Tite Bond glue for a 27' strip plank hull?

[alan white]

I like polyurethane glue a lot. One thing I use it for is to bond hardwood (usu white oak) gaff/boom jaws, cleats, and fairleads to spars (along with screws). What I find is that when a fit is really tight and clamped, the glue will not so much squeeze out of the cracks. Yet there is expansion pressure in there, which is consequently forcing the glue deep into the wood pores. The fit has to be very very good to do this, and may after all squeeze out in some places, but not enough to release all the expansion pressure.
I'm interested in the fiber-filled glue, Joe. What quantities are available, and what is the storage requirement/shelf life?

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[joeevans]

I've bought it it pots of about half a litre. It keeps indefinitely as long as absolutely no moisture gets in. It sets in reaction to the moisture content of wood, so even the humidity of the air will set it foaming and setting over time. In practice, that means that once you've opened a pot it needs to be used within a few months. I would therefore buy bigger quantities in the same small pots, if you see what I mean. Robbins Timber have a good information sheet here:
http://www.robbins.co.uk/Pdf%20Files...nformation.pdf
I haven't used the fibre-gel one myself, but I'd consider it. If you were building a wooden structure - a shed or workshop, or even the framing for a house - you could put a blob in all the joints and massively increase the strength, even if the joins were extremely roughly fitted. I used the rugular Balcotan the other day when I was short of a few longer 2 x 4 joists on a building job. I overlapped the short ones by a couple of feet, glued them up with two nails each for clamping, and that was that. Easily as strong as a single piece of wood.
For boatb uilding and in particular strip planking, the big advantage seems to me to be that when it comes to fairing, the excess glue is a light foam and easily cut or sanded, unlike epoxy.

[alan white]

Thanks much! I know what you mean by not buying too much in one container. I wonder, though, if it could be re-canned and stored in the freezer?
Price would be much less that way. and what you say about strip planking--- I agree, and I particularly like the fact that no batch has to be used up or else wasted, as with epoxy. There's the hassle of epoxy, besides the mess. You have to commit to a batch, and the measuring of small quantities is a pain.

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[johnnyv]

Originally Posted by alan white

Thanks much! I know what you mean by not buying too much in one container. I wonder, though, if it could be re-canned and stored in the freezer?
Price would be much less that way. and what you say about strip planking--- I agree, and I particularly like the fact that no batch has to be used up or else wasted, as with epoxy. There's the hassle of epoxy, besides the mess. You have to commit to a batch, and the measuring of small quantities is a pain.

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You can repackage as long as you take care to exclude moisture which includes the moisture in air. Putting in the freezer is not needed unless the glue is unstable(allophonate formation) to begin with which is unlikely.
Moisture is the problem when you need to open the container many times, for a standard style MDI based 100% solids moisture cure poly it takes less than 30 grams of water to fully cured 1000 grams and much less to make the viscosity to high to be workable.

On a related note i happen to be working on pu construction adhesives right now.
The good thing about pu compared to epoxy besides being 1k is that i can get much faster cure times, > 9 MPa at 20 minutes.
I would not use pu for wood that is always wet though, unless it was glassed both sides.
For a boat that is only in the water for hours at a time and is sealed with epoxy it would be an excellent choice.

[alan white]

So far, I've used PU only above the waterline, to scarf spars, glue thin bungs, or anything subject to outdoor weather. I would readily use it to glue a strip hull sheathed in epoxy. I am not sure about always-wet wood at all. I am not sure it wouldn't work either, but if you say it doesn't like the wet, you must have some reason. Have you any tests you can refer to?
Also, the more heavy-bodied variety must be more flexible, able to stand some immersion.

alan

[Raggi_Thor]

Have you discussed Gorilla Glue, called Elephant Glue in Europe?

[johnnyv]

Test is lap shear on hoop pine strips, have done straight immersion and immersion/dry cycling.

Generally you get failure at about 60% of the normal value when wet, recovers after drying. In formulations with a higher proportion of hydrophilic polyether soft segment you get lower failure values.

Sealing the hoop pine with epoxy before bonding with pu, was not seeing any great reduction in strength after three days wet(takes much longer for the pu to moisture cure this way though).

You infact do get a reduction in strength with epoxy joined wood as well because the wood gets weaker when it is saturated but it is not as drastic as with the pu's.

[alan white]

I appreciate the research. PU has its place. So does epoxy. One thing I like with PU is a near invisble glue line. I recently made mast hoops for my gaffer by steaming (boiling water submersion). The wood was ash, and about three wraps around pipe, wired tight, which left the wood a little bit damp after about 12 hours.
I then used PU Gorilla glue, band-clamped to pipe. Varnished, they look like one solid piece of wood. After a season on the mooring, they show no signs of having been outdoors. Epoxy would also have worked well, but would show a darker glue line. This is particularly important with light colored woods. The glue line is a light honey color.
In building a canoe of cedar strips, the difference will show between epoxy and PU also. If a really lovely grain pattern is desired, PU will make a difference.

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