What's the best way to epoxy in plywood?
First, the basics:
The wood underneath the cockpit sole of my sailboat has rotted out. I was able to access the area from underneath and remove all of the rotten wood. I plan on epoxying in new marine grade plywood as a replacement. The area to be replaced is a basic "T" shape about 3 feet long by three feet wide with the "arms" and "body" of the "T" being about one and a half feet wide. My plan is to cut a single sheet to fit this area and to epoxy it in.
Now, the questions:
Is it best to use one solid piece of plywood, if possible, which I think it will be, or to epoxy smaller sections in at a time?
If a single piece is used, how do you get the air out of the epoxy from between the existing fiberglass and the new sheet? Should I drill some holes through the plywood before epoxying it in place just for this reason (to give any air pockets somewhere to get squeezed out)? Or is this why I should epoxy in small sections?
About how thick should I mix the epoxy with filler, and how thick should I spread it on? Do I spread it on both surfaces or just one (I know to wet all surfaces with unthickened epoxy beforehand)? Do I spread it on with a putty knife, bondo spreader, or one of those spreaders you use for grout or floor adhesive?
Any other advice is appreciated.
I Just Use A 1/4" Grout Style Used In All Floor Type Applications,use 1 Piece Of Wood ,put Glue Only On 1 Side ,whch Ever Is Easiest,smash Down New Piece Best You Can, Put Some Weight On It ;cut Your Board A Little Shy @1/8" Per Side So It Drops In Freely ,seal The Edges Good ,that Will Last A Lifetime, If, You Get It Sealed Good,all We Have To Do To Repair A Boat, Is To Do A Better Job Than The Builder,
"Pigslo" is right to point you toward West system because it is completely reliable. However, there are a few tips maybe only learned from experience. I built a 30' catamaran in strip cedar/epoxy hulls and cabin roof, deck and cabin sides in sheathed ply. so I think you will accept I have real world experience.
Dry fit everything first before starting any coating. It is a matter of choice but I would be inclined to make the new sole removeable so you can check and replace it at any time. If you agree, then two sections will be easier - just put a strip under one side as a "land" for the other section. Get all screw holes etc in place so that no drilling is needed after coating. Bond the landing strip to one section using epoxy thickened with microfibres (not balloons or microlight). A cheap paintbrush is OK - You could wipe it off and put it into white vinegar - also good for cleaning hands & tools) but it is safer to use a new brush each time - any residual vinegar on the brush can affect the epoxy. Wear latex gloves and use paper towels to keep everything clean as you work.
For such a small area, the West System pumps are not really essential, but be careful to get the mix proportions right (5 to 1) - use a couple of old bottle lids as measures). Plastic butter containers are ideal as mixing pots. Don't mix too much at any one time. Also watch the temperature - if too cold there may be curing problems, If too hot, the epoxy may kick too soon, High humididy can also cause problems. Put four coats of epoxy onto all surfaces. Let it go off until hard, then scrub with a scourer and sandi lightly between coats (not the other way around or the sandpaper just cloggs). This removes any amine bloom and any lumps in the coating.
Rather than epoxy the sections in place, I suggest you a epoxy-bond a couple of cedar or ply bearers to the boat then use stainless or monel screws to hold the cockpit sole in place. Seal around all edges and screw heads with polyurethane sealant (Sikaflex or 3M best). Epoxy is not very UV resistant, so after installation, use a one-pack polyurethane paint.
Finally, if you decide to make the sole permanent, do exactly as above but use microfibre-thickened epoxy to create a "fillet" around all edges instead of using screws and Sikaflex
Hope this helps
I'd agree with alanl's suggestions. Also would recommend a good respirator to absorb epoxy curing solvent fumes.
Thanks Sailingdog - forgot to mention that. Actually. personal reactions to epoxy vary considerably from one individual to another and until you are sure you will not suffer a reaction, best to err on the safe side. That said, some people also react to latex. Personally, I have never has a problem using latex gloves and a light mask with a replaceable foam filter. The industrial single or twin respirators are better, but they are heavy and uncomfortable. For repair work on small areas. I use paper masks, but they are notorious for letting in dust around the edges
Another reason to use a mask is that the microfibres (and other fillers) axthough non-toxic, are very fine and breathing them is not smart. The same applies when sanding between coats
I'd recommend nitrile gloves over the latex, as they are a bit more chemical resistant and not as likely to trigger allergeric reactions.
Russ & Others
Too late now as you started from below ....
You do not need to keep outer skin intact. Simplest way to recore a deck or cockpit floor is to cuto out the top layer of Gelcoat & glass and the underlying wood. Will need a wood chisel and a grinder to get rid of all the wood. then build upward with layers of cloth & glass matt, then wood, then cloth & matt then skim coat. Was taught this method by a boatbuilder who now buys and resells 25 year old boats.
Cut out the wood (in sections is OK). Then place matt and cloth down on lower layer of glass and thoroughly saturate with resin. Put the wood in place and place weights on top. Grind any excess then build up with layers of cloth & matt until level with existing area of deck. Grind smooth and fill with resin mixed with a sandable filler. I used West 407 for this.
For non painted boats roll on gelcoat with a stipple pattern in a taped area. You will be surprised how close it looks to original. If the deck has been painted it is even easier.
You do not need to use epoxy for this job. The long cure times lengthen the process. A polyester resin is fine and cures in approx 90 minutes allowing 3 -4 layers to be applied in a single day. West epoxy is also fine but makes the job a very drawn out affair.
I recently recored my cockpit floor in this manner and the entire job took 4 days. A major improvement over the bouncy floor I started with. 2 years ago used same method around chainplates. You cannot even tell that a repair was made in that area.
Full Tilt 2
I think some of you may have missed the part about him already removing the rotten wood from underneath.
Dry fit a piece of 3/4 marine ply. Pre-install the desired number of layers of fiberglass on the side that will be facing down. Make a T shaped brace somewhat smaller than your plywood. 2x4's will work fine. Get a couple of small jacks or other suitable items to hold everything in place. Pre-wet the top side of the ply and the bottom of the sole with a roller. Using epoxy here will be an advantage because it gives you time before it kicks. Mix epoxy and cabosil to a mayonaise to peanut butter consistency. Trowel it on with a plastic 1/4 knotch trowel as suggested earlier. Brace it in place. Glass in the edges with the desired layers of cloth strips.
After it dries overnight, remove braces and reinstall any removed hardware. Sail.
This project could easily be completed from the point you're at in a weekend.
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