Deck re-core from below

[sailingunity]

My 48 year old boat has had a somewhat inconsistent and pestering leak on the port side for a while now. As far as I can tell, the previous owner had issues with it as well and never could nail it down. I've rebedded hardware in the immediate area to no avail, as best I can guess the leak must be coming from somewhere "uphill" on the topside, and running horizontally inside the deck until it gets to an opening (which happens to be either above my workbench or in the aft cabin chain plate area).

Over the years, this has rotted out a good portion of the coring, as evidenced by the hollow sound of approx. 8 feet of side deck. There are no soft spots, per se, but my stanchions do move slightly as I walk down the deck.

My plan is to cut the skin out from below and remove the rotten coring, then see if I can pinpoint the leak. Reason for going in from below: I live in FL which gets rain almost daily, and this project will take me several weeks as I only have about 4 hours each Saturday to work on it.

I'm not quite settled on what to replace it with. I've read varied opinions on how how great / awful foams are, as well as how great / awful balsa is. Though I'm not super inclined to go with Balsa again, I can admit it has good physical properties and it's cheap. Alternatively, I thought about H80 + Coosa or G10 where reinforcement is needed (like the stanchions). It does seem like it would be easier to apply a board from the bottom than the mesh backed balsa.

Anyone care to change my mind?

[thinwater]

Originally Posted by sailingunity

My 48 year old boat has had a somewhat inconsistent and pestering leak on the port side for a while now. As far as I can tell, the previous owner had issues with it as well and never could nail it down. I've rebedded hardware in the immediate area to no avail, as best I can guess the leak must be coming from somewhere "uphill" on the topside, and running horizontally inside the deck until it gets to an opening (which happens to be either above my workbench or in the aft cabin chain plate area).

Over the years, this has rotted out a good portion of the coring, as evidenced by the hollow sound of approx. 8 feet of side deck. There are no soft spots, per se, but my stanchions do move slightly as I walk down the deck.

My plan is to cut the skin out from below and remove the rotten coring, then see if I can pinpoint the leak. Reason for going in from below: I live in FL which gets rain almost daily, and this project will take me several weeks as I only have about 4 hours each Saturday to work on it.

I'm not quite settled on what to replace it with. I've read varied opinions on how how great / awful foams are, as well as how great / awful balsa is. Though I'm not super inclined to go with Balsa again, I can admit it has good physical properties and it's cheap. Alternatively, I thought about H80 + Coosa or G10 where reinforcement is needed (like the stanchions). It does seem like it would be easier to apply a board from the bottom than the mesh backed balsa.

Anyone care to change my mind?

Working from the underside, it is MUCH easier to install a light kerfed material like balsa or foam than heavy wood. After cleaning out the trash, you butter the underside with a generous helping thickened epoxy or polyester and push the core into it. Finish fairing it into place with more mix, and then glass it over after it kicks.


If you fit a board, how do you hold it in place, and how do you know you got a good bond, with no gaps, on the top surface? Very difficult unless in small pieces. In fact, there is generally no good reason to apply repair core in large sections.


These is nothing wrong with cossa in small areas. Don't bother with G10; you will do better just laying up solid glass where you need it (not glass cloth; 1708 biax is easier to work with and builds more strength.



(Yes, I've done this a few times)

[wingssail]

Originally Posted by sailingunity

My 48 year old boat has had a somewhat inconsistent and pestering leak on the port side for a while now. As far as I can tell, the previous owner had issues with it as well and never could nail it down. I've rebedded hardware in the immediate area to no avail, as best I can guess the leak must be coming from somewhere "uphill" on the topside, and running horizontally inside the deck until it gets to an opening (which happens to be either above my workbench or in the aft cabin chain plate area).

Over the years, this has rotted out a good portion of the coring, as evidenced by the hollow sound of approx. 8 feet of side deck. There are no soft spots, per se, but my stanchions do move slightly as I walk down the deck.

My plan is to cut the skin out from below and remove the rotten coring, then see if I can pinpoint the leak. Reason for going in from below: I live in FL which gets rain almost daily, and this project will take me several weeks as I only have about 4 hours each Saturday to work on it.

