: 3 coats on the bottom. 2 if you are really good at painting on an
: even coat, I usually find I have a few pin holes after two
: coats.

Just a thought here--something you might try would be to "paint" your fabric with the solvent or base of your paint before applying the first coat of paint to the dampened surface. For example, if your paint is water-based, use brush on water and lightly dampen the fabric before you apply the paint. The idea here is that the pre-dampened surface would allow the first coat of paint to soak in a bit deeper, and pin holes would not form.

Pre-wetting the material works in a different manner than simply thinning the paints. You can try this with watercolors on paper and see the effect with "wash" techniques. If you prewet the surface, the fibers of paper or cloth absorb the moisture (on freshly sanded or planed wood this would be absorbed through opened pores.) This causes the substrate to swell slightly, expelling trapped air before the paint is applied. If you simply thin the paint it will soak in deeper, but the material is diluted, and sits on the surface as a thin layer which can run, and as the paint hardens,the underlying fibers are busy swelling and squeezing out that trapped air into the partially cured paint--where they get trapped as pinholes.

It is a similar idea to one which is familiar to epoxy users: apply the epoxy warm and let it cool as it sets so that trapped air is NOT expanding.

With oil-based coatings you would want to use a paint thinner as your precoat. Maybe. Here the progam gets a bit iffy, and definitely you would want to experiment on some test swatches. Some solvents do not cause the substrate to swell. They just don't work like water does. When they don't swell the substrate, though, they MAY satureate deeper, and draw in the first paint coat through capillary action. This would work for you, too, but through a totally different process. (Win-Win???) And is some cases it won't do a darn thing. :(

In his book on canvas covered boats, George Putz suggests wetting cotton duck fabric (canvas) with water and then applying an oil-based paint directly on top of the damp cloth. I had a hard time understanding the reasoning behind this, for it is the common perception that oil and water do not mix. However, (as best as I can figure it out) the water will swell the fabric, and the water vapor can evaporate through the back of the fabric as the oil-based paint is displacing it and slowly soaking in on the face of the fabric. The technique has worked for him for quite a while.

Which leads to one more experiment: if you are using an oil-based covering, are you better off dampening it (not saturating it, just getting it damp) with water before applying the first coat.

Cotton swells quite a bit when it gets wet. Will this translate to synthetic fabrics like nylon and polyester? It should, but the swelling effect won't be so dramatic. Both of these fabrics swell slightly with increased moisture.

If you would like to try some samples, get a few embroidery hoops at the fabric store. They make these up to the size of a kayak cockpit for just a few dollars, and the smaller ones are even cheaper. You should have plenty of scraps of cut-off fabric. Hoop up the biggest pieces you can (stretching and shrinking is going to be more obvious in big sections of fabric) and try some dampening and an ounce of your coatings. Once they harden you can remove them from the hoops and reuse the hoops for another test. Alternately, you can make some frames and staple your test fabric to them.

If you can reduce the number of coats of paint you apply you can save the cost of the materials and the time involved in recoating and witing for that last coat to dry. Saving time and money is a good thing.

Just a couple of thoughts for you.

PGJ