It starts with a small leak around a piece of deck hardware or even a pinhole in a resin-starved layup. Water seeps between the layers of fiberglass, rotting balsa and plywood cores and turning them into mush. Even rot-proof foam cores can be progressively delaminated by sailing stress and the repeated expansion of ice during freeze-thaw cycles. There are few things that send a potential buyer scampering or start an owner sweating faster than a soft deck.
The traditional cure is to peel the deck open from either above or below, replace the rotten core, and relaminate and finish. This is expensive to contract out and demanding of skills for the DIY. A lot of sailing time can be lost. What if we could simply inject something into the space to replace the collapsed core and rebond the skins? We’ve read about epoxy injection in books, but it runs counter to every bit of conventional wisdom about surface prep. No way around it, you’re sealing a wet, ruined core in place.
But looked at a different way, do we really need the ultimate bond? The core is a relatively weak material; foam or balsa vs. glass or carbon fiber. Perhaps an expanding foam that bonds to the skins is strong enough. As for dampness, epoxy requires less than 12 percent moisture in wood, resorcinol less than 15 percent, but Gorilla Glue and polyurethane expansion foams can tolerate up to 30 percent moisture, which is what you are likely to find deteriorated core. Polyurethanes like Gorilla Glue use water as their curing agent. While we’re not suggesting injection to repair highly-stressed areas or high value boats, there are many aging boats with soft decks that could use a little stiffening without breaking the bank or triggering a major rebuild.
We also need a glue that is compatible with wet conditions. Realistically, you are not going to get the damaged core very dry. So epoxy may not cure or bond properly.
How We Tested
We bonded fiberglass skins to both new and uniformly rotten plywood to create test coupons. The rotten plywood was dry when bonded, because the core would have been dry when first created. After they had cured, we soaked them for a day and then allowed them to dry for two days before moving on to injections. We also laid-up a virgin balsa core coupon for comparison. We then injected the rotten samples with a variety of adhesives. Both the controls and the test samples were then tested for stiffness and strength.
We repaired a stand up paddleboard we found on the rocks. The skins had been punctured multiple places, the underlying foam crushed, and everything was soaked and growing algae. We looked for project boats for testing, but the damage was never uniform enough for comparison testing, so we relied on the synthetic test panels described above for product comparisons.
Finally, we repaired a ruined foredeck hatch with a rotten balsa core. We’ve been jumping on that for a year.
What We Tested
Two adhesives in our lineup should be familiar to most sailors. West Systems 105/206 is a popular combination from Gudgeon Brother, used for a variety of boat repair projects. The original Gorilla Glue is omnipresent in hardware stores. Inject-a-Deck is described as a structural marine foam and adhesive that claims to cure as hard as wood. According to the company’s website, the product was developed by a sailor who was involved in the aerospace industry.
Injectable Repairs
| Product | West Systems 105/205 | Inject-A-Deck | Gorilla Glue Original |
|---|---|---|---|
| Strength (Pounds) | 80 lbs. | 50 lbs. | 123 lbs. |
| Comments | Shear failure at top of glue pillar | Shear failure at thickest void later | Shear failure at top of glue pillar |
| Number of injection points | 10 injection points | 3 injection points | 5 injection points |
| Price | 119 | 299 | 11 |
| Size (Ounces) | 152 oz. | 48 oz. | 8 oz. |
| Cost ($/Ounces) | 0.78 | 6.22 | 1.37 |
Observations
Strength. All of the products would pass a walk-on and light stomp test, because the deck is supported in two dimensions, a far stronger structure than the narrow beams we tested. However, all of the injected coupons were far weaker than virgin plywood laminate, which was several times weaker than the balsa cored beam.
Composite decks generally fail when the core shears. Although plywood seems like a strong material, it does not work particularly well in a composite structure. Because wood fibers are not as stiff as glass fibers they can’t effectively share the tensile load created during bending. For comparison, imagine a nylon rope tied alongside a chain; no matter how strong the nylon rope is, the chain does all the work until it fails. Thus, the only important stress on the core is shear, created when the two skins try to move in opposite directions as the panel bends, and plywood is weak in shear. Foams range from very weak to moderate, and balsa is one of the best materials available for shear loads.
