FIBERGLASS TRILOGY III: BLISTERS & VOIDS Part I: Causes. INTRODUCTION As described in Trilogy I, gelcoat is just polyester resin containing colored pigment that is used to produce a smooth shiny surface for boats, RVs and other manufactured items that are constructed of fiberglass laminate. It is laid down in the mold first, before the laminate so as to produce a shiny and attractive exterior coating. Gelcoat is thicker and much cheaper to use than paint. Unlike paint, however, it is less durable and not completely impervious to water, even when new. If you have a wooden boat coated with a good marine paint, you do not expect the wood underneath to be sodden with water, because the paint is waterproof. Similarly, if you had a steel boat, you would not expect it to externally rust, if the steel is well protected by paint. Unfortunately, even new gelcoat does allow some water to permeate. I saw this first hand back in 1994, when I had an emergency rudder made for my boat (in a hurry) and the people who made the rudder covered it in polyester resin because there was "no time" to do it properly with epoxy paint. When I tested the rudder, leaving it in the water for a few days, I noticed that the resin became "milky" because it had absorbed water. You have probably also noticed rust stains etc that can occur, even on fairly new gelcoat above the water line. This is because the gelcoat is somewhat porous to water-borne stains. This problem gets worse with age with actual visible pores forming as the gelcoat oxidizes (www.islandgirlproducts.com/techinfo.html ) This would be less of a problem if water-resistant vinyl ester resin or (especially) epoxy resin were used for boat construction. However polyester resin is still used because of cost considerations but with a "barrier coat" of two-part epoxy paint or resin applied to the underwater portions of the hull. That such barrier coats really work is well documented both by the manufacturers and by collected anecdotes form boat owners. Here is mine: About 4 years ago, my Gulf 32 had to have the waterline raised because of a slight list to starboard (All the batteries were on the starboard side). When the boat was hauled, there were obvious gelcoat blisters only on the upper area of gelcoat that had not been covered by the original factory barrier coat. How do blisters and voids form? The discourse below is not based upon any specialized knowledge that I had, but is an overview of all the things I have learned from reading other people's views and findings, including a sort of "round robin" questionnaire we did on www.Sailboatowners.com THE THEORIES & MYTHOLOGY OF BLISTERS. 1. They are caused by osmosis (water passing from a less dense to more dense solution, through a semi-permeable barrier). 2. They are caused by hydrostatic pressure. 2. They are caused by individual fibers sticking through the gelcoat acting as "wicks". 3. They are worse in warm water 4. They are worse/better in fresh water compared to seawater 5. They are caused by poor lay up of the fiberglass, certain types of boat etc. 6. They were not a problem on older boats. 7. Boats that are hauled regularly and dried out do not get them 8. Voids & de-lamination are not related to blisters. 9. Paint does not form osmotic blisters, only gelcoat. Actually, it seem that all of the above theories have some truth in them, but are not the "only truth". Indeed, the only absolutely true fact is not even listed above: WATER DAMAGE TO FIBERGLASS RESIN (INCLUDING BLISTERS) IS CAUSED BY WATER PENETRATION OF THE RESIN AND HYROLYSIS OF THE RESIN, REGARDLESS OF OSMOSIS. To a varying degree all cured polyester resins have some water soluble materials remaining from the curing process (usually about 5%) but much more in a poorly made hull and/or made with materials that may not be up to standard. These water-soluble materials include pthallic acid, glycols and styrene. As discussed above, gelcoat is a poor barrier to water when constantly immersed and the water that penetrates through to the first layer of laminate dissolves these water soluble residues at the interface of gelcoat and laminate, forming an acid solution that can start to further break down the resin, forming more of these water soluble materials. This process is made evident by lack of clarity (“milkiness”) of the underlying resin. If this process is localized, blisters start to form by the attraction of further water outside water, through the gelcoat to these localized areas of acid “blister fluid” by the process of osmosis. [Osmosis is the passage of water from less dense to more dense solutions though a semi-permeable barrier]. Ironically, blisters may have become more obvious in newer boats because gelcoat on boats of about 20-30 years in age was actually more permeable to water and barrier coats may have been less common. But older boats also tended to have very thick fiberglass lay-up. Therefore water permeated in a more generalized manner so that some outer layers of the lay-up may have partially hydrolyzed, becoming somewhat "soggy" and less rigid but there was still plenty of fiberglass thickness remaining for adequate structural strength, and there was not the localized build up of pressure that caused obvious “blisters”. It is also thought by some that construction technique and materials were better in the old days. By contrast, blisters are caused by localized water permeability - thought to be more of a problem on newer less permeable gelcoat. This tends to bubble up the localized area of gelcoat.into a "blister". If left too long without treatment, the process continues into the next layer of the fiberglass lay-up. This is more serious, since it causes loss of strength or even de-lamination. Then, on a modern thin hull, especially foam-cored hulls, we are talking serious structural