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!
Try searching pointers up, or just go to a local hardware seller, such as lowes. Theyll give u quick tips just giving them a call!
References :
your plan sounds pretty good, but suggest that you take a look at the following site for complete instructions on how to do your deck repair.
http://rotdoctor.com/glass/GLrotrepair.html#floor
take time to read the full article on fiberglass repair including the area on products. there are lots of pictures and illustrations. also go to the tab on customer project for more examples on floor replacement on a fbg boat.
this is a great site that also discusses wooden boat repair
I hope this will answer all your questions
References :
old salt, boat builder and boat restorer
This may help ya some:
http://www.boatbuilding.net/article.pl?sid=06/01/12/157249&mode=thread
References :
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!
References :
This work is quite o.k. for the home builder – but many of the materials are very harmful to an unprotected worker. A professional attitude, and professional level personal protective equipment is a must – not a luxury. The potential health issues are absolute and very real.
Main reason for paying for marine ply is the total lack of internal voids in the inner layers. Marine ply is a very high quality, stable, standardised, (expensive!) structural building material. Unfortunately there are cheap (not to the customer) versions – not just Asian either – out there. Buy from the large known companies who have a reputation to protect. Exterior ply is not a substitute due to the internal voids.
When you pulled the old floor you may have noticed some heavier timber sections, used to stiffen the floor. A more cheaply built boat may have relied a lot on the foam to stiffen the floor – a fairly temporary arrangement. I have actually removed pour in foam from a few hulls now – this stuff is again a short term thing. I would strongly suggest closed cell polyurethane foam noodles (thick as your wrist, two feet long and up) as a good flotation media.
Sanding pour in foam will be absolute pus – just don’t.
For you to screw down the floor there must be some form of webbed structure between the hull and the new floor. This is built of ply sections (15mm good, 19mm better for the main load areas) mounted vertically and longways. These sections are shaped to the hull on the lower edge and make a level datum on the top edge onto which the floor will mount. If those sections are gone the job will be that much harder, as they add strength and stiffness and locate the floor. There must be gaps against the hull to allow any water to drain to the lowest point and out the transom drain plugs. Floor ply should be at least 3/8", but 1/2" is better – the further apart your support timbers, the thicker the ply must be.
Epoxy is the resin of choice, polyester is too brittle and not even permitted as repair on any insurance job or vessel under commercial survey. All wood should have at least three layers of mixed resin applied wet on wet – that means you allow the preceding one to gel off before applying the next one. This lets you get three layers done in one day. When fully cured you must sand the epoxy surface (and any areas on the existing hull well for a key for the glue and any glassing to the hull or other elements.
(The base epoxy resin on having various powders (called modifiers) added becomes a fairing compound, or a very strong structural adhesive, it can be incredibly tough, slippery, stiff or flexible, even heat proof with graphite. This gives great flexibility to the possible uses of the material – for our use we use it to laminate, glue and fair)
I am in Australia, the top brands all make a good product, I use West System. You will need modifiers to use the epoxy for fairing or gluing, the hardener speed depends on your ambient temperature, whichever product you choose the maker will have all the pack sizes and appropriate quantities for a given area/job. The dispenser pumps are unique to the type of product you choose, basically they allow you to mix accurate volumes with each pump giving a precise amount of either resin or hardener. There is no reason to thin epoxy. Thinned product might penetrate a little further into the timber, but has much reduced strength and many voids within the wood allowing free water entry and rot. The chemical and physical links of epoxy with timber are incredibly strong, and vastly superior to polyester which can only make a mild mechanical link with the surface, and relies on compressive strength when combined with glass fibre for it’s structural integrity.
Glass fibre chosen should be for epoxy use.
I like to fit I.P.s (inspection ports) into the floor, for additional ventilation when out of the water. It is critical that air be able to access all areas of a boat, any foam encapsulated within the hull must be totally impervious to water, or be able to fully dry. Any water unable to escape will eventually cause issues – no exceptions. Fit these where they are accessible, but not where you walk all the time or you’ll break them, and they can be slippery.
Two pack finishes are the optimal for GRP and epoxy – again as there are so many good makers around this will be personal choice. The product chosen will dictate the method of application. Use sugar liberally over the last coat while wet – when the coating has cured rinse well to dissolve the sugar – perfect grip!!
I would flow coat the inside of the hull before dropping the floor if the GRP is exposed. Two pack would be o.k. if well sanded and 2 pack high build primer is used. Water enters GRP very very easily, then it steadily degrades it.
Good luck.
References :
you have a lot of good answers here already — I’ll just share my own experience.
I used 3/8" B/C EXT (exterior grade) plywood for floor and casting deck in my boat. Marine grade is just too expensive. I expect they won’t last as long — like maybe 15-20 years instead of 40.
I used polyester resin. Epoxy is just too expensive (I would use only epoxy for exterior hull, or transom repair, though). Brushed on the resin without catalyst until the wood wouldn’t absorb any more (a couple coats is all it took), then applied one layer of fiberglass cloth to the top side only of the floor, and to both sides of the deck (for strength).
This was 4 years ago — might paint it, might not. It makes a fairly good non-slip surface as is, and it fits with my garage-sale decor. I understand that poly resin is not, strictly speaking, "waterproof", but I’m ok with that.
I have one section of flooring (about 2 1/2′ by 4′) that I replaced 6 years ago — it’s just B/C ext ply painted with 2 coats of rustoleum oil-based primer and 1 coat of water-based topcoat (rustoleum’s recommended products in this application). I was in a big hurry and planned to replace it again when I did the other work anyway, but it’s holding up quite well.
I’m pleased with my result.
References :
You have gotten some excellent advice! Here is my two cents:
1. Go with marine ply,
2. Use epoxy,
3. Do not use foam under the floor,
4. Do not use screws or nails to fasten the floor,
5. Cut the ply to fit, then cover BOTH sides and edges first with fiberglass, then install into the boat.
6. Do not sand the top coat of fiberglass unless you have applied a fairing compound first. (go with west system, they have everything you need for your project, including "how to" manuals on all of there products)
7. Use the proper PPE (personal protective equipment)
8. Good Luck! A do it yourself project like this can be very satisfying!
References :
AS degree, Boat Maintanance and Repair
I like the foam idea! I’d screw 1/2" plywood(make sure you coat the bottom side of the plywood with epoxy first…just brush it on) and if I did the foam, and I see no reason why you cant… after I screwed down the plywood, I’d cut some holes in the plywood and pour the a/b foam mixture in under the plywood. Do not use a dense a/b foam mixture, it will add too much weight. Glass in the plywood around the edges to seal everything is a good idea too. Then, I’d either lay nonskid material over the plywood or paint a super thick coat or two or three of gel coat(any color you’d like!) If you had all the material you could do a 14 ft. boat in a weekend no prob.
References :