Stiffness. The injected coupons were 10 to 20 times stiffer after injection, but not as stiff as the balsa coupon. Under bending stress, the core is also subject to compression loading, as the skins try to move closer to each other. Even before the coupons failed, either the columns of glue would flex from side-to-side, voids would compress, or the relatively soft injected foam would compress. However, you’ll probably only notice the difference if you compare it to a section of good deck, or if it is in a highly loaded area, such as under a stanchion.
Inject-A-Deck
The kit came complete with everything we needed, other than common shop supplies. The injection gun is smooth and strong, and the motionless mixer tips very effective. Within a few minutes after injection the foam expands 6-8 times, depending on the space available and the moisture content. It cures within an hour, and if you go to revise the repair later, it will be easy to remove, no more difficult than removing other core materials. Only three injection points were needed for a 10-inch sample (4-inch spacing). Because of the strong expansion, this was more than enough for this heavily rotted plywood, and the 8-12 inch spacing recommended by the manufacture seems about right for most deck projects.
The down side is that the foam is weak and friable. The Inject-a-Deck coupons were ten times stronger than the floppy coupons we started with, and we’re pretty sure that a repaired deck well supported by beams could withstand vigorous foot traffic for a while. But they were weaker than samples repaired with Gorilla Glue or epoxy, five times weaker than the virgin plywood coupon, and 14 times weaker than the balsa coupon.
We’re also concerned that the expansion of the foam can force the skins apart, since it has nowhere to go. Two of the samples were placed under weights, to prevent the pressure from forcing the skins apart. We thought this might simulate the way good sections will hold bad sections together. In fact, the foam lifted the weights off the ground, exerting an expansion force of 2-4 psi (576 pounds per square foot). Some of the foam will come back out the hole you injected it through, but if the deck is weak, expect some bulging. The instructions say to walk on it to force it back down. (This didn’t seem very practical to us, given the force exerted.)
Based on our testing, this high-expansion foam will fill huge voids, minimizing the required number of holes. But it’s messy to work with, provides minimal strength, and the pressure caused by foam expansion may further delaminate the deck and even make it bulge upwards and downwards. It will stiffen the deck, but it will not restore the original strength and toughness.
Bottom line: We would only use this if the boat was otherwise headed to the dumpster.
West Systems Epoxy 105/205
Like most epoxy adhesives, the West System formula does not expand and does not spread far from the injection site unless there are huge voids. In effect, you are building a grid of epoxy posts, gluing the top to the bottom. We used the West Systems 105/205 fast hardener system. Our impression was that the epoxy had stopped soaking in before the epoxy kicked, but a slow hardener might give slightly better results. That said, you will spend an hour adding a drop here and a drop there, trying to keep the holes full as the epoxy soaks its way in. We tried forcing it in with a syringe, but it couldn’t be rushed.
We used 10 injection points on each coupon, in two rows with 1.5 inch centers. Because the epoxy does not penetrate far, more would help, but that’s a lot of holes.
Will you be fixing it right later? Foam is easy to dig out with scrapers and a wire brush, often as far as a few inches under good skin. This can be important if the repair is near stanchions or some other complex area. Gorilla Glue will be more challenging to remove but feasible with some vigor. Epoxy will require complete skin removal and serious grinding. We’d avoid injecting epoxy if we felt sure we would be fixing it right later.
Long accepted as a quasi repair method for small problem areas, we reached this same conclusion. The epoxy does not really spread, so the strength of the repair depends on close spacing of holes and the pillars they create. Bonding is poor and would have been worse if the test samples had been wet. Not hard to do, but weak.
Bottom Line: Recommended for very small areas of damage, no more than a few inches in size.
Gorilla Glue (Original)
Based on polyurethane and using water as the curing agent, the wood workers reading this know how Gorilla Glue behaves around moisture. Under overly dry conditions it doesn’t want to cure, much like some polyurethanes. The solution is to lightly mist the surfaces to be joined, give the water 10-20 minutes to soak in, and then apply the glue and join. If there is too much moisture, the glue foams; not as much as a true expansion foam, but enough to force a good bit out of the joint and weaken the bond. Thus, the proper way to use Gorilla Glue is with just enough moisture and enough clamping force to prevent it from being forced out. A foam-filled joint is a weak joint.
