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Author Topic:   Hull moisture
Restorwhaler posted 08-06-2001 03:36 PM ET (US)   Profile for Restorwhaler   Send Email to Restorwhaler  
Am restoring an '85 BW 18' Outrage. Tubes were coroded thru and moisture is in hull. Have made several repairs on chines and old screw holes using heat lamps and paper towels to draw out moisture. Seems bone dry when I make the repair, yet over time I get an vinergar smelling brown fluid ouzing out from the repair/original material interface. I've opened them back up, dried out and re repaired. Still happening. Called Whaler and they clain that the foam won't absorb water and neither the fiberglass not the foam will break down. The acidic fluid makes me think otherwise. Any experience with this phenomena, explanation on what causes it or recommendations on how to fix it?
LarrySherman posted 08-06-2001 05:22 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Well, you have come to the right place. You need to answer these questions before we contine:

1) How long has the boat been out of the water?

2) Trailer or blocks?

3) What was done to repair the drain tubes?

4) Where are screw Holes?

5) what was condition of foam when last inspected (color texture smeel pyysical description)

6) describe your fibreglass technique and products used. Includ name and brand of key materials, and how prep work is preformed.

7) History of boat. Kept in water or out? North or south? Salt or Fresh? West or East? Good maintence or not?

You get the picture, start typing. Well figure this out.

LarrySherman posted 08-06-2001 10:33 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
I'm waiting....
Restorwhaler posted 08-06-2001 11:44 PM ET (US)     Profile for Restorwhaler  Send Email to Restorwhaler     
Thanks for your reply!
1)I've had the boat for 5 months. I bought it from a fellow in Florida that had it for 3 to 4 years. I'm fairly sure he trailered it(as I do) as the boat has no evidence of marine growth on the hull. He used it without doing much maintenance on it. I saw pictures when he first bought it and it looked to be well maintaned. The hull was painted prior to his buying it. I believe it was a yaght tender at some point as it had "T/T name" that could be seen under the paint.
2)The boat has been on an aluminum, bunk type trailer manufactured by Owens & Sons since 1997.
3)The brass tube in the rear sump was corroded nearly in half when I got the boat. I had it and the front drain tube replaced at a repair shop. The shop owner claimed to have dried the hull prior to replacing the tubes. He used brass tubes with an adhesive/sealant.
4)The screw holes that I am having trouble with were in the transom and were used to mount a swim platform. The two below water line had wobbled out and were not well sealed. Also, I am not able to seal gelcoat chips on the chines and keel that had exposed the fiberglass.
5) The foam I have seen appears to be structurally sound, dark in color and has an acidic (vinegar) smell. This is the foam around the small areas I have opened for repair and from looking in the inpection hatches.
6)The starboard front chine had about a 2" spot that had structural damage (fiberglass beneath gelcoat had been smashed and was no longer rigid).It had been Marine Texed over. I removed the Marine Tex, ground out the soft area, feathered the area around the hole back on about a 15:1 taper, built the area back up with woven mat/resin of decreasing sizes, shaped the hardened fiberglass, applied gelcoat over the area and sanded it down to final shape. I just went out to look again and I haven't had problems with this repair.
The areas that have a dark brown, acidic smelling liquid oozing out are 1)screw holes below the water line that I previously described 2) gelcoat chips below the waterline that exposed the fiberglass 3) quarter inch inspection/weep holes I drilled through the hull to try to dry out the hull when repairing the chines.
I have tried repairing these by 1)chamfering the hole and patching with gelcoat paste (manufactured by Spectrum Color) 2) not chamfering and using gelcoat paste 3) chamfering and not chamfering, patching with Marine Tex.
7)I believe the boat has been used primarlily in saltwater and I would guess in the southeast. I have sanded the paint off of the transom and starboard side and restored the gelcoat. No indication of damage. Started working on the port side.

Chuck at Whaler stated that the saltwater would not deteriorate the foam or fiberglass. I remember reading in a West Fiberglass book that the saltwater would breakdown the fiberglass. YOur thoughts?
Any idea what the brown acidic liquid is?
I put a heat lamp on the areas to be repaired for days and stuffed rolled up paper towels into the quarter inch holes to wick out the liquid. I let it sit for days afterward and tested for moisure with paper towels. It would be dry before I patched but still will eventually start oozing out the brown liquid.
If you have a number where I can reach you, I'd be happy to call you so that we could discuss. Thank you for your interest and help.
David Smith

LarrySherman posted 08-07-2001 09:53 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     

Glad you posted back. Some basics first. Gelcoat acts much like a semi-permeable membrane, allowing water to pass in one direction, and not another. While Chuck is correct in stating the glass can not absorb water, he is omitting that poorly cured glass/resin most defiantly can (or at least seem to, which is I think what you have going on here). The problem is called ďosmotic blistering,Ē and while you have not mentioned anything about blisters on the exterior of the hull below the water line, the vinegar smell and the brownish liquid are tell tale signs.