I'm not quite settled on what to replace it with. I've read varied opinions on how how great / awful foams are, as well as how great / awful balsa is. Though I'm not super inclined to go with Balsa again, I can admit it has good physical properties and it's cheap. Alternatively, I thought about H80 + Coosa or G10 where reinforcement is needed (like the stanchions). It does seem like it would be easier to apply a board from the bottom than the mesh backed balsa.

Anyone care to change my mind?

I've done both. Currently I prefer to work from the top since I can pour into a hole easier than force upwards into a void.

Did you say 8 feet?

You can get a lot done in 4 hours on a Saturday.

The key thing is...what does the top skin look like? If it is painted non-skid, fine, that's easy. If it is a molded non-kid, then it is harder but still doable.

Day one: Cut the top skin and dig out the soft core, then cover it and let it dry.

Meanwhile seal any holes in the bottom skin.

Day two: fill the open hole with the core of your choice (small pieces) then remove them and put in your thickened epoxy and reinsert the core blocks.

Same day: pour epoxy into the area and fill until level, the replace the top skin and let dry

Fair as needed.

Paint.

[Fore and Aft]

Wingssail don't forget you are going to need a bit of time on the first day to tape up the yacht inside with plastic drop sheets to keep the fiberglass dust out of the interior.
Sailingunity fiberglass dust is a real itchy SOB so the more you contain it the better. Repairing from the underneath is my favourite way to repair decks (not the easiest) as you don't disturb the exterior gelcoat finish.
Cheers

[Sailor Sailor]

I work from the top, as wingsail does, except I wash the newly exposed area with Acetone, which seems to dry it, and apply new balsa core with silica-thickened epoxy that same day.

The unknown is how far the rot extends. I drilled shallow holes in the deck, then used those for entry of a multipurpose tool to cut the deck. Keep cutting out until you see regular core, not the blackened rotted stuff. You can then cut and arrange your balsa core pieces. I used the bottom of a cardboard box to arrange them in a comparable space, then applied after an application of epoxy. Once you get a layer of glass cloth on top, you are fine. It will kick and cure and rain should be no problem.

I painted my entire nonskid deck with new nonskid paint. It matched and looked new. To the extent you lay new gelcoat areas, just paint with white marine enamel. It oxidizes and looks like gelcoat after a few weeks.

[Nicholson58]

Originally Posted by sailingunity

My 48 year old boat has had a somewhat inconsistent and pestering leak on the port side for a while now. As far as I can tell, the previous owner had issues with it as well and never could nail it down. I've rebedded hardware in the immediate area to no avail, as best I can guess the leak must be coming from somewhere "uphill" on the topside, and running horizontally inside the deck until it gets to an opening (which happens to be either above my workbench or in the aft cabin chain plate area).

Over the years, this has rotted out a good portion of the coring, as evidenced by the hollow sound of approx. 8 feet of side deck. There are no soft spots, per se, but my stanchions do move slightly as I walk down the deck.

My plan is to cut the skin out from below and remove the rotten coring, then see if I can pinpoint the leak. Reason for going in from below: I live in FL which gets rain almost daily, and this project will take me several weeks as I only have about 4 hours each Saturday to work on it.

I'm not quite settled on what to replace it with. I've read varied opinions on how how great / awful foams are, as well as how great / awful balsa is. Though I'm not super inclined to go with Balsa again, I can admit it has good physical properties and it's cheap. Alternatively, I thought about H80 + Coosa or G10 where reinforcement is needed (like the stanchions). It does seem like it would be easier to apply a board from the bottom than the mesh backed balsa.

Anyone care to change my mind?

I have done this exact repair. See my photos here on CF.

I used only USComosites 635 THIN Epoxy resin compounded with 3M micro balloons. I used refillable calking tubes to pump the resin in. Very long working time, slow cure, minimal heat.

Use a moisture meter from inside the cabin.
Cut holes with a hole saw, short pilot drill to make 3” diameter holes in the inner skin.

Dig out the wet core. Make more holes as necessary until you are in dry core. Dry thoroughly.

Cut glass mats, cardboard, thin flexible plywood as a backer. Sandwich in order; plywood, corrugated cardboard, heavy polyethylene film, carefully fitted glass patch.