Dry the core the best you can. Protect the area from the weather, use fans, heat guns, and even vacuum to pull the water out. Dry is best, but the reality is that core will remain slightly damp. If you really want it dry, you need either a lot of time or to peel it open. Thus, the best glues are those that tolerate moisture. In northern climates repeated expansion of trapped moisture, such as ice, will further damage the core and continued delamination.
Mark the injection points in a grid and apply masking tape. This can minimize any chipping of the gel coat. Additionally, the adhesive will bubble back out of the hole, and drilling through tape makes clean-up and finishing a lot easier. With Inject-A-Deck we recommend draping the entire work area as though prepping for surgery; massive amounts of foam can come back out.
Drill a grid of holes. If the delamination is slight and you are using a low-expansion product (epoxy or Gorilla Glue), drill 3/16-inch holes on 1- to 2-inch centers. The adhesive will not soak far. If the deck is really floppy and you’re using Inject-A-Deck, drill ¼-inch holes on up to 10-inch centers. The foam will travel farther and the ¼-inch holes provide more room for the excess to come back out.
On vertical surfaces, angle the drill downwards so that the glue won’t just run out. Use a clamp-on drill-stop on the drill; you don’t want to drill into the cabin, although if you do, just slap some duct tape on the underside. You need to drill all the way through the core to insure maximum penetration, but you don’t want to puncture the inner skin.
Inject-A-Deck will expand and come out of the holes. Topping off is only required if the voids are huge. With Gorilla Glue, and even more so with epoxy, expect to spend the next 20 minutes topping-off the holes.
Working from underneath is possible with Gorilla Glue. Just slap some tape on each hole as soon as you fill it; expansion will keep it full. This is not as effective as working from the top, but you don’t have to bother with refinishing to cover the holes. We tried it once and it seemed to work.
If you are dead set on using epoxy, we suggest using a slow hardener and warming the deck (not the epoxy—it will exotherm) to 115F; noticeably warm to the touch but not hot. This will thin the epoxy and allow better penetration.
Use a razor to shave off excesses while the adhesive is still green. This will save a lot of sanding. Remove the tape.
Depending on surface damage and the characteristics of the product, you may need to sand, fair, and finish, as we did on the standup paddleboard. Even if the surface is smooth, it will look like a pegboard. Another alternative is simply to drill out the top 1/16- to 1/8-inch of each hole and fill with matching Marine Tex or Gelcoat. Not perfect, but it may work for just a few holes.
It is easy. If the core was plywood or balsa, there is still some rot in progress and you’ll be back in a few years. If the core was foam and the damaged area is small, maybe you’re done.
We used a single row of five injection points because we thought the moisture-trigger expansion would cause the Gorilla Glue to spread farther. Although not as strong as epoxy, the Gorilla Glue foam is very high density and is much stronger than injection foams. However, it spread only 0.5- to 1-inch in each direction, so additional holes should increase the strength proportionately. We used a closer spacing when repairing the paddleboard.
What about long-term exposure to water? Although Gorilla Glue and Inject-a-Deck are rated as waterproof in short term tests, there have been reports of failures of polyurethane foams and Gorilla Glue in outdoor uses. One problem is ice; if water migrates into the pores it will force the skins apart with every freeze/thaw cycle. We also suspect the users may not have followed the instructions regarding clamping pressure and tight joints. We’ve used Gorilla glue successfully on outdoor projects. Will it hold up to long term saturation?
Is the repaired core actually going to be exposed to super high moisture for long periods? We sure hope not. Injection does not arrest the underlying cause of the problem, which is probably moisture intrusion, leading to rot in balsa and plywood cores and freeze-thaw damage of foam cores. Unless you fix the leak, the problem will recur within a few years, or perhaps by spring if it freezes. If you repaired the leaks, the core may see some dampness but should never be soaked.
Our paddleboard, repaired by injection with Gorilla Glue and faired with epoxy, has been knocked round, thrown on the beach and jumped on. So far, so good. It has not been immersed in water for long periods.
Renowned for its ability to bond damp wood (although not always strongly), it had been suggested to us by several readers. It does not expand as much as Inject-a-Deck, but enough to force its way a short distance into nearby cracks and voids. We wonder if plugging or capping the injection points after filling would have improved penetration. It bonded as well or better than epoxy to damp surfaces, and produced three times the strength per injection point. Although not nearly as strong as a good balsa panel, a Gorilla Glue repair could approach the strength of a poor plywood panel.
