of the tighter weave glasses will not wet-out as
transparent. I've used some tight weave 4 oz. glass that would not wet-out
to a transparent level. Usually the more open weave glass will wet-out
better and produce a transparent lay-up.
I use open weave 6 oz. e-glass and 4 oz. s-glass for my
strippers.
Fiberglass cloth is coated with a special sizing to make
it compatible with epoxy resin. This sizing is sensitive to water and can
be damaged or removed if water comes in contact with it. The result will
be a glass weave that looks white. Be careful not to have water on a surface
or on your hands, that could come in contact with fiberglass cloth. Be
wary of a "sale" on cloth that might be water damaged.
HOW TO apply fiberglass and epoxy to a stripper
to achieve a totally transparent lay-up.
Strategies to Make and Keep Epoxy Thin
Heat
Like any syrup, epoxy will be thinner the warmer it is
and thicker the cooler it is. Too much heat will cause the epoxy to set-up
faster. An ideal temperature to make epoxy thin enough for our task is
85°. More on how to do this later.
Slow Hardener To counter the
quick set-up nature of epoxy when exposed to heat you must use a slow hardener
which is designed to slow the epoxy set-up in higher temperatures.
Small Batches Epoxy will also
set-up more quickly in larger batches, because the mass of resin will generate
it's own heat, speeding set-up. Smaller batches keep the resin from generating
heat and keep the resin thin. Furthermore, epoxy in any size batch will
start to thicken the moment hardener is mixed in, so using multiple small
batches will keep the resin thinner over application work time.
Flat Tray After the resin
is mixed it should be immediately poured into a flat tray. Spreading the
resin out into a thin layer will retard the set-up process, keeping the
resin as thin in consistency as possible.
Roller The flat tray and roller
work together to keep resin thin and spread a thin even coating of resin
on the wood or fiberglass for the best penetration and wet-out.
Thin Resin The bottom line
is that if your resin is not as thin as possible, you will not wet-out
the fiberglass to a transparent level. Manufacturers will tell you you
can work down to X degrees but that doesn't mean you'll have a transparent
lay-up. They're in the business of selling resin so they are going to tell
you what you want to hear. I've learned epoxy loves heat. Give it a nice
very warm place and it will wet-out glass, dissipate bubbles and saturate
wood very nicely.
Methods of resin application:
The rough surface of the weave of fiberglass cloth
naturally creates foam with all application methods.
Squeegee -
Spreading a pool of resin is quick on a flat surface.
This is great for small surfaces like bulkhead panels.
On curved surfaces you must chase runs or let them fall.
This makes controlling the resin application dependent on slope and gravity.
On vertical surfaces application of resin is very difficult at best. Gravity
is in control, not you.
A cup full of resin and the means to spread it around, make it irresistible
to pour on a lot and smear it about.
A large batch of resin in a cup will set-up fast. Resin
poured on glass will make glass float on top of resin and wet wood unevenly
making a blotchy appearance. The pool of resin, whether above or below
the glass, will be forced through the glass weave by the squeegee. As the
squeegee presses down on the glass, especially when the glass is floating
on resin, a wave of glass precedes the squeegee edge, forcing resin through
the weave, creating a micro foam that will give the glass a milky appearance.
This micro foam is very hard to remove or dissipate. Wood/glass can be
starved for resin if the squeegee and pool of resin passes over the cloth
too quickly. All these issues are a big negative to me for wetting-out
large areas of glass.
Would you paint your walls using a squeegee? The mess
involved in doing so is obvious. Just because a lot of the surfaces on
your boat are not vertical doesn't mean you won't end up with a terribly
uneven blotchy application.
Spreading resin on the interior of a hull seems like a
natural right? Big bowl shaped surface, the resin can't run off of. This
is one of the biggest mistakes you can make. Again, pouring a pool of resin
on glass will soak through and float the glass on the excess resin. When
the resin thickens (as it does from the second you add hardener) you will
have a lot of excess resin trapped under the glass adding unnecessary weight
to your boat.
The only positive for the use of a squeegee for resin
application is that it's CHEAP. If you really get off on being cheap you'll
love the squeegee because you can use it over and over and not pay for
roller covers or disposable brushes.
I only use the squeegee for removing excess resin from
the glass wet-out (See photo above/right) or for small flat
panels, like bulkheads, where they will not be seen.
Brush
I just don't like the brush method. The amount of resin
a brush will hold is small. Application is slow. The coating is irregular
which means more sanding to level. More sanding of an irregular surface
makes a fair surface harder to achieve. Little foam is generated, which
is the only appeal of the brush method for me.
Both the squeegee and brush methods will work naturally
from the epoxy mixing cup. This is a mistake, which will cause your resin
to set-up more quickly and wet-out fiberglass poorly.
