It seems to be a fact of life that you only figure out the best way to do something right around when you don't need that information any more.
I've had a challenge with some light, tightly woven fiberglass I was talked into buying. I've had problems getting the cloth wetted out and also with bubbles forming under the resin. Also I've even had a build-up of resin under the cloth forming bumps and ridges. This has meant some pretty intense concentration and still not getting a very good result.
My "technique" has been to pre-fit the cloth, and then using a brush and a plastic putty knife to spread the resin around and through the cloth chasing bubbles out. This more or less seems to follow the suggestions in the plans. During my last couple of pieces on the deck of the Weekender, I tried one of the methods that the plans said didn't make any difference. I first lifted up a section of the pre-fit cloth and applied a fairly good layer of resin to the wood and spread that out with the putty knife to ensure that any divots etc that I didn't fill well enough before hand were full of resin. I then laid the cloth on top of this and brushed it down. Magically the cloth soaked up resin from below, stayed in place where I wanted it to be, and then I just had to fill the weave from above. There still were a few bubbles but nothing like what I had before and especially where the cloth was down the sides, wetting out the cloth and making it stay in place was much easier.
I don't know if this will be useful to anyone else or whether it is something that only works with light, tightly woven cloth but it seemed to work for me.
Good learning experience. But a bit of a challenge to get there. Just be careful you don't sand thru that lightweight cloth.
There is a treatment applied to fiberglass cloth during mfg. A sort of "sizing" which helps keep it looking nice and "finished" as well as helping to keep the integrity of the weave. With lightweight fiberglass this sizing can often close up the weave so tightly that a lot of resins won't penetrate the cloth if the solvents in the resins don't break down the "sizing". Most of the fiberglass cloth is treated to be used with polyester resins containing styrene and other chemicals which will cause the "sizing" to disolve and allows the resins to penetrate the fabric easier.
Unfortunately there are a lot of these that epoxy isn't compatable with and has a problem in penetrating. So it is always a good idea to check to see if this particular fiberglass fabric is compatable before purchasing it. Good deals are not always good deals at all when they won't work the way you need them to. :?
We had to always check to see if the cloth would be Ok to use with Polyesters, Vinylesters or epoxies and which epoxies. Most of the "esters" will work fine with any cloth treated to work with polyester resins. Unfortunately not all of those were compatable with epoxies.
We found that with lightweight cloths over plywood it was always a good practice to apply a sealer coat of epoxy or other resin to the plywood surface first. Let it cure to the "safe to touch" point and then lay out the cloth. It would stay where we put it just fine and then spreading the resin on with one of the plastic squeeges worked great as did the rollers. Brushes always gave us bubbles in working with the cloth. Seemed that the bristles just didn't have enough pressure to work the bubbles out.
We would wait just until the resin had kicked off and then apply another coat to fill the weave. Then if a flat panel we rolled on a sheet of 4 mil polyethelene and let it all cure. When it was cured the poly sheet simply pulled off cleanly and the glass required little sanding or further filling.
Barry has a good point about sizing. On cloth that has questionable sizing, shake the crap out of it. I mean treat it like a bath mat that is as dirty as it can be. The violent snapping, and shaking will loosen things up. Yup, it'll mess up the edges and make lots of little threads, but it will free up many of the fibers so you can get penetration. Of course this type of cloth shouldn't be used in structural applications.
Technique can be changed to help in light cloth, particularly polyester, which can float on the surface, making it a real chore to iron down. One trick I've used, which I employ when working over head or on vertical surfaces, but can be just as effective on horizontal areas, is to lightly mist the area with spray adhesive. I use the 3M regular duty stuff and very lightly dust the area with it, let it flash off, before placing the fabric. It will grab the fabric, but also let it be repositioned. It doesn't let it float and you can be more aggressive about applying epoxy without bunching up a pile of cloth.
Another trick is to wet out the area, then wait until it just barely has any tack left in it, then lay your cloth down, which does the same thing as spray adhesive, but takes longer.
It's always a good idea to apply cloth over previously epoxy treated materials. Out gassing can cause bubbles and pockets of pooled resin. If the surface is coated with epoxy (cured) then the cloth is applied, then this isn't an issue.
Paul, so if I coat my hull with CPES, before I glass, It will acctually be a good thing? I was wondering about that.
Thank You
Brian.
Yes, epoxy will seal the wood and prevent out gassing (mostly, depending on coverage and lumber type) Unfortunately, when going this route you must coat all sides, edges, holes, cutouts, etc. to "encapsulate" the pieces(s) or it isn't effective as a moisture barrier.
CPES or other penetrating epoxy isn't a complete moisture seal, in fact some paints are better in this regard. CPES has very limited use on taped seam builds (stitch and glue) as it's primary role is as a bond promoter for other things. It does have some uses, but not on the designs typically seen on this board.
I often have this conversation with small craft owners/builders about epoxy. It's use (correctly used) can add considerably to the cost of a small boat, maybe doubling the materials and labor, during the build. This is a lot to ask of a small boat and many can live without it.
