We have just had a seat carved from an oak tree felled on site.
Unfortunately it has brown rot on the seat surface, soft enough to
pick out with finger nail. I think there is a "runny" form of
polyester resin that is used to fix rot in beams. Can anyone suggest
Is there anything inherently more weather proof and UV resistant than
ordinary polyester resin for car repairs?
Has anybody any experience of:
Is there a cheaper source as I intend to coat the whole exposed
surface, there are no holes to fill as yet.
On Sun, 26 Oct 2003 20:00:02 -0000, "stuart noble"
The thing is will the bog standard polyester work as well, or better?
Will it penetrate as well before it starts going off?
I am told the Bondawood type products are extremely runny and will
penetrate well into the wood before the moisture in the wood starts to
Anyway thanks to you and Simon for the input.
if you look on the site I posted, they've also got something called G4 clear
it's used for sealing ponds and marine use, it's UV stable, once the wood
hardener has gone off, a coat or 2 of G4 clear and it should be completely
weather proof and good for many years.
Laminating resin is thixotropic and probably a hundred times more viscous
than wood hardener
I've known GRP moulds pulled off of damp surfaces that haven't set in weeks
because of reticulation. Polyester requires an exothermic reaction to set,
and, in the presence of dampness, you need to use a seal between the
moisture and resin and the exotherm needs to be greatly accelerated for any
chance of getting the polyester to set at all. Have you worked with this
stuff? Because I do, Daily.
Moisture curing doesn't mean it goes off on contact with moisture, moisture
curing means that moisture is the catalyst and starts the clock ticking, do
you think this stuff goes off instantly?
What products? polyester won't go off in cold wet conditions at all unless
you kick up the peroxide to around 30% .. and then you have a good chance it
will fry in the bowl before you ever get it on, let alone penetrate
Which by the time they're finished isn't going to be a lot different to a
Ronseal varnish. The beauty of polyester as a wood hardener is that its
volume doesn't decrease because there are no solvents to evaporate. Plus
it's less flexible than G4, which is what we're after with a wood hardener.
No, not really. I was just showing off that I knew something about
styrene:-) Normally I restrict my advice to things that are easily
available. 500ml of fibreglass resin from Halfords etc.
Hang on, it's a long time since I worked seriously with this stuff but isn't
there another cold weather catalyst altogether? I can't believe that 30%
isn't going to affect the finished article. Do Freemans Distribution still
exist? IIRC their catalogue was pretty comprehensive.
I seem to remember testing this when I was using car body filler a lot, and
the stuff would set normally between sheets of wet kitchen towel. You could
almost use water as a release agent except now and again it would actually
stick to a surface that had been wet. That said, the aggregate in filler
helps retain the heat and obviously the thinner the layer the longer it
takes to cure.
I think the OP probably stopped listening a long time ago. Sensible fellow.
Heavily thinning it actually makes the polyester, a brittle material, even
more brittle. A little flexibility IS what is needed so that it can move a
little with the wood. I wouldn't use Ronseal, G4 is vastly superior. Wood
hardener has a lower viscosity and will penetrate a lot deeper and it's
setting is not dependent on exotherm in the same way as polyester.
If you need to know where to buy it in future ... to avoid the substantial
mark up that Halfords put on what, I consider, is a very inferior
laminating resin ... let me know ;-)
Not exactly....... you still use peroxide, you just have to increase the
Cobalt because it's the mix of Cobalt and peroxide that cause the exothermic
reaction that gets the resin to set. Cobalt and Peroxide are highly
volatile in close proximity to each other, even the fumes mixing can be
explosive. Atmospheric temperature doesn't affect polyester as much as
direct contact with moisture. Yes, 30% will greatly affect the quality of
the resin. but what affects it most is the reaction of heat and not the
quantity itself, cooked resin is very brittle. When dealing with moist
surfaces, in thin layers, we only do this on the surface coat, because we
are trying to counteract the retarding effect of the moisture, the moisture
retards it and stops it cooking so it doesn't get brittle, it has to be done
quick or it will fry in the bowl before you've finished and it takes a lot
of experience to be able to take all the environmental influences in to
consideration and get the timing right (I know 1 or 2 mould makers that keep
journals that take in to consideration atmospheric moisture, but I find that
a bit anal and go by the seat of my pants ;-) ..). Too slow and you're
doomed to be sitting there with a heat gun for an hour, too fast and it's
gone off in the bowl before you've finished, it's a very fine tolerance.
Here, this depends on volume and mass, if you have enough mass, then the
exotherm can take place. Mass has a huge effect on the setting time of
polyester, it doesn't affect PU or Epoxy to the same extent. In the small
amounts that we are talking about in terms of sitting in the pores of the
wood, there wouldn't be enough mass for the exotherm to take place in a damp
An Example would be in something i did recently. I used tinted polyester as
a surface coat on some MDF furniture to make a tough scratch resistant
coating, this was made during the summer, on dry MDF, only the inherent
moisture that resides in the MDF naturally. I wanted it to set reasonably
fast so I went with about 10% peroxide. The stuff in the bowl went off in 10
minutes, the coating on the MDF was still sticky after 24 hours, purely
because of the intrinsic moisture in MDF and the thin section of the
coating. It took 72 hours before all traces of stickiness had vanished.
