Glassing before construction?

Apr 16, 2010
Hi, all. I'm another new guy, filled with new guy questions. I apologize in advance!

I've gotten the Uncle John's pirogue kit, and ordered my glassing supplies from RAKA. Talking to the very helpful guys overe there when I was ordering my fiberglass and epoxy, they suggested glassing the plywood (or luan) sheets before cutting or construction. I have to say, that does seem like it would be easier for a novice like me to fiberglass a big, flat rectangle than a 3-d boat-shaped object.
My concerns would be the difficulty this might cause during construction. For example, would the sideboards flex as easily to form the "boat" shape? Would construction be more difficult in general?
I'm leaning against pre-glassing, unless someone can recommend otherwise.


a Bald Cypress

Well-Known Member
May 7, 2007
Northwest Louisiana
YO, welcome to the madness.

I know for a fact that this has been a subject of " BS " {Boat Science} [TM] before but, as you may well expect once you reach geezerdom, it gets harder to remember and easier to dis-remember things.

I do however believe that the general thought about "pre-glassing" was that it was not that good an idea.

The reasons you stated were of prime concern. ie.

Difficulty in bending the pannels, and cracking of the "stiffend " wood.

All in all, not a recommended procedure.

NOW: I am sure that one of the younger [GITs] {geezers in training} will chime in with the true results of the unofficial pre-epoxy poll.

Till then, try to restrain yourself and hold off on the build for a day or two,.


Well-Known Member
Aug 25, 2003
Central , Florida
Attaching the bow piece to the side boards is a snap , when tackling the stern the one side is fairly easy but that last one takes some pushing and holding ( best to have someone helping in that ).

Pre glassing the bottom and sides would make the glassing easier but I am not sure about when you go to bend them in to the stern piece. Off hand I would say that there would be more resistance , how much (if any ) I have no idea.

Plus by pre glassing you would have to glass tape the seams between the sides and the bottom to make sure it was secured , sort of a double glassing where if you glass it when it is together that step can be avoided since the glass seals the seams. You might be able to skip the tape is you run a good fillet along the inside seams and then glass the outside with a solid piece of glass. Unless you pre glass both sides of the boards then you need to tape it.

The thing I can see that sets me against it is the bottom piece. I always leave a 2 inch extension on the bottom , all the way around so I know it will fit. Then when it is on I trim that excess off. Using hand tools it is harder to cut threw the wood after it is glassed then when it is not glassed.

Each way has its advantages and it's disadvantages , that is something the builder has to decide on.

As far as the boat shape , it will have a wave in it even after you attach the ribs. The railing is what eventually makes it look like a boat and smooths everything out for you. .



Well-Known Member
bpbpthomas said:
Hi, all. I'm another new guy, filled with new guy questions. I apologize in advance!

I've gotten the Uncle John's pirogue kit, and ordered my glassing supplies from RAKA. Talking to the very helpful guys overe there when I was ordering my fiberglass and epoxy, they suggested glassing the plywood (or luan) sheets before cutting or construction.
I surprised they recommended doing this. Really surprised actually.

You be adding unneeded stress to the fiberglass weave and would be doubling up on fiberglass and epoxy needed.


Well-Known Member
Aug 25, 2003
Central , Florida

It surprised me also and I wondered why they said that , especially to a new builder , It had to be someone besides Larry at his place.
I can see someone who has built a few boats trying it or actually doing it ( I think a few folks on here have done that ) but for someone learning the steps it just did not compute. As you said , it is basically doubling up on the work and reducing your pleasure.

Heck , I was going to try it on the Bayou Skiff when I made it and canceled that thought before really getting serious about it. One reason was the lack of room to do it and the other was a stroke of luck. One day I will try it to see how it works but only for the inside of the boat. I want glass wrapped all the way around the outside.

"O" Well , everyone marches to a different drummer and that keeps life interesting....:wink:



Active Member
Jan 8, 2009
Lapland, IA
Time to enter my $.o2 worth- or less. The first UJ I made, I did exactly that-Glassed all the inside surfaces before I assembled it. Then I had to go back and tape the seams after the fillets and some sanding, then more sanding the edges of the tape, befor filling in the weave on the inside. Tne outside was covered with one piece of cloth.
The 2nd UJ became a four rib version on Larry's advice, and I did it the normal way-assemble fillet, then glass the interior. IMHO, the suggested way, glass after assembly is much easier, and less frustrating to try to get decent appearance. My boats don't match some of the looks on this forum, but hey, they float and I'm happy til the nest one.


