Sealing plywood cored thru holes

[AKDoug]

I have to drill several holes through my foredeck to mount the anchor windlass pedestal, the deck being fiberglass over plywood over fiberglass, perhaps an inch and a half thick. I need to seal the wood core, but have no idea how to go about it in the best way. If it were a balsa core, it's well documented. Can I just use something like "Git Rot" as a penetrant sealer for my 3/8" through holes for the base mount?

Drilling oversize holes doesn't seem like the best answer.

Looking for some tips here I will post some pictures of the finished project when done, the project just being at the "fit the pedestal" before final welding on the chain pipe. And boring holes in my foredeck with a drill and a few hole saws...

 

[dwhatty]

Two or three coats of West (or similar) epoxy? I've done it and seems to soak in to the ply and hold up okay. Take the blush off the epoxy between coats. As to the advisability of thinning it to make in penetrate more see: WEST SYSTEM - Projects - Thinning WEST SYSTEM epoxy

 

[kchace]

Drill oversize and use 5 or 15 minute epoxy to line the hole. Then seal and bed properly using something like 4200.

Ken

 

[dwhatty]

Then seal and bed properly using something like 4200.

Ken

X2

 

[psneeld]

I drill oversize by 1/2 an inch or so....tape the bottom...fill with epoxy and filler blended...then I drill though the epoxy only to mount.

It takes longer but it's the ticket...

 

[AKDoug]

In balsa cores they advise thinning the resin to penetrate the core before filling the void. I was thinking there must be something that will penetrate "new" plywood (not old holes) deeply enough to seal it. The plywood is relatively uncompressable, so the usual routine with oversize holes in a core seems like overkill. Drilling "straight" through the center of the pour seems unlikely as well, unless the hole was hugely oversize.

Brain at work here, thinking about what makes sense.

 

[psneeld]

In balsa cores they advise thinning the resin to penetrate the core before filling the void. I was thinking there must be something that will penetrate "new" plywood (not old holes) deeply enough to seal it. The plywood is relatively uncompressable, so the usual routine with oversize holes in a core seems like overkill. Drilling "straight" through the center of the pour seems unlikely as well, unless the hole was hugely oversize.

Brain at work here, thinking about what makes sense.

Thinning epoxy can be problematic unless you are good at it.....and even then there is a debate whether it really does any good.

If you can't mark and drill new holes in something that has a 1/4 inch clearance all around..maybe you shouldn't be doing your own maintenance.

 

[AKDoug]

OK, another search found the suggestion of using a Dremel to remove the plywood under the fiberglass, like the balsa pick on a drill chews out the fiber. I now have a plan. Thank you all very much for your suggestions.

 

[AKDoug]

Thinning was fiberglass resin vs epoxy. I had the recommendation from a local fisherman that I use what my boat was constructed of rather than epoxy as much as possible. I was talking WEST to seal and fill my cored roof for a skylight/hatch install in the pilothouse, he pointed out the advantages of matching construction materials. It made sense.

1/4" all around the hole through a non compressable material seems excessive, the sealing is against moisture intrusion, not against compression of the core. The load is in shear, so moisture intrusion is the issue in sealing.

 

[psneeld]

Thinning was fiberglass resin vs epoxy. I had the recommendation from a local fisherman that I use what my boat was constructed of rather than epoxy as much as possible. I was talking WEST to seal and fill my cored roof for a skylight/hatch install in the pilothouse, he pointed out the advantages of matching construction materials. It made sense.

1/4" all around the hole through a non compressable material seems excessive, the sealing is against moisture intrusion, not against compression of the core. The load is in shear, so moisture intrusion is the issue in sealing.

You answered your own concern...the 1/4 inch is for no other reason than making sure you can drill through that new area without missing and nicking the core...not for thickness of waterproofing. The compression resistance provided by epoxy and filler is a good thing though.

Hey do whatever....just telling you what works in the yards, marine businesses I work in.

