Fabric reinforcement for boats; an incomplete tutorial

As plywood quality has changed for the worst in recent years and it does not look like the rain forest will be back soon, I have tried fabric reinforcement on three boat hulls, a number of smaller sub units and many test pieces. Recently, I have used fabric or fiberglass tape sandwiched between layers of plywood. Be cautioned that this does not make me an expert on the subject.

For the those new to boat building... Over the years builders have devised their own methods for testing adhesives, paint, plywood, etc. Many surprises have been found in these amateur tests, and I value them FAR above what the manufacturers claim.

Fabric choice
The fabric you choose may work better with paint, or better with glue.

When tested to destruction, heavy, courser weave (lower denier, .019" thick) is stronger, more puncture resistant, abrasion, cut and tear resistant. BUT... When it is impregnated with paint, glue, varnish or other fillers, the finer weaver, (more shear, .003") thin Dacron outperformed the courser, heavier fabric. The increase in puncture resistance was the biggest surprise. I can't even guess why this would be so, but I would use the sheer, fine weave Dacron you can find.
 

  Be cautioned that the fabric you test could very well produce far different results.  

As for abrasion resistance, the glue leaves some tiny bumps in places. I just sanded them off without damage to the fabric (or fiberglass tape, below). If your wood is halfway decent looking, you may even be tempted to varnish instead of paint giving a unique look to your boat.

Be sure to iron it (not too hot) before gluing to your Flapdoodle. I diluted the wood glue 50-50 and worked it smooth with my hands as it died. Kind of fun actually. Keep a bucket of water handy for cleaning your hands.

Canvas
Canvas was the first fabric I experimented with, and used polyurethane paint as the adhesive. The idea came from a site on the Internet that referred to it as "poor man's fiberglass".  The results were not all that good for me, but that may be in part to the resinous pine hull.

Dacron
I very much recommend making test pieces of the Dacron you are considering along with the adhesive or paint on the same type of wood you intend to use.

I had not shared all of the experiences with the X-Doodle. On one panel the Dacron was laminated to the wood with my favorite Glidden Deck and Porch polyurethane oil base paint. I did not think to iron the fabric first. Thankfully it was a hot day, because I worked with the palms of my hands for a very long time getting the wrinkles and air pockets out until the paint had enough tack to hold it. By that time my muscles were like rubber bands.

The next panel had a thin bead of polyurethane glue holding the edges of the fabric. After the glue had set, I used a (somewhat hotter) iron to shrink the Dacron. I have done this a lot, so I am good at it, BUT I had never done an area anywhere this large. Plywood that looks flat really isn't. The result was more air pockets that had to be massaged out with the palms of my hands. I can't remember if I used glue or paint that time.

By far the easiest is diluted Titebond II (I have not encountered Titebond III). I suggested a 50-50 mix with water, but the best ratio will have to be determined by you depending on temperature, humidity and personal preference.

HINT   Look at light reflected off a panel as the glue dries, and apply more glue to areas that look more dull then surrounding areas. This helps assure a uniform amount of glue. Glue will soak into areas that are more porous. This method also works with paint.

Paint is a huge mess and quite a workout, glue is kind of fun and goes quickly.

Tyvek
I have only tried this a few times with varied success. One problem was separation (delamination) of the Tyvek. It worried me enough to stop testing it. Save it for making sails or a boom shelter. Run it through the washing machine a few times will make it soft, more flexible, and far less noisy in the wind. DON'T dry it in the clothes dryer. There are types of Tyvek that are UV resistant, most are not.

Sources
Your local fabric store of course, eBay has remnants, Dollar stores have bed sheets.

Adhesive choice
I have used polyurethane paint, acrylic latex paint, and several wood glues. Other builders have successfully used varnish or epoxy. You will have to decide which is best for you. Again, make test pieces.

I have had good results using Elmer's Probond, Titebond II, and Glidden polyurethane deck and porch paint. For more information try an Internet search for " [product name] review "; For example a Google search for "Probond review"

If you are laminating, keep in mind that the larger the piece, the longer the drying time if you use water base glue. Avoid varnish or paint until you are certain that water base glue is dry.

Prime factors in adhesion to wood is: the species, amount of resin or pitch, and porosity. Some woods contain a natural wax.  In my experience, plain looking wood has tested stronger than fancy grain wood.

Preparation
When fabric is purchased from any source, there is no way to know if it has been treated. It may be impregnated with various things to make it softer, or less wrinkled to encourage purchase. It is best to wash the fabric in a machine but without fabric softener.  Almost all fabric softeners are tallow based.

If your clothes dryer has been used with fabric softener sheets, it would be better to dry your fabric on a line, or even over the bathroom shower curtain rod. This is because the softener sheets leave a residue on the drying drum that can be transfered to the fabric and may cause poor adhesion of your lamination.

Iron the fabric! Do not use a temperature setting higher than what you need. Too much heat may weaken the fibers, or in the case of Dacron, cause shrinkage.

Application
For smoothing fabric to hull panels, I use the palms of my hands. For laminated pieces, a small piece of plywood scrap.

Repair or reinforcing a small area
I have used smaller pieces of Dacron to reinforce small areas. Round the corners of the "patch" first. Sand the area.  I used Titebond II then apply, and smooth it as the glue set.

Sand lightly.  Apply wood filler around the edges of the patch and allow to dry.  A foam sanding pad made blending into the surrounding area easy. Once painted if can be difficult to find where the repair was made.

Fiberglass tape
I have only recently started experimenting with this for laminating plywood, but the results are very promising. The tape is meant for drywall (plasterboard, gypsum board) and can be purchased in large rolls inexpensively.  I have used it on seams in plywood boats with great success with just wood glue.

The number of fibers used in the tape can vary considerably from brand-to-brand. Shop around a little, and you will be able to see the difference with your eye. Go for larger, thicker glass fiber bundles.

In tests, the best results when laminating plywood were obtained when the fiberglass tape is running diagonal to the wood grain at about 45°. I used polyurethane wood glue; the kind that sort of foams as it sets.

I highly recommend two screws in addition to clamps as the glue dries, because, as it foams, the pieces try to "float" off to the side even though they are clamped or heavily weighted. Bricks, cans of paint, old car batteries are good for weights.