Roller
I like the roller method best. The roller can apply
a thin even coat of resin quickly. If you have drips or runs you're applying
too much. The roller allows great control of how the resin is applied.
This is very important because this allows you to roll on resin on the
cloth bias (diagonal strokes to the cloth weave) which will smooth out
any wrinkles in the cloth during application.
The one thing most people don't like about foam rollers
is that they can generate foam in the resin. If you roll back and forth
vigorously you will generate foam, so don't do this! If you follow my suggestions
below for thinning your resin, any foam will dissipate during the glass
wet-out. Foam generated during fill coats can simply be removed by "tipping
off" (dragging the tip of the foam brush) over the resin surface with
a dry 4" foam brush. I find this tipping off a real advantage because
it also allows me to smooth any out drips/runs I didn't see and results
in a smooth surface requiring less sanding.
If you find you have problems with drips and runs you
are applying too much resin! This is easy to do with Squeegee and Brush
and the will to fill that weave. Three thin coats with a roller (you can
put on too much with a roller also) will save time over sanding and scraping
drips and runs.
Application
To further slow the resin set-up and keep the resin as
thin as possible apply the resin with a 3" wide paint roller frame
and a special foam roller cover designed for use with epoxy. This narrow
roller width will conform well to the curved shapes of a stripper. Roller
covers are sold in 7" and 9" widths. Buy the 7" widths and
cut the roller cover in half to use on the 3" roller frame. The best
roller covers I've found are sold by "West Systems Epoxy". These
roller covers have only 1/8" of foam on them and generate very little
foam.
Some people are afraid of applying epoxy with foam rollers
because the foam roller covers will generate foam in the epoxy.
This problem is greatly reduced or eliminated by: 
Using very thin epoxy, the "West System" roller covers, and by
not "over rolling the surface". Roll the resin on slowly and
don't roll back and forth briskly. Follow up fill coats with a foam brush
"Tip -off" which will eliminate air bubbles and smooth out drips
and runs.
I start my wet-out in the center of the hull or deck and
apply the resin with a roller toward one stem. Roll on the bias (diagonal)
of the cloth to smooth out any wrinkles. Then go back to the middle and
work toward the other stem. Then squeegee the excess resin off the first
half and then the other half. If you start at one stem end, you will be
pushing any wrinkles the whole length of the boat and can have problems.
I use squeegees cut from plastic milk cartons. This is
stiff enough to remove resin but not so stiff it will starve the glass
or move glass. See photo at right.
Reducing the Struggle to Absorb Resin
On a stripper you must coat the wood and wet-out the fiberglass
cloth with epoxy resin. Some builders apply dry cloth over dry wood and
wet-out both at the same time. This causes a struggle for the epoxy to
be absorbed it two different directions. One to the wood and one to the
glass. This can cause an uneven wet-out of the wood, resulting in uneven
blotchy coloring. And this can cause uneven wet-out of the glass resulting
in a less than transparent wet-out with white areas of resin starved glass.
Starved glass will show up as a whitish area and can be
structurally weak in the final glass surface. It is harder to know if your
wood has all the resin needed for optimum strength, because you will not
have as clear a visual indicator.
To eliminate these potential problems, wet-out the wood
first, then once the wood surface is tack free, lay on the glass and wet-out.
Separating the wet-out of the wood and glass ensures a transparent lay-up
with consistent wood color.
Seal Coat application to bare wood.
Coating Bare Wood (Seal Coat) Before Glass Lay-up
Roll on a single coat of resin using all the procedures
outlined above for maintaining thin epoxy. The wood will absorb the resin
at different rates in different areas. DO NOT apply more resin to a spot
that looks dry. If you try to do this you will build up extra resin in
adjacent areas which could effect the wood color making it look blotchy
and creating high bumps of unabsorbed resin. The single coat of resin will
do the trick. Do not sand the surface.
Room temperature is a very important consideration
during the coating of bare wood. When temperatures
are rising, air in the open cells of the wood will expand and expel from
the wood, creating air bubbles in your epoxy. If you think this is a myth,
try coating a piece of wood and placing it in the sun or under a spot lamp.
Be careful of having spot lamps near your hull when you are coating with
epoxy.
And I can certainly understand that it's not convenient
to wait to heat a whole shop up to 85 or 90° and then let the temperature
drop a few degrees before wetting out your glass. It is worth it however
to insure the best results.
The rising of a few degrees will have an effect. On the
interiors of my hull and decks I'm often pressed for time and I will not
wait for temperatures to drop. With all the other factors being, equal
per my lay-up conditions, I've noticed bubbles in the lay-up
and staple holes (yes, I use staples on my hull bottoms) blowing bubbles
in the resin. On the hull and deck interiors this is not noticed nor a
structural concern.