There are faster methods using polyester and or 4200/5200....but I like a more sure bet.

 

[Xsbank]

Pour in some CPES first to penetrate the wood.

 

[kulas44]

You ask how to do it correctly. PSNeeld told you how to do it using accepted best practice. Then you got advice from a local fisherman to do it his way using vastly inferior products and slip shod methods. I dont get it, why ask ?

 

[AKDoug]

A single reputable author listed 6 different ways to do the job. Some removed more material and some removed less. Some bored a single larger hole through the deck and some a larger hole from the top and a little one from the bottom, or the whole top and bottom as with a hole saw. Replacing the whole core or enlarging the hole too much didn't make sense.

I am using this forum to get my own thought together about the process I want to use to get my job done. I am not being contentious, and professional qualifications have to be noted to be considered. I appreciate all comments and suggestions, they have helped me to form my plan.

Don't question the qualifications of my "local fisherman", he does outstanding fiberglass work well recognized in the local community. His demand far exceeds his ability to meet it.

I am not familiar with CPES, didn't see it in my West Marine catalog. What is it?

My plan is to route out the plywood below the fiberglass with a dremel type bit and fill with thickened epoxy, without enlarging the existing holes in the fiberglass, and then to drill, as suggested.

Sometimes it takes a while to decide what you want to do, and how. Thanks all.

 

[kulas44]

I usually drill thru the top layer of FG with a hole saw then pry out the FG plug. Then drill out the plywood with a forstner bit, being carefull not to drill thru the bottom FG, then mop the hole with regular epoxy, then fill the hole with epoxy thickend with cabosil or milled fibers (or saw dust) to a peanut butter consistancy, then press back in the FG top plug. The new hole to be drilled in the holesaw pilot hole. Easy and strong. Much less compressible than plywood. It is of utmost importance to seal wood cores in a similar manner. Wood is always compressable and once it is compressed it tends not to come back completely. If the bolts are tightend on a cold day the wood will be compressed when the deck heats up in summer and expands. This will leave a small gap the next winter that WILL get wet. Rot is inevitable. The epoxy plug is harder and even if compressed will come back, not leaving a gap. Even if water does get under the fitting the epoxy seals it from the wood. Polyester resin will crack if used in this manner. Some poly tooling gells are used for this purpose but rarely.

 

[HopCar]

CPES is similar to Git Rot. It is a penetrating Epoxy Resin.


Just today I bolted an outboard to a plywood transom with fiberglass on both sides.
I drilled the hole, pumped it full of 5200 (Girly Men use 4200 ), put a bead of 5200 under the bolt head and fender washer, shoved it through, tightened the nut and washer down into the 5200 that was pushed out the other side, cleaned up the mess with WD40 and a rag. I'm confident that water will not get into the plywood.

 

[N4712]

CPES is similar to Git Rot. It is a penetrating Epoxy Resin.


Just today I bolted an outboard to a plywood transom with fiberglass on both sides.
I drilled the hole, pumped it full of 5200 (Girly Men use 4200 ), put a bead of 5200 under the bolt head and fender washer, shoved it through, tightened the nut and washer down into the 5200 that was pushed out the other side, cleaned up the mess with WD40 and a rag. I'm confident that water will not get into the plywood.

That's how I've always done things. Gobs of 5200 and multiple rolls of paper towel, and GoofOff. Works great for cleaning up 5200 and others sealants/adhesives.

 

[O C Diver]

I drill oversize by 1/2 an inch or so....tape the bottom...fill with epoxy and filler blended...then I drill though the epoxy only to mount.

It takes longer but it's the ticket...

This is the best way. There are other ways to do it, none better than this. If you don't have the time to do it right, where will you find the time to fix it later.

Ted

 

[psneeld]

In all fairness, kulas44 in post 14 probably described the best way I would do it...especially when the fastener or hole size becomes larger. Keeping the lower skin can help a lot...but it does involve a bit more work and tools.

