Hi,

I just tried out foaming polyurethane adhesive for the first time and
wondered whether there are any tricks for making a neat job? It's the
sort that goes on as a brown treacle-like goo and foams up after a few
minutes.

I applied liberally and then spent the next 20 minutes wiping it off and
still had a lot to trim away the next day. (note to self: I still owe my
wife a new bottle of nail varnish remover).

It didn't seem to be very sandable, or was I just not enthusiastic enough?

Perhaps my problem is that I want it to fill the gaps in the joint but
leave a clean edge on the exposed outside.

thanks

dan

In article ,
Dan Smithers wrote:
Perhaps my problem is that I want it to fill the gaps in the joint but
leave a clean edge on the exposed outside.

IIRC, you'd best not leave it exposed to the outside - it deteriorates
rapidly in sunshine or maybe even just light. Cut it back slightly and
cover with a cement fillet.

--
*Proofread carefully to see if you any words out or mispeld something *

Dave Plowman London SW
To e-mail, change noise into sound.

First off, disposable gloves are essential.

Polyurethane glue works best in closely fitting, and firmly clamped
timber joints. Whilst it will gap-fill, the foam has no strength. It's
pluses are the strength of the joint where it is well compressed, and
that a good joint is truly waterproof.

Experience will tell you how much to apply. On a good tight joint, you
will get some foam expelled, but you can take that off with a scraper
once hard, and then sand or plane the face - but I would emphasise the
good, tight joint.

What sort of work are you doing wit it?

RubberBiker wrote:
First off, disposable gloves are essential.

Ummm, yes.

Polyurethane glue works best in closely fitting, and firmly clamped
timber joints. Whilst it will gap-fill, the foam has no strength. It's
pluses are the strength of the joint where it is well compressed, and
that a good joint is truly waterproof.

Experience will tell you how much to apply.

That's the bit I was missing. I slopped it around liberally and was then
horrified as it expanded. A typical first time use mistake I guess.

On a good tight joint, you
will get some foam expelled, but you can take that off with a scraper
once hard, and then sand or plane the face - but I would emphasise the
good, tight joint.

What sort of work are you doing wit it?

I am repairing a wooden dinghy - pin and gluing a batten to strengthen a
repair. The underneath board is not completely flat so something that
fills the gaps is useful.

I did follow the instructions that said to remove excess with acetone
but in the end I did as you suggest and trimmed once hard. Next time
I'll try spreading it more thinly - a thin smear over the mating
surfaces and a little more in the gaps.

thanks

dan

On Mon, 15 Jun 2009 11:55:58 +0100
Dan Smithers wrote:

RubberBiker wrote:
First off, disposable gloves are essential.

Ummm, yes.

Polyurethane glue works best in closely fitting, and firmly clamped
timber joints. Whilst it will gap-fill, the foam has no strength. It's
pluses are the strength of the joint where it is well compressed, and
that a good joint is truly waterproof.

Experience will tell you how much to apply.

That's the bit I was missing. I slopped it around liberally and was then
horrified as it expanded. A typical first time use mistake I guess.

On a good tight joint, you
will get some foam expelled, but you can take that off with a scraper
once hard, and then sand or plane the face - but I would emphasise the
good, tight joint.

What sort of work are you doing wit it?

I am repairing a wooden dinghy - pin and gluing a batten to strengthen a
repair. The underneath board is not completely flat so something that
fills the gaps is useful.

I did follow the instructions that said to remove excess with acetone
but in the end I did as you suggest and trimmed once hard. Next time
I'll try spreading it more thinly - a thin smear over the mating
surfaces and a little more in the gaps.

thanks

dan


I think for a boat repair you would do better with a two part epoxy,
used with a filler to gap fill. It will be interesting to find out in a
year or so how the polyurethane glue worked out in the long run.


I use poly quite a bit, I find you don't need more than a smear on one
surface (wet the other) for a well-fitting joint. I never wipe the wet
glue-foam up, it's better to take it off with a sharp chisel when it's
set.

R.

I am repairing a wooden dinghy - pin and gluing a batten to strengthen a
repair. The underneath board is not completely flat so something that
fills the gaps is useful.


would masking tape help?

[g]

I am repairing a wooden dinghy...

