Plywood boat and fiberglass as sealer?

I have a 16x8 jon style boat it is plywood contruction now in order to get a long lasting boat i have been thinking i should build a thin fiberglass shell around it, instead of buying resin and mat couldnt i just get a couple gallons of filler and spread it out in a nice even surface to create a sort of shell?

if my plywood is my strength and the glue is my water sealer i wouldnt need much fiberglass to just add that little extra seal right?

 

Correct, but mat was never the right material for your job. Cloth would be, applied to the bottom only, and it's up to you whether you want to spend for four yards or so of glass.
Except for the seams, no glass is needed to provide strength. Only for abrasion resistance.
You talk about "filler", but what's really effective is epoxy without any additives. Tape the seams outside and then apply three coats of unthickened epoxy to both inside and outside. This may be a lot of work since there's probably paint that has to be removed.
I'd suggest you f.g. tape/epoxy and fair the chine seams and transom and epoxy/glass the outside bottom up past the waterline. You seal the inside with epoxy to keep moisture out of the wood.

 

well i have not painted to boat yet so this should be no probplem

Why wouldnt i use a long hair filler like bondo type and spread it out and finish sand it then paint it, sence i have a raised platform there is no need to make the inside of the floating area nice just have to seal it so it can last a long time.
1 gallon of filler is 30$ i cant get cloth and resin for that much. im going to try a small chunk of wood and spread the filler on it do you think i should lay resin on the wood just for the extra measure of sealing it?

 

Okay, it sounds like you're about to use all the wrong materials on your boat. What is the name on the label of resin and the filler?

Do yourself a favor and download the user's manuals and product guides from www.westsystem.com and www.systemthree.com. These will go over the details, materials, methods and techniques you need.

Bondo, fibered or not, has no business on a boat. It's an automotive filler that's nearly useless in the marine environment.

You can use proper encapsulation techniques and have a long life for your boat, or you can use whatever method you dream up and have to make repairs a few years from now, because you attempted to save some bucks.

I'm not trying to insult you, but it sounds like you're about to smear polyester resin and light weight automotive fillers all over your plywood boat. This just doesn't work very well and I replace dozens of polyester coated wooden parts every year.

 

it is bondo made but it is for boat repair so why wouldnt this work if it was made to repair holes in big boats why wouldnt a small thin layer help with wood preservation and sealing on plywood?
the only difference i see in cloth vs paste is tensile length strength i talked with a local repair boat repair shop and he uses this stuff all the time to repair golf ball size holes in big boats now i have 1/2 inch plywood all im going to do is use the paste as thin extra seal and paint on top to do another small seal.

No insult taken, i understand the thought and i live in michigan so every winter i can have something to do if i have to patch dings and scratches.

 

Because you've been told that a polyester based putty product is ideal for small holes, your assumption is that it also would make an ideal sealer. However, just because a company claims that their product is a "marine" product doesn't make it so, since longevity comes into play and I suppose any product could be called "marine" for a while, even cream cheese.
You've asked what to do and the answer is, no, you're going about it the wrong way. The polyester based product you mention will not adhere well and even if it did, it is not very waterproof, although it would appear at first glance to be a perfect sealant. It offers little strength, and mediocre waterproofing, but it will add weight and potential problems in several years.
Do some reading on the subject.

 

The putty, if it is the fiber strand type, can't be spread thin. You can use mat and polyester, specially is the boat won't be continuously in the water.

 

i wont use it then so its fiber tape and resin at the seems then right?

if im lucky the boat spends 16 hours a week in the water do you think the gorilla glue will hold with this minimal use?

 

The MEK Peroxide in Bondo hardener (keep away from your eyes) also tends to gas and blister paint after the job is finished.

 

Gorilla glue is waterproof and will hold.

 

Note: Gorilla glue is more expensive than epoxy per unit of weight or volume but it is available in tiny quantities. There are questions and discussions here on the forum discussing whether Gorilla glue is suitable for constant immersion. Look at what it costs per ounce and compare. Meanwhile, the same epoxy already suggested for sealing the hull and laminating fiberglass cloth (see PAR's link "West System") is the stuff you should be using to glue wood together. A gallon with a quart of hardener will cost about $130.00 from West Marine (no relation to West System) in California. This seems to be about the quantity you'll need if you are finishing the whole hull as described.

 

Follow the advise given here and you'll have a boat that will hold up for many years. Polyester = NO, Epoxy = YES. Take a look at the photo of the foredeck I did a couple of years ago. You can do this too, it's not rocket science but you do need to follow System Three's or West's directions. Here is the way the plywood was finished......

1. Two coats of System three clear coat resin to seal the plywood. I use a foam roller for this step 1/4" chemical resistant. Some people on this forum who have much more experience than I do say that this step can be performed using System Three general purpose resin and one coat instead of two. You see, Clear Coat resin is much thinner than the general purpose type so I need two coats. Either way you want to go is fine IMO. Wait about 12 hours between coats, shorter if the first coat cures faster, but don't go over 12 hours as a rule.

