Restoration of wood, balsa-core repair, refinishing

[drburke]

For the record, the Factory Store is just down the street from me, about a quarter of a mile. If a member has an urgent need, let me know and I likely can drop by and pick small quantities up.

DAN

[Steve Smith]

This application note was originally a collection of notes for owners of ferrocement boats, as those have occasional structural defects: Voids in the concrete, sometimes really large ones. I wrote those notes in the late seventies. In the ensuing years, I had occasion to help owners of balsa-core boats, and I learned what defects were common and how these led to failure in small or large areas. I suggested repair techniques, and the owners carried them out, and a further set of notes grew, of what was practical to do for balsa-core structures. Eventually all these got glued together, and impregnated with enough additional words to give a sense of continuity.

Just thought you would like a bit of the history of the following:

It may happen that you have a boat deck or hull made of wood between two layers of glass-reinforced polyester resin (GRP). It may further be that construction or maintenance was deficient and water leaked into the wood core of the structure. Such leaks most commonly derive from no caulking or bedding compound around through-deck bolts or screws. These leaks will also come from the teak deck screwed down against dry GRP with no bedding compound, or a pilot hole drilled for a screw but the screw forgotten, and similar workmanship.

It may happen that you have a ferrocement boat, and the paint does not stick on some areas of the hull. The pattern of paint failure may be little blisters in some region, or the paint may come off in sheets. Fillers may not stick to apparently dry concrete and the failure may be apparent in the yard a day later, or in the water a year later. The filler may turn to mush after water immersion, but that is invariably due to poor filler mixing.

It has been my observation (and that of Jim Campbell, a pioneer in the application of modern adhesives and coatings to ferrocement boats) over a period of thirty-five years that epoxy adhesives and coatings can stick for many years (more than ten, with no definite failure point) to dry, fully cured concrete. It has further been observed that in every case where an organic coating known to stick to such cement does not stick in a particular case, that either the concrete was not sufficiently cured (e. g. 5 years at about 70øF) or a silicone water-repellent had been applied, or (and this is the most common) there is some source of water that keeps the concrete wet. I still have some copies of the 1978 publication "How to finish your ferrocement hull" that are free to email requests via the main website www.smithandcompany.org.

The three most common sources of water in ferrocement hulls are (1) a void in the concrete, usually in the thickest section above the keel, (2) leaking integral tanks, and (3) a paint which is an effective moisture-diffusion barrier applied simply everywhere inside the hull. The reason the latter creates a problem is that a ferrocement boat, sitting in water, will inevitably get some water on and in the concrete. That water will diffuse through the concrete and can evaporate out of bare concrete or that which has a breathing coating. If all water evaporation is prevented, the concrete will eventually saturate with water and then external underwater paints fail.

Similarly, gel-coat blisters in GRP boat hulls are caused by water diffusing into the hull faster than it can evaporate off the inside surface, raising the concentration of water in the GRP laminate and thus promoting the chemical decomposition of polyester resin. The decomposition products of this reaction are water-soluble and promote the osmotic diffusion of more water into the laminate, creating blisters. In order to stop and prevent such decomposition, a moisture diffusion barrier coating is applied to the outside of the GRP laminate hull. I invented this technology about 1974.

A ferrocement hull has different liabilities and a similar cure. Excessive salt water in the hull promotes the rusting of the steel reinforcing. When steel rusts, it expands. Eventually the hull develops many cracks, chunks of concrete pop off, and by then it is too late. An intact moisture-diffusion-barrier coating on the outside, and the available means for moisture to evaporate off the inside surface, and this failure mechanism is prevented. That has been my observation of the various boats done in various ways over 35 years, seeing what failed and what did not.

All these problems and solutions have in common the need to dry something on the inside when water cannot easily or adequately evaporate off the outside surfaces. There is a technique for drying such regions, so that the rot in a resin/wood/resin laminate can be dealt with, or coating failures addressed. I invented this technique about 1975. It consists of vacuum drying the affected laminate or cement structure from the inside. The principle involved is simply that water evaporates more rapidly at lower pressure. A vacuum pump of the particular type recommended can reduce the pressure to a fifth of an atmosphere or less, causing water to evaporate much faster, and drawing it out of where you cannot get to it without dissecting the structure. In order to measure progress, the vacuum pump exhaust condensate is captured and measured every 6-12 hours and the quantity plotted on a graph. When the collected condensate graph falls from a higher to a lower level, then the system is collecting only condensate from atmospheric moisture from air leaking into the hull or laminate. That means you are done. Then a conventional protective coating system may be applied and usually everything works fine. There are, however, no guarantees. Your application is beyond my control, life contains hidden data, and the universe is not always fair.

