Blow torch - Osmosis treatment

SailingEcosse

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Speaking to a guy in the boat yard at the weekend who told me a story about an osmosis specialist from years ago, who would go over a hull with a high powered multi head blow torch :eek: to dry it out and burn off the acid/salt/styrene/glycol etc, buried in the laminate.

It seemed a bit extreme to me, although I could see why it might work i.e. localised high temperatures, able to vapourise moisture, styrene etc, but because it is concentrated in small areas for short periods of time, it doesn't damage the laminate (beyond the odd scorch mark of course:D )

So I'm just wondering if anyone else has seen this done first hand and whether it is a valid way to dry a hull, or whether it is something that was tried back in the day and either didn't actually work, or possibly did work but was maybe regarded as too dangerous (images of hulls burnt to crisp :( ) to continue with?

Or is it just an old boatyard story with no or little basis in reality?
 
D

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Could Be Relevant Based On This Book

..... Or is it just an old boatyard story with no or little basis in reality?

No idea on the validity of the story but I understand that most polyesters need high temperatures to cure fully, temperatures not normally realised in older lay up facilities. However the story may be compared to this snippet of information.

6. In order to permanently stop the hydrolysis and
restore the bond between glass and polyester two
tasks were found inevitable.
First: Heating of the laminate to 80-90C.
A. In order to post cure as much as possible of the
uncured enclosures.
B. To restore the bond between the glass and the
polyester.
C. To get all pthtallic acid dissolved and fluid.
D. To make the cured polyester temporarily soft
and enable removal of deep situated hydrolyse
residues and remaining uncured polyester.

The above quote is from "Osmosis, Myth and Reality About Hydrolyse Blistering and Delamination In FRP Boat Hulls", Bengt Blomberg. The book makes interesting reading and is available from the internet to download.
 
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sailorman

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Speaking to a guy in the boat yard at the weekend who told me a story about an osmosis specialist from years ago, who would go over a hull with a high powered multi head blow torch :eek: to dry it out and burn off the acid/salt/styrene/glycol etc, buried in the laminate.

It seemed a bit extreme to me, although I could see why it might work i.e. localised high temperatures, able to vapourise moisture, styrene etc, but because it is concentrated in small areas for short periods of time, it doesn't damage the laminate (beyond the odd scorch mark of course:D )

So I'm just wondering if anyone else has seen this done first hand and whether it is a valid way to dry a hull, or whether it is something that was tried back in the day and either didn't actually work, or possibly did work but was maybe regarded as too dangerous (images of hulls burnt to crisp :( ) to continue with?

Or is it just an old boatyard story with no or little basis in reality?

a mate of mine took his gel coat off with a Hot air gun
 

sailorman

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That Osmosis book has been made as a free download by the author, its essential reading for anyone that is 'hands on' with their own boat maintenance.

Its available (legally) from the authors website here

http://www.osmosisinfo.com/handb9a.pdf



As an example I can now, July 2001, present the HotVac
system developed by the English team Terry Davey and
John Ashton. It is based on heated vacuum mats and after
thorough tests I can verify, that it functions fully as well as
HYAB and without any environmental problems. Also it
needs much less manual labor.
Visit their web site www.hotvac.com

Terry Davey is a Surveyor in the Ipswich area ;)
 

BAtoo

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Not seen that but have seen someone drill out individual blisters, dry, fill etc. year after year.......

OK if you have the time...

(& no money) :rolleyes::rolleyes:
 

William_H

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Hot air or torch on f/g

I am sure the blow torch would work and well. However you would need to be so careful and lucky to get the temperature just right. Not hot enough does not do the job too hot is the real danger. Damaging the resin. Scorching and much smoke would result.
The vacuum treatment seems like a good idea as water evaporates much quicker under low pressure and you could add a little heating at the same time to, I would imagine, fairly quickly remove moisture.
olewill
 

sailorman

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I am sure the blow torch would work and well. However you would need to be so careful and lucky to get the temperature just right. Not hot enough does not do the job too hot is the real danger. Damaging the resin. Scorching and much smoke would result.
The vacuum treatment seems like a good idea as water evaporates much quicker under low pressure and you could add a little heating at the same time to, I would imagine, fairly quickly remove moisture.
olewill

Hot Vac is a clue ;)
 

SailingEcosse

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Hotvac I have seen and had priced :eek: but the boat just isn't worth the cost i.e. £4k (although this did include the epoxy treatment as well) but it's twice what I paid for the boat (26ft colvic).

