Cascamite Vs Cascaphen

[Sixpence]

I have to laminate several layers of 4mm ply to construct a replacement section of the foredeck on my 21ft Debutante so the question is
Which one would be best for the job ?
Obviously I expect the deck to get a regular soaking but it's not intended to be permanently immersed , so which one would be best
Cascamite or Cascophen ?

 

[chrishelen]

Cascamite would be best if you have some,but failing that one of these new gap filling resins is just as good,i have just replaced part of the stem on my Eventide the part where the bolt for the bobstay goes through after cutting out the deadwood and shaping a new piece i found all my cascamite gone,a shipwright mate gave me the leftovers of a tube of this gap filling resin,sqeeze a tiny bit out as it expands to a foamlike substance,totaly waterproof,i cant remember the name of it,but B&q sell it.

 

[cliffordpope]

On a boat I would regard everything as if it were going to be permanently immersed. Even if it isn't, it will quite likely be in a damp atmosphere. I didn't know cascamite would stand that treatment.

 

[oldharry]

Balcotan is a modern Polyurethane one part glue widely used for wooden boat building and repairs, and considerably stronger and more durable than the older urea formaldehyde resin glues like cascomite, which - to quote my boatbuilder - "have no place in a modern boat".

He speaks from the experience of having to deal with failed cascomite glue lines on a number of older boats, which as they age is an increasingly common problem.

The only problem with Balcotan from the amateur point of view is that it is not gap-filling. It foams up to fill a gap, but the foam is weak. For boat repairs it has the advantage of being moisture cured so works well on timber with high moisture content.

Cascomite is still available as it is widely used as a furniture glue, and is now marketed usually as 'Extramite'.

Cascophen is a good boat building glue, but has the disadvantage of being thermosetting - that is it needs a minimum temperature to set off, quoted variously between 50 and 70F - not easy to acheive in a boat repair environment, though an adequate bond can be acheived at 40F. Timber gluing requires a maximum moisture content of 16% for a full bond.

Balcotan being a one part moiusture cured glue is a much more obvious candidate, and is single part - no mixing!

 

[Tranona]

The obvious adhesive is epoxy resin, probably thickened with silica. As oldharry says, Balcaton is very popular as it is cheaper and easier to use and for most jobs is satisfactory. Presumably you are building up the deck thickness with 2 or 3 layers to make the bending easier, in which case you need a good adhesive. Whatever you use, your biggest problem is ensuring even pressure while the adhesive is curing. Staples and weights such as concrete blocks are a common way of holding panels together for the second and third laminates.

You say you are laminating several layers of 4mm ply. a foredeck is unlikely to be more than 12mm and if you are doing the whole lot in one go then you should be able to do it in one thickness. If you are just patching then you might find solid veneers easier to work with than ply - even 4mm does not like bending over short distances.

Hope this helps

 

[chrishelen]

No your dead right,thats why that gap filling resin(if i could only remember its name)is good,also its seawater PROOF,or so it says on the tube.it can also be applied to damp wood Harry.
Chris.

 

[Sequoiah1]

Sounds like Balcotan

 

[trouville]

Ive used Balcotan polyurathene as its easy to find and works well,it dose expand but best results are when its clamped untill well set.

Cascophen and airodux are really great glues used to build aircraft they last very well when used in the warm and well clamped

I have to say that ive been useing with succsses Balcotan for many years as its easy not expensive and can be found every where(almost)and dose a good job

 

[andrewbodenham]

Although you don't intend the deck to be permanantly wet it would be safer to assume that it will be. So the waterproofness of the adhesive is one important factor to consider.

I'm a great fan of polyurethane glues (Balcotan et al), for their ease of use and good performance. However, PU would probably not be suitable for this job. I assume you will be building up the deck in-situ, adding layers one at a time. PU glues can generate considerable pressure in the glue joint as they foam up on curing, and over a large area this will tend to force the sheets of ply apart. The foam has little strength, so the integrity of the joint would be compromised. I doubt you could get enough pressure on the area with weights or stapling to hold the mating faces in sufficiently close contact.

So what you need is a waterproof but non-expanding glue, ideally with a long open joint time to allow positioning etc. I'd suggest Extraphen (what used to be Cascaphen) as a readily available glue which ticks all the boxes. Or you could use epoxy if you can control the heat / humidity conditions sufficiently.

Whatever you use you'll have to find some way of applying lots of pressure evenly over the glued area. How big is the area which you are replacing?