What happens is that in the layup process, esp. with older boats (60ís &70ís), small areas form in the hull where resin and catalyst did not cure properly, for whatever reason. This small pocket of un or semi-cured resin actually draws the water through the hull into the void created when the hull was laid up. The water mixes with the resin to form a nasty brown, bad smelling acidic liquid. As more water is drawn into the pocket, pressure is built up, and if there is a week bond between the layers of glass, they are slowly delaminated, through pressure and chemical reaction.

What you say? Fiberglass canít absorb water, so how does this happen?

Well gelcoat is decidedly porous, and glass will wick water along the axis of the layers of cloth and mat, through any week bond you have.

Here is the good news. One of your repairs did work! We have hope. In general, this is normally a cosmetic problem, which you can either spend a fortune trying to repair, or do what you can to mitigate cost effectively, and enjoy your boat. That is your decision. I assume our short term goal is to make the repairs for the screw holes and chine work.

You did not tell me what products you are using for the repair, but Iíll assume itís West System. If not, then make it so! First, go to West marine and buy the West System book on Gelcoat and Blister repair. This will be your bible.

My gut on the screw holes is that you transom has absorbed a good amount of water into the ply wood and wood rot is setting in. Up to you if you want to repair it. I think failure to repair the holes is to be found in technique.

Put away your paper towels. Drill out the hole to the next larger size, take a syringe of acetone and inject it into the hole. Do this 3 or four times over the span of say 20 min. Then, take a syringe of west system epoxy (mixed of course) and shoot it into the hole. Now take a length of wood dowel slightly less then the depth of the hole, and the same diameter as the drill you used to ream the hole, and drive it into the hole with a hammer. Countersink the dowel slightly, no more than 1/8 of an inch. Paint the face of the dowel and the edge of the hole with epoxy, then add some 410 (I think thatís the number) barrier additive to the remaining epoxy and build up the recess until flush. Once cured, sand, then barrier coat the transom in the area of the repair.

This repair is not perfect, but will certainly last until it is time to rebuild the transom.

As for the chine, when the glass is sanded out and you are ready to begin repairs, do this: Wipe area with acetone liberally. Let dry for 20 min. Now take a clear plastic and tape it securely over the perimeter of the area to be repaired. Try a cut up zip-lock freezer bag and use duct tape. Make sure the tape is well applied to trap moisture, and will not allow any in. In 24 hours, check the plastic.

If itís clear, re-wipe with acetone, and commence repair.

If it is fogged or other evidence of water exists, you are going to have to dry the boat out before you begin the repair. Smell the raw glass area after you remove the bag. Smell like vinegar? Thatís the acidic liquid formed in the blistering process. To dry the boat out is tough, I say we just try to dry this area. Make a tent over the area to keep it dry and hold out heat. Get a propane heater with built in fan, and set it up to direct the blast of hot air on to the hull. You donít want the hull to get too hot, but certainly warm. About 115-120 should do it. Do this for days. Recheck with plastic/tape test. When no moisture, commence repair.

Also look at other posts in this section from me about drain tubes and betting!

Let me know if this helps, and if you want to talk, email a phone number to me.


Bigshot posted 08-07-2001 10:37 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Nice job Larry!
LarrySherman posted 08-07-2001 10:49 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Thanks dude, just another day on the forum...

Ever watch south park?