Bottom line: Recommended for repair of damaged core. After 6-months of immersion testing, it may graduate to our Best Choice status.
Conclusions
If you’ve ever seen the messy, wet mulch removed during a typical re-core job, you’re probably not surprised that our injection test strips were pretty weak. You’re gluing a damp, dirty surface using mulch-thickened resin. You will fill some voids and add some stiffness, but the rot will continue.
If the deck is very spongy, the boat is old, and the alternative is the dumpster, a high density foam like Inject-A-Deck can make the boat serviceable for inshore use in light conditions for years.
If the core damage is more limited, perhaps the result of impact, Gorilla Glue is strong, has enough expansion to fill small gaps and can tolerate damp conditions. We recommend spacing similar to that used with epoxy (a 1-inch grid), which should result in considerable strength.
Epoxy injection didn’t impress us. Holes have to be drilled on very close centers and the result will be difficult to repair properly later. If we were sure it was only localized delamination or a crushed core, and that the core was sound, we might give it a try.
If the damage is in a high stress area, the boat is high-value, you like to doing things right, or you have a sneaking suspicion you will want to do it right later, bite the bullet and do it right the first time. Core replacement is time consuming but really not all that difficult to learn. The finishing can be a bit tricky; maybe you can combine it with repainting the deck.
We’re leaving samples soaking in water for six months to see what happens long-term. We’ll report back.
INJECT-A-DECK,
www.injectadeck.com
GORILLA GLUE,
www.gorillatough.com
WEST SYSTEM,
www.westsystem.com
Where is the rest of the article about fixing rotten deck cores?
Well, where did the article leave off for you?
Good information. But I couldn’t figure out exactly what you meant by “coupons”.
I may wait the 6 months or so, and then decide if want to drill holes or cut up the deck.
“coupon” is just their term for the sample skin-core-skin sandwiches made up for the study.
Several companies (TotalBoat, Westmarine, …) sale a “Penetrating’ epoxy. It would be interesting to see how those would work in this application.
I’ll second that. If PS will be repeating this test, I would really like to see CPES and other penetrating epoxies designed for stopping and binding dry rot in situ. Barring that, would PS be willing to share the process for creating and testing the coupons?
Thanks a lot, I like old boats with polyester resin, avid and careful diy:er can fix everything eternally. BUT these cored decks… Good tips. !!! Thx a lot. (Also have included bronze screws on slightly less than 100% do it right jobs.
The coupons in this case were made by bonding fiberglass shower surround material to rotten plywood using a moderate coating of epoxy on each skin. The intention was to bond the materials into sheets we could cut into sections, but not enough to soak into the plywood and create any real strength. The result was uniform weak coupons, as illustrated. We then injected products according to common instructions.
We wouldn’t bet on penetrating epoxies going any real distance into the core. If there is ANY dampness, the epoxy cannot penetrate that anymore than oil can penetrate water. It can only fill gaps and won’t bond well. The extent of penetration will vary wildly with the core material, so your best bet is to take a piece of something similar to your core, inject it with the product of choice, and then slice it after it cures. Unless there is nothing left of the wood (big rotten holes), the penetration will be only a small fraction of an inch. And if it is that rotten, what are you bonding to?
If you are not going to peal the skin and do it right, we strongly recommend looking at Gorrila Glue or some other structural polyurethane. These glues expand and much better suited to damp environments than epoxy.
We have found a few more soft areas in our test boat. I bet we’ll be following up this fall. Our choice of repair method will depend on what we find.
Drew, it’s been a year since this article came out. Just curious, have you learned anything new in the past year? I just bought a power boat with some moisture reported in the transom by the surveyor. He and one shipwright I have spoken to suggest they would use Smith’s CPES (a very liquid low viscosity epoxy from what I understand), but it sounds like Gorilla Glue (a polyurethane) might be a better choice that should be considered. I plan to mention it and this article to the shipwright before I hire him, to at least have the discussion. -Ron
I was very excited to see this article. I’ve been planning doing this work for summer—one week it’s too hot, the next it’s too wet.
