Wet core repair without major surgery.

[Hayden Watson]

I have recently been following a couple of threads where wet deck core is being repaired by cutting off interior or exterior skin and full replacement of the core. Two years ago I thought that I was in for the same on my 1988 Catalina 30. I found a crack in the deck that was weeping brown water and a moisture meter showed that the starboard side of the cabin top plywood core was saturated (40% +) from the mast back to the cockpit. When I removed the traveler, about 1 gallon of water poured out of the through-bolt when I removed it. The traveler had not been properly bedded with the boat was built in November of 1987 and the gap between the deck and fiberglass headliner had been filling ever since.

At that time another member of my sailing club was repairing the deck core on his boat so I could watch the process but was not thrilled by the prospect of losing the molded nonskid. If I ever decided to sell Papillon anyone who looked at her was ask “what happened” and it would probably reduce the base value of her as a result.

As an engineer with a minor in physics I theorized a different plan. I knew that I could not dry the core with it encapsulated in glass because drying wood requires air flow. I briefly wondered if it might be possible to blow air through the core to allow drying but dismissed the idea. Then I came to the realization that the only way to get the water out was to boil it out so that it could be removed as a vapor.

It would not be practical or possible to heat the deck to 212º but if I lowered the boiling temperature of the water… Basic physics lesson, increase in pressure causes boiling point (BP) to increase which is why we use pressure caps on radiators. Decrease in pressure causes BP to decrease which is why an air conditioner needs to be evacuated before recharging the system. Theory: if the deck can be put under vacuum the water will boil at room temperature and will come out as a vapor.

I purchased an AC vacuum pump from Harbor Freight for $100 dollars and used ¼”ø plastic tubing and aquarium fittings to connect to every hole in the wet area to the pump. The first day I got 1 quart of water which decreased every day. I ran the pump all day long any time the sun was shining for the whole summer. At the end of summer my moisture meter showed the core to be from 0% to 12%. I then used the same system of ports to infuse the deck with ultra-low viscosity epoxy. It pulled in about 2 quarts and then quit pulling any more.

Two years later the deck is still dry and very solid.

 

[jviss]

Wow, that's great. Where did you inject the epoxy?

 

[Ken Cross]

Nice job. Our boat also had elevated moisture, but after fixing the leaks, it gradually dried out. I was told by our surveyor that it may dry on it's own once the leaks are gone. Now if I could just find that last leak. I have no moist deck to help me locate it.

Ken

 

[Jumpstart]

Sounds like a plan except the core is shot. Plywood falls apart after being soaked in water. You could get most of the water out but the leftover plywood would have the structural integrity of dust. Here is a pic of me digging out the wet plywood from my cockpit sole. It had been in a heated dry building for 2 months. The plywood had no structural integrity and literally crumbled. The resins holding the plywood together were totally compromised.

 

[Hayden Watson]

Sounds like a plan except the core is shot. Plywood falls apart after being soaked in water. You could get most of the water out but the leftover plywood would have the structural integrity of dust. Here is a pic of me digging out the wet plywood from my cockpit sole. It had been in a heated dry building for 2 months. The plywood had no structural integrity and literally crumbled. The resins holding the plywood together were totally compromised.View attachment 141650

I agree that if the deck is totally compromised that my system might not work. My deck was not soft but I did find brown ooze coming out of a crack that I assume was caused by freezing of the water in the ply over the winter. Also note that I did not just dry out the core. After I got the core dry I infused it with epoxy resin. First I pulled the deck to a full 30" vacuum and I started at the extreme end of the previously wetted area and worked my way back toward the port closest to the pump. Each port had a quarter turn valve that I would hook to a large syringe with the plunger removed which funneled the resin into the port. This way the sections of plywood that were rotting were filled with epoxy which solidified them into a lattice of epoxy. This is the same process as you would do with Git-Rot but was done without opening up the outer plies of the sandwich. Git Rot Kit - Shop Now | BoatLIFE I plugged the one through-bolt hole that would have allowed the epoxy to be drawn into the large gap between the head liner and the sandwich deck. I was able to get the deck to take 2 quarts of epoxy into the composite so I had a fair amount of rotted wood to fill.
One important thing to remember in this technique is to get the core dry enough. When you buy kiln-dried lumber it is 19% moisture. The reason for this standard is that wood decay cannot grow at moisture levels of less than 22%. By reducing the moister to 12% I killed off the decay.

 

[njlarry]

Great technique. Thanks for sharing it.
Do you have any pictures of the deck to vacuum ports. I am curious how you made them air tight also how you controlled the epoxy distribution.
Nice work.

 

[agprice22]

Nice innovation!
I wonder whether the hardened epoxy, which is now thickened with the plywood dust, will maintain enough elasticity to support the deck, or will it crack under loading?

 

[RoyS]

Very interesting! What do you think of drilling many small holes through the bottom of cored laminated deck when the boat is built. leaks would show up immediately while draining and liquid spread would be limited.