Definitely the way to go if the core is more easily compressible than ply.

 

[FF]

Another way to solve the problem is to do as suggested , drill oversize and plug with reinforced epoxy then redrill.

Then grind the area where the windlass or stanchion , whatever is to be mounted and epoxy down a flat (store bought) hunk of laid up glass.

At about 1/2 thick it will help spread the load , and ease the loads on the backing plates.

BEST!!! of all it will raise all the seal area under the item by that 1/2 inch and give a really flat area to mount to..

Standing water on deck will need to be over 1/2 thick to even test the quality of the seal goop.

 

[AKDoug]

I really like the suggestion in Post #14 too, it will be my back up plan if I don't feel like my Dremel bit is getting enough material out for a good seal. My foredeck has a little bit of a hump, so it isn't flat enough for a base plate. I am using washers under the corners of my pedestal base to level it and leave a good layer of 4200 under the base to avoid squeezing too much back out bolting it down.

On another note, the holes through the deck for the chain pipe and for the cable routing also have to be sealed. Since they aren't sealed (open from the bottom) like a bolt would be, is just sealing the exposed edge of the wood with something like Verathane (outdoor formula) appropriate? Moisture could drain without being trapped between layers...

Appreciate opinions

 

[psneeld]

I really like the suggestion in Post #14 too, it will be my back up plan if I don't feel like my Dremel bit is getting enough material out for a good seal. My foredeck has a little bit of a hump, so it isn't flat enough for a base plate. I am using washers under the corners of my pedestal base to level it and leave a good layer of 4200 under the base to avoid squeezing too much back out bolting it down.

On another note, the holes through the deck for the chain pipe and for the cable routing also have to be sealed. Since they aren't sealed (open from the bottom) like a bolt would be, is just sealing the exposed edge of the wood with something like Verathane (outdoor formula) appropriate? Moisture could drain without being trapped between layers...

Appreciate opinions

Along the lines of FFs post....if the deck is crowned....

one of two ways.....

build a dike and fill with thickened epoxy that will self level....

or glue down a panel of rot resistant material with thickened epoxy to level and glue it.

 

[AKDoug]

My pedestal is a 7" deep 316 stainless 3/16" box, mounted flat side down with an open top. The motor will be inside the box, and the chain pipe passes through inside the box to the chain locker. The pedestal height is at bow height (deck is below bow level) and will have another 1" of plate steel and plastic bolted down on it (for required windlass deck thickness).

How would you seal the plywood where the windlass wiring passes through the deck? And where the chain pipe passes through the deck? I was planning to seal the pedestal well and leave the bottom open to the chain locker. What kind of a seal on the plywood would you recommend?

These are 2 1/2" and 3" holes. The pedestal's top is already at the same height as the bow. For better visualization...

 

[AKDoug]

Route it out and fill it I guess then. I sure am having to learn a lot of new things since having moved up in boats! It sounds like epoxy is the standard answer to everything

 

[psneeld]

Me.....the 4 bolt holes would be oversized and filled and redrilled.

The chain would go down though a bronze or stainless through hull that had the ply coring taken back a 1/2 inch or so and filled with thickened epoxy.

The wiring is tough because I'm not sure what I have to work with there...but possibly a piece of flexible tubing or pvc to above deck level, epoxy holed like the bolts or through hull pull the wires full then goop it watertight.
But hard to say because of several puzzle pieces I am not sure of.

It is less about water getting in the locker as the chain brings it in anyhow....it is about the deck coring and keeping it dry.

 

[FF]

I have had luck with using brass pipe epoxied in place to take the compression loads.

A bit of time and a file will do , although the bolts to the item must be loosley installed when the fitting is glued in to save the alignment.

Car wax makes a parting agent , if the mounting bolts are removed before the epoxy gets rock hard.

A sailboat cored deck mounted winch is an example of high load.