Views on heat and vac-pads in 'osmosis' treatments...

[NealB]

Views on heat and vac-pads in \'osmosis\' treatments...

Like most of you, over the years I've read loads of articles, books and websites about hull blisters (their causes and treatments).

I'm very well aware of the ''ignore it...no boat has ever been lost due to blistering.....it's a cosmetic thing only"' school of thought, and can see lots of merit in it.

However, I'm interested in hearing views on commercial treatments.

eg

- are they too quick to condemn, and peel, saveable gel coats?

- are there cases where the use of localised heating has damaged the laminate?

- is the use of vacuum-pads a 'good thing'? Are there any downsides to their use?

All thoughts on this welcome, as I'm trying to decide whether to have a commercial treatment done on the motorboat.

 

[vyv_cox]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

I only know what I've read. PBO did a big article on it within the last year. The word in that was that heating takes an age to dry the boat out and, of course, is a large consumer of energy. Those who used vacuum drying claimed that it was very effective and that a dry state could be achieved in days, compared with weeks for heating.

My hull showed signs of blistering and Sadlers have been known to suffer osmosis. Many have been peeled and re-gelcoated. I stripped all antifouling at the beginning of a winter ashore, then Gelshielded in the spring. I have never seen a blister since.

If you can get someone to agree to it, I would think that a combination of the two, i.e. vacuuming followed by Gelshield, might be a reasonable way to go. Problem is, as you have highlighted, most contractors will want to do a major job on it.

 

[oldsaltoz]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

[ QUOTE ]


1- are they too quick to condemn, and peel, saveable gel coats?

2- are there cases where the use of localised heating has damaged the laminate?

3- is the use of vacuum-pads a 'good thing'? Are there any downsides to their use?

[/ QUOTE ]

1-If the fault can be traced to a failing gelcoat there is no point in keeping it. It provides little protection if it's a standard poly resin, if epoxy it can be repaired but only after you have checked the application was done properly and it's not failing.
Note: areas of osmosis or wicking may only be visible 'after' the gel coat has been removed.

2-Local heating with the right equipment regulated to maintain a particular temperature range is fine, this will reduce the required drying time by many months in some cases.
But even a well dried area can be treated in the wrong conditions, ambient temp' should above 22C and relative humidity below 72% for most epoxy resins.

3-Vacuum pads should be used in conjunction with heating, the areas being treated will also need regular rinses with fresh water to dilute the contaminants.

So, if you have a standard poly resin gelcoat showing blisters, my advice would be to grind the area and look for a fine light brown line, continue grinding till you find it's end, it may be several inches from the blister, you should come across some whiter glass abd be able to see small holes in the lay up; this must be removed.

If you are in a hurry, use the heat and vacuum systems, be warned this is not a cheap option.

Look for someone who puts at least one layer of epoxy resin and cloth over the area before fairing.

Hope this helps.

Avagoodweekend......

 

[deep denial]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

I think I have at least a partial answer to this. My Warrior 35 (1977) was found to have osmosis on prepurchase survey, and the price was dropped accordingly. After some research We accepted a quote from Hayling Yacht Company, who appear to be leaders in this field. they had the boat for hot vacuum treatment, and in addition aplied a complete new sheath of epoxy/glass. They were very thorough and professional, the guy in charge is a very pleasant, down-to-earth trustworthy sort, and did what seems to be an excellent job. Although this was only last year, so I can't give you long term view, I am confident that we shouldnt see any osmosis problem in the forseeable future. The cost I felt was actually very reasonable - well under 10k for all that, and with basically now a new hull on a 30 year old boat. I can recommend them and their hot vac treatment.

 

[castaway]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

I have my boat in having this job at the moment.

Basically what started as having the rather knackered 20yr old hull paintwork flatted and repainted with 2 pack has become rather more involved. This started due to the poor adhesion of the old paint and the necessity to remove it all before starting painting.

Of course the mosture levels in the laminate were to high so the boat has been sitting (outside) with a dehumidifier running for the last 4 months but doesn't really appear to be making a lot of difference.