If epoxy is used on a limited number of sides and not completely encapsulating the material, it is little more then expensive primer for paint or varnish. It will seal the side it's on, but will permit moisture to get in other ways (fastener holes, end grain, etc.) which will eventually cause the wood or plywood to "sheer" just below the penetration point of the goo, or permit rot to form, possibly trapping moisture because it didn't have a good avenue of escape.
I recently worked on a 1957 lapstrake runabout that wasn't epoxied, nor had any stick-um in the seams. It didn't leak, but at the damaged area, which was caused by a car backing into it. The plywood planking was in great shape and just needed a fresh coat of paint. I currently have a 1956, double planked utility, that is in better condition (both are very good) which I bought from a desperate house wife. It was double planked with 2 layers of 1/8" plywood and is just fine. Both boats have had good care, not exceptional. Both have original plywood planking. Each hasn't seen a drop of epoxy or other goo, just paint or varnish, kept covered, dry, in good repair when necessary and used with kindness.
The double planked boat could easily have been epoxied. The lap boat, could have had her seam "welded" closed with the stuff, but would they have lasted 50 years later? Though the goo has been in use longer than these boats are alive, I've yet to see an example of well cared for epoxy construction, this old and still in reasonable shape, let alone the wonderful condition these two boats I've described are.
To answer your question again, yes CPES is a good thing if it's application is understood. These boats have to rely heavily on the goos and hard adhesives we have available now. Many designs, like these, wouldn't exist if it wasn't for epoxy and the polys in a tube.
Thank You Paul I really am considering using the CPES, I am so far satisfied with it on my keel so maybee I could put it on my side pannels as I cut them, give them a good all around coat before I attach them, I am using hydroteck marine ply, would I be wasting my time doing this?
Brian
I'm using polyester resin so perhaps my situation is different - but it was suggested to me that I don't pre-coat any panels that were to be bent later. The concern was with the coating being brittle and cracking. What I've done instead is to make sure to coat and paint if appropriate, any surface while it is at it's most accessible. That's why the inside of my hull is coated and the inside of the cockpit painted before I put the cabin on.
This may not be the case with CEPS though. I've never used it.
A coating of laminating epoxy is very brittle, and doesn't do much good, as far as strength or abrasion resistance is concerned. Laminating epoxy (the regular stuff we all use) requires some sort of reinforcement to provide the qualities we need. The reinforcement could be fabric of differing weights or fillers of differing materials. The combination of reinforcements is extensive, but most are familiar with some of them, like wood flour, 'glass cloth, micro balloons, etc. When epoxy is mixed or applied with a reinforcement, it then becomes a very tough and durable material.
CPES is now a generic name for penetrating epoxy. Sort of the Kleenex of nose tissue in the goo world. Penetrating epoxy is not brittle, but dries to a reasonably soft, pliable coating, that gets into the wood fibers and seals it (sort of). It will provide no strength, nor will it make a plywood panel any stiffer then it was without it. All it does is soak into the cellular structure of the wood, where it dries, filling most of the pores of the wood, well enough to prevent most of the moisture from getting in and causing problems. The whole point of penetrating epoxy is as a "tie coat" (like a paint primer), it has no other function that can't be done with other, less costly products (like paint).
Penetrating epoxy isn't like laminating epoxy and has different physical properties as well as chemical. Chemically it has solvents that must flash off (evaporate) before it can complete it's cure. Regular laminating epoxy has no solvents that need to flash, everything in the hardener and resin, stays in the cured matrix (100% solids content after full cure). A small amount of unreacted materials (amines) may form on the surface of some epoxies, which is kind of like a waxy stuff. This amine blush as they call it, can interfere with additional applications of epoxy, so it has to be washed off, or otherwise removed. Not all laminating epoxies have a chemical combination that causes amine blush to occur, some being specially formulated to prevent this from happening. All penetrating epoxies that I've used (several brands) have never shown a blush, but the manufacture of your penetrating epoxy should be consulted first. If you are using a major brand penetrating epoxy like Smiths, System Three, West System, Raka or a repackaged product, like that available from Glen-L, etc. then they will not have a blush.
The trick with this encapsulation thing is just how the word sounds, complete and total embalming of the piece, before it goes in the boat. This must include all screw holes that will hold the part in place, every side, every cutout, etc. If the embalming isn't complete, you're just using it like expensive paint and it will rot because moisture can get into the wood, with limited access to getting out.
With plywood boats, you have to seal the wood. The choice is to completely seal it with epoxy or permit natural moisture gain and lose with paint coatings. Both methods work. Paint lets the wood expand and contract with moisture contact. Water gets in and then it gets out, when the boat dries out. Epoxy places a plastic bag around all the wood, preventing moisture from ever getting in. An epoxy coating can last a lot longer then paint, but the coating requires more upkeep to insure it remains waterproof. Paint can be neglected longer then a breach in an epoxy coating can, but has to be redone every so often.
The best method is an epoxy sealer (encapsulation), covered with paint. The least costly is just paint. The least amount of maintenance is an epoxy coating, left raw (only in areas it will not see any sun light), the combination of paint (varnish is paint) over epoxy is very good, but the complete seal must be maintained. Using just a paint coating doesn't require this maintenance vigil.