poly or epoxy for plywood floor

[mark123]

Which would be a better floor covering epoxy/ cloth top coated with do it yourself 2 part truck bedliner coating or polyester resing and fiberglass matting and then gelcoat. I originally did epoxy/cloth and paint and it wore through after a few years and I have a mess now so i will get it all sandblasted and do it again. Locals do the polyester method. The weak link in epoxy covering is the top coat so I think the bedliner might be a good solution.

[alan white]

The epoxy sheathing was the superior choice, but something must have happened to the actual job itself. Normally, a correctly done epoxy/cloth sole sheathing would last a very long time.
I've experienced polyester letting go from a plywood substrate quite a few times, enough to avoid repeating the original method.
I think the bedliner idea is not worth the expense. You need to use a heavy cloth and completely fill the weave (as many as four coats of epoxy), followed by wehatever non-skid/paint system you like.
You may have done the original job improperly--- not enough epoxy, poor bonding due to what might have been coating the plywood, wrong ratio, any number of things. Don't make the mistake of using polyester to solve your problem. It makes a poor bond in comparison with epoxy.

[mark123]

I don't mind using epoxy but it is the paint topcoat I dislike, it wears too fast. Could I topcoat the epoxy/cloth with polyester,matting and gelcoat. Is there anyway to get them too bond well.

[alan white]

It makes no sense to do so (add polyester and mat). You can buy nonskid material and cut it to fit, and glue it on. That would be a good solution.

[PAR]

Polyester will not stick to epoxy and is generally inferior to epoxy in every regard.

I'm not sure what failed in your epoxy and paint job, but it wasn't the epoxy's fault. As Alan said, if applied correctly, the wood will fail, before the epoxy. Paint coatings are what they are.

I've used truck bed liner over epoxy and it wear exceptionally well. It has to be applied correctly too.

[Ilan Voyager]

I agree with you Par. I'll add that's better to use two layers of a small weave cloth like a satin of 240 gr/m2 than a thick cloth. The filling of the weave is better and smoother, the proportion of glass is better also thus stronger.

Bed liner works rather well. There is also some antiskid paints polyurethane based which work well and are durable.

[BurnabyRocket61]

So for topcoating epoxy coated marine grade plywood, what do you guys suggest and why? And what weight cloth should I use for a 16 ft runabout that will be for recreational use only, for about 20-30 days a year.

[alan white]

A single layer of 10 oz cloth well saturated in epoxy (3 coats average should do it). You could also simplify and omit the cloth, and just coat the plywood with epoxy alone. If the plywood is fir, however, a layer of cloth improves the surface protection and looks, since fir grain tends to become wavy and splintery under paint alone.
Any marine plywood except fir could just be epoxy coated and the paint alone would protect (abrasion would show as paint worn away, and its presumed the owner would keep up the paint as soon as this occurs).

[Jimbo1490]

Originally Posted by Ilan Voyager

I agree with you Par. I'll add that's better to use two layers of a small weave cloth like a satin of 240 gr/m2 than a thick cloth. The filling of the weave is better and smoother, the proportion of glass is better also thus stronger.

Yes the satin weaves really are superior cloth. You could add that the reason they are satin is that each tow in the weave does not interleave with each tow it crosses the way it is done in plain weave. Instead each tow only dives back to the other side of the cloth every 8th time (the typical pattern) that it crosses another tow.

Why does this matter? Because for one thing, every time a tow crosses from one side of the weave to the other, a little tiny bend or 'crimp' is left in the tow. So instead of being straight, the tows now looks like little 'zig-zags'. Later after being set in a resin, the tows have to 'straighten out' first before they can take up bending loads applied to the composite structure. So all theses little crimps add up to less structural stiffness. Satin weave has 80% less crimps than plain weave. This is a big reason that non-woven biaxials are all the rage; they have no crimp at all so produce stiffer laminates for a given weight of cloth.

Satin also has a lot less friction between tows, so when you bend or fold it, it gives and conforms readily. The 'drapability' of the satin weaves is just amazing. As you probably know, the drapability of the biax and triax non-woven cloths is about *zero*

There's a guy on ebay that sells the stuff in small lots very cheap, so if you can't find it locally, just ebay it!

Some cloth style numbers

1581
7781
181 (if you can find it )

Jimbo

[alan white]

Good technical information. Certainly applicable where stiffness and strength are involved. The question is still, what is the best way for a novice to cover a plywood sole? The strength is already there, in the form of plywood. What's wanted is a simple but waterproof covering for that plywood. Materials must be easily obtained in a small quantity and applied by a person who has only a modicum of experience, possibly outdoors.

[BurnabyRocket61]

Ok, so what I'm thinking is, and please let me know if I'm otl, is that if I give the 5/8" m-grade fir a couple of good coats of epoxy on all sides it should be good. As for the fir being wavy, I know what you mean, but I've had good results on other components during the build by not sanding to much and removing the softer grains in the wood, then with a couple coats of epoxy the surface finishes quite well. As for load bearing the sole will be well supported by the aluminum stringers so the glass won't be needed for support, As for impact resistance, worse case scenario would probably be dropping a 15lb lead downrigger weight on it, and glass or not, it more than likely would leave a dent that would need to be repaired. As for wear resistance isn't that the job of the top coat? And speaking of top coats, do you guys have any suggestions, do I go with a two part poly paint with grit or maybe that 1 part stuff that you roll on with a textured roller that results in a rough dimpled look. Or is there something else out there that's anti-skid and durable that I should consider.
Thanks guys, all your input and knowledge on this site is greatly appreciated by me, and I'm sure many others.

Alan was right on the money, apply 3-4 layers EP (take care to fill the open edges sufficiently), then paint it. Cannot comment on the non skid stuff, never used it. But do´nt worry too much about that (same is valid for the resin), the cheapest stuff will do the job. And the paint (not the EP) you will repair after a while due to wear and tear.

Regards
Richard

[PAR]

Epoxy will only seal the wood. Light weight cloth set in epoxy will provide light abrasion protection. Neither the epoxy alone or with a light weight cloth sheathing will impart any significant strength to the panel.

A top coat can offer some abrasion resistance, but it would have to be the truck bed liner route. As a rule the topcoat is just for looks.

Douglas fir will check and split with age. This is unavoidable so my recommendation on Douglas fir is to sheath it with cloth, the heavier the better. This will halt the checking, if the sheathing is heavy enough. 12 ounces would be a minimum on a fir deck. On your deck, probably needing more, like 18 ounce and up. It's best to apply this in multiple layