Tech Tip Tuesday

I'm blushing. 

No, really  - blushing. 

How can you tell? 

I've been using epoxy.

Rather than lash frames, we've opted to bond the stringers to the frames with epoxy.  In this case, I happened to have a left-over kit of System Three's general purpose epoxy resin.  To create the adhesive, we have added fumed silica to the resin. (Note the dust mask that the student who was mixing the silica into the epoxy was wearing!  An excellent idea as you don't want to inhale the stuff!)  The System Three general purpose resin blushes a bit.  By that, I mean that it has an amine blush that rises to the surface f the bond joint.  This particular epoxy is amine based and the amine blush is a waxy coating that rises to the surface of the curing resin. 

This amine blush can raise havoc with the curing of finishes and the bonding of successive coats of epoxy if you want to apply them.  However, it is easy to remove this blush.  There are two tried and true ways.  One is with soap and water, the other is with household ammonia.  As we intend to coat the frames we're building with varnish or polyurethane before skinning them, we want to remove the blush to prevent problems with curing that can include retarding the cure or fish eyes in the finish.  You need to remove the blush before sanding so that you don't simply spread it around.

There are some resins that claim to be "blush free" - particularly clear-coat epoxies.  I tend to treat this with a grain of salt and assume that any epoxy that I use may have some amine blush.  It's a case of "better safe than sorry".

I'll tell you why I tend to be careful.   The first strip-built boat that I glassed with a particular vendor's epoxy said that I should prepare the surface before putting on a protective layer of UV filtering varnish.  I made the assumption that they meant sanding, and thoroughly wet-sanded the hull with water and fine-grit paper.  I then applied a good quality spar varnish with UV filters.  The next day, I went downstairs and touched the hull, leaving a finger print.  I figured that it was a bit cool in the cellar and let it wait.  I came home from work - same thing.  I let it sit two more days - a third finger print. 

After a call to the manufacturer's help line, I finally wound up removing the uncured varnish with solvents - a nasty, messy process.   I then prepped the hull per their instructions (ammonia and water) and then used their recommended proprietary coating.  I did have success, but learned a valuable lesson.

ALWAYS REMOVE THE BLUSH!

Tech Tip Tuesday

Don't be afraid of the Goo...

I've said it before and I'll say it again - students seem to be intimidated by working with epoxy. It's not as scary as it may seem. I think the biggest concern that most people have is that it is going to set up before they're ready for it to, or that it will not set up at all.

First, let me say that while I've posted an image of West System's 105 epoxy resin, there are many good epoxy manufacturers. West System is one, System III, Raka, MAS and others all make good epoxy. Choose one that is appropriate for your use. If you're building a canoe that you want to have a clear finish on that shows off the beauty of the woo, the clarity of the epoxy is an important choice. If you'll coat with a colored paint, this isn't such an important feature of the epoxy. Recently, my students have been working with West's 105/207 resin-hardener combination with good results.

Before you ever start working with the epoxy you should prepare. Read the manufacturer's instructions carefully. Get proper protective equipment including gloves, barrier cream, goggles, and organic vapor/particulate masks and/or great ventilation. You want to avoid exposure to the resin so that you will reduce your potential for sensitization to the epoxy. Get good materials to clean up after your epoxy - white vinegar is good for cleaning up uncured epoxy and acetone (some vendors recommend their proprietary solvents...) is good for cleaning up cured epoxy. Avoid using acetone or other solvents on your skin as they can drive the epoxy through your skin and into your system. Disposable wipes and paper towels should be handy as should drop cloths to protect surfaces that you don't want to have spoiled with epoxy. Set up a workstation with the supplies you will want - epoxy and pumps or other metering equipment, mixing cups and sticks, fillers, reinforcements, tape, scissors, razor blades, rollers, squeegees, brushes (foam or chip bristle - but if you use bristle, trim them short to make them stiff and apply epoxy to the base of the bristles near the ferrule to retain the bristles) a waste basket and spare gloves - in short anything you think you might want. Wear clothes you don't value much, or buy Tyvek (tm) coveralls - you will likely get epoxy on yourself.

If at all possible, work with items which are ultimately disposable if they will come in contact with epoxy.

Are you ready?

Nope. Not quite.

If at all possible, you probably want to work with a friend and plan your work. One person should be applying the epoxy, the other should be supplying them with mixed resin and materials as required. It really reduces the panic potential. Have a plan worked out for who will do what ahead of time - and whatever you do, don't let the person mixing the epoxy get interrupted and mess up the mix ratio. If you want pre-cut pieces of glass-cloth reinforcement, or bias cut strips, prepare them now.

