Repairing Wet Core in Cockpit Floor of Tanzer 22
The Survey done on my Tanzer 22 indicated that I needed to fix the floor. It felt spongy and moisture meter said it was wet.
The plan was to cut open the floor, remove the top layer of fiberglass, dig out the bad plywood, put in a new sheet of meranti and close it up adding a layer of glass over the floor. Everything was going to be covered with a lavish coat of epoxy.
I carefully measured the size of the fiberglass cloth needed, and also where I should cut. Then went ahead and cut the wrong measurement. I cut the area where I was going to have my new fiberglass sheet, not 2 inches inward where the wood was. So in my first day I cut open my floor and spent the next 3 days fixing that mistake! In this case I had accurately measured, BUT just never put the brain in gear.
Grinder has diamond blade
I used a discount grinder I picked up for 39,99 in New Canadian Lumber and the little thing refuses to die. I've had it for several year and it has been a great tool. The Diamond blade cost more than the grinder and works very well. Last job it did for me was cutting out mortar to do tuck pointing on the garage.
Measure twice still cut wrong!
Little grinder cuts easily through the quarter inch or so of floor. It is very light and doesn't kick back so it's easy to control. I am actually wearing goggles, ear protection and respirator. I moved to the side benches to cut. No weight on the floor after this. Good thing because I am cutting the wrong line and actually cut right through the floor! There was an awful sinking (not quite literally fortunately) feeling when I realized what I had done.
Under the floor, with the first coat of carbon fiber kevlar cloth. I put the camera down there. There is only a couple of inches clearance when I'm there too working. I can't focus to really see. I had one moment of panic and claustrophobia but I got over it. The resin kept dripping on me as I painted it on. I eventually got a dollar store mirror and LED lights and at least could inspect with the mirror. I had to go in to work though.
I then spent 3 fabulous fun filled days stuck under the floor repairing the floor I had cut. I sanded around the cut, put a first layer of resin, then applied 2 layers and in several places 3-4 thicknesses of carbon fiber Kevlar and regular glass. I had the fancy carbon fiber from my mast project. It sets very strong and quite stiff. I added a couple of layers of resin on top to make sure the cloth was properly filled.
It was cold, snowing, raining, gale force wind and claustrophobic under there. It was also full of fiberglass dust. I will never forget this mistake. The repair is stronger that the rest of the floor. I also filled the saw cut with a mixture of silica and cotton fibre. Even though I was using quick set MAS epoxy, it took a day to set because it was so cold.
The previous owner had painted the topside of the boat with white non slip paint. This proved to be very resistant to removal. Eventually I used a belt sander, a random orbital sander and a little diamond sanding pad. I ground off the paint and the texture on the floor. Since I am planning to put a layer of glass cloth I needed to get to at least the gelcoat. In many places I ground through this to the glass resin below. Epoxy can stick to scuffed up gelcoat and to polyester fiberglass but not the other way round. I always use epoxy, I'm familiar with it and find it really reliable.
I deliberately left a small section at the front opening to the cabin so I would have somewhere to step.
I looked like a very dusty martian with all the dust and protective gear.
The floor has been repaired and the floor cut mark filled with epoxy thickened with silica and cotton fibres. I used a seringe to put in epoxy first then brushed it in to make sure the groove was coated then used the seringe again to put in the thickened epoxy. It is a very strong mixture. I have ground the top paint and texture off, and sanded everything smooth. The top layer of the original floor seems ok. Some discolouration on the inside but quite rigid. There are a few cracks in the gelcoat but it doesn't feel weak. That's good because I intend to reuse the top. It is easier than having to carefully fair a new top.
I have cut a bunch of holes into the wood core to check if the floor is wet everywhere. It is. I marked the proper cutting line and cut the floor. it's amusing that the floor is stronger and less bendy with my repairs. The wood core is not the same distance on the port and starboard sides. There is a difference of about one half inch.
The floor was hard to get up because I actually started in the least damaged corner. Once it started lifting there was no problem removing the floor at all. It is quite thick and rigid. I took it and put it on top of the plywood in the cabin. Nice and flat so it will not warp.