I’ve got the ultimate “project boat” (it came for free, the “most expensive boat I’ll ever own”). It’s an Albin 27FC Trawler, with the cockpit window frames leaking into the balsa sandwich cores a couple of inches. The boat is tarped, has been for several years. I’m digging out the old rotted balsa. Then the slots can be filled with strips of stiff foam 1/2” sheets, providing watertight integrity.
I have two horizontal decks that are soft and will address that work next.
This is a 1983 boat, and has been on the hard for over 10 years. Today is cool and dry: Gorilla Glue time!!
I drilled holes like you did, in the inner (bottom) skin. I reamed out rotten balsa using a bent bicycle spoke in an electric drill. Did a bit with a heat gun and left over the off season to let the core dry. Using 1/4″ syringes — leftovers from home healthcare, but also available cheap from livestock websites because you use them to pill horses — and West Epoxy and filler, I injected in one hole until it started oozing out the next one. Sealed with a duct tape patch and then kept moving hole to hole. Don’t know, boat’s still together, but it sure seemed to avoid the “pillar” problem you observed in your test. For my other boat’s hull, I used the traditional remove the inner skin method. Much less messy and a better, full, bond with gravity on your side.
There is a way of repairing wet cored hulls that you did not cover in your review. Briefly, a vacuum pump is used to draw dried air into the core to dry it out. Leaks can be located with a small positive pressure. Only 8 psi was used for positive pressure. Some soapy water will show the leaks as the positively pressurized air leaks out. Holes are drilled into the hull to strategically direct dry air to the wet areas. Then the vacuum pump is used to draw the dried air into the core. After the core is dry, the vacuum pump is used to pull epoxy into the voids in the dried core. Foam core does not have to be replaced, only rotten wood core does.
You may see further details at this website. Look at the posts by DDW. His main post was done on 1/23/2019: https://www.trawlerforum.com/forums/s16/remove-water-hull-42686.html
What about using a core drying system like Dryboat? It’s basically a vacuum pump that’s hooked up to a bunch of penetrations and pulls dry air thru the core. Once the core is dried, use the same vacuum system to pull thru thin, penetrating epoxy. Kind of like vacuum bagging.
All very interesting…I owned an O’Day 22 for 39 years. Its deck was “balsa cored,” over the years the balsa rotted in some places. After some though I came up with the following procedure. I wanted to do a repair that did not entail cutting the deck open and breaking its integrity. I outlined the “soft” area on the deck. Drilled small holes (1/8″) around the circumference and in and towards the center. Using “NON-EXPANDING” foam insulation (hardware store), inject into the holes. It may foam-up through neighboring holes. No problem as it can be trimmed off with a knife. After the foam has “set-up,” use the drill to clear a shallow hole in the foam at deck level at each hole. Fill these holes with epoxy (Marine-Tex?).
After the epoxy is hard go the an auto parts store and pick-up a small contained of auto touch-up paint that matches your deck color. Put a drop or two of the paint on each epoxy plug. This may not be the most professional job but it costs little and keeps you on the water!
I repaired a small area of foredeck this way. Drill grid of holes and use an endmill to spot face the lower skin.
Use an Allen wrench in a drill motor to break up the old core as far as you can, also skiff the upper and lower skins with it.
Obviously the larger the hole and the closer together , the more area will be repaired, a balance.
Put a shop vac on each hole for several minutes to draw out debris and water.
Inject west six 10.
Repaired area was 3×3 and bulletproof. It might weigh slightly more than a saturated deck and obviously more than dry balsa core.
I have used “git rot” in the same way to harden up the forward deck of an older Mako and also to firm up a transom on a small fiberglass skiff. Both projects produced good results.
“ We’re leaving samples soaking in water for six months to see what happens long-term. We’ll report back.” – June 25, 2020
I’m wondering how those samples and the report are doing?
Repaired a soft spot recently with G Glue. Lacking a good source of large syringes I used a trigger-clamp on the glue bottle to squeeze the glue in, which worked just fine. The glue travelled easily. In one spot it travelled at least 5” horizontally from the closest injection point, and then vertically 6” to completely fill a hairline gap between boards in our companionway. The demoralizing soft area is gone for now.
The classic product for this application is Git Rot. I would have been pleased to see that be one of the products tested. I note one of the commenters used it successfully.