Restorwhaler posted 08-07-2001 12:17 PM ET (US)     Profile for Restorwhaler  Send Email to Restorwhaler     
There are no external signs of blistering. Are you suggesting that it has blisters on the inside of the hull? Any means for checking for this?
Didn't try the plastic sheet moisture test, but definitely got the area dry. As I stated, I had a heat lamp on for days and used the paper towel wick to test for moisture. It was bone dry in the area prior to repairing. I did use acetone to clean the area prior to repair, but not in the quantitity or manner you described. I'll try that.
If I understand you on the transom repair, I need to get epoxy down before patching with gelcoat.
Interesting point you made on the gelcoat. You said it is porous. I thought the main reason for gelcoat (other than cosmetic) was to have a resin rich barrier between the water and fiberglass so that the water would not wick into the fiberglass along the glass resin interfaces.
Would like to talk with you. My number during the day is 281- 366-3066. I should be available after 2 pm central time. If evenings are better for you, 281-347-1460 is my home number. still somewhat confused as it appears that I did most of what you are suggesting and am still having problems.
Again thanks for your time and input.
Bigshot posted 08-07-2001 01:48 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Saw the one Sat night on sex education. My wife was appalled. Can't believe the crap hey get away with sometimes. No worse than Howard Stern though.
LarrySherman posted 08-07-2001 10:23 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Dave, Just called you. Left message on you machine to call me at work tomorrow. Talk to you then.
LarrySherman posted 08-07-2001 11:08 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Some reading until we talk:

You have just finished hauling your boat for the winter. You have blocked her, pressure washed the hull, cleaned the topsides, and are about to button her up for the long winter's nap. One last stroll around her, gazing at the long lines, the sleek hull...sleek! eek! MY BOAT HAS THE CHICKEN POX! Don't worry, it's not really Chicken Pox, it's blisters, and, as in most early childhood diseases, it is not terminal. But it does take some understanding of what causes blisters and what to do when your pride and joy shows up with them.

Water being absorbed through the gelcoat and fiberglass laminates in the hull causes blisters. Once thought impervious to water, it has been discovered that constant contact with water can cause it to be absorbed through the gelcoat from the outside and through the exposed laminate on the inside of the vessel (from standing bilge water). The water absorbed causes changes in the physical makeup of the hull and reacts with the resins, which build up residues and finally raise blisters by increased pressure on voids between the laminate and the gelcoat. This is what you see on the hull. This phenomena usually starts occurring, although it may occur earlier, from the fifth to tenth year after the manufacture of the boat. It occurs when boats are left in the water for long periods of time and happens more frequently in fresh water.

Once blisters start to show up, it is not necessarily time to panic. If you have a good antifouling paint on the hull and you only see a few blisters but no cracks in the gelcoat, you need not be too concerned at this point. However, if the number and size of the blisters increases and you start to find cracks in the gelcoat itself, it is time to jump into action to repair the problem.

The first step is to remove the antifouling paint and get to the blister problem first hand. The next step is to open up the blisters to allow them to "bleed" the excess water. You may find areas where you can't actually see the blister but you do see water "weeping" from the gelcoat. Take a pocket knife to start the opening of each of the blisters and weeping areas and then grind down to solid laminate. Once you have opened these voids you will be rewarded with a very distinctive aroma which is generated from the foul residues. (Remember, water may also penetrate from the inside so make sure the bilges are dry.) Once all the blisters have been ground to solid laminate and the entire void exposed, allow the hull to dry for as long as possible. This may require a month or two or more. Older boats or boats in cold, damp conditions will take longer than newer boats or boats in hot, dry conditions.

A good technique to test the hull for dryness is to tape a clear plastic sheet, about one foot by one foot, over the clean hull surface. Make sure all the edges are sealed with tape and adhere to the hull. After 24 hours, check to see if there is any condensation under the plastic. If not, you're ready to continue. If you find condensation you need more drying time. You can make a plastic skirt around the hull from the water line to the ground and place fans or, with great care, heaters to speed the drying process.

There are many products available to make the repairs to the blisters. If you plan on doing the job yourself, talk to others in your boatyard or marina who have had success and ask them to recommend products. It is important to follow the product directions carefully. Once you have your blisters exposed and dry, fill the voids and ground areas with the epoxy or fairing compound that you have selected. Once dry, board sand the bottom to fair in the repair and repaint with your antifouling paint. (Fair is a term used in ship building by which is meant the restoring to original shape any part of the ship's structure not damaged seriously enough to necessitate actual removal from the ship for repair. In this case it means that you want to use a large enough sanding area so the repairs blend in and are not noticeable.)

How can you prevent blisters? Well...the key is to keep the hull as waterproof as possible. Some boaters recommend the use one of the good epoxy coatings to coat the entire hull. This can be time-consuming and moderately expensive however, it seems to cut down on the dreaded "chicken pox."

