Very cool video - hot molding

[Alan H]

I knew that something called "hot molding" plywood existed, but I had no idea exactly what the deal was.... until now.

[PeterSibley]

Interesting ..thanks ! No gloves with that glue . It didn't look like resorcinol, what would it have been?

[Alan H]

I really enjoyed seeing the autoclave. It appears that the first layer of veneer was stapled to the mold, which is interesting. How'd they get it off the mold when they were done? I mean, it looks like they just lifted it off.

Definitely not resourcinol, but probably some sort of heat-activated stuff.

I had been under the impression that hot molded setups were done at significantly higher temperatures than what the movie says...about 100 deg. That's steam that's been pumped into the autoclave. That's also vacuum-molding, that stuff with the "rubber bag" and all, which is still done with production fiberglass layups.

[wsgilliam]

I really enjoyed seeing the autoclave. It appears that the first layer of veneer was stapled to the mold, which is interesting. How'd they get it off the mold when they were done? I mean, it looks like they just lifted it off.

Definitely not resourcinol, but probably some sort of heat-activated stuff.

I had been under the impression that hot molded setups were done at significantly higher temperatures than what the movie says...about 100 deg. That's steam that's been pumped into the autoclave. That's also vacuum-molding, that stuff with the "rubber bag" and all, which is still done with production fiberglass layups.

Fascinating video. I am wandering that myself. He clearly staples the first and second layer on. What gives.....

[Minorhero]

They mention that they remove the staples from the first layer as they apply the second layer. Also its 100 degrees Celsius so that would about 212 fahrenheit. They also mention they steam it while its in there. Not sure if that would matter if it were vacuum bagged, but presumably it does something.

[Rich Jones]

This has been posted before but is always fun to watch. I had a 1959 20' Highlander Class sloop built this way. Beautiful mahogany.
I thought the glue was resorcinol also. Video says its a synthetic resin, whatever that means.
I think there are steps that we don't see in the video. As in cold molding, the first staples are pulled as the second layer goes on. They leave staples in on the final layer (which probably go all the way through to the mold) all along the keel which you can see them pulling when they take it out of the oven. Probably along the sheer also.
I'm thinking that if they're pumping steam in there, the temp has to be a lot higher then 100 degrees.

[Redeye]

yup. staples in the first layer. Someone must know...

[Redeye]

damn you guys are fast...

[Rich Jones]

They mention that they remove the staples from the first layer as they apply the second layer. Also its 100 degrees Celsius so that would about 212 fahrenheit. They also mention they steam it while its in there. Not sure if that would matter if it were vacuum bagged, but presumably it does something.

Yep, I was too busy watching and not listening! Celius! Screws me up every time!
They must have to work fast to get everything glued together and vacuum sealed before the glue starts to set up.

[Garret]

212f - 100c.

ETA oops - I was late...

[John Meachen]

I found it interesting that the deck was pre-fabricated.I also wonder whether the process might allow less than prime boatbuilding woods to be used,given the temperature.I know that Fairey used agba for their hot moulded hulls and haven't heard of it more recently-anybody here encountered it?

[Todd Bradshaw]

I believe that the original glue for hot moulding was casein, which was later replaced with urea formaldehyde, which was more heat and moisture tolerant. There was a bit of a swelling problem of the veneers from the moisture in these powder and water mixed glues and eventually the best choices became urea formulas which used a liquid hardener other than just water.

[Alan H]

Urea formaldehyde.... ye Gods, where was OSHA back then? I grok the idea of using small amounts of formaldehye glues, but with urea? and HOT? Oy...

Interesting... WikiPedia says that casein glues were used for early airplanes, but fell out of favor because it's susceptible to bacterial breakdown. Didn't John Guzzwell use a casein glue to cold mold his revamp of Trekka? --- Dolly?

Taking the first set of staples out as the second layer goes on makes sense, especially if the glue started to set up a bit, which would sort of help to keep everything together.

Re: temperature...100 C = 212 F. **facepalm** duh.

[Alan H]

Not knowing diddly about wood glue, and being scared by the two words "urea" and "formaldehyde", both of which are seriously nasty compounds for human beings, I went looking. Our friend Christine de Merchant has written up a nifty little page which contains a lot of information.

http://www.christinedemerchant.com/a...maldehyde.html

note this quote -- "Upon addition of water, in high temperature, cured urea formaldehyde can hydrolyse and release formaldehyde, this weakens the glue bond. For this reason it is not considered waterproof but rather water resistant and is not used for marine plywood."

