Hi, I am in the process of replacing the plywood floor of my old fiberglass boat. I’m very mechanically inclined, but it is mostly automotive, not so much marine construction. However, I’ve decided to tackle this one myself.
So far, I have ripped out the old floor. I’ve removed the carpet, and cut the edged of the plywood around the boat. The old floor was rotted, so I have to replace it. Basically, I now have a boat with glassed stringers, and nothing else. The foam that was in there was obviously open-cell because it was water-logged. It wasn’t molded foam, it was more like 2 by 4’s of foam. I have decided to replace it with closed cell foam.
Okay, now to my questions. From my research, this is what I plan to do. If you have a more practical route, please let me know.
1. I will order some sort of pour in polyurethane foam. I think this will be a good idea because it is closed cell, and will virtually eliminate all negative space. The boat is a 14 foot tri-haul fiberglass boat, so the stringers are pretty shallow. How much foam do you think I’ll have to order?
2. I’m going to sand down the foam, and nail plywood over that. I’m thinking 1/4 inch to keep weight down. I’ve read that it makes a difference weather or not you use marine quality plywood. Regardless, I’m planning on glassing over it so will it actually make a difference? Is 1/4 inch okay?
3. After I screw down the plywood, with stainless steel screws of course, I am planning on fiberglassing it. This is what I need most help on. Is it like bondo? Do I have to lay fiberglass sheets? Like the fabric stuff.
4. After it cures, I’m going to sand it, and apply some sort of marine paint. I’ll make sure it has the texture in it to prevent slipping. I don’t want to put carpet back down because it is heavy, and it smells when it gets wet and never dries.
So, if anyone has done this before and has some pointers, by all means let me know. I am basically starting from scratch so all advice will be appreciated. And for those of you who are experts in this, product brand names, and types, will also be helpful. Also, estimated amounts of material needed for a 14 foot boat would be helpful.
Thank you SOOOO much in advance for any help you have to offer.
Have a great day!!! (or night for that matter…)
Let’s start with the plywood. In the old days marine plywood had water proof glue and other types did not. Now almost all plywood uses water proof glue.
1/4′ is to thin. the weight will not make a big difference, you need the strength….go with 1/2 inch.
I don’t know what you are going to Screw to…….you normally "glass it in place. Use polyester (fiberglass) resin and yes the "cloth" strips to join the plywood at the edges and stringers. Then a light cloth or mat (16 oz.) and more fiberglass resin to coat the floor. you can add non-skid material if you like but do a test first to see if you really want it.
Bondo is filled polyester resin. That’s not what your looking for.
I know alot about urethane foam in boats. i think it will be easier to buy Foam board, 1" and 11/2" thick and just lay it in place. You can get this at Home Depot (the yellow not the pink foam with foil on one side, plastic on the other. Cuts with razor knife (I can hear the moans now) Yes I know……but in your case the foam in place is an added complication. If you fill 75-80% of the void your good to go, and this will not adsorb water like the other foam did. And just fit is as best you can, don’t worry about sanding it down. Even put two or more layers where you need to.
Fiber glass "cloth" actually looks like cloth. Mat on the other hand is random and works better for floors.
Mix pigment in the resin and you will not need to paint at all. experiment, and get pigment at the paint store (you can also use a thickener or micro balloons).
On a 14′ tri hull three sheets of plywood will have some left over…..a 1 1/2 gal of resin 2 packs 60×90 mat, maybe 30 ft of 6" strip cloth. Some filler and pigment…3 or 4 4×8 boards of foam.
If you deside to decide to foam in place the kits come in 2 quarts/ or 2 gal. You want to get 2 pounds per cubic foot density pour foam. and your going to need 8 to 10 cubic feet. that’s a 2 gal.kit.
You can get wood and foam at home Depot/ Lowes and fiberglass resin there or auto parts places, also at Walmart.
Good Luck!