Laminating sheets of plywood together

[Konrad in Lincoln]

Hey guys,

I'm starting an iceboat project, and am mulling over the plywood side decking for the fuselage. The prints are circa 1950's, and they call for a 14'-0" long, 1/2" thick sheet of plywood. (Yeah right, like THAT exists. :shock: )

I can laminate 2 layers of 1/4" ply sheets to obtain the required thickness and length, (staggering joints in the plywood sheets 4 ft on center) and my structural engineer says the strength will be very good. So that's not my question.

My question is what glue would you use to do this? Terry did this a hundred years ago when he built his Weekender, and used contact cement, but later stated that he'd have used a different method if he had it to do over again. Epoxy is pretty danged pricey, so I'm thinking about our ubiquitous urea formaldehyde glue. Any other suggestions are appreciated.

Hey Bruce, you wanna build one of these?? Oh wait, you're in FLORIDA. HAHAHAHAhahaha.....

[Bill Jones]

I recently used epoxy spread with a notched trowel on a Chebacco I'm building, but it used ALOT - about 16 oz per side, and the area was well less than 3/4 of a sheet.

Consider using a fiberglass butt joint with spline, which which how I joined the bottom and side panels. Route a 1/4" rabbit in the edge of the 1/2" ply, cut a spline from 1/4" ply to fit, and glue it up. I used 4" biaxial tape on the each side of the ply and got a very strong joint. www.people.vcu.edu/~wmjones for some photos.

BTW, I tested the joint by standing on a 2" wide section of the bottom that I cut out for the centerboard. It held my 250 pounds without a problem. I'm not sure that the spline is really necessary, but it did help with alignment.

Bill

[Barry Pyeatt]

Urea /esin glue will work just fine for laminating plywood sheets. The biggest challenge with thin sheets is getting them to lay flat.

We laminated lots of sheets using a vacuum press and Urea/resin glue applied with short nap rollers. These were in large sizes up to 26' long and could have been larger. We used scarf joints, half lap, butt joints with splines or just plain overlapping butt joints. Never had one fail.

I've personally laminated door skins onto 1/4" plywood sheets just using the urea/resin and sandwiched between 3/4" thick ply with sandbags holding it down for pressure. It gave me good results.

Personally, if you need 14' 1/2" ply, I would use a 12-1 scarf and epoxy the joint. It will be incredibly strong. Just don't squeeze all the epoxy out of the joint.

[Mark Gudschinsky]

You actually can get longer plywood (at least in marine grade) It would probably take a week or so to get (from a decent lumber yard) but often the savings in time and other material more than make up for the wait.

[Barry Pyeatt]

Yes, I've had 12' & 16' sheets on occasion in 1/4", 3/8", 1/2" and 3/4" Marine and in 3/4" AB exterior Doug Fir. It isn't stocked by the majority of the dealers, but they can order it. It really wasn't all that more expensive, but most of them charge for special handling if it doesn't get shipped with a regular order.

[Konrad in Lincoln]

Ok then, a few questions:

1. If this alleged super-long plywood does exist, anyone have some contacts?

2. I am only familiar with scarfing rubrails and toerails on my Vacationer. How do you make a 12:1 scarf with 1/2" plywood? That sounds a bit involved.

3. I also was planning on doing the sandbag weight thing. (or old concrete blocks, potted plants, the 4 month old child...)

Thanks for the input.

[Barnacle Jim]

Hi Konrad,

We laminated the sole for our Vacationer/Friendship Sloop. For added strength we also used scarf joints (cut across an 8 foot span). I did have some doubts about the project when we began, yet everthing turned out ok. The plywood laminate was 8 x 20.

We used epoxy as an adhesive, not only for its strength, but also for its gap-filling properties.

Here is a picture of the joint. The wood on top is a hickory stringer.

[TexasPhil]

Konrad,

In answer to your question, how to scarf a full sheet of ply, I think Phil Gowans has the best answer on his site: http://www.pragdata.com/philboat/ConScarf.html

However, that requires a lot of trust in your eye to get it just right.

I used a "lap joint", where I basically used my router to trim half the thickness of the plywood from both sheets. Alignment was tricky, but it worked out quite well once aligned. I logged my notes on my site:

http://www.phil-davis.com/boat

Click on: Construction Log -> 05/12/2002

Hope this helps

[Barry Pyeatt]

Scarf joints

http://www.glen-l.com/wood-plywood/scarf-butt.html

http://www.boat-links.com/Scarfing.html

http://www.boat-links.com/scarf_bevels.html

Gougeon Brothers scarfer attachment is available. They are the West Systems owners.

This attaches to your Rotary saw and makes the cuts quick, accurate and simple.

[capt jake]

I have a 4" Makita power plane that I plan on using for scarfing. There is an attachment made for these down South somewhere. I think it is Uncle Henrey or Uncle John??? He has an advertisement in the back of Wooden Boat on occasion. The attachment is about $125 but it seems like it might be worth it. It will cut a 12:1 scarf in 1/2" ply.

He doesn't have a website. I used to have an e-mail address, but I can't locate it at present.

Try this http://media5.hypernet.com/cgi-bin/UBB/ultimatebb.cgi?ubb=get_topic&f=4&t=000837&p= it is the John Henry scarfing jig.