11-18-2006, 12:15 AM
11-18-2006, 09:18 AM
Concrete?
Just kidding....
The fiberglass - embedded in resin of your choice - coating serves a couple of purposes. The adds puncture resistance, abrasion resistance, and (to me) most importantly, provides a smooth sheath over your plywood hull. Most fir plywoods are rotary cut (peeled) off of logs. This means that over a fairly short amount of time, the surface of the plywood will "check" or crack. Fiberglassing will help prevent this as it is basically acting as another surface veneer.
Now - with that said, I have built several small boats using very cheap "luan" plywood that is often sold as bathroom underlay. It doesn't have a tendancy to check (don't know why). Since these boats are stored under cover and not in the water, I have either just painted in one case, or used standard auto polyester resin as a coating and then painted with either latex house paint, or my new favourite - rust paint. These boats have held up fairly well - even the one that was just painted although after about 5 years there is some rot in places on it. Polyester resin is NOT water "proof" though. It is only water resistant but it resists water long enough for my purposes. Epoxies are water proof. I'm not sure about vinylesters.
Some people have also experimented with truck bed liner spray and other common substances. You could probably paint it with roofing tar and be reasonably sure of it being water tight - for a while at least.
In short - if you're using fir plywood, you'll want to fiberglass it otherwise you'll be forever sanding and repainting. Otherwise it depends on how much the boat will stay in the water and how protected it will be out of it and how you want to balance the life of the boat to the amount you spend.
As far as the salt water factor goes, I think - and may be wrong - that should only be a factor with whatever exposed metal you have.
Just kidding....
The fiberglass - embedded in resin of your choice - coating serves a couple of purposes. The adds puncture resistance, abrasion resistance, and (to me) most importantly, provides a smooth sheath over your plywood hull. Most fir plywoods are rotary cut (peeled) off of logs. This means that over a fairly short amount of time, the surface of the plywood will "check" or crack. Fiberglassing will help prevent this as it is basically acting as another surface veneer.
Now - with that said, I have built several small boats using very cheap "luan" plywood that is often sold as bathroom underlay. It doesn't have a tendancy to check (don't know why). Since these boats are stored under cover and not in the water, I have either just painted in one case, or used standard auto polyester resin as a coating and then painted with either latex house paint, or my new favourite - rust paint. These boats have held up fairly well - even the one that was just painted although after about 5 years there is some rot in places on it. Polyester resin is NOT water "proof" though. It is only water resistant but it resists water long enough for my purposes. Epoxies are water proof. I'm not sure about vinylesters.
Some people have also experimented with truck bed liner spray and other common substances. You could probably paint it with roofing tar and be reasonably sure of it being water tight - for a while at least.
In short - if you're using fir plywood, you'll want to fiberglass it otherwise you'll be forever sanding and repainting. Otherwise it depends on how much the boat will stay in the water and how protected it will be out of it and how you want to balance the life of the boat to the amount you spend.
As far as the salt water factor goes, I think - and may be wrong - that should only be a factor with whatever exposed metal you have.
11-19-2006, 03:27 AM
Laminating epoxy alone will not provide very much abrasion resistance (read next to none) to plywood and absolutely no puncture or penetration resistance to this material. Laminating epoxy will also not remain water tight for long without reinforcement (cloth) on raw plywood. Cloth set in epoxy will provide both, though the cloth will serve much better on the inside for puncture resistance, than on the outside. Penetrating epoxy alone will not provide either feature, it just partly seals the wood with a flexible plastic membrane.
On trailer boats, with the wish of not using epoxy, a hard paint will serve quite well. A linear, two part polyurethane will be the toughest, followed by the single part version, followed by epoxy based paint, in terms of hardness. Modified oil, straight oils then acrylics (latex) round out the list in paints, for durability and hardness. If the boat is dry sailed (trailered) then you don't need anti fouling bottom paint.
Andrew is very correct, in that the amount of care the boat receives, will determine what type of coatings to use and how long they will survive.
I currently have a test for truck bed liner on plywood and a few other types of wood (solid), to see how well it holds up. The plywood already has signs of separation from its coating, after almost a year in a 5 gallon bucket of water. It (the samples) has dried and been wetted repeatedly during the process, mostly from rain, with some dog spit tossed (they like to drink out of my text buckets) in for good measure. My conclusions aren't looking good for truck bed liner on Douglas fir ply, though the solid cedar is still looking pretty nice.
Again, Andrew is right, that fur will need a sheathing skin over it or it will look terrible. Fur has dramatic density differences between the winter and summer growth rings. This causes a washboard effect to appear when it is sanded. You can't sand it smooth. The more you try to smooth the surface the more softwood is removed and the greater the washboard effect becomes. The surface has to be filled, then sheathed (fabric and goo), which will hide the unevenness of the surface and prevent most of the checking from "printing through" the sheath. Eventually all thin sheathings will show some print through, but on trailer boats this may take many years.
Salt water does affect coatings differently than fresh, but all good quality paints can handle it with little difficulty. Salt water is reasonably easy on the paint, compared to UV and rain water collecting and not getting out of the boat. No boat ever rotted from the outside in, while in salt water. Fresh water is the enemy and why boats have to be covered and well ventilated. Even the condensation that appears in the morning dew or evening cool down can build up and cause problems. The first line of defense, after the cover and ventilation is paint (varnish is paint) and it needs to be the best you can afford, if you want long life.
On trailer boats, with the wish of not using epoxy, a hard paint will serve quite well. A linear, two part polyurethane will be the toughest, followed by the single part version, followed by epoxy based paint, in terms of hardness. Modified oil, straight oils then acrylics (latex) round out the list in paints, for durability and hardness. If the boat is dry sailed (trailered) then you don't need anti fouling bottom paint.
Andrew is very correct, in that the amount of care the boat receives, will determine what type of coatings to use and how long they will survive.
I currently have a test for truck bed liner on plywood and a few other types of wood (solid), to see how well it holds up. The plywood already has signs of separation from its coating, after almost a year in a 5 gallon bucket of water. It (the samples) has dried and been wetted repeatedly during the process, mostly from rain, with some dog spit tossed (they like to drink out of my text buckets) in for good measure. My conclusions aren't looking good for truck bed liner on Douglas fir ply, though the solid cedar is still looking pretty nice.
Again, Andrew is right, that fur will need a sheathing skin over it or it will look terrible. Fur has dramatic density differences between the winter and summer growth rings. This causes a washboard effect to appear when it is sanded. You can't sand it smooth. The more you try to smooth the surface the more softwood is removed and the greater the washboard effect becomes. The surface has to be filled, then sheathed (fabric and goo), which will hide the unevenness of the surface and prevent most of the checking from "printing through" the sheath. Eventually all thin sheathings will show some print through, but on trailer boats this may take many years.
Salt water does affect coatings differently than fresh, but all good quality paints can handle it with little difficulty. Salt water is reasonably easy on the paint, compared to UV and rain water collecting and not getting out of the boat. No boat ever rotted from the outside in, while in salt water. Fresh water is the enemy and why boats have to be covered and well ventilated. Even the condensation that appears in the morning dew or evening cool down can build up and cause problems. The first line of defense, after the cover and ventilation is paint (varnish is paint) and it needs to be the best you can afford, if you want long life.
04-07-2013, 11:18 AM
Well...that answers that question before I had to ask it :p ( I love the search function hehe) , my buddy was telling me that with the new epoxy resins I would not have to use fiberglass. I however will use it, and proceed per the build instructions.
Regards,
  Will
Regards,
  Will