PDA

View Full Version : coating with epoxy before building



dposner
03-26-2016, 09:04 PM
I have a question for the forum. Can one apply epoxy to planks before building in a stitch and glue boat?. To do so while the plywood planking was laying flat would make it much easier, but the question is whether or not the flexibility is lost to a degree that it would make assembly of the craft difficult. I've heard of this being done, but I'd like the opinion of the forum.

dposner

Larks
03-26-2016, 10:16 PM
I have a question for the forum. Can one apply epoxy to planks before building in a stitch and glue boat?. To do so while the plywood planking was laying flat would make it much easier, but the question is whether or not the flexibility is lost to a degree that it would make assembly of the craft difficult. I've heard of this being done, but I'd like the opinion of the forum.

dposner

I can't see why you'd want to, with stitch and glue, there'd be no real benefit that I can see as is just as easy to do it once stitched together and when gluing up. Also as you bend the planks you'd compromise the integrity of the epoxy anyway, so I think it'd be a waste of time and epoxy.

slug
03-27-2016, 12:28 AM
Sure...you can pre coat, sand flat on a table before assembly

On some structures its the best way to go .... saves very much time, epoxy and consumables.

Also keeps your shop a bit ceaner because you can sand outside or away from the build zone.

precoating stiffens the panel , so be careful if you are building something that has a lot of shape

precoating very thin panels can cause them to warp.

Be sure that secondary bond zones are well sanded and clean before assembly

boat fan
03-27-2016, 02:51 AM
Sure...you can pre coat, sand flat on a table before assembly

On some structures its the best way to go .... saves very much time, epoxy and consumables.

Also keeps your shop a bit ceaner because you can sand outside or away from the build zone.

precoating stiffens the panel , so be careful if you are building something that has a lot of shape

precoating very thin panels can cause them to warp.

Be sure that secondary bond zones are well sanded and clean before assembly

Most definitely.

Much easier done on the bench or a pair of saw horses .

Especially the sanding. You can get a better finish a lot easier that way.

Bent panels can get much stiffer though , so it may not work in every case.
If it`s a difficult bend without epoxy , it may make it near impossible coated.

You can leave the tape line un-coated ( raw plywood ) to aid adhesion at taped joints like chines etc..

skaraborgcraft
03-27-2016, 03:19 AM
As above, for "some" jobs it is a worthwhile thing to do, especially if dealing with large flat panels that may end up as a vertical surface; but for a s+g boats planking, i would not do so myself. There is enough sanding to be done with this build method without doubling it to prepare for bonding with pre-coated panels. I do not consider it to be time saving or material effective for small boat planking.

wizbang 13
03-27-2016, 06:41 AM
I would not bother.
More fun to sand a boat than a board.

dposner
03-27-2016, 08:22 AM
seems like a split decision. I went to CLC demo, and one of the members of the CLC staff had a 12 foot sassafras there, and he had coated the panels before assembly. He advised me to do it that way. the beauty of this forum is that everyone disagrees with each other. Love it!

Larks
03-27-2016, 09:40 AM
What are you building? If it's a flat shapeless hull, perhaps no problem, but it can be awkward enough to get the cut ply panels to pull nicely into shape without them being stiffened more with epoxy.

But - the beauty of building your own boat is that you get to try any method you want and no-one is really going to tell you that you are wrong - whatever suits you is the right method. So for the sake of possibly wasting a bit of ply and some epoxy - why not compare a couple of test pieces - i.e. one epoxied and one not - and see what sort of difference there is in bending and shaping them.

chortle
03-27-2016, 10:28 AM
seems like a split decision. I went to CLC demo, and one of the members of the CLC staff had a 12 foot sassafras there, and he had coated the panels before assembly. He advised me to do it that way. the beauty of this forum is that everyone disagrees with each other. Love it!

Definitely precoat if you can. I was a little skeptical that you could but I am in the process of building a PT11 and the designer recommended building it this way, (6) 1/4" plywood planks, 6" to 12" wide, 11' long with 4oz cloth and a fill coat of epoxy on one side. Coated them all at once on a flat table. It worked beautifully. The entire interior of the boat is now ready for priming and painting and I did not have to do it around the bulkheads and upside down by hand but with the boards flat on the table with a random orbital sander with a vacuum for the dust. The panels were not noticeably stiffer with the glass and epoxy on one side than without.

Dave B
03-27-2016, 11:04 AM
I've pre-coated and glassed planking on 3 different boats and wouldn't do it any other way. MUCH easier done flat.


Sent from my iPhone using Tapatalk

Todd Bradshaw
03-27-2016, 02:14 PM
You can often expect a big difference between bending an inside-glassed panel (like the inside of a dory's side) and one where the glass winds up on the outside of the hull. The glass on the inside of the curve is just being compressed a little bit, which it will usually do pretty easily. On the other hand, glass on the hull's outside is being put in tension and stretched. It doesn't like this and resists the bend a lot more. At some point, it can either fracture down in the weave with lots of little white spots forming, or in extreme cases, split wide open. It's all a matter of just how much bend is involved. Remember that the actual time for epoxy to fully cure is usually 7-10 days. Before that point, the possibility of visible fractures, where the tension is actually moving the yarns inside the epoxy and breaking fibers loose in there is a lot higher. Give it time to cure well before you start bending it.

Oldad
03-27-2016, 02:28 PM
No. Waste of time and material on a stitch and glue boat which is what application the poster asked for. Coat as you build.