 

[Sixpence]

The hole is about 300mm by 300mm and yes it will be easier to do in situ as seen here

 

[Seanick]

Epoxy. You will need a B pack to sheath the deck anyway.

 

[Sixpence]

Sheath the deck ?

 

[oldharry]

Errr yes - Blacotan - Baclotan - Blatocan - BALCOTAN.

Thats the stuff.


And Tranona: the decking of a Debutante is THICK! I had a Tucker Mystic in the early 70s which was very similar, and the main deck was laminated ply at least 25mm thickness because it took the weight of the mast unsupported, depending on form stability with quite a strong curve to take the load. It could only be made by laminating successive sheets of thinner ply, and I would assume the Debutante is the same.

Epoxy best, Balcotan second best for this job, but it is quite a big area so would be £££s.

I would guess that the pressure of the curvature of the ply would apply sufficient pressure as the successive laminates go on as long as there is no compound curve to complicate matters.

 

[donncha]

EDIT: Sorry just read the above post and understood the need for laminating.

 

[Sixpence]

Yes , the deck is quite thick at about 20mm and although the curve is quite acute it's not too complicated and yes , I believe it will hold itself down because of that , so it's just a case of which glue to use . Fillers that expand are a non starter because they'll push each layer apart too much and I don't want to use anything that is like plastic on her

 

[Sixpence]

20mm ply doesn't bend , I tried it , anyone want to buy a sheet of 20mm ply ? 300mm by 300mm

 

[Seanick]

Yes, after you have repaired the deck, in is standard practice to sheath it in epoxy resin and glass cloth so it lasts forever. You will also reglass the chines (externally) to help those poor brass screws keep the ply on the chines and make the hull totally leak proof. Don't confuse epoxy sheathing with polyester (GRP) sheathing as its a totally different beast.
I know the ply wasn't sheathed before, but if it had a choice it would have been, and now you would have fewer repairs to do...
I rebuilt a Deb about 12 years ago and did similar jobs to what you are doing now. I locally repaired the deck, then laminated another 6mm on top. Did the same with the bottom. You need to really beef up the structure where the keels bolt through as I have seen 3 Debs and two Gallants with the keels broken off. The ply becomes brittle as it ages and the longitudinal stringer allows too much flexiing untill the keels fall off. I would/did fit transverse floors from keel hog to chine to prevent this inconvenience!

They are great boats, I did Chichester to Falmouth and back and kept ther for about 5 years.

ps they really need a spinnaker off the wind to hit that 5 1/4 knot top speed.

 

[Tranona]

Looking at your piccy, I would be inclined to double up the existing beamshelf and glue butt straps of 12mm ply to the underneath of the existing deckhead. That will give you a really sound base all the way round the repair to take fastenings. I did a similar repair to the coachroof on Tranona with two laminates of 6mm ply to make up the original 12mm.

You sound averse to using epoxy - but I bet the original builders of ply boats wouls have fallen over themselves to use it if it had been invented! The amount of epoxy required is very small and provided you have the right curing conditions - running a fan heater underneath would help - the repair will outlast the boat!

Not sure it is necessary to fully sheath the deck, just epoxy coat the final surface and make sure the butt joins and the outer edge under the rubbing strake are well sealed with epoxy. Paint it with deck paint and you wont be able to see the repair.

Good luck

 

[Seanick]

[ QUOTE ]
I would be inclined to double up the existing beamshelf and glue butt straps of 12mm ply to the underneath of the existing deckhead.

[/ QUOTE ]

Not really a professional approach.
4" half laps more than adequate. A router makes this sort of repair so easy.

I agree another 6mm ply all over not really nessercery, but as I said, all ply becomes brittle with age, so adding a little extra to the structure is better in the long run. It also gives a pefect fair deck to sheath. Debs have no deck beams.

 

[Tranona]

Seanick. The picccy clearly shows a deck beam. Not clear whether there is a separate beamshelf inside the hull panelling and gunwhale, but whatever it does not look very wide and this is where the stress is going to be pulling the ply down to make the curve. Yes, routing out a rebate in the existing ply would be one way, but to make up the 20mm thickness using 4mm there are going to be 4 rebates. You will still have the problem of providing a firm landing for the first layer where it meets the existing ply.
As the underside is hidden a butt strap is not a problem and much easier to do. For neatness it could be rebated into the deck beam, but as its purpose is to provide a sound landing for the new panel it could be fitted in two parts either side of the beam.