You should both be prepared with an almost Zen-like calmness. There is no reason to rush and panic - you should be working within the temperatures that the manufacturer recommends for the resin system you've chosen. There are some things that will let you have more working time - don't leave mixed resin in a mass in a cup - put it in container that will spread it out a bit or apply it to the boat to slow the process down a bit. Keep in mind that typically for every 10°F rise in temperature, curing time will be cut in half and for every 10°F drop in temperature, the curing time doubles.

Are we ready yet?

Nope. Not yet.

We need to make sure that our work environment is correct. I know that there is no ideal workspace, but you need to do the best you can. It should have good lighting, be dust/dirt/fur/bug free, have good ventilation, out of direct sunlight, no animals, children or other distractions, be 70-75°F (for most resins, but again - read the manufacturer's instructions) with the ability to control temperature.

Ready?

Almost.

You've got to make a decision about how much time you and your assistant will have to work with the epoxy at a session. If you've got limited time, you'll need to let the epoxy set between coats (which requires a proscribed time/temperature combination for the specific epoxy system), and prepare the surface per the manufacturer's recommendations prior to applying subsequent coats. Typically this includes washing off amine blush with some form of liquid cleaner (usually soap and water and/or ammonia and water) and then lightly abrade the surface to provide a mechanical bond - 3M's Scotch-Brite (tm) is a good way to clean and abrade at the same time. We usually use denatured alcohol to wipe the hull down after that to assure that there isn't any residue left.

Ideally, I would have all boats we work on hot-coated. Because of the limited amount of time in my classes, we don't usually "hot coat" as there isn't enough time. I've discussed this before. This is because the hot-coating process provides for both a chemical and mechanical bond between the layers of epoxy. The downside? It takes a whole day (usually about 14 hours or more) to do this for the outside of the canoe.

We also usually put a sealer coat of epoxy on the hull before applying cloth - this helps minimize bubbles and "starved cloth" which is weak, structurally and not cosmetically pretty. When applying epoxy to bare wood, the ideal situation is to warm the work space up to heat up the wooden hull - to say 80°F or more. Then turn the heat off and allow the hull to cool as you apply epoxy - this avoids off-gassing of the hull which makes bubbles and improves epoxy saturation of the wood. If you try to epoxy in the sun, the sun will heat the wood, driving off gasses and giving you MILLIONS of bubbles. Not good.

After we've got the hull saturated and have prepared the surface, we drape the hull with fiberglass cloth. Fiberglass cloth has a coating - sometimes Volan (tm) which is a water-based coating that help the cloth saturate with either epoxy or polyester resin. You don't want to handle the cloth with bare hands and get oils from your body on the cloth which may prevent good saturation. Wear your nitrile gloves. Also, keep the cloth clean and dry to avoid loss of the coating and loss of transparency. To cut the cloth, it is a good idea to pull a single thread from the cloth's edge where you want to cut to give you a mark to cut along. This isn't as hard as it sounds, but requires a bit of practice to avoid breaking the 'glass yarn in the middle. Roll or "flake" the leftover cloth and store it so that it stays clean and dry and doesn't crease.


Smooth the cloth over the hull and work out any irregularities by carefully "massaging" the cloth with gloved hands. Avoid snagging the cloth on sharp edges.

Now we're ready to apply resin.

We measure out the proper ratio of resin/hardener and mix for at least 1/2 a minute being sure to get into all of the corners of the container to properly mix the epoxy. While we do this, we avoid mixing in excess air - you're not trying to whip the epoxy. Only mix an amount you are comfortable working with - if you mix too much, you're likely to waste it. You can always mix more, you can't mix less.

Apply the resin to the hull starting from the middle of the hull and working outwards methodically, avoiding wrinkles. The goal is to get all the cloth wet out so it is transparent. Pay attention for dry spots and bubbles. The most difficult thing to do is to apply epoxy to vertical surfaces with a squeegee - I usually hold the edge of the squeegee near the sheer against the hull and pour a little resin on the hull just above the squeegee and pull upwards towards the keel. Don't panic at this point - I tell students that it usually takes about 3 or 4 canoes before you really get comfortable with the process. I'm joking here, but not much.

If the epoxy you're working with starts to heat up or gel - stop using it and put it aside. You'll only make a mess if you try to use it.

When the hull is wet out, we go back, starting at the center of the hull and use the squeegee to remove excess epoxy by working from the keel towards the sheer with light pressure. This is because the cloth tends to "float" on the resin adding weight, but not strength. You should be able to see the texture of the cloth when this is done properly, but without white areas that indicate resin "starved" cloth. We wipe the excess epoxy off the squeegee using a paper cut with a vertical slit in it about 2" down from the rim. When the hull gets to the "green" stage - just starting to cure - it can be trimmed at the sheer and stems and reinforcements added at the stems and wet out. This is much easier than when the cloth is fully cured and hard.


