and More Shop Tips

Updated 2/19/15 How-to Make a Transparent Glass Lay-up

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.

“Good judgement is the result of experience and experience the result of bad judgement.” - Mark Twain

The Problem

First off, epoxy is weird stuff. It's easy to overlook the obvious, since I've been working with it for almost thirty years. I can't remember anyone talking about this, you just find out the hard way.

Epoxy is similar in viscosity to pancake syrup. At 70˚ F. it is fairly thick. In colder temperatures it will become thicker and in warmer temperatures it will be thinner. So external/shop temperature is an important variable in changing the viscosity when handling epoxy.

To change the epoxy into a solid, a hardener is added to create a chemical reaction and this chemical reaction produces heat. This internal heat generated by the epoxy mixture is greater when the epoxy is in a mass like a mixing cup, or it can be slowed by spreading it thinly in a flat tray (like a roller tray) or spread in a thin coating. So warmer epoxy cures faster, cooler epoxy cures slower.

The wild card is the hardener. So to work with epoxy you must think about the external heat, room temperature, and how the hardener creating internal epoxy heat will work with or against the external temperatures. Typically, if you have colder temperatures you would want to use a faster hardener to counter the exterior cold with interior epoxy heat. BUT, since the cold external temperature will make the epoxy thick and the fast hardener will cure quickly this scenario is a poor one for wetting out fiberglass cloth as the thick resin will cure before the glass can be saturated.

If you are working in higher room temperatures you would add a slower hardener to counter the room temperature influence to make the epoxy cure too fast.

AND warm room temperatures will make the epoxy thin and slow hardeners will give the epoxy a long cure time, both of which are ideal for wetting out the fine twisted fibers of glass in fiberglass cloth to a transparent condition.

REAL pancake syrup, poured on a surface, will self level over time since the viscosity does not change.

The moment you mix hardener with epoxy resin the epoxy mix is getting thicker, reducing it's leveling capacity.

Since epoxy resin / hardener mix is changing the viscosity immediately, the epoxy mix may or may not have enough time to level as it cures. Most often the epoxy does not have enough time to level, so it reflects the rough texture of the fiberglass cloth.

Faster hardeners and warmer temperatures also make the epoxy molecules dance faster so they will cure (freeze) in a rougher surface.

Each epoxy manufacturer has different ideas of what an epoxy should do, so they mix different additives giving each epoxy different characteristics.

I have worked with West System epoxies, MAS and System Three epoxies. Each is different and the hardener combinations of each epoxy add more variables.

If epoxy is applied to a smooth surface it can create a smooth surface when cured.

Epoxy is thick at room temperature. Mix it up and pour it on a flat surface and unless the surface is PERFECTLY flat, epoxy will run right off an edge. Slowly, but surely! This gets a lot of people in trouble because they want to have a thick coat of epoxy. The novice tendency is to apply a thick coat and find out later, how epoxy drips and runs and flows onto the floor, even though it looked nice and smooth ten minutes ago. The best controllable method of building up a greater thickness is with a number of thin even coats of epoxy.

Laminating with Epoxy

Epoxy is a syrup consistency. Lay-up transparency with fiberglass cloth can only be achieved if you can make the epoxy thin enough to totally wet-out the 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 totally transparent fiberglass wet-out! If you can only raise room temperatures to 70 degrees you may be able to get a decent transparent 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.

EVERY epoxy is different! Every epoxy manufacturer has a different formula that has qualities that can be an advantage or a disadvantage. For instance, the System Three General Purpose resin I use, with slow hardener at 85˚ is great for glass wet-out. It allows all bubbles to dissipate and results in a transparent lay-up. System Three says I can re-coat up to 72 hours without sanding.

MAS epoxy works well at 80˚ and sets-up in half the time. MAS says I must sand after it is tack free. I've had a lot of problems with bubbles in the fill coats using MAS, even with tipping off or hitting bubbles with a heat gun.

System Three goes on smooth and bubbles are easily removed by tipping off with a foam brush to produce a surface as smooth as varnish.

I'm currently wetting -out my exterior glass and fill coating with System Three General Purpose resin.

I use MAS for interior glassing and gluing parts due to its faster set-up.

System Three resins provide a huge advantage for the home builder, over other resins.

System Threes resins provide a chemical bond for up to 72 hours before sanding between coats is necessary! All System Three hardeners have a longer cure time than other resin systems.

Longer cure time means, more time for bubbles to dissipate, more time to allow the resin to totally wet-out cloth and wood, and this allows the resin to trap less bubbles to begin with curing to a smoother, bubble free surface, requiring less sanding than other resins.