 

[agprice22]

Rather, builders use balsa that is cut into squares and encapsulated, so water can only infiltrate a single square. I know Beneteau uses this for hulls, but do not know about decks. But I bet somene here will know!

 

[Hayden Watson]

I will try to answer questions in order from my last post.
njlarry: Sorry, no photos. Making airtight connections for vacuum application is easy. I attached the ports by sticking the end into the bolt holes and then sealed them with a blob of Maine Sail's butyl caulk. At the crack I placed a worm of butyl in a ring around the crack and used a piece of heavy plastic film (old clear shower curtain). I used a hole punch to make a hole that the tubing was threaded through and sealed it to the film with butyl. As soon as the vacuum was applied it would suck down tight with no leaks. It is most important to get everything air tight. You test this by turning off the pump and timing how long it takes for the vacuum to be released. Distribution to the core was done by pulling the deck to a full 30" vacuum. I let the pump run for several hours prior to the infusion while I was preparing all of my stuff. This way any air void in the deck was under a near perfect vacuum. The vacuum was released by flowing the epoxy into the voids during the infusions process which draws the epoxy into all of the voids under vacuum.
agprice: In a composite sandwich you do not need elasticity, you need rigidity. In sections where the ply had turned to dust, the epoxy would be a solid block. In sections where the ply was honeycombed, the epoxy would form a lattice which is supported by the remaining wood which is encapsulated in epoxy. In areas where the skin had delaminated from the ply the epoxy would bond the ply to the skin. All of these result in the desired result.
RoyS: In the case of my 1988 Catalina 30 the deck is constructed in two pieces. The outer deck is a structural sandwich panel consisting of FG skin / plywood / FG skin. The interior head liner is a separate molded FG liner. The two are joined together by smearing in blobs of Mish-Mash and gluing them together. I could not see the inner skin of the sandwich and drilling holes through the head liner in most cases of deck leak would not show anything. In my case I had a direct path from the outside to the headliner / deck gap because the through bolt was not sealed.
agprice22: Catalina did not use end-grain balsa or foam core in 1988. they used exterior grade plywood. End-grain balsa or foam would have limited the problem to a much smaller area than I had to deal with.

 

[agprice22]

Good job! However... WE DEMAND PICTURES!

 

[Hayden Watson]

Sorry, I did not take any pictures. suffice it to say that it looked like a patient on life support with tubes running everywhere.

 

[heritage]

How did you connect multiple 1/4" plastic tubes to the vacuum pump?

 

[Hayden Watson]

Any way I could find. Mostly I used aquarium stuff from the pet section at the Walmart. I took a photo of my stuff but cannot find out how to upload it.

 

[Hayden Watson]

Here is a photo of my gear. pretty basic. For infusing I used one port to pull a vacuum on the whole system and then put an aquarium 1/4 turn valve on each port with a short stub of tubing. I then used a an epoxy syringe with the plunger removed for a funnel. With the value closed it would stick the syringe into the tube, remove the plunger, top off with epoxy and open the valve pulling the epoxy into the deck. when one port would stop taking epoxy, I would stick the plunger in an pressurize to force more in. this would also cap the syringe so that I could move it to the next port.

 

[Hayden Watson]

I mentioned that I checked the moisture content of the core to determining when it was dry. I used a $40 Ryobi Pinless moisture meter and it worked great. http://www.homedepot.com/p/Ryobi-Pi..._8903vry57826_pcrid_73529852758671_pkw__pmt__

 

[JimInPB]

Wow,
Lots of great information. Thanks for posting.

 

[jibes138]

Nice job Hayden. This is pretty much how resin transfer molding works. What did you use for resin and how much did you mix at a time?

 

[Hayden Watson]

This is the product that I used although others might also be suitable. https://www.fisheriessupply.com/system-three-epoxy-clear-coat-penetrating-epoxy-0600k40?uom=0&qty=1 I talked to the engineering departments of several manufactures on which epoxy to use. I knew that I needed an ultra-low viscosity product but this one was recommended because it does not have any volatile solvents. Solvents could cause a problem in the sealed environment between the two skins because they would not be able to evaporate and might cause the skins to soften.

I watched several videos on how vacuum infusion casting works and saw that I would be doing the same thing. In this process, the cloth is laid into the mold dry and covered with a plastic tarp that is sealed around the edges. The vacuum is applied to compress all of the fibers and then resin is pulled through the cloth causing it to fully wet out.

 

[Crazy Dave Condon]

There are varying degrees of repair for core rot but once was told to drill holes after checking with a moisture meter say 1/2 inch every foot and pour down epoxy resin spreading it by use of an air nozzle. In some cases weight had to be added to the deck if raised any but suggestion of a cover so the weight applied would not scratch. In the extreme of course was to dig out the rot and repair. Then reverse non skid was used to put back the non skid patteren.