...so I wonder if it actually was used in hot-molding.

[Alan H]

WikiPedia has a nice article on Fairey Marine, which hot molded dinghies and larger boats after WWII. Here's the text from that article on construction techniques.

====================================

Construction methods

The hot moulding process was an adaptation to post war boat building of the method originally developed by de Havillands in the 1930s for "stressed skin" wooden aircraft production, using layers of thin birch plywood sandwiched together with glue over a male mould and "cooked" in a large oven called an “autoclave” By using true mass-production techniques, Fairey Marine were able to turn out vast numbers of identical boats at an unprecedented quality and price. Moulds were constructed from spruce, built up on a steel base plate. Seven by three inches planks cut to the waterplane sections provided the starting point. Working from the sheerline, the planks were built up in a series of steps, arriving quickly at a close representation of the designed shape. Subsequent fairing yielded finished dimensions. Rebates for the keel, stem and transom completed the mould building process. Although the veneers used to produce Fairey boats may appear to be parallel sided, every one was in fact profiled. Rather than shaping each veneer to fit on the mould, as in traditional boat building, Faireys saved an enormous amount of time by sawing complete sets of veneers to precision patterns. Veneers were produced in stacks of six. Boat were then typically built in batches of 24 or 36. Early boats used 1/8″ spruce ply, surplus to the War Department’s de Havilland Mosquito aircraft programme. When this material became unavailable it was replaced by 2.5 mm agba veneers.

Chosen for its high gum content, agba formed easily without splitting and glued well. All the dinghy classes used just three agba veneers while some of the bigger boats used up to six. Initially all the veneers were laid at 45° while later boats changed to fore and aft outer planking for aesthetic reasons. With the keel, stem and transom in place, veneers were applied starting on the centreline and working out towards the shear. Each veneer was held in place by just three staples at the keel, bilge and shearline. Roller-application of Borden One-Shot waterproof glue preceded each veneer except the first. With all veneers in place a vacuum bag was drawn over the moulding and secured in place using a clamp plate and G-clamps. Early vacuum bags were made from war surplus barrage balloon fabric. After about 1950, individual rubber bags were prepared on the moulds using uncured rubber sheets which were subsequently vulcanised in the autoclaves used for production.^[6]

Placed in the autoclave, the vacuum was drawn down to 27/28 inches water-gauge and steam at a pressure of some 50 pounds per square inch introduced. Processing took about 45 minutes at 100 °C. Curing at elevated temperatures under vacuum not only ensured that all the veneers were firmly consolidated – a process requiring many thousands of staples using the conventional cold-moulding process – but allowed for the use of a truly waterproof, single part, high-temperature curing glue. During the curing process the glue impregnated the wood resulting in a virtually rot-proof finished shell. Components such as side-decks were also hot moulded while other parts required for assembly were cut to patterns in the same way as the skin veneers. For one of the more complex boats, the International 14, the time for final construction from bare hull to finished boat was set at 230-man-hours compared to 400–500 hours associated with traditional construction.

[Todd Bradshaw]

http://www.hallmarkfraulo.co.uk/asse...n_One-Shot.pdf

[Alan H]

HAHA! I figured "Borden"....as in the dairy company, meant a casein-based glue, for sure! You learn something new every day.

Probably not the same company, eh?

[Redeye]

Just to be clear, urea is not a terribly nasty substance, in fact you pee it out. It is widely used in fertiliser. In terms of risk, you might get an irritation or burn. At high concentrations it denatures proteins, but this can be reversible - In fact we use it in the lab to study protein unfolding and refolding.

Formaldehyde, however, is particularly worrisome and adequate protection should be used ,especially eye protection, glove, and breathing protection.

[PeterSibley]

Just to be clear, urea is not a terribly nasty substance, in fact you pee it out. It is widely used in fertiliser. In terms of risk, you might get an irritation or burn. At high concentrations it denatures proteins, but this can be reversible - In fact we use it in the lab to study protein unfolding and refolding.

Formaldehyde, however, is particularly worrisome and adequate protection should be used ,especially eye protection, glove, and breathing protection.

None of which were in evidence !

[Jim Oppy]

Amused by the music. And the narrator talking about graceful beauty while the boat careens through the harbor.

[Redeye]

None of which were in evidence !

I know!! Scary stuff, but they were all so clean!!!

[MN Dave]

Thanks for the link Todd.