problems - hence the relationship to "voids". Whether or not the "wick effect" of loose fibers is a major contributor is not known for sure. There is probably some role, however, because sections of old fiberglass hulls often show water penetration being worse in areas where such fiber penetration has occurred. This is probably one good reason for the use of finely woven fiberglass cloth on the outer layers of the boat, just below the gelcoat. Blister problems have to be worse in warm water, as in the tropics. It is intuitive that all decay (rotting, rusting, oxidation etc) happens faster in warm, wet conditions, but there are also common sense reasons. Microscopic pores will tend to be more open in warm water, marine growth attack of barrier coats is faster and ALL chemical reactions are faster too. Here in Hawaii, fiberglass boats (at least the sailboats that live in slips) seem to have many more blister problems than I saw at yards the SF Bay area. However a contributing factor could also be the fact that it is far more expensive to haul boats out here and so they may be left longer between haul outs. Also boats in really cold (snow/ice) climates are often hauled onto the hard during the winter reducing both the time of exposure to water and allowing thorough drying - all supporting - to “myth number 6”! Hard factual evidence that warm water accelerates water penetration is presented in a videotape on "gelcoat blister repair" by Gougeon Brothers Inc (makers of West Systems Epoxy). They actually did the definitive experiments of measuring gelcoat blisters and/ or water penetration (measured by weight increase) in the lab under controlled conditions. As temperature of the water rose to tropical levels, so did the degree of water penetration of the gelcoat. On the question of salt water versus fresh water, science tells us to expect osmotic pressure (between less dense and more dense liquids across a semi-permeable barrier) to be greater in fresh water. However, I know of no hard evidence to support this assumption. Why? Lake water is generally colder than sea-water and, in any case, boats used on lakes tend to be trailered or hauled for the winter, thoroughly confusing any fresh versus salty comparisons. Only a properly controlled experiment with pieces of fiberglass hull at fixed temperature would answer the question properly, if rather academically! I do have an anecdote, however: When my boat was hauled there was a "rash" of small blisters (actually in the barrier coat) just below the outlets to the galley sink where fresh(er) water had been exciting. Now to hydrostatic pressure: This is greater at the bottom of the keel than near the water line but I have never heard of more problems lower down on the hull compared to just below the surface. Of course, in tropical climates, the water near the surface is warmer that could accentuate blister formation. On the other hand, when a boat is first hauled (as mine was) no blisters may be visible at first, because they were compressed by the hydrostatic pressure provided by the displacement of water by the boat hull. Then, as the boat sits on the hard, they first start to appear. At first one sees the "rash" of small blisters (often just in the barrier coat) and then the larger blisters start to appear. This is one good reason to insist on enough "lay days" for the boat and not to quickly redo the bottom pain×aupd re-launch under the assumption that all is well. When all blisters have appeared, they can be punctured and opened up.- but wear eye protection (the acid stuff in the blisters is a nasty mix of chemicals)! Finally to poor lay-up, voids and de-lamination:. Undoubtedly, incomplete curing of the resin between layers must be a contributing factor, because that is where uncured resin will be present that could be a focus of the events describe above. Often, too, laminating is stopped for the weekend then continued the next week, causing differences between apparently identical boats. One manufacturer reckoned that complete UV treatment of every layer could completely eliminate water penetration by ensuring that EVERY LAYER is completely cured hard. Anecdotally, on the Gelcoat and Plastics Forum of www.Sailboatowners.com, one boat-owner reported that two people with identical boats of the same year, kept in the same area saw blisters on one boat and not on another. Voids and de-lamination obviously also result from poor bonding between fiberglass laminate layers and between laminate and underlying core material. Often, however, structural damage due to collision or “working” of the laminate is the precipitating factor. Anyone who has had a rudder fill with water could point to the relationship between the processes involved. One last thing is that surface "rash" can form in painted surfaces. I once painted a '67 Cadillac with acrylic lacquer. I was after a show-quality paint job. The original paint was well sanded, primed and a sealing coat applied. After 4 coats I wet sanded the entire surface with 400 grit wet/dry abrasive prior to applying the next four finish coats. The car was so big it took all day to sand and there was no time to paint. Then the "impossible" happened in Northern California. It rained daily for almost 2 months (well into May) because of the first of the recent "El Nino" weather patterns (early 1980's). I had a regular job and needed the car for work, so I had to drive it in the rain. I could not wax the car, because I was waiting for a dry weekend to finish the paint job! Then, to my horror, I started to notice little pimples (a rash) appearing in the new paint and spreading. When pricked, they contained water. How did they form? Well the microscopic "cuts" in the acrylic paint made by sanding had made the paint very thin and, in part, porous, while underneath, it is