A couple of months back we, ( myself and the painter) agreed that whilst we were doing all this work we might as well blast the bottom back to bare gel and 'GEL SHIELD ' her as well.

All a good idea and designed to keep the value up on a good old boat.

Only trouble is that she still isnt drying out nearly enough to even start thinking about 2 pack painting.......so my painter has suggested that to both speed things up and also do a more thorough job we give her a 'peel' as well ! This will get rid of all the old repairs/ and also what appears to be a coat of polyurethane paint ( once apparently thought to prevent osmosis ! ...I wish).

I hope that this will result in a nice clean epoxy bottom/ moisture levels down to a reasonable level/ and beautiful shiney top sides.

I might add that all the work is monitored by a surveyor, and that I also hope that the cost will be recouped in the increased value of my boat.

Once you start down this road you really do not know where it will lead, however with lots of good 20-40 yr old GRP boats still giving great service and with care looking good for another 40 years or so I can see this being a bit of a boom industry !

All best Nick

 

[yoda]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

The whole point of the hotvac process is to create the conditions where the undesirable products will evaporate off. I forget the actual temerature at ambient pressure but it's high, the vacume drags that temperature down and the combination with heating should do the trick. None of this will work however if gelcoat is still applied and prevents the cemicals being released. The whole process does of course cost and you need to consider if it is worth it. I went the DIY route, got rid of the blisters and know that at some point in the next 10 years will need to go through the process again however on a boat worth £10k a professional job just isn't owrth it.

yoda

 

[Graham66]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

Is Hot Vac still in business ?

 

[mikejames]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

Ten years ago Forethought (westerly GK2) had Osmosis treatment:
Antifouling hand scraper removed - to avoid AF flakes contaminating the laminate. A whole week of evenings by myself and my wife.

Then the yard took over with gelcoat shot blasted off.
Then a weekly steam wash to clean surface laminate until moisture content dropped.
A couple of weeks indoors with heaters. Once surveyed as dry enough the finishing commenced .

One coat of gelshield followed by epoxy filler fairing layer
followed by 6 more coats of gelshield

The whole process took about 3 months. Including a near-miss where Forethought was removed to the drying shed a week before a storm which toppled a big Swan onto the space where Forethought was being stored.

(I know this because I have in my hand a hull sample I took while cutting a hole for a paddlewheel log transducer the other week).

To give you hope there has been no blistering in 10 years, the last 5 or so constantly afloat, except for one blister that appeared on the skeg which is full of water so probably will never dry out (it is bolted to the hull and is a separate moulding)

It cost £4000 including £800 for fairing the keel at the same time , back in 1997 at Hamble Yacht Services.

 

[zlod]

Re: Views on heat and vac-pads in \'osmosis\' treatments...

There seem to be a lot of conflicting views on what the root problem of osmosis is. What seemed most plausible to me was that there were acids lying around due to esters that had not properly cured (or something like that: I believed it 9 months ago). It then seemed plausible to me that the issue then should be to try to remove those acids / esters (which is what the hotvac system is meant to do). It seemed implausible to me that trying to get the hull thoroughly dry (without necessarily trying to remove the driving force for the osmosis) and then trying to encapsulate that dryness in a new gelcoat would work (with a boat being in the water, this seemed like it would be a losing battle).

I took the view that the issue was the salts / esters and that the wetness was a consequence of this issue. Sorting out the wetness was not my concern, sorting out the salts / esters was.

So I thought that the most plausible solution to the osmosis problem was a hotvac treatment, and epoxying (as per Hayling Yacht Company's suggestions). I thought that the hotvac treatment was the most likely way to get rid of the salts / esters (and if it got some water out too, then all well and good).

I got a layer of cloth added as part of the epoxying process. I did this because I thought this would add to the structural integrity after peeling the gelcoat (I assumed the peeling would inevitably peel some of the boat itself too). I'm not convinced by the argument that an extra cloth layer will stop the blisters coming through: even if it does, I think the issue with osmosis is the degradation of the hull rather than unsightly blisters.

I guess in a few years time I'll find out whether I took the right course of action.