Seems one of the big problems with penetrating two part epoxies is that they cure (thicken) too rapidly. Boatlife suggests mixing only 4 oz at a time. I’ve never worked with UV curing epoxies, but it seems that if the UV sets off the reaction and the reaction can continue to polymerize continuous resin that doesn’t get directly illuminated, one could provide a longer penetration time. Conceivably, one could fill the voids, let the resin saturate the core, drain the excess, and then start the polymerization with UV. In my case, the underside of my deck is “clear” polyester fiberglass. This might also require a longer “cure” time. Does UV curing work in the way I’m “hoping”? Thanks.
I used to sell some coatings to a flooring manufacturer who also used UV cure on their stair treads. In the case of their coating, whatever didn’t get hit with the UV light didn’t cure. (Which is why they bought a catalyzed Polyurethane from me; to finish the edges and bullnose. Coating performances vary wildly, so this anecdote doesn’t answer your question. It only illustrates that some UV coatings do not cure in a chain reaction, even along the surface of flat boards.
Thanks Jason…. This is the kind of feedback I was hoping for… but kinda disappointed…doesn’t seem to be a viable alternative.
It looks like on the epoxy tests that the holes went thru both skins? Is that what you did?
It seems that doing it with a thru hole, reaming out top n bottom with a Dremel bit as Rod Collins shows to epoxy pot a deck thru fastener hole might be very strong. As well it might open pathways to voids to fill. Consider testing that method.
The easiest finish would be to paint the deck.
Maybe I should add that my “cored” appears from the underside to be “scrap” plywood of various shapes, but the the largest dimension being 2-3″. There are lots of continuous voids, lots of opportunity for end grain penetration, but also lots of expense if I have to fill those voids.
Yes, I thought Gorilla Glue would be a great adhesive especially since any residual moisture acts as a catalyst for the glue. The problem I have found is that Gorilla Glue becomes brittle and degrades within a year or so. I fixed a badly delaminated cockpit sole using Don Casey’s “This Old Boat” suggestion of cutting several parallel long strips through the top layer with a circular saw. I slightly thinned some epoxy with acetone just enough to aid in flow and wet everything out, and injected epoxy under any delaminated area which was easy to get at by lifting long cuts. Afterwards, I laid wax paper on top, then a wooden board on top of the wax paper and a board under the sole, screwing them tightly together like a big old sandwich. After curing, removed the screws, boards, wax paper, and then filled screw holes with thickened epoxy, and redid the whole cockpit sole non-skid with KiwiGrip. Came out structurally solid and looking great. After 5yrs, the KiwiGrip got a bit warn, but the sole has remained rock solid.
I used GitRot on a soft spot on the deck of my Flying Scot about 10 years ago. I recall it was much thinner than traditional epoxy for better penetration. I also recall using shop vac to suck out the holes. The repair has held up ever since with no side effects other than a theoretical few ounces of additional boat weight.
Good luck to all those doing this for the first time.
Make sure you have good ventilation and are using personal protective equipment.
The horrid photo in this email with all those loose strands, sharp edges and drips, indicating that they did not use a great finishing product called Peel-Ply .
It’s a fine weave nylon cloth that is phobic to layup resins that will peel off the cured epoxy layup leaving an excellent bonding finish with no strands or rough edges.
It’s worth the extra cloth and you’ll end up with professional results.
Anyone have experience with Dr. Rot or similar? It’s a one part product.
As for epoxy, some people thin the West product with kerosene to produce a more penetrating product. West cautions that significant strength is lost as the product is thinned.
In Canada, there is an epoxy called S2, which is like water in consistency when applied. I filled some rotten plywood core under my winches. So far so good. Would like you to test that if you can get it.
I did this job years ago, Drilled the deck, and cleaned out the old balsa with a wire bent on the end of a drill. I tapped the deck drill hole and using a cheap grease gun pumped in acetone, quickly because the gun doesn’t last long. The Acetone it hit drilled weep holes underneath the deck. Put dry air pressure on the deck fittings to dry out. Let sit in hot sun for a week. Then used a couple of cheap grease guns with slow cure west epoxy and pumped into the deck under pressure. Worked great
Good article, very interesting.