2. Cut 4oz / square yard fiberglass cloth to cover surface.

3. After the clear coat cures (but again no longer than 12 hours), apply a single coat of System Three general purpose resin to the fiberglass cloth and stick it down. I've found that you can use a foam roller, but a rubber squeegie works much better. You can find a decent squeegie at Lowes or Home Depot for $5. The foam roller needs to be chemical resistant and I'd get these from whoever sells you the epoxy resin. Only apply enough resin to wet out the cloth (cloth turns clear). What you don't want to do is over apply resin. When you are done with the squeegie you should have a smooth surface and you should be able to see the weave of the fiberglass cloth and the plywood beneath.

4. After the resin cures (but no more than about 12 hours after you applied step 3) apply a second coat of epoxy. This "fills the weave" of the fiberglass cloth. Since you applied the resin so soon after the first coat went down you also get a decent chemical bond instead of an inferior mechanical bond. Depending on your skill and patience you might be done here or you might need another coat of resin to fill the weave. Can you say "12 hours"?

5. Once you have the weave filled and the resin has cured fully you can go ahead and paint. I like to use Interlux Epoxy Prime Coat and Interlux Perfection as a finish coat. Follow the Interlux directions and you will get a great result.

Other people on this forum who have much more experience than I do have said that you don't need to use expensive "yacht" paint and they are probably right. The Perfection does do a nice job though and it is very hard when cured.

Best of luck with your boat,

MIA

This is how it looks before painting. The side decks are douglas fir (note the wild grain) the cabin roof is the good stuff (okoume). Note the difference in grain and how nicely the okoume finishes. The okoume is more expensive than the doug fir, but consider that I needed an additional couple of coats of epoxy to get a decent smooth finish on the douglas fir that I didn't need on the okoume. You live and learn (right PAR & Alan & Gonzo?)!

 

You live and learn. If you are wise enough you learn from other people's mistakes, but it is good to make your own too sometimes.

 

no argument that epoxy is a better material, it grabs better, lighter, more flexible..
but yes poly IS cheaper and can be done too. first coat has to be thinned a lot with acetone to help it grab deeper into the wood, its nasty stinky, and so is polyester.
not saying you should use poly, just that you can, I've used it too.

with small budget plywood projects, inside chine logs, double taped seams, and 3 coats of poly rolled on (after that 1st thinned coat), rough sanded, cleaned, then 3-4 coats of (believe it or not) good semi-gloss exterior latex paint cured 10+ days, you'll come up with something pretty fair and plenty usable, we're not talking a baby-grand piano

not knocking the REAL boat guys (they are the real deal and DO know their stuff), but for a fairly cheap home built plywood get out go fishin machine, sometimes it's pretty easy-convenient to grab some poly resin at autozone and "git-r-dun".

epoxy isnt much more expensive either really, I've bought quite a bit of both types of resins from 'fiberglasssite.com' is pretty reasonable. they tell you the truth about off the shelf resins, you have no way of knowing how long the stuff has been on the shelf and it DOES have a shelf life (hello my stinky friend acetone?). sometimes its a matter of what youre up to, or what youre expecting, or how fast you want to be out fishing.

epoxy IS better, a layer of cloth to the bottom with either type resin will do lots for abrasion resistance, this is boats, and s#it does happen. the typical bumps and scuffs I've had here-n-there still havent ever done more than scratch a little paint off the poly-resin coated ply, I wasnt trying to drag it across a buncha rocks, HONEST!!

also note, the thinner epoxy clearcoat as a primer to the wood, is about the same kind of concept as thinning some polyester for the 1st coat to get it to grab better/deeper.
(disclaimer - I'm not trying to instigate some kinda pissin match with this stuff!)

 

oh hey.. it was years ago a neighbor coated the bottom of his sons driftboat THICK with a stuff called "gluvit" or something very similar. pretty impressive stuff! looking around I'm seeing more fans of "Coat It" nowadays, supposedly tougher and slipperier, also lays down a bit thinner and smoother than gluvit.

stumbled into this trying to remember "gluvit", http://www.armacoatings.com/marine.html
also seeing mention of Ultra High Molecular Weight poly sheeting being glued to driftboat bottoms for being super slippery = more speed?

another mentions http://www.fascoepoxies.com/products.html
STEELFLEX SUPER SLICK EPOXY COATING #9X-2000 -sposed to be for airboats,
Contains Teflon plus additional friction reducing additives.

it's the "chit happens" stuff, jonboats, sometimes bashing around fishing, that brought driftboats to mind and the thicker foamier type epoxy like gluvit. its been a few years since living on the rogue river. it'd probably still want the taped seams and a thinner primer coat first for better bonding, but you could hit that old gluvit stuff with a hammer and it sure didnt care about dents, divots, or voids in ply, it'd just fill em and give you a slippery skin. it strengthened the floor of that driftboat a lot too, was only 3/8 ply.
that "coat it" stuff might be the answer youre looking for, idk.