Pour THIN Epoxy on the glass. Use a throw away chip brush to spread and work the resin. Paint the patch area of the hull to wet it with epoxy.

Lift the patch and secure in place using flexible (thin) wood struts. A helper here is a must.

After curing 3 days, remove all backing. The patch will appear clear at the 3” holes. Identify one or more low points and high points. Pick a rubber hose size that works with your calking tubes. Drill holes and press fit short hose bits in the holes. You must cut diagonal reliefs in the ends of the embedded hoses or the hose end may be blinded by the upper deck.

Mix resin and balloons. Keep it soupy. Fill the Caulking tubes and start pumping in at the low points. You will be able to see the progression of the resin front past the holes. Fill until your high vents are blocked.

U

[sailingunity]

Thanks for the replies. It's good to know some condone working from the bottom.
My main reason, besides the weather is also the molded in non-skid. My boat does not have a repeating pattern (like diamonds or whatnot). There is nothing to key off of so it's difficult to get transition from old to new that's not obvious.

When I said "board" I suppose I should have said sheet, because I meant it would be easier to hold up a sheet of H80 than balsa. Working in small sections, this would be maybe a 12"x12" patch of H80, slathered with thickened epoxy on the top to fill in all the voids. But then again if I'm working with that small of a patch, it would not be difficult to use a small piece of plywood to hold up the balsa.

I'm no pro but I'm also not new to fiberglass work, my typical fiberglass grinding / removal kit consists of a tyvek suit, respirator, goggles that seal. This is from experience, I'm familiar with the itch! For working inside I'll use a multi-tool to reduce the dust, but also have to add a box fan with a filter on it.

[thinwater]

Replacing core from inside.

https://www.practical-sailor.com/boa...rom-underneath


Not sayin' it's better. It all depends on the geometry.

[mike d.]

I did it in 3 locations on our boat I used a makita cut off wheel to just cut through the under skin, to dry core pealed it out removed the bad coring , washed with acetone, then went reverse ! I used West system epoxy, and 6_10 epoxy in tubes ! Slathered the under deck, then the core,pushed it into place covered with plastic, then used 3/8 ply with supports to keep it nice and tight till epoxy cured ! Did same for re-glassing underside ! Surveyor gave job a thumbs up !

[sailingunity]

Mike, what is the advantage to using 610 epoxy vs regular thickened epoxy?

[s/v Jedi]

I have both ways and next time I’m gonna do it a little different again: I will work from below, cut the skin and dig out the rotten core. But instead of gluing core into the void, I will glue it onto the cleaned up skin that was cut out, and make it fit into the cavity as good as possible, attaching a piece of plywood to the underside (with plastic foil in between) that sticks out all around to align it, then use piece of 2x4 and a hydraulic jack to setup the clamping system.

When all is ready, use thickened epoxy liberally and clamp it in place. After cure, grind out around the perimeter where the cut is and use some fiberglass tape to reinforce it.

[mike d.]

6-10 is a premix in that it is 2 tubes attached together so equal amounts of hardener and resin come out equally, and it is thick so you don't have to add micro balloons etc! you just squeeze it on in a cross patch pattern with about a 1 inch spacing depending on what your doing ! Push it up down, what ever you are doing ! when you push it into position depending on the curve of the work it squishes in all directions and covers the whole area of contact ! All things being equal that is what it is supposed to do ! You never really know if you make full contact, but when I went back on deck after application and tapped the deck, there were no dull sounds anywhere, and surveyor agreed ! Other than cutting out the repair you can't tell if there any voids ! But I brushed on regular West system to wet out the core ! Sounds like doing extra, and maybe it is, but it was easier than mixing a thickener !

[Benz]

If you use balsa but haven't quite fixed the leak it will just rot again quickly. Better to use foam. Definitely go up from below.

[gonesail]

seems like working from the bottom will risk air pockets. maybe that's not a big deal. but gravity is going to be a problem.

[psk125]

We repaired 8' of cabin top on our previous boat from underneath with balsa. (Leaky handrails, both sides.) Lasted at least until we sold the boat 24 years later. Messy to do, but simpler than trying to match nonskid pattern and color where it's visible. Thinwater seems to have been where you are too.