possible that some of the primer/sealer was a little damp (always use a good water trap before the gun). Also the lacquer primer that I used in those days contains talc and is porous. As the water penetrated, it dissolved some of the material from the primer, producing an osmotic gradient - sound familiar? Therefore the little pimples grew. I eventually (when the weather improved) had to sand off most of the lacquer to open all the pimples and allow full drying.. I had to completely redo the paint finish. This is one reason why I used two-part epoxy primer and a polyurethane top coat for my next project (a ‘66 GTO). When I hauled my boat, I also saw a rash appearing after a few days under the bottom paint. When sanded you could see the top of the rash was the barrier coat underneath. When pricked they contained water, but the gelcoat underneath still looked sound. As for my old Cadillac, I sanded the rash away and redid the barrier coat before the bottom paint was applied. Part 2 Repairs and Prevention. General: Ideally a boat should be hauled once a year, dried thoroughly and inspected. However this usually only happens in cold climates or with trailerable boats and they don't need it! In most cases, 2 years go by between haul outs, sometimes longer. In the tropics, cruisers often find the opportunity (and cost) unavailable and the job is done whenever. The exception is multihulls that can be beached for inspection. The days of “careening” (using the tide to deliberately beach a boat) seem to be over for modern sailboats! In the yard, the boat is hauled, usually by travel lift and the bottom is pressure-washed to remove marine slime and sea-grass. Wear protective clothing before starting any bottom work on your boat (reinforced paper suit with hood, mask. gloves and EYE PROTECTION). Before painting or using resins use a charcoal-filtered mask - a positive airflow mask would be even better, particularly if you have a beard that prevents a good seal around conventional charcoal-filter masks. Barnacles are not removed by pressure washing.. They are usually on props or other metal fittings. Barnacles do not hold onto anti-fouling paint. but do sometimes get up into water intakes that should be inspected. Thay have to be chipped off, sometimes with the aid of muriatic acid that dissolves the "cement" that they use for attachment. Then the prop is wire-brushed and the zincs inspected and replaced if necessary.If you have the "Spurs" linecutter attachment on the prop, remember that it has its own zinc to prevent destructive corrosion. For reasons, mentioned last time, it is a good idea to leave the boat for one or two days before looking for blisters, as the lack of hydrostatic pressure that has been “flattening them” underwater then allows them to pop up and become more visible. Some yards no longer allow dry sanding of boat bottoms in a (vain) attempt to rid the yard of bottom paint dust that is toxic and causes stains in the gelcoat (although easily removed by ISLAND GIRL Pink). In rainy climates, it is a good idea to have the boat inside, or inside a temporary "tent" of tarps or polyethylene sheeting so that the underside of the boat gets a chance to dry during the bottom job and so that you can work without getting wet. Blisters: lÙ–n small blisters ("rash") may be only in the old epoxy barrier coat that overlays the gelcoat under the water line. It is usually of a different color to the gelcoat and is very thin (gelcoat is usually about 16th inch thick). If the rash is in the barrier coat, sand it off (use an orbital sander if possible). Then rinse with lots of fresh wate and dry thoroughly, before repainting with a good two-part epoxy barrier coat (2 coats is better). At this time, you may also notice real blisters that have grown up between the gelcoat and the underlying laminate. Sometimes these are also like a rash or "pox". They should be probed with a sharp awl to open them up and may then be sanded and treated similarly to the paint blisters except that they are best filled with a good coating of a thickened epoxy resin from West Systems or equivalent, prior to the barrier coat. Some people advise forgetting about such gelcoat “rash or pox" , I think that it best to fix it, since the bubbles are bound to grow bigger in response to the osmotic process and could cause larger scale separation between the gelcoat and underlying fiberglass laminate. Larger blisters are “popped” with an Awl or other sharp object. Remember (from last time) that the fluid in the blisters is acidic and could cause eye injury! Then open them up with a die grinder (air driven) or dremel tool with a carbide bit. The makers of West System Epoxy recommend a countersink tool with electric drill, or gentle abrasive blasting procedures. You should open up wider than the blister, to the point that the gelcoat is solid and attached to the underlying laminate. Now press with the awl to see if the underlying laminate is hard and not softened by water absorbtion. If it is hard then just lightly sand or grind to make a “key”. The laminate should be clear and not “ milky “ (another sign of water absorbtion). Then water rinse with fresh water (prefereably hot water or steaFd to remove all traces of acid and breakdown chemicals that caused the problem in the first place. THIS IS IMPORTANT because if such chemicals remain, they are the focus of new blistering, even under the repair. If the water damage has extended down into the laminate, open up the area wider and deeper until clear, hard resin is reached. At this point it is best to use a moisture meter to record moisture content of the gelcoat that should ideally be less than 4% (actually the meter made by Novanex has a scale showing whether dry or moist). All numbers are relative and should be locally written and dated with a