The blow torch method has a strange appeal although the consequencies of getting it wrong don't!

Possibly temp sensors on the inside of the hull with a visible readout while applying the heat to the outside, section at a time?

I've also investigated a DIY vacuum system, and it doesn't look that difficult to build TBH, but finding a good enough pump and a heat mat at reasonable cost was the problem, as the pump needs to manage high vacuum levels (better than 10pa I gather) and be able to run continuously for maybe several days per section being worked.

It would certainly be safer than the blow torch route though, maybe vacuum on the outside + hot air gun on the inside of the hull, again section at a time, would be an option.

Needs more thought I reckon, but the mast is being stepped this week so I'll get that out of the way first, but if anyone has any other idea's (no matter how "out there" :D ) feel free to throw them in

Thanks everyone
 

DownWest

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A source of vac pumps is milking machinery. I have two for laminating, rated continuously at high flow rates and good vac levels. The larger was to handle the 40 x 6ft sides of a catamaran, so might be good for this application.
 

bbg

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On the plus side, if you get it wrong with a blowtorch you won't have an osmosis problem any more!
 

SailingEcosse

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A source of vac pumps is milking machinery. I have two for laminating, rated continuously at high flow rates and good vac levels. The larger was to handle the 40 x 6ft sides of a catamaran, so might be good for this application.

Thanks, I'll do some googleing and see what I can find, they sound just like what I would need for the diy Hotvac route


On the plus side, if you get it wrong with a blowtorch you won't have an osmosis problem any more!

Very true :D
I'm not sure what my (close) neighbours in the yard would make of that ending either :eek:
 

Grajan

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I saw a reasonably big yacht being done by this method umpty years ago in Mallaig of all places.
quite scary when you saw the guff that came out of the hull,
the treatment comprised of the "torching" of the hull scraping off the brown oooze that came out of the laminate then grinding and finally four coats of I believe hot applied epoxy coating.
not sure about the last part as didnt see the coating application but the company doing the job had the equipment with them. I believe it was a Scandinavian company who carried out the work.
 

richardabeattie

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"just had a letter from Screwfix.
They said that they're not a dating agency. "

SWMBO got confused by the two compay names, "Screwfix" and "Do it All" and asked an elderly Edinburgh lady for directions to "Screw it All"

I just thought you ought to know.
 

William_H

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I've also investigated a DIY vacuum system, and it doesn't look that difficult to build TBH, but finding a good enough pump and a heat mat at reasonable cost was the problem, as the pump needs to manage high vacuum levels (better than 10pa I gather) and be able to run continuously for maybe several days per section being worked.

It would certainly be safer than the blow torch route though, maybe vacuum on the outside + hot air gun on the inside of the hull, again section at a time, would be an option.

Needs more thought I reckon, but the mast is being stepped this week so I'll get that out of the way first, but if anyone has any other idea's (no matter how "out there" :D ) feel free to throw them in

Thanks everyone

Why a Hi vacuum? I would have thought from physics any vacuum even reducing pressure by half would be beneficial. Certainly it should be easy to get a pressure down to 1/4 or less of ambient with great evaporative results.
Hi vacuum normally implies very little air remaining as in sucking out a refrigeration system. Not at all necessary in this case.
You will need a hi capacity pump if you have a lot of leaks and or a lot of gunk coming out. I would try a standard air compressor with outlet open and inlet connected to the job.
Have I got it wrong? olewill
 

charles_reed

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Hotvac I have seen and had priced :eek: but the boat just isn't worth the cost i.e. £4k (although this did include the epoxy treatment as well) but it's twice what I paid for the boat (26ft colvic).

The blow torch method has a strange appeal although the consequencies of getting it wrong don't!

Possibly temp sensors on the inside of the hull with a visible readout while applying the heat to the outside, section at a time?

I've also investigated a DIY vacuum system, and it doesn't look that difficult to build TBH, but finding a good enough pump and a heat mat at reasonable cost was the problem, as the pump needs to manage high vacuum levels (better than 10pa I gather) and be able to run continuously for maybe several days per section being worked.

It would certainly be safer than the blow torch route though, maybe vacuum on the outside + hot air gun on the inside of the hull, again section at a time, would be an option.