With body filler you retain the mass to cause the exotherm. The exotherm on
the MDF was extremely retarded by the thin section and moisture. But try it
yourself as an experiment, buy some laminating resin, mix as per
instructions and paint a thin layer on some MDF and compare setting time to
the stuff in the pot. I would think you'll find, that if you followed the
mixing instructions, the stuff in the pot would have gone off within 20
minutes and the MDF would still be sticky this time next week. In fact, you
can see the difference purely in mass. You could fill a cup with resin, and
fill another cup an 1/8th full, and the full cup will likely boil long
before the 1/8th of a cup has gone beyond the gelling point. In mass,
Polyester will go off underwater, the surface will remain sticky and won't
adhere to anything, but the body of the polyester will set, in fact, we use
a bucket of water, to discard any excess polyester, because if it's left in
the mixing bowl, it will start to fry in thicknesses above half an inch, the
water retards the resin and stops it frying. Frying resin turns all the
styrene to gas and can be rather noxious.
Except that the type of wood this is normally used on would have given up
natural movement many moons ago. It can swell if it gets water logged but
the ambient expansion/contraction thing doesn't happen because it has
technically ceased to be wood.
I used to buy from a local GRP factory where they made incredibly large
moulds in primitive conditions. It was the size of an aircraft hanger with
water running down the walls, windows missing etc. I suppose that's what
convinced me that anything was possible with the right chemistry.
I think maybe they use a different resin for filler because it's very
effective as a "skim" on sills etc. It certainly cures much faster than
laminating, even in thin layers.
Again, I think a different type of polyester may have behaved better. Scott
Bader used to do various resins for different applications. I can't believe
there would be sufficient moisture in mdf.
Don't they add wax to help prevent surface tack? IIRC the idea is that the
wax forms a film on top of the curing resin and supposedly keeps it warm.
Dunno, it was a long time ago when I faffed about with all this.
Even Kiln dried pressure treated and aged wood needs aclimatising .........
there'll still be some movement ... and a brittle polyester with a weak
matrix would crack up after time and surface would go like crazy paving ...
once it's stabilised .. then the movement will be more controlled ... people
stabilise bog oak, mammoth tusk and god knows what else for making custom
knife handles, all because there is still some chance of movement and to
control deterioraton. (I was a joiner for 10 years before moving to what I
do now, so i know wood too .. ;-).. )
There is .. the right Chemistry is PU ;-) ..at least for the OP ... because
he don't want to be messing around with highly volatile chemicals at home.
They probably do
Yep, Scott Bader and Norpol are the 2 major PE Resin manufacturers that i
use (I prefer Norpol)... and they do supply different qualities of resins
... but it all still boils down to polyester, which for some tasks is an
unsuitable resin due to it's brittle nature, dislike of moisture and
exotherm and mass dependent setting. Casting polyester has a much lower
viscosity than laminating polyester, but I still wouldn't use it for this
purpose, for the reasons of exotherm retardation.. ... If you don't believe
me ..... and I was a little surprised too ... and i use this stuff regularly
..... try it! .....
Most good quality laminating resins already have Wax in them .. and you can
add more wax if required ... but this wasn't just a tacky surface ..... this
was still sticky resin .. you could still push a fingerprint in it after a
Ah, a jack of all trades eh? ....:-)
Seriously though, what I find with polyester filler on rotten windows is
that after a couple of months the wood dries out to the inside of the house,
whereupon it shrinks to give a crack round the filled area. But, once this
is filled, there is no further movement. This is what leads me to believe
that relative humidity doesn't really affect old wood. I have a front door
that swells every time we get heavy rain because it physically absorbs
water, but my Victorian interior doors don't move at all (they're still as
pissed as they were 20 years ago after the central heating was installed).
I believe you, I really do :-) I remember Bondaglass selling those castings
of a tin of beans, half poured out, with the falling beans frozen in time. I
think they were fashionable for five minutes in the 70s. Still not sure how
they did that but I reckon you might be about to tell me :-)
When all's said and done, it's difficult to tell whether resin that's
disappeared into wood has cured properly or not. I recently advised someone
on here to use the Halfords resin, and he replied and said it had done a
grand job, he'd re-painted the windows, and everything was hunky dory
....... only he decided after all not to use the hardener.
LOL ... well as I consider that the kind of work i do is a young man's job
and I am a few months off 40 ........ perhaps I shouldn't tell you that
after nearly 10 years in the trade, i am retraining for another that will
see me in to old age more comfortably. ;-)
Ahhhhhhhhh ..... so you are saying that the rotten wood DID move???? .....
But, once this
Well what you have there is that it did move after you added the polyester
filler .. but once you filled it at it's driest point ...... any moisture
absorbtion would be pressing and compressing the wood fibres against the
filler, so no further cracks would appear. Doesn't mean the the wood isn't
moving, just that you filled it, the second time, at it's greatest extent of
I have a front door
But the central heating caused the old doors to move when it was installed?
... so imagine an old piece of wood that was sealed and then exposed to just
about the driest year we have ever had, like this year.
Yep ..... seen them ... made some similar things for commercials and stills
The beans were cast seperately, and then mixed in to the sauce resin and
filled a mould of a sculpt to look like it was poured from a can ..... and
everyone thinks "how did they get it to go off as it was poured?" :-O ;-)
Hmmmmmmm ??? ... the intention is to stablise the wood so it NEEDS to go off
in the wood otherwise it isn't stable... if I am doing small parts i will
also pull a vacuum on the wood with it sitting in some resin
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