marker pen, so that you have a baseline to follow as the hull dries out. This is helped by opening up the boat and using fans, heaters etc. If you do not have a moisture-meter, “milkiness” in the resin is a good indicator of water-penetration.. Again rinse each opened up blister with fresh (preferably hot) water or (even better) steam. This is gets rid of residual acids etc but without undoing the drying process. The next stage is really important- Drying!. Ideally, the hull should be allowed to dry for several days (or weeks, or months!) in the hot sun with the hull protected from any rain. In the real world, yards make you pay for “lay days” (over $40 per day out here in Hawaii). Therefore use a hot air blower or heat lamp, if necessary to speed things up until the opened up areas are dry. Ideally final moisture readings should be below 3%. Airing the inside of the boat is also thought to help in drying. Next, lightly abrade the opened-up surfaces, wipe out with acetone and fill the blister. Vinyl ester repair kits (3M) are easy to use (my own experience some 3 years ago) but now, I would probably use epoxy resin and hardener from West Systems or equivalent. They provide any thickener needed to make a past for filling small blisters. Where damage extends down into the laminate, use the epoxy resin with fiberglass mat to restore structural strength. Make sure that the mat used is compatable with epoxy resins (this has been a problem in the past). Then fair with the catalyzed epoxy paste or vinyl ester paste. Finally, fair with “Red-Hand or similar waterproof fairing compound (easily sanded) , or just use the epoxy filler. Sand smooth, and sand down all of the existing bottom paint to provide a good “key. Then apply two-part epoxy barrier coat, either to the repaired areas or else to the whole bottom. This is best if you can afford it but all bottom paint should first be removed. West Resins can be used with special additive to make barrier coat that it applied by roller in 3 coats applied from different directions. Then apply bottom paint. It is a good idea to put a coat of one color (ideally a harder, non-ablative paint) followed by 2-3 coats of a different color Alternatively another coat of epoxy resin (West) can be used with a copper addtive for residual anti-fouling. The newer bottom paints contain an algal inhibitor called Irgarol. The general idea is that as the outer layer of bottom paint wears one can seen the color change and you know its time to redo the bottom. If you have lots of money, you could look into use of the new hard barrier coat/bottom paints such as "Copperepoxy". All of the above applies to the usual “do it yourself” situation and is an amalgam of various recommendations and usage. If gelcoat is very exensively blistered so that it is coming unstuck and/or if there is a complete layer of water damaged laminate underneath then professional help is necessary. A full peel and epoxy replacement is necessary. Costs are prohibitive unless the boat is very valuable or is covered by warranty (or you have a yard use for a few weeks and are willing to tackle the job yourself). If you are overseeing the work try to get them to use a peeling machine rather than sand blasting. If sand blasting has to be used, special small-sized grit and a gentle "layer at a time" approach has to be used to remove the gelcoat. Otherwise, the particles of grit and/or bottom paint get imbedded in the resin and can form the focus of new “pockets” of that can be the focus of new blisters. A peeling machine acts to more evenly peel down to the top of the laminate or into the laminate if a whole layer needs replacing. The gelcoat (and any necessary underlying laminate replacement) is then replaced by an epoxy version and you will then NEVER get blisters. especially with the added insurance of an extra barrier coat under the bottom paint. Voids: These are different in that they are caused by physical delaminatedon brought on by flexing and (more importantly) poor adhesion between layers of fiberglass laminate or between laminate and core material. Voids are often seen over foam-cored areas, where penetration by water can be an additional complication or cause. I am not an expert on this subject but from my inquiries, I have gathered that: 1. You detect voids by either "tapping" or proper sonic testing with a proper instrument. You then open up the voids by drilling to examine and to let out any water. In some areas (cored decks) there are penetrating epoxy treatments that can be poured down through the holes to fill the voids, but additional holes are needed to let out air from the pocket. If the fiberglass has "bowed " away from the underlyng surface, it has to be ground off until proper integrity of the fiberglass laminate is reached. Then "feather edge" the area and replace the laminate with fiberglass matt, then woven, cloth (outer layers) with polyester, vinyl ester or epoxy resins. Be VERY careful about using solvents on foam cores. For instance, polystyrene foam will dissolve in undiluted citrus cleaners. Better to just air dry. New urethane foam (via areosol) can also be applied to replace old or wet foam. Rudders have to be opened up, water drained and the above approach used. This is best done off the boat (like repairing a surf board and you can use similar materials). However it might be best to get a new rudder! They are available via www.Sailboatowners.com. I would be glad of any feed-back concerning the above article - just send an e-mail or post on the "gelcoat and plastics" forum on www.sailboatowners.com. There is an excellent VHS video on gelcoat blister repair by Gougeon Brothers Inc., makers of West Systems Epoxy. Tel: 517 684 7286. Steve Dion has several website addresses which give even more detail. He can be contacted via this site.