First sight of the wet floor is disheartening. It is wet throughout and very damaged where the main sheet attaches. The surveyor was correct that there was not much strength there. I expected to see one large sheet but instead the floor had a series of strips of plywood. Between some of the strips there was resin but others touched. If the strips had been separated by resin then water penetration would have been reduced, I'm thinking. Under the sheet attachment the wood is black and completely rotted through. The underside of the plywood was worse than the top, not surprising really. Everything is wet. The top part of the photo is the top covering layer I just lifted up. It is stained wood colour and has a wood grain imprint.
Some spots are rotten through and come off very easily. Corners and edges are stronger and harder to remove. The bare fiberglass looks like wood complete with woodgrain. It is very flexible and would be damaged if I stepped on it. The plywood has 5 layers and must have been good quality. The glue lines are still very strong where the ply is not too rotten. Stripping is tedious. In 5 hours I did a section about 4 sq feet. Corners are not completely done though.
I've not been using any power tools to strip the wood out ... yet. I'm terrified of nicking the the lower fragile layer of fiberglass. It would not be a disaster but would add time to the repairs. I think I will use a drill today if I can't get to the corners. They are wet but not as rotten as the rest.
Hole!! Good thing I had repaired my (wrong) cut line and there was some carbon fibre patch just beside the hole. It actually patched some of the hole and helped support that section.
Along the side I ran across a spot where there was no glass at all. I had actually put some carbon fiber just next to it so it helped support it. I don't know if the hole was there originally or if the fiberglass deteriorated and just crumbled. It looks like they simply did not have enough material there originally. The Gelcoat on top of this spot was quite cracked. I'll put a patch behind it next time I work on the floor. The bottom layer is not very strong at all and I think I will lay a sheet of glass on the inside before I put the plywood in. If I curl the glass I can connect it to the bottom of the floor and it will strengthen the bottom layer. I expect to put a fillet of silica cotton fibre to smooth out the overhang at any rate. it's nice not to have to worry about weight. In my little Skerry I was always thinking about not adding too much fiberglass to save on weight.
I use boards to support my weight. The bottom board is on foam block and supported by the bulkhead under the floor.
I brought a board with foam blocks to support my weight while I work. I have set it across the bulkhead under the floor. The weight rests on the pink foam blocks. I put a board across the seat and lean over this while I kneel on the floor board. I have an old cushion. Not very comfortable but not impossible. I tried sitting on the board on the floor and working this way but it is murder on my back. Still it is much better than squirming under the floor painting epoxy resin. I estimate It will take about 10 to 15 more hours to strip the rest of the floor, if it is in the same condition as the section I have already done. I think that the side would support my weight at any rate. With my repair it is stiffer than it was. Funny that some good came of that mistake.
Back is now mostly stripped to a thin fiberglass skin. It is quite flexible. I still have to dig out on the edges and under the end. The overhang is there because I was afraid of cutting too close to the edge. The overhang is only about 3/8 of an inch port side but on the starboard it is almost a half inch wider. Makes it harder to dig stuff out but I'm lucky because the wood is more rotten on that side. I can't see why but so it is. This was the end of day 1 after opening.
The area where the sheet attaches is so weak the fiberglass just crumbled and tore off. The white behind the hole is a piece of high density polyethylene that I used to back up the attachment I put on.
When I took off the plywood where the original holes had been drilled the fiberglass was so deteriorated that it just crumbled. I guess there must have been quite alot of movement at this spot. Lucky when I installed the new attachment, I had put a large plastic backing board. The wood at that spot was black from mold and just crumbled off. The white can be seen under one of the scrapers I use. The fiberglass is stained and has imprinted with wood grain pattern.
I'm being careful and not using power tools at this stage. If I was handier I suppose it would be ok.
I had left a small section just under the opening to the cabin to make it easier to get in and out. I now made a few exploratory holes with my drill to figure out where the wood ended and if it was wet. It was very wet. I cut as close to the edge as I dared. I actually nicked the bottom in a couple of places but not badly. The top gelcoat layer came off quite easily and is stained. It is quite strong but needs to be cleaned up. I put it on top of the plywood in the cabin until I can get to it.