There is a particular kind of vacuum pump best suited for this application. It is an Oilless, Rotary-Vane vacuum pump. The smallest recommended size is in the Granger catalog, cat. #4F740, a 1/3 HP unit. Where more pumping speed is desired or there are many air leaks, such as a porous ferrocement hull, a bigger unit may be required. When drying a ferrocement hull I would recommend you drill with a masonry drill a hole into the thickest part of the hull, above the keel, about every foot or two along its length. Glue a hose-barb-to-pipe-thread adapter into each hole. Use thick-wall clear vinyl tubing to tie them all to a manifold on the inlet to the vacuum pump. Leave any old paint on the hull, as it will only cut down the air load on the pump. The exhaust of the pump may be hot if it is pumping a significant air load. In this case you will lose the condensate in the hot air and you need that condensate so you can measure it. Try a coil of 1/2 inch diameter copper tubing, perhaps fifteen feet in length, on the pump exhaust. That should cool the exhaust air enough to allow the condensate to mostly be collected.

With a wood-cored deck you will need to drill holes every so often and glue in similar fittings. The spacing between fittings may be every two or three feet....what is important is that one fitting be in every region of damp wood. When a vacuum is applied to this kind of structure the top and bottom skins of the laminate are pulled towards each other with a force of more than ten pounds on every square inch, equivalent to more than 1400 pounds per square foot. This can seal off damp areas from each other and from the effective pumping action of the vacuum pump, preventing drying.

GRP ("fiberglass") boat hulls that develop gel-coat blisters can be dried by a variation of this method, wherein the gelcoat is ground off (or, at least, every blister opened up) and then a "vacuum blanket" put on the outside. This is a sheet of 6 mil polyethylene (clear, so in case something interesting happens it is visibly interesting) on top of a blanket (any thick porous material should do) taped up against the hull with duct tape all around to seal. The vacuum pump inlet line simply penetrates the polyethylene (seal it with more duct tape) and becomes a manifold of smaller tubes, or preferably half-tubes or tubes with many small holes. The idea is to have a high-conductance gas (water vapor) path from all over the surface to be vacuum-dried so water vapor can easily get to the pump. The advantage of vacuum-drying a GRP hull is that otherwise one can pay for many months of being hauled out in an expensive yard with dehumidifiers in a tent below the boat in the summer. With a vacuum blanket you can actually dry the hull in the winter in the rain.

The drying process may take only a few days but may take much longer...every boat is different. You should budget two weeks for the drying, and more time to set up.

Once the excess water has been removed from the structure, you can actually use those same fittings to impregnate the structure with Clear Penetrating Epoxy Sealer.. That glues together the slightly deteriorated wood fibers and leaves the entire porosity of the structure impregnated with a hydrophobic epoxy resin system, doing good things for the probable life expectancy. Do not use more than five pounds pressure to force CPES into a ferrocement hull....one instance at ten pounds blew off the entire transom. Preferably, use only gravity feed from within a few feet of the deck. Put funnels in the tubing ends and pour CPES into the ones at bow and stern. Look for liquid showing up in the next ones. If it is milky let it drain until clear, then feed into those and thus progressively impregnate an entire fine network of voids. Sometimes there is one huge void in a ferrocement hull, and when the impregnation is done you will drain out quite a bit when you drop the filling tubes to ground level...have buckets handy.

Having impregnated the structure, the solvents in that product must be removed in order to obtain the full benefits of that treatment, and that solvent removal must be done promptly, before the resin system cures. A vacuum pump may be used for that purpose, but there is the additional concern that the vapor, any condensate from the pump and the exhaust of that pump have flammable liquids and the vapor may be explosive, as is the vapor of any flammable liquid. This sort of work is best done by someone familiar with the safe use of plumbing and electrical equipment.

Once the impregnant solvents have dried, any voids may be filled with liquid or paste epoxy fillers, as appropriate.

[drburke]

Steve,

To me it is obvious that you should purchase one of the several Hatteras yachts for sale in the Bay area. Clearly this would be a legitimate business expense as you continue to test and refine your blister repair technique

DAN

[Steve Smith]

Dan, how do you put that smily-thing in your text? I can't get that feature to work for me.

Business expenses...yes...it's all I can do at this point to restore an antique 12-foot Chris-Craft Kit Boat. I'll keep the Hatterii in mind.

[mike]

At the risk of sounding like a shill, FWIW, I have used Steve Smith's products for over 30 years on many types of boats, doing wood, FRP and steel restoration. Projects included complete transom replacements and keel repairs on wood cruisers, to an inside-out replacement of a failed rotted wood transom and stringers on an offshore race boat. My current project is the restoration of our 53' Hatt MY, having just sealed the inside of the engine room hull with CEPS and his faring compound, followed by an Ameron Epoxy top coat, and am now working on the bottom. In every case over the years Steve has been very helpful giving his time and advice freely, he is a wealth of knowledge, the bottom line is his products WORK, esp. if you follow the instructions. I have NEVER had a failure with any of his products; the 1:1 mix ratios are easy to use and very forgiving. As way of a disclaimer my comments are unsolicited, I have no connection with his company, just a satisfied customer. Mike

[Steve Smith]

Thank you, Mike.