I had similar problems on my O’Day 22 (1972) sailboat. To repair several “soft” deck spots;
Drilled small (1/8″) holes around the spots & in the center of the spots. Using “non-expanding” aerosol insulation foam (Walmart or hardware store) injected this into the holes. It should set-up overnight. Some foam will expand out the holes, cut off this excess. With your drill countersink a bit of the foam into the holes. Fill the holes to “deck level” with epoxy. Go to an auto parts store and pick-up a small bottle of “touch-up” paint that matches your boat color, dab on the epoxy……your done.
For wood core I get acetone into as much of it as possible. Acetone is miscible in water, and will speed up the drying. When the acetone smell is gone, then CPES which has many volatiles which also mix with water. Shoots right into the core. When the smell is gone it is cured, and hopefully fairly dry. After that comes thinned epoxy at 10% pure alcohol. Fast cure epoxy if available (watch out for runaway cure). When cured, do it again until the laminate will hold no more. Leave open until cured. This could take weeks but could be done underway. It’s a hassle but beats the alternative, maybe.
You can’t unrot the wood. I have recored many decks and I understand why people fall for these snake oil solutions. It is a lot of dirty work. It is not difficult or very expensive for diyer, just time consuming.
Great article, thanks.
But, didn’t get or understand which product
You would recommend out of the 3.
Fair winds, and may there be no Dragons where ye go !!
Which issue has the 6 mos report on water immersion? Thanks. -Val
You can create a lot of injection pressure by using a grease gun. Drill and tap the fiberglass laminate for Zirk fittings. I pour the filler resin into the grease gun, reassemble the grease con, then inject. You can remove the Zirk fittings at any time, and even reuse them. Of course, you have to be careful to not over pressurize. I just use a small cheap grease gun and discard it afterwards.
On “Someday” a peculiar problem. My practice is to bring my tender aboard at night and invertit over the foredeck until next need. Various things are randomly stored under the boat. I discovered the upper fiberglass skin was delaminating in places from the balsa core, but many random test points from both top and bottom disclosed no rot in the balsa. I think maybe the storing of the dingy was creating a very high humidity level under it, which in effect steamed the bond between the polyester resin fiberglass deck and the top of the core (hypothesis). No rot was found by any of the test holes from the bottom.
I cured by drilling many, many 1/4″ dia holes on appx 1″ centers over the entire area, just thru the top glass, let dry covered be a shade spaced to allow breeze underneath. forgotten how long, but at least a week; and injected 105/206, first thinned w/ Mek, under the shade, then full strength, about a week later, under hot sun. walked around on it as I am doing this, in hopes of spreading the epoxy between the surface glass, and the balsa core. Topped off as apparent need appeared. Looked like a mass of dots for a couple weeks until I painted over. Surprisingly, the “dots” are hard to find in the painted over non-skid.
Its been five years, and no sign of any give or softness. Seems adequately bonded. I am careful to allow air circulation under the tender on bow now.
Working on restoration of 2 Lightnings. Using West Systems method of drilling holes to dry the core. Used large plastic sheeting to bag the boat, holes facing down helps speed the process, with a dehumidifier set on hi and hose leading out of the bag and a fan to help circulate more air. Used non-destructive moisture meter, painters tape tabs to mark moisture readings at start so progress could be monitored. Went from full scale to nothing with time. Then inject West slow epoxy, corks can help the injection process by plugging holes as you go. First hull sounds solid as rock. Foam hull core wet but not rotted, considerable delamination. One boat had suffered previous owners sorry attempt to re-core. That was all stripped out and re-cored with balsa. Could park a truck on that fore-deck now. West Systems tech support has been great.
Git-Rot requires that the wood is dry before adding the epoxy. I believe this test was conceived to not require drying the core. Interesting though. I also would like to find out what happened with the coupons which were left to soak up water….
Good info, thanks.
I ended up stripping the top layer off and digging out the rotten core for several feet of my main deck, port side Tartan 37 yes, had some help. Pretty big job. Re-glassed, fared and painted total decks.
A friend drilled and filled with epoxy on his Endeavor 42. But after drilling he took an Allen wrench and used it on a drill, long side in the drill chuck. Gouged out rotten wet stuff, blew, vacuumed and heated the area. Before epoxy. Again pretty big job about 4 sq feet. He did manage to get a lot of the moisture and pulp out. None of this is fun.