West Systems epoxy would be the most widely used product for glue/
filler type repairs on wooden boats.

http://www.westsystem.com/ss/

TheOldFellow wrote:

I think for a boat repair you would do better with a two part epoxy,
used with a filler to gap fill. It will be interesting to find out in a
year or so how the polyurethane glue worked out in the long run.

Foaming polyurethane glue is a standard glue for boatbuilding. I think
the only problem this time around was the user's inexperience. PU glue
foams much more than one would expect and it only needs a light smear of
glue, as you observed.

Steve Firth wrote:
TheOldFellow wrote:

I think for a boat repair you would do better with a two part epoxy,
used with a filler to gap fill. It will be interesting to find out in a
year or so how the polyurethane glue worked out in the long run.

Foaming polyurethane glue is a standard glue for boatbuilding. I think
the only problem this time around was the user's inexperience. PU glue
foams much more than one would expect and it only needs a light smear of
glue, as you observed.

Thanks Steve, I had been recommended this by several people who repair
wooden boats.

You're quite right, it is mainly my inexperience. Can I use a spreader
to make a thin layer (obviously disposable) or does this upset the adhesive?

On Mon, 15 Jun 2009 13:24:51 +0100
(Steve Firth) wrote:

TheOldFellow wrote:

I think for a boat repair you would do better with a two part epoxy,
used with a filler to gap fill. It will be interesting to find out in a
year or so how the polyurethane glue worked out in the long run.

Foaming polyurethane glue is a standard glue for boatbuilding. I think
the only problem this time around was the user's inexperience. PU glue
foams much more than one would expect and it only needs a light smear of
glue, as you observed.


You live and learn, thanks for the info. I'll have more faith in it
outside now.
R.

On 15 June, 14:30, Dan Smithers wrote:
Steve Firth wrote:
TheOldFellow wrote:

I think for a boat repair you would do better with a two part epoxy,
used with a filler to gap fill. It will be interesting to find out in a
year or so how the polyurethane glue worked out in the long run.

Foaming polyurethane glue is a standard glue for boatbuilding. I think
the only problem this time around was the user's inexperience. PU glue
foams much more than one would expect and it only needs a light smear of
glue, as you observed.

Thanks Steve, I had been recommended this by several people who repair
wooden boats.

You're quite right, it is mainly my inexperience. Can I use a spreader
to make a thin layer (obviously disposable) or does this upset the adhesive?

I don't know anything about boat building, but I got a gunnable tube
of polurethane glue recently, and apart from the necessity for gloves
and making sure that the end of the tube is well sealed after each
use, I'm in all favour of it.

It's the 5 minute set type which again may not be the boat building
variety, but having had the brown goo type in a tin, the gunnable type
is so much easier to apply and doesn't go off in the tin.

One asset I didn't realise is that it will glue more than just wood; I
haven't tried on on stone or concrete yet, but I have glue aluminium
to aluminium and Al. to wood.

I would go with the cleaning up afterwards - meths works for cleaning
it when wet and can be got in 5l containers so is a bit cheaper than
nail varnish cleaner!

Rob

Dan Smithers wrote:


Thanks Steve, I had been recommended this by several people who repair
wooden boats.

I think it's the best of the one-shot glues available, it takes the
place of the older phenolic/casein glues.

You're quite right, it is mainly my inexperience.

Eyeballing how much to use comes with practice. It's a good idea to play
with glueing scrap first to get a feel for it.

Can I use a spreader to make a thin layer (obviously disposable) or does
this upset the adhesive?

Yes, that's fine but you have to work fast. The glue starts to foam very
quickly.

Two-part epoxy filled with glass microballoon fillers as mentioned by
TheOldFellow is also good but it takes a different type of skill and it
also works out much more expensive IMO.

One trick you can use is wax to coat the bits you don't want to stick,
but this obviously causes problems later if you decide you want to glue
something to a part you have waxed. Another is to use masking tape
(preferably blue) to mask off bits of wood you don't want to have to
trim foam from.

TheOldFellow wrote:

You live and learn, thanks for the info. I'll have more faith in it
outside now.

You're welcome, just remember that it's not UV stable. So you need to
cover it with paint or varnish if it is exposed to sunlight. Oddly
enough although polyurethane glue goes brown in sunlight two-pack
polyurethane varnish is stable and remains transparent. I've used
two-pack polyurethane over both expoxy and PU glue and it stops damage
by sunlight - I've got pieces that are ten years old and have been in
salt spray and sun all of their life.