Subsequent coats of epoxy can be applied with your choice of brush, roller or squeegee until the cloth is "buried" - avoid sanding the cloth which weakens the actual composite and ruins the transparency.

Not that hard, really, it just takes some patience, knowledge and practice.

While you're working, avoid contact and work as neatly and cleanly as possible. If you spill, stop and clean up - you'll only be spreading uncured resin everywhere. When done, clean up and throw away the items you can. One caveat here - avoid throwing away large amounts of mixed resin as curing epoxy is an exothermic reaction (it generates heat!) and can cause some real problems when it gets hot enough to smoke, melt cups and could potentially cause a fire. Dispose of carefully!

Tech Tip Tuesday

Cat recently sent me some pictures of the canoe that she is working on. She's chosen to use White Pine for the strips. It's not a bad choice, really - while not as light as cedar it is fairly lightweight, shapes well and is inexpensive. Some of the downsides include the fact that White Pine can be brittle, isn't really rot resistant and can have pitch pockets. Brittleness isn't a biggie if you can strip the boat with it and the rot resistance should be taken care of by the epoxy and fiberglass encapsulation. The pitch pockets, however...

Let me start with a little story - my father made a pair of nice Adirondack chairs for my DW and I that were out of White Pine. White Pine being a resinous wood, contains pitch pockets which are little areas that may or may not be seen and contain pitch. Being a rather savvy guy, I knew that before I painted them, I should seal them with shellac to keep the pitch from bleeding at any knots or pitch pockets. I then primed and painted over the shellac. The color was a nice hunter green. When I put the chairs out on the deck, they warmed up in the sun and the pitch pockets that I'd carefully sealed bled through. The chairs are still in the cellar - one of these days I'll put them out to see if the pitch has hardened up and I can fix the finish.

Back to Cat's canoe. She says that she has only a few small pitch pockets - about 5 on one side and she hasn't looked at the other. She was debating what to do about them. Here are a few of the pitch pockets:



I'm concerned that leaving the pitch pockets will cause the fiberglass layer to delaminate. As they are small areas, it might not be a huge problem, but it's better to be safe than sorry. One problem here is that there may be more pitch pockets than she can see, but the strips are fairly thin (~1/4") so most of them should be making an appearance.

To deal with this issue, she was thinking of excising the pitch pockets with an X-Acto knife and then filling the void with either a mixture of wood flour and carpenter's glue or a wood putty with mineral spirits.

First of all, the best approach is to avoid the pitch pockets before you put them on the boat. One method is to use a different species of wood that doesn't have them. If you're going to use a wood like White Pine, just be selective about the strips you put on and leave the strips with pitch pockets behind. You can also cut the pitch pockets out and scarf the strips together.

If you've built the boat, carefully excising the pitch pockets with a small sharp knife is not a bad idea. If there is residual pitch, a bit of denatured alcohol to remove the remaining pitch would be OK. Whatever you do, avoid the use of mineral spirits on the hull - residual material absorbed by the hull can prevent the adhesion of the epoxy and fiberglass coating that you'll be putting on the wood. For that reason, the wood putty with mineral spirits is not a good idea as a filler. I had a student try to find glue spots with a cloth dampened with mineral spirits at home. his epoxy/fiberglass layer had issues in the future and he had to remove contaminated areas of fiberglass and put repair patches in.

The use of wood flour and carpenter's glue is not necessarily a bad idea but, if you will be claddin with epoxy there are two issues. First, it doesn't saturate with epoxy and looks "light" in color. Also, epoxy doesn't bond well to the glue. I don't recommend the wood flour and carpenter's glue mix for that reason.

The best ideas is to use Dookie Shmutz. Dookie Shmutz is the name for a mixture of epoxy, wood flour (from the hull sanding) and fumed silica. (Cab-O-Sil is one trade name) The epoxy gives you the hardness, the wood flour the color and the silica is a thickening agent to keep the epoxy from bleeding out of the mixture. Once you've mixed a batch of epoxy, you add wood flour until it is the consistency of warm organic peanut butter. You then add silica until it is a creamy peanut butter consistency. This mixture is applied with a plastic spreader into the checks or voids in the hull. Avoid spreading on excess as it is difficult to sand off and can leave a blotchy finish on the surface of the strips. Masking areas you don't want to coat with tape works well, too - just remember to remove the tape before the epoxy sets.