If you want to undertake this endeavor, make sure the entire hull is clean and free of antifouling paint, any other foreign materials and moisture. Sand the gelcoat enough to make sure all the shine is gone. The color should be consistent and bright. Again, using your favorite epoxy which is intended for boat bottoms, build up a generous coat. Remember, the epoxy is what gives the protection. Try to get a minimum of 15 mils of thickness. This is about five times the thickness of a coat of paint and about the thickness of typical gelcoat. Once you have completed this operation and sanded to fair the hull, reapply your favorite antifouling paint.

Blistering is the most common reason that potential boat buyers back off or make substantially low offers. Repairing blisters once they have occurred, or taking steps to prevent them, can improve the resale value of your boat.


Or, better yet, go to, and in the box type "gelcoat blisters" or "osmosis"

Lots of reading to do...

Also, check in the general section under "Refrence material"

John W posted 08-09-2001 10:43 AM ET (US)     Profile for John W  Send Email to John W     
Great info, Larry. One thing to point out is that not all boats will ever form blisters, and many older fiberglass boats from the 1960's and early 1970's never get blisters despite being kept in the water. My father's 1969 Chris Craft Commander does not have a single blister after 32 years of year round use in the water, the last 15 years in fresh water. I've heard of very few cases of blistering in older 1960's & 70's Bertrams, Chris Crafts, or Hatterasses...but I've seen alot of blistered boats of 1980's vintage, particularly in cheaper brands. I've had a marine surveyor I know tell me the same thing...the older glass boats have fewer blister problems. I don't know if this is due to more care in the construction process then (less voids in the laminate), different materials used, or what. I've heard the same thing on other boating boards, with some speculating that they left boats in the mold longer back then...but that doesn't make much sense to me.
Dr T posted 08-12-2001 01:40 AM ET (US)     Profile for Dr T  Send Email to Dr T     
Great information.

Question: How big are typical blisters. While I was crawling around under the boat today working on the trailer and identifying areas of road rash on the hull that need repair, I notices some clusters of small (less that 0.25 in.) bumps in the sponson and center hull (what is this called?) of my sport 13. The boat is a 1982 and I have trailered it since buying it in 1989. It did, however, start life as a yacht tender on the Gulf Coast and Lake Texoma--but I have no idea if it was kept in the water during that time.

Thanks for the help.

LarrySherman posted 08-12-2001 02:31 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
Dr T,

Does your boat have bottom paint? Some epoxy based bottom paints can blister (VC 17 did for me once), due to poor prep prior to application.

So if bottom paint, take it off. If its the hull itself, the easies way to repair is to drill two holes in the blister, 1 at the bottom, another towards the top. Squirt acetone in there a bunch of times over a few days. I would put tape over the bottom hole for a few min each time to let the acetone penitrate. Then shoot blister full of epoxy, mixed with 422 barrier coat, with the bottom hole plugged.

This is the cheap and easy way to do it. Not necessarily the right way. The blister may come back, and the raised are will always be there. The alternative would be to grind it out as JimH describes in the Refrence section. Thats considerably more work. Your call.

Dr T posted 08-13-2001 10:52 PM ET (US)     Profile for Dr T  Send Email to Dr T     
No bottom paint. I first took it to be a minor imperfection in the molding, but your post made me wonder.

Thanks, Larry.


Hawaiian Bob posted 08-15-2001 04:12 AM ET (US)     Profile for Hawaiian Bob  Send Email to Hawaiian Bob     
Why squirt Acetone? Does it help the epoxy penetrate?
LarrySherman posted 08-15-2001 09:35 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
It aids in drying the surface to be epoxied. Nothing will bond well if the surface is moist.


jimh posted 10-01-2001 08:21 AM ET (US)     Profile for jimh  Send Email to jimh     
[Changed topic to "moisture".]
jameso posted 10-01-2001 09:09 AM ET (US)     Profile for jameso  Send Email to jameso     
The boat survey guy has some good info on how moisture penetrates fiberglas and also what causes that acid type smell. Do not have the URL, but it is good informative reading
Makonut posted 10-02-2001 12:44 AM ET (US)     Profile for Makonut  Send Email to Makonut

great site..If I lived in Florida I'd love to meet him

Gene in NC posted 04-06-2004 10:25 PM ET (US)     Profile for Gene in NC  Send Email to Gene in NC     
My 15 year old '73 Pacemaker 30 didn't have a single blister.
jimh posted 04-10-2004 10:07 AM ET (US)     Profile for jimh  Send Email to jimh     
[Closed thread after almost three years between its creation and this most recent addition.]

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