A test with a product from PC-Woody would be worth the time.
I have used their products and consider them fantastic.
This company, De Neef, specializes in stopping leaks in water systems with a number different foams and epoxies that work in water. Calling the rep would help in directing to the right product since there is many.
https://gcpat.com/en/products/de-neef-waterproofing-injection-solutions
I had the problem on a balsa-cored deck some 20 years ago. The solution on how to totally dry out the sandwich laminate was a bit different and for sure requires that you know what you are doing- using microwaves. First, yes microwaves are dangerous stuff and you must understand that you need a “dosimeter” type of warning device to make sure you or anyone near the repair is not exposed to too much energy since it for sure is damaging creating hot spots that damage tissue.
You start with an old microwave owen and saw out the bottom and make sure the door is permanently locked.
This will be your source of microwaves and the feature of setting time and power is very handy.
Next step is drilling a pattern of holes evenly spaced at about 40mm just thru the top skin in the affected area, the holes will be where the moisture disappears out and where you later will inject epoxy with a compressed air glue gun. The nozzle for that thing should be slightly conical and you chose your hole size to fit that nozzle.
The drying part is fun. Cover the inside of your deck with normal aluminum foil, this will be a reflector of the microwaves from the oven you place on top of your deck, if no reflection no even distribution of the microwaves, and hence only drying just below the magnetron as well as the fact that the microwaves that pass straight thru the fiberglass skins will not be contained and are dangerous! The small gap between your deck and the microwave oven also has to be covered with aluminum foil and be generous with this so your deck is covered at least 150 mm out from the oven and taped to the outsides of the oven.
Now to the dangerous part, the actual drying process. The Owen has a power setting and a timer. ( Power is actually just the magnetron turning on and off with differences in the time on and off.) Start at a low power setting and something like 2 minutes on. Start the thing and walk off the boat and some 10m (30 feet) away from where the repair place is, do not let anyone enter closer while the owen is running. Ideally, you rent or buy a microwave detector that will beep if you are getting close to an exposure that could be dangerous. It is not radiation but microwave energy and the danger is having heating of sensitive tissue like the eyes. If you have a detector it would beep indicating to you that you need more distance from the source and once it stops beeping you are safe. I used one and know that properly done the leakage of microwaves if sealed of by aluminium foil is very small and hence I got no indication if not very close to my device.
Back to setting the drying regime up, you do not want to get the fibre glass skins warmer than 60 degrees Celsius since they ar then getting a bit softer and you like your skins to be like before. Once you found your device’s settings of power and time ( it is advisable to run lower power for a longer time) you simply just run it and test the moisture level thru the holes with a moisture meter for wood. I can assure you that the drying process is pretty amazing and that it is easy to get it back to a level of a few percent moisture content.
When the area is dried I used a sharpened Allen wrench in a drill and put it into the holes removing core material. It is now dry and easy to vacuum the powder thru the holes if you simply do not want to leave it as a filler for the epoxy that will be injected.
So next question is filler to mix with slow hardening epoxy ( I used West system and their high density filler) Theyhad single use cartridges that I could fit into my compressed air glue gun ( this one is also a must to caulk large areas of a teak deck..). I used pretty high pressure on the air, put the conical nozzlwe into a hole with pressure enough to seal and then injecting for a few seconds, waiting with the thing still in the hole, some more injecting and you will most likely see now clear epoxy seeping up from a neighboring hole. Shift the hole and continue. Once all is cured sand and if needed laminate a light woven e-glass mat on top of the area.
After 20 years the repair is still intact and the result is a slightly heavier but very strong area of the deck. The feel of the area once repaired was as if someone had put 20mm steel in place and I can assure you that no jumping in the world gave any other feeling than that this perhaps was an overkill repair. At the time as was rebuilding the whole boat and really wanted a lasting repair. If anyone interested do not hesitate to write with questions.
I have no experience with the West System, but the Total Boat penetrating epoxy is a very low viscosity product. The low viscosity allows it to flow across large areas, and the rate that impaired wood soaks it up is pretty amazing. Using the standard hardener in 70-80 degree weather gives about 10 min open time and full cure in a couple hours. I am pretty confident this would wet out a larger area of core than the three products tested.