I took this photo standing in the cabin looking back. The white dusty section has the fiberglass sawdust, the wet looking part is what I just uncovered. I don't know why it is more rotten than the back but it is very mushy. Maybe the previous owner had it on a slant while she worked on the boat. This boat was on dry land for several years.
The front half of the floor was much easier to strip of bad wood than the previous back part. It was more rotten and I guess I was more experienced. Just when I get experienced with something is when I figure out I will never need to do this again. EVER.
This is the end of day 2 stripping and scraping. Most of the time was spent scraping under the overhang digging out wet wood. I have to be careful because the original fiberglass at the curve is very thin and weak. I still have about 3 linear feet of overhang to clean up and bits and pieces still stuck on. I also have the covering layer waiting for me in the cabin.
This is the end of Part 1.
I have completed stripping the wet plywood out of the floor. I have an overhang that varies from 0 to three quarter inch around the edge. The centre, where the sheet attaches has a hole and is badly damaged. There are some very thin spots and a couple of holes around the edge particularly on the port side.
The floor is very flexible and soft and is not even. It bulges down just behind the bulkhead, (which is solid)
There are still some small pieces of wood sticking (strongly) to the underside of the overhang. The starboard side was particularly difficult to strip and the wood was not as rotten as other places.
My concern NOW is to put it back together so it can easily support people and the strain of the sheet.
I had originally planned to:
- Open the floor and clean out the rotten floor
- Cut a piece of plywood and drop it in the empty space after coating it with epoxy.
- fill the overhang with thickened epoxy
- replace the original top piece and stick it in with thickened epoxy
- add a layer of cloth on the top and fair everything
After reassessing my original plan will not be strong enough. I need to reinforce the edges otherwise the plywood will not be solid and reinforce at least the centre of the floor where the sheet attaches, where the material is damaged. I will also need to support up the floor as I glue down the plywood otherwise it will not touch everywhere. Lucky for me, the edges of the cockpit are strong and have not bent at all even with my weight in one spot. So here's the revised plan:
- Crawl once more under the floor and put a layer of cloth across the bad section, it will extend from side to side and overlap slightly the repair that I made which is very solid.
- While I'm having fun under the floor I will put a couple of small patches/strips where there are substantial holes.
- Prepare a piece of plywood covered with wax paper or plastic and use this to brace the floor while the patch in 1 sets. I will use wood lengths to brace the wood up to the height of the bulkhead.
- Prepare a layer of cloth and apply it to the top of the exposed floor. I still have some carbon fibre Kevlar cloth and will use this. This will extend to under the overhang. I will have to make sure the existing remains of wood are absolutely dry and saturated with resin. The carbon fibre is too thick to curl up much but I can add some regular glass cloth strip if I feel I need it. I will prepare it in case.
- I will support the floor in the back to prevent sagging while this sets. Once the carbon fibre has set it will not be very flexible.
- If everything is solid and looks like I can continue working, I will put some thickened putty in the overhang using a combination of microfibres and silica and possibly wood flour if I'm confident that the carbon fibre layer is good. I'm confident, from my experience building my Skerry, that the thickened epoxy is very strong.
- I will cut the plywood to size, in particular I will cut out where the bolts will attach to the floor plate for the main sheet.
- The plywood sheet will need a heavy coat of resin in particular on the edges.
- Working with slow set hardener I will make up a batch of thickened epoxy and use this to cement the sheet of plywood into the floor cavity. I'll pay attention to getting the plywood evenly set so the top sheet fits in evenly.
- I'll put some thickened epoxy in the oversized bolt holes that will later be drilled and hopefully be waterproof.
- Once this is set I can replace the top sheet gluing it down with thickened epoxy.
- I expect I will need to fair before I can put a final glass layer over everything. I don't think I will need a very thick layer but I'll assess at the time.
- It will then be a matter of fairing and sanding, then priming and painting. I plan to use a paint and additive to give a no slip surface to the centre of the floor. The edges will be smooth.
- Then, it's back under the floor to attach the plate with a backing, I will reuse my original High Density Polyethylene boards and Pl 4200. Then I will collapse and scratch the now solidly embedded fiberglass all over my body.
On to Part 2, REBUILDING
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