Fiberglass over wood restoration

I am restoring a wood boat that was fiberglassed when built. I will be striping all the glass from the hull in order to repair some damgae to the wood and to re-glass with modern epoxy. The glass is two layers of woven cloth. I am not positive but it appears two be 6oz. woven cloth. I am sure the cloth was applied for abrasion and not for strength. Since the cloth is on for abrasion could I use chopper mat in stead of the cloth?

 

A bit more information wanted. Where are the abrasions -sides, or signs that she's been 'dragged' up the hard. And why was fiberglass applied in the first place. Was it part of the original 'design' - or merely added for extra strength/waterproofing.

 

Cloth is much better than mat. Cloth stays flatter when glassing than mat.It adds strength, gives a smoother surface.
easier to work with.

 

A thin sheath of cloth will not add much strength, but does add considerably to water proofing and especially abrasion resistance. Mat isn't the choice for this particular application, as it's a bulking material typically used within a laminate of several different layers.

Standard 'glass cloth is usually fine, but a better material is Dynel (a polyester fabric), which will provide 3 times the abrasion resistance then standard 'glass. Xynole is another fabric (better still) and it's just about 6 times greater then standard 'glass for abrasion. Both of these fabrics are a little more difficult to apply (and more costly), mostly because they don't go transparent during wet out and they can float if too much resin is used. These two things require some experience to get accustomed to, but aren't difficult to overcome if you have reasonable 'glassing expertise.

Sheathing wooden hulls, requires well maintained coatings and quickly repaired breaches in this skin. A nick in a painted wooden surface can cause some problems, but generally the moisture can escape and the area will dry out. The same type of breach, on a sheathed wooden surface, can lead to localized pockets of rot forming, because the moisture only has the small breach in which to escape from and this can promote the continued growth of rot. Since hulls seem to breed dings, nicks, scratches and other bumps in the night in surprising numbers, careful examination is required and prompt repairs made of these breaches in the sheathings.

For the average 20' or less trailer boat, that will not be asked to tolerate dragging up on beaches or over racks, then a single skin of 6 - 8 ounce cloth is fine. If you expect heavier use, frequent beaching or dragging over rough waterfronts, then you can consider doubling the chine and keel areas, installing sacrificial rub strips on the bottom, multiple fabric layers or more exotic fabrics (some mentioned), to provide the additional protection you need.

Specific sheathing schedules would require more detail about your boat and more importantly how it will be used.

 

Fiberglass over wood restoartion

Thanks for the help. To answer the question regarding the boat and it's use. It is a 1971 40' plank on frame hull. The majority of the damage is rot from leaks around the screws that hold the teak toe rail in place on the bow. The plywood deck, planking, upper portion of the frames and some of the stem have rot. At this time it appears the damage is contained to the area where the deck and hull join together. The Hull sides below the first plank and bottom appear solid at this time. However, I have not stripped the glass on the sides or the bottom yet. The glass is part of the original design. The entire hull, deck and cabin are covered in glass. I am guessing it was added for abrasion, water proofing and maybe for fairing. All glass boats were hitting the market at the time and this may have played a factor as well. Since the hull currnetly has two layers of 6oz. mat would I be ok using a sinlge layer of heavier mat say 10oz. or not reglass at all if the glass is causing the problem?

 

If your boat has mat, it likely also is laid up with polyester resin, which has caused many sad stories over the years on wooden structures. Most of the time, the sheathing traps moisture between the wood and the plastic skin.

Places I'd look for problems would be at the lower portion of the frames, outboard ends of the structural floors, cheek pieces, inner keel or keelson, bottom of the stem, bottom of the stern post or lower areas of the transom framing, etc.

Sweet water is what causes rot, not salt water. Rain, wash downs, condensation, often from leaking decks, fasteners, roofs and in your case the hull to deck joints, permits fresh water to collect in the bilge. This eventually rots out the lower portion of the members located there.

Another major problem is working fasteners. As the wood dimensions change with moisture content, the faster holes elongate, become distorted and loose there grip on the metal fastener. If the fasteners are bronze, you may be able to refasten with the next size up. If the fasteners are steel, you'll likely have "fastener sickness" which affects the wood surrounding the fastener holes and of course wastes the fasteners away to nothing in time.

On a vessel of this size, it would be wise to have her surveyed or have an experienced boat carpenter look her over. There's plenty of areas that are easily missed or over looked by the amateur repair person. Much is dependant on how experienced you are with these types of structures and the repairs necessary to accommodate your needs.

When accessing this size hull, which needs extensive repairs anyway, I'd just go ahead and yank the garboards. They'll likely need to be replaced and the components you need to see will be right there, in all their glory, for easy inspection. The keel pieces, stop waters, frame ends, floors, cheeks, etc. will be easily to evaluate and access is much enhanced for repairs. Call a pro and have them look her over real well. Explain you goals, budget and desires for the boat and they'll be able to offer repair options as well as the structural assessment. Consider it cheap insurance to get all the problems noted. You can attack them as priority dictates, probably with a much better idea of what needs to be done and possible solutions on how to do it.

 

Thanks again for the advice PAR.

The boat was looked over by a professional boat bulider that is why I am making the decision to restore this boat and how I have the information I have provided. Again the major damage appears to be to contained to the forward area of the deck and the upper bow. It also has some rot on the cabin roof. Where the tower and helm chairs were removed and the fastener holes left open. When the glass is stripped I will take your advice and have the garboard removed for inspection. This boat has been caught up in a bankruptcy for the past 8 years. It has been sitting in a boat yard and has'nt recieved any atttention with the exception of being ***** and pilaged. Given the fact the boat is nearly 40 years old and the damage seems to be contained to the sections desribed it is my opinion the original glass has performed pretty well. Given the superiority of modern Epoxy vs. old school resin. Can I achieve the same or better barrier using a single layer of 6oz. or 10oz. mat and epoxy vs. 2 layers of 6oz. that were used?

Thanks again for the advice.

 

Epoxy is far better barrier then poly. You can use mat, though regular mat is designed for ploy, it can be used with epoxy. There also is mat designed for use with epoxy. You'll have a much easier time getting a smooth finish with cloth then mat. Mat, by it's nature is a pretty irregular surface, requiring much filling to smooth. Cloth has a uniformly patterned surface (the weave) which can easily be filled with subsequent coats of epoxy. This of course assumes the underlying surface has been smoothed also. Get the base surface smooth as possible before applying additional fabrics. It saves a lot of trouble.

 

Thanks again for your in put PAR.

My original idea was to use mat becuae of cost. After the info recieved in the posts I am going to use cloth.

I must appologize in my last post I was using the term "mat" but in my mind I was refering to "cloth". As originally constructed the boat has what looks like 2 layers of 6oz. cloth. Do you think I would achieve the same or hopefully better barrier using one layer of 8oz. or 10oz. cloth with epoxy? It should be considerably lighter and of course less work.

Your in put is appreciated.

 

8 ounce fabric will be fine. Dynel or Xynole would be much better for abrasion resistance, though more costly and more difficult to apply.