That reminds me of something else...GRP osmosis blisters. I didn't have that on my mind until you mentioned it. I have something else that might be of interest to Hatteras owners, since I gather they have GRP hulls....

Back in the early seventies, when I accidentally got into this coatings business, I was selling my products to people with boats in the San Francisco bay area. One day a fellow asked me to come down to the local Richmond boat yard and look at his boat. I did, and it had strange bumps, perhaps the size of quarters or half-dollars, and some spots of fuzzy glass fibers in soft patches.

He said that many boats had this problem, and the laminate seemed to be dissolving, and no one knew what caused it or what to do about it. I took a nearby screwdriver and (just out of curiosity…physicists do things like that) gouged into one of these bumps, and something squirted out and into my eye (chemists do things like that). It was quite painful.

From such things do great discoveries flow.

Now, being a physicist and chemist, it was clear that this was not ordinary sea water. It hurt too much.

I knew that polyester (many esters) resin contained a cobalt napthenate (a metal soap) cold-set promoter, and the “catalyst” used for curing was a 40% solution of methyl ethyl ketone (MEK) peroxide in dibutyl phthalate (an ester) and I knew that esters and such decompose in the presence of water and acid catalysts, and the cobalt napthenate would become cobalt hydroxide and napthenic acid, and the polyester resin and dibutyl phthalate would both create phthalic acid, and that stuff in my eye certainly felt like an acid.

I was thus the guy who discovered why GRP boats have blisters.

Considering that some of these decomposition products were water-soluble, I recognized that the GRP laminate, in the course of decomposing due to water diffusing into it, would have the interesting quality of creating a runaway osmotic blistering condition, wherein more decomposition led to more water-soluble molecules being created, and the osmotic pressure would increase, drawing in more water with a greater driving pressure, and I saw that this was literally enough pressure as to rupture the laminate and the gel-coat on top of it.

The obvious solution to this is to stop the water from getting into the laminate, and make it easy for the water in the laminate to get out. The way to do this was to put an epoxy water-diffusion-barrier-coating on the outside, and specifically improve ventilation on the inside.

I was thus the guy who invented the barrier-coat technology that stops and prevents osmotic-blister failures in GRP boats.

My repair technology was used by many local people at first, and later by those around the country as Word Spread. It proved successful, and about ten years later some folks in Europe licensed it and trained boat-yards there to do such repairs, with a warranty backed by Lloyd’s of London.

Now, I have a one-page application note about how to repair a GRP hull, and that’s probably not too long, and I could post it…probably as a separate thread. I also have a much more detailed story of the history and the details of the repair technology, and it runs about eight pages. It’s an interesting read but might be too long to post as a thread unless you-all really want me to.

What’s your pleasure?

[Timm]

Just a quick note on the CPES availablity. West Marine has it set up as a "managers buy" part and any store manager can have it ordered and stocked in their store.

Having been a WM manager, (Palo Alto, Antioch and San Jose, California) I can attest to the salability of this product and once the local repair guys find out their local stores carry it, it flies out the door.

I have personally used it on my 1964, 57' Chris Craft (vessel I had prior to my 53' Hat) and a 1960, 16 foot CC runabout that we restored from the keel up and found there is nothing better.

WM stores that currenty stock the product in the SF bay area are: Sausalito, Antioch and San Jose.

Tim

[drburke]

And Tim, although WM Richmond does not (I think), Steve's company is about a half mile away, so add Richmond Factory Store to the list

Someday I need to go by and pay a personal visit for guru consultation.

DAN

[mike]

Mark, I can't let your comments go unchallenged, specifically your statement "so why don’t you just buy an ad in a magazine? Then everyone knows what the motive is". I have asked Steve many times in the past to post on this forum because of the value of his knowledge and effectiveness of his products. You may perceive it as just another BS commercial, however his posts are factual and spot on. If you have a problem with FRP and wood and you won't find a more knowledgeable, honest and helpful guy. My motive was a simply one of wanting to get alternatives in front of this forum so people can become aware of options to the "big guys" approach to blister and deck repairs. So if you don't want to read about this information, don't, but at least don't slam the guy for trying to be helpful. Others just may find his information insightful and useful.

[Finalee]

Here is the rub. This site is for Hatteras owners to talk about their boats and their experiences. It is also used as a referance guide for Hatteras buyers.
Every promotional thread that has been started has required a counter response from forum members. If allowed to run unchallenged the threads could paint a picture of our boats they do not deserve. Its good business for a vendor to be willing to offer opinions when asked. Just keep you're hands of the wheel of the threads.