Well-Known Member
Apr 5, 2007
on the bank of Trinity Bay
Hey Guys,
Follow this and then I want some comments on wheather this is right or wrong or just doesn't matter.

When you glass the panels before stitching, the glass on either side of the panel is relaxed, just laying there. When you bend the panel to stitch it togeather you wind up with the glass on one side under tension and the other side under compression. If you glass after stitching the boat togeather then the glass is just laying there netural in the shape of the boat. Any outside forces placed on the boat will give tension on one side and compression on the other side giving resistance to the forces applied.On a pre glassed panel what happens when an outside force is applied to the boat? Would the glassed after construction boat be stronger than the glassed before construction?


Well-Known Member
Jul 22, 2006
Denham Springs, LA
might be on to something Bob,

similar to a post tensioned concrete slab for your house - concrete under compression, steel cables under tension, already preloaded for new stresses and considerably stronger than conventional reenforced slabs.


Well-Known Member
Aug 26, 2009
Longview East TX
I pre glassed my panels (inside) and where bends are not severe it was no more difficult to assemble than without (Did both ways) but as Chuck points out you should tape the inside seams which adds extra (minimal) weight, it did simplify things with compound corners, but in a regular shaped hull I doubt the benefit would be the same,


tx river rat

Well-Known Member
Feb 23, 2007
Waco Tx
Personally I think it would be stronger.
Inside is glassed ,and bent ,yep that glass is compressed.What happens when you hit a rock the outside takes the blow so puncture strength is important. The inside is braced because you try to strech the glass and cloth ,if you preglass and compress that it will take more puncture penitration to reach the point where the glass and cloth starts to strech.
Boy hope you can get thru the mud and understand what I just wrote.
Apr 16, 2010
Wow, guys. Thanks for all of the thoughtful responses.
Seems like maybe a good way to get the best of both worlds is to glass just the insides of the side walls before construction. That will compress the glass when they're bent, making them stronger. But by not glassing both sides, the exterior wall will not have fiberglass that would have to stretch (and therefore weakened.)

So I'll glass the inside of the walls, then assemble, then tape the inside seams/do the "floor" inside, and the whole outside (including over the seams and up the outside walls.) That way I won't be "doubling up" on the glass except for one spot: the bottom of the inside walls.

What say you?


New Member
Apr 16, 2010
Ha! The "bpbpthomas" stands for "Ballpark Blueprints" + "Thomas" (my first name).
I was the co-founder of a graphic arts company called Ballpark Blueprints.
Thanks again, everyone, for advice. I'll keep you posted!
been watching this post and thinking....ohoh, he's thinking again.
Anyway, this is an Uncle John's. The bending of the panels is minimal and I think the whole issue of compression and stretching is completely moot. Fibreglassing a flat panel is ten times easier than a shaped boat. Laying flat on a bench would eliminate the worries of runs etc.
The extra tape require to assemble would also be minimal weight wise. I see this as the ideal way to do a boat like the UJ Pirogue. If one had a bench large enuff, several panals could be done at once with 50" cloth then cut apart with a razor knife. Worries of snapping panels when you use el cheapo ply would be gone.
That's the way I see'er


Well-Known Member
Call me the dead-thread resurrector!

Anyway...not much experience building boats, but some with both wood panels and fibreglass. I can see pre-assembly epoxy coating to give a good adhesion substrate for later glassing, and possibly glassing ONE side of the side panels, but not both.
Interested to find out more here.


Well-Known Member
Mar 4, 2009
makenmend seems to be the only person on here to actually build a boat using this method. Anybody else build this way or any new information.



Well-Known Member
May 13, 2014
Central Kansas and Central Texas
Guess I might as well pass on my experience and give you something to read. Sometime ago I glued a stripped deck and glassed on side to get ahead of the game. A few weeks later pulled it out of the shed to find it had warped so bad it wasn,t useable. About a month ago I had a good start on a pirogue. Glassed the outside, and had to quit because of some medical issues. Pulled it out today to start the inside, the tops of the sides are warped, and it is no longer perfectly square. All recoverable but will be added work. My thoughts are if you glass one side, don't wait too long to do the other side. It's more warped then the picture shows.
warped piro.jpg

Kayak Jack

Well-Known Member
Aug 26, 2003
Okemos / East Lansing Michigan
Andy, sorry to hear of the bad experience. Was the non-glassed side epoxified? A saturation coat may(?) have slowed or prevented absorption of humidity?

I've built only 4 boats. I got the wood building done before any glass application. Glassing was near the end, over a completed hull and deck. But, then, I prefer crunchy peanut butter tather than creamy.