These features make it the best for home builders because, the home builder does not need to rush, or worry about the resin setting-up before they finish application. And the long chemical bonding window means you can do a seal coat one night, a glass wet-out the next night, a fill coat the next night and so on. This breaks the tasks into smaller, less rushed, easier steps, and reduces variables.

System Three epoxy cures to a smooth surface requiring less sanding.

System Three is not paying me for this endorsement. I think this is significant information to make strip building easier for the novice.

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.

Usually, a more open weave glass will wet-out better and produce a more transparent lay-up than tight weave fiberglass cloth. I've used some tight weave 4 oz. glass that would not wet-out to a transparent level and remained looking slightly white.

I use open weave 6 oz. e-glass and 4 oz. s-glass for my strippers.

Fiberglass cloth absorbs epoxy resin slowly, so give it time to absorb. The epoxy must displace all the air surrounding each fiber in each strand in the cloth to become transparent. It's best not to over work resin into a small area until the glass is totally wet-out because this can introduces bubbles. Apply resin to the cloth and move on, to coat the next area, giving the resin a little time to soak in.

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 for a Transparent Lay-up

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 (System Three regular resin and slow hardener) thin enough for our task is 85°. I've used MAS epoxy and slow hardener at 80° with similar results. Resins and hardeners are different. Read the instructions provided with or on-line. The System Three resin with slow hardener took 8 to 12 hours to become tack free. The MAS epoxy and slow hardener was tack free in 4 hours. The best advise is to work up a test panel to gage results.

Recently, West Systems published a chart, showing when their epoxy was at 70˚, it became twice as thin and more, when heated to between 75˚ and 85˚. I suspect other resins will do the same, so heat is a critical factor in achieving a transparent lay-up. BUT heating the resin alone is useless if it is applied to cold materials.

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 (I never mix more than 6 oz. at a time) 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 bubbles and 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, makes it irresistible to pour a lot on the fiberglass and smear it about.

A large batch of resin in a cup will set-up fast. Resin poured on fiberglass will make the fiberglass float on top of resin and wet wood unevenly and can leave 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 below / 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. However the need to brush over and over to spread out the resin in a uniform coating introduces more opportunities for bubble generation.

Both the squeegee and brush methods will work more naturally, directly out of the epoxy mixing cup. This will cause your resin to set-up more quickly, wet-out fiberglass poorly and add weight to your boat.

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!

95% of foam can be eliminated by allowing the foam roller cover to absorb resin BEFORE you try to apply resin to the boat.

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.

I've found MAS epoxy especially prone to holding bubbles and requires going over the surface with a heat gun to pop them, along with the rest of the technique above.

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.

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:
Allowing the foam roller cover to absorb resin BEFORE you try to apply resin to the boat.

Use very thin epoxy, the "West System" roller covers, and don't "over roll the surface".

Roll the resin on slowly in one direction and on the cloth bias to remove wrinkles. Don't roll back and forth briskly trying to work the resin into the cloth. Give epoxy time to absorb into the fiberglass cloth. 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 in 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 if possible. I use System Three Resins which allow up to 72 hours before sanding is needed. Check the information provided with your epoxy or contact their tech support for when sanding is required. If you must sand, sand only lightly with 120 grit to create a tooth for adhesion, don't sand off the seal coat!

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. This is called "Off Gassing" 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 using spot lamps near your hull when you are coating with epoxy because they will heat that area and cause off gassing.

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.

Rising temperatures of a few degrees can have an off gassing 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.

During the glass wet-out, using these techniques, I find any air bubbles created by rolling on resin will dissipate.

A seal coat is ONLY used on the hull and deck exterior, to ensure a transparent lay-up.

 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 80° to 85° 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 80° or 85° 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.

A single layer it all that's needed. After thirty years of using glass I stopped adding a second layer on all my boats, because I've learned one layer is all you need.

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.

The first "Fill Coat" applied to the fiberglass surface is the most prone to creating bubbles. The newly wet-out fiberglass has a stiff and very rough surface. Any resin application method or "tipping off" of the surface that drags the tool over the surface will produce bubbles. I use a roller for resin application which does not drag across the rough glass. I do tip off any remaining bubbles with a dry 4" foam brush touching the surface very lightly, so I'm not creating more bubbles than I'm breaking.

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,


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 existence. This makes it hard to name a brand or style and have it stay available.

 New Updated version of Rob's Kayak Building Instruction Book!

This book comes with all of Rob's Kayak Plans.

OR, buy it separately, and use it to build any designers stripper kayak, faster and easier.

All the great innovations Rob pioneered are included, such as stapleless stripping using hot glue, bending strips with a heat gun and magnetic hatch covers!

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detailing the building techinques of Rob Macks

NEW! "Magnetic Hatches & Cockpit Coaming"

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