Needs more thought I reckon, but the mast is being stepped this week so I'll get that out of the way first, but if anyone has any other idea's (no matter how "out there" :D ) feel free to throw them in

Thanks everyone
Rather than use a blow-torch, it might be an idea to use an hot-air gun, as used for paint removal - more controllable and no combustion products.
 

SailingEcosse

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Why a Hi vacuum? I would have thought from physics any vacuum even reducing pressure by half would be beneficial. Certainly it should be easy to get a pressure down to 1/4 or less of ambient with great evaporative results.
Hi vacuum normally implies very little air remaining as in sucking out a refrigeration system. Not at all necessary in this case.
You will need a hi capacity pump if you have a lot of leaks and or a lot of gunk coming out. I would try a standard air compressor with outlet open and inlet connected to the job.
Have I got it wrong? olewill

Not my specialist subject to be honest, but I got my info from a post on the boat design forums, which seems to be saying that the high vacuum is required more to reduce the the boiling point of water/fluid to a level that allows it to evaporate as much as actually be sucked out of the laminate

Once you have hit 28-29" of vacuum, you should see water vapor start to come from the pump exhaust. This is water that was in your hull. At 29" of vacuum, the boiling point of water is 76 degrees F., so it's better if you can draw down 29 1/2" or more. Obviously you want to do this on a hot day if possible.

29" of vacuum, from what I can understand of it, is regarded as "high" vacuum, but as I'm just learning this stuff I could easily be way off on this?

I'm coming round to the idea of giving it a try now though, as it would seem a more controlled approach than the blow torch route (however appealing that may be :eek: ) and as I have detailed moisture readings from my hull it will be easy to determine how successful it is in practice
So all I need is a pump, although on the milking pump suggestion, I've only been able find "new" ones, which are quite expensive, so I'm still looking.

Cheers all
 

30boat

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Why a Hi vacuum? I would have thought from physics any vacuum even reducing pressure by half would be beneficial. Certainly it should be easy to get a pressure down to 1/4 or less of ambient with great evaporative results.
Hi vacuum normally implies very little air remaining as in sucking out a refrigeration system. Not at all necessary in this case.
You will need a hi capacity pump if you have a lot of leaks and or a lot of gunk coming out. I would try a standard air compressor with outlet open and inlet connected to the job.
Have I got it wrong? olewill

I tried that with a my compressor and it started sucking oil through the rings.An oilless compressor might work though.I once treated a boat with a makeshift heating and vacuum arrangement.I used a small vacuum pump of only 100w.For heating I used a plastic flexible heating thing ,a bit like a cable,that has a heating coil inside.It was sewn to a fabric base.That was taped to the hull and on top went a layer of vinil to which the hose from the pump was attached .I let it running for 24 hours at a time and when the vacuum pads were removed there was liquid water there.If I do it again I'll use a milking machine instead.That'll allow larger vacuum pads which will reduce the time needed for the whole treatment.
 

SailingEcosse

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I tried that with a my compressor and it started sucking oil through the rings.An oilless compressor might work though.I once treated a boat with a makeshift heating and vacuum arrangement.I used a small vacuum pump of only 100w.For heating I used a plastic flexible heating thing ,a bit like a cable,that has a heating coil inside.It was sewn to a fabric base.That was taped to the hull and on top went a layer of vinil to which the hose from the pump was attached .I let it running for 24 hours at a time and when the vacuum pads were removed there was liquid water there.If I do it again I'll use a milking machine instead.That'll allow larger vacuum pads which will reduce the time needed for the whole treatment.

Thats good info, thanks, can you say what temp you had your "heating thing" running at though?
I'm thinking underfloor heating mat, but it seems to max out at about 40degrees, so I'm just wondering if this is enough or if it needs something more powerful.
Although I suppose it would depend on the amount of vacuum reached i.e.
  • greater vacuum = lower boiling point = less heat required
  • lower vacuum = higher boiling point = more heat required
Makes sense in my head anyway :D
 

DownWest

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Some figures for my larger pump.
1.5kw motor
1100 lt/min of free air.

About 30boat's problem with the oil passing the rings of a compressor, these are eccentric vane pumps and are lubricated from a reservoir of 10/30 oil that is then collected from the output manifold into a sump.Could be reused.
 
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