After you've applied the epoxy filler and let it cure, you need to sand off the excess. Because it is significantly harder than the surrounding wood, if you try to hand-sand this, it will cause the softer wood to sand away first, leaving irregularities. To avoid this, use a sanding block or longboard and work carefully.

Tech Tip Tuesday

Glassing the inside of the canoe tends to intimidate lots of builders with the "What do I do in the ends?" question. As I wrote in my previous post, I simply trim the fiberglass (Before saturating with epoxy) as close to the stem as I can get it.

One of the most important points that I try to make is that you don't want a nice smooth finish on the interior. There are a three major reasons:

• If the finish is smooth, you'll wind up sliding around, particularly with wet feet.
  
• If the finish is smooth, it's probably shiny and the finish can be blinding in the sun.
• Extra coats of epoxy only add extra weight.

I usually try to wet out the cloth with one coat of epoxy and squeegee off excess epoxy so that the weave of the cloth is still apparent. I do the best job possible so that sanding will not be required. This gives a non-skid, matte finish even after a coat of varnish.

Like an ant in a syrup jar...

I guess I didn't really complete my story from my time up at WoodenBoat in in the middle of the summer. I sort of left folks hanging here.

To finish that tale up, I'll take you back to Wednesday morning of our second week building the Wee Lassies. As of that morning, the hulls were complete and we did a little bit of finish sanding to get them ready for fiberglass and epoxy. The process was very dusty between the sanding and cleaning both the boats and the shop before applying the epoxy. This is the point at which the biggest variation from the class I normally teach came into play. With a limited amount of time, we decided to hot coat the hull. Hot coating is a process where you lay up successive coats of epoxy before the prior coat has fully cured. It speeds up the process immensely.

We'd been given special access to some experimental epoxy from the folks at West System. It was a new version of their 105/207 epoxy forumulation. (resin/hardener) The 207 hardener we had was much clearer than the current product and a bit thinner, which aided the saturation of the 'glass. This was one of those times when taking a class at a place like WoodenBoat is really nice - first, we had access to this special material, and second, we had access to epoxy metering pumps (AKA : Goo Grinders...) to simplify the measuring of the epoxy. If you've ever got a project where you'll be mixing a lot of epoxy, get one!

Things went very well, overall and we managed to get 4 coats of epoxy on all of the canoes by the end of the day. Still, no matter how hard you try to work "clean" and to keep things neat, it seems that the epoxy gets everywhere. As a friend once remarked when working with epoxy, "I feel like an ant in a syrup jar."

Between the dust and the epoxy, I didn't bring my camera out at all that day, so no pictures.

Overall, it was a long, hard day, but by the end we had much to show for it. Here is a picture taken on Thursday morning:

Tech Tip Tuesday

Today's tech tip is an "advanced technique. It's called hot coating. and is used to apply epoxy quickly.

With my new students, I try to keep things simple and do things in stages. Once the hull is prepared, we apply a sealer coat and let it cure. We then lightly sand the sealer coat and wipe down with denatured alcohol (or acetone if you prefer...) Once this is done, the hull is draped with fiberglass cloth of the appropriate weight for the canoe. We then apply epoxy to the hull with a squeegee and once the hull is wet out, we remove excess epoxy to wind up with a uniform textured finish. Two bias cut strips are then applied to the stems before the first coat cures. After this cures, the hull is wiped down again and more epoxy is applied. This is repeated until the weave is "filled" and you have a smooth coat of epoxy - the cloth should be buried in the epoxy to the point where sanding the epoxy will not result in sanding the fiberglass cloth which causes the fiberglass/epoxy coating to lose transparency.

That's the long way.

To hot coat, you need a "blush free" epoxy for best results. With the hull prepared, you drape cloth on the hull. You then apply epoxy with a squeegee and then apply the two bias cut strips to the stems. Be careful to make sure enough epoxy is applied so that the cloth isn't "starved" which is seen as whitish areas. Here is where the hot coat part happens. After about an hour or two (depending on temperature) the epoxy is tacky and doesn't lift when you touch the hull with a gloved finger. At this point, it's time to apply another coat of epoxy. Repeat until the weave is filled. It should be possible to apply as many as 4 coats of epoxy in a day. It really speeds up the process, but requires doing a good epoxy job.

This is an important skill to gain - if you have a tight schedule, it's the only way to apply epoxy.

Please note - the picture above is for illustrative purposes only - I do NOT recommend his choice (or lack thereof) of safety equipment. You should avoid skin exposure, wear gloves and eye protection and work in a well-lit and well-ventilated are when working with epoxy. Some people even prefer to go the extra step and use a respirator mask with organic vapor cartridges.