Urea and formaldehyde are the starting materials used to make the adhesive. Neither compound remains after the reaction, so the glue itself is not particularly hazardous.
http://www.hallmarkfraulo.co.uk/asse..._Home_MSDS.pdf
The boat should only be sailed in a well ventilated area, e.g. a lake, on hot humid days because some formaldehyde can be released when hot and moist.

[Bobcat]

This has been posted before but is always fun to watch. I had a 1959 20' Highlander Class sloop built this way. Beautiful mahogany.
I thought the glue was resorcinol also. Video says its a synthetic resin, whatever that means.
I think there are steps that we don't see in the video. As in cold molding, the first staples are pulled as the second layer goes on. They leave staples in on the final layer (which probably go all the way through to the mold) all along the keel which you can see them pulling when they take it out of the oven. Probably along the sheer also.
I'm thinking that if they're pumping steam in there, the temp has to be a lot higher then 100 degrees.

I had a 1954 Highlander built this way.

You need to remember that "Cold molding" is called that to distinguish it from this process

[Andrew2]

I am pretty certain it was an early version of resorcinol. The hulls lasted way longer than those built of 1088 marine ply and urea formaldahyde glue (Aerolite) There are still quite a few Atalantas sailing around. Not to mention Charles Stock's 'Shoal Waters' based on a Fairey hull.
It was popularly supposed that the Atalanta's cabin top was made in the same mould as the little tender they sold, certainly looked similar. The looks are a bit odd by current standards, but they certainly performed well. I sailed one from Sardinia to St. Tropez and enjoyed the trip.

[Todd Bradshaw]

We used Weldwood Plastic Resin Glue, which is urea formaldehyde, for the stripping process on all the strip canoes we ever built. I find it to be very easy to work with - no fumes, a powder you mix with water and it sands really well compared to gooey glues like Tightbond. Much cheaper and easier to deal with than epoxy for the stripping steps of the process. We would clamp half a dozen strips together using spring clamps with the glue face (one side) up and roll the Weldwood on all of them at once. You can buy it on Amazon if you can't find it locally. It is good stuff.

[Alan H]

So Todd, I assume those canoes were "cold molded" with Weldwood Plastic Resin Glue? What are your thoughts on building a performance dinghy that way?

[Todd Bradshaw]

No, they were wood strippers with fiberglass sheathing inside and out. In terms of cost, ease of use, gap-filling ability, sandability, and the ability to throw away a half-used batch without feeling like you just tossed a lot of cash in the trash, the Weldwood was awfully hard to beat for constructing the wood strip cores. If I wanted to cold mold something I would definitely use epoxy though. Nothing works better and it would be silly to risk the quality of the boat with anything else. Cold molded hulls don't usually rely on cloth sheathing for their strength. They may have it, but their strength is in the construction itself. Strippers are a different story, where the sheathing is reinforcing a core which couldn't stand alone and do the job.

I'm not saying that you couldn't cold mold a hull using Weldwood or other UF glue, but it's one of those "Why bother when there is something better available?" things.

[PeterSibley]

We used Weldwood Plastic Resin Glue, which is urea formaldehyde, for the stripping process on all the strip canoes we ever built. I find it to be very easy to work with - no fumes, a powder you mix with water and it sands really well compared to gooey glues like Tightbond. Much cheaper and easier to deal with than epoxy for the stripping steps of the process. We would clamp half a dozen strips together using spring clamps with the glue face (one side) up and roll the Weldwood on all of them at once. You can buy it on Amazon if you can't find it locally. It is good stuff.

Sold here as Selley's 308 Resin.

[John Howland]

I have a Jet 14' class (Hot molded) tiger striped mahogany from 1954. I got it for free out of wooden boat magazine in 2003. It was a little tired looking when I got it.
Most all the mahogany parts have been replaced deck, transom, keel box, seats etc... they are not hot molded but the hull is all original with no rot. It is as tough as Fiberglass warm as wood to the touch and easy on the eyes.
It is my little Missoura River runner. Hit a snag once and jabbed a 1" hole in the bow section. Just pushed it back out and screw a piece of mahogany with some FG on the inside of it 15 years ago or so.
I just through a can of urethane on it once in a while and away we go. She seems to over come her bow wake fairly easily in anything over 15 knots, very light no ribs 1/4" thick or so.
Jet 14' class 2.jpg

[JimConlin]

I have happy memories of racing a Firefly in my long lost (1950’s) youth.

[johngsandusky]

I think there's a molded racing dinghy for sale near here, reasonably priced. I've seen a few over the years.