When temperatures are dropping the opposite happens. Air
is sucked into the wood cells. You can use this action to achieve a bubble
free wood surface by always coating your bare wood with the temperatures
falling in your shop. One coat on the wood is sufficient to give the wood
most of the resin it needs and to produce an even coloration of the wood.
This will greatly reduce the battle with the glass
to absorb resin. One coat of epoxy is not sufficient to create an air tight
or waterproof surface or seal the wood cells, so you must repeat the falling
temperature routine during the glass wet-out to ensure a bubble free lay-up.
So if I know this effect is going to happen, I can use
it to my advantage to pull resin into the wood cells. It makes sense that
if the wood cells are pulling resin in, that I'll get a stronger bond too.
On the glass wet-out using these techniques I find any
air bubbles created by rolling on resin will dissipate.
Glass Wet-out
with roller.
Shop Temperature
If your resin is warm, but your wood is cold, or your
glass is cold, the warm thin resin will cool and thicken when applied.
The best procedure for warming the epoxy resin, keeping
all your materials warm, and applying resin during dropping temperatures
is to heat your whole shop up to 85 to 90° and then watch your thermometer
drop.
If you apply all the above lessons, your resin will remain
at its thinnest state for the longest period of time, which will allow
air bubbles and foam to totally dissipate. And any uneven resin absorption
of the wood will even out, eliminating a blotchy wood appearance.
If you apply any of the points I've outlined above, the
clarity of your lay-up will improve. If you apply all the points I've outlined
you will CONSISTENTLY produce a transparent lay-up.
If you can't heat your shop to 85 or 90° then you
must use one of the specialty epoxy resins that are very thin and designed
specifically for glass wet-out.
Even when using a special, thin, wet-out resin, you must
apply all the above outlined procedures to have the best chance of achieving
a transparent lay-up.
However, if your shop temperature is below 70° your
chances of achieving a truly transparent lay-up are greatly diminished.
Additional Layers of Glass
If you are going to add a second layer of glass below
the waterline it is best to do this AFTER the full glass layer is tack
free. West Systems has done research and found the best multiple hand lay-ups
result by doing it this way. Two layers of glass wet-out together will
swell more with resin and excess resin cannot be removed to make the most
light-weight lay-up. AGAIN, follow all my tips above for achieving a transparent
glass wet-out.
Filling the Glass Weave
After the glass wet-out, additional coats to fill the
weave require "tipping off". Drag the tip of a dry foam brush
over the surface of the wet resin to remove any air bubbles. If you apply
a seal coat to your bare wood and then wet-out your glass as I suggest
the wood will be totally sealed and you will no longer have any "off
gassing" of the wood. This means you can use cooler shop temperatures
and a medium hardener with your resin for a faster set-up times for the
fill coats.
Any Exterior Seam Tape glass applied to your boat such as exterior deck/hull seam tape and
stem reinforcement must also be applied utilizing the warm temperature
/ thin resin techniques outlined above, for it to be transparent.
A Transparent
Glass Lay-up
Is it Worth It?
Some professional builders are unfamiliar with the techniques
I've outlined to produce a truly transparent glass lay-up. They go to great
lengths to avoid applying a reinforcement layer of glass over joints and
seams because these layers will be visible using their glassing technique.
These builders use and advocate devices such as laminated stems and the
sheer clamp method of joining the deck and hull, so they can avoid using
a second layer/strip of glass in these areas. Home builders who are unaware
of the reasons for these devices often use them AND apply a second strip
of glass reinforcement, defeating the purpose of these devises and adding
much more work to their project.
Understanding just how clear and transparent a lay-up
is possible, is hard, if you have not seen a truly transparent lay-up.
Many novice or even pros builders, use a squeegee and medium hardeners
with their resin plus cooler temperatures during glassing. And they are
happy with the results. But what looks good in the low light of a shop
is revealed in ruthless full sun. If you can see "silver fleck"
this silvery glass weave visible at some angles to the surface, the glass
has not been thoroughly wet-out. There may be micro bubbles in the surface
that you may not notice except under close inspection.
This may not be an issue for you if this is your first
boat. When we build our boats, our noses are 3" from the surface and
we see flaws we will forget and few others will notice later.
I'm a professional builder. My standards are much higher
and that's how it should be. If you wish to take the little extra effort
to have the best results possible, you can follow my suggestions on how
to achieve a truly transparent glass lay-up.
One possible drawback to achieving a transparent lay-up
is, if you have not done a good job of sanding your wood, any scratches
left in the surface by poor sanding will show up like a sore thumb!
All the best,
Rob
I realize more and more how small details make a big
difference. Using the right foam roller covers, or a certain varnish or
sanding with soft interface backing pad on your random orbital sander can
make a huge difference in how a technique works. The constant problem is
when companies new and improve the good stuff out of existance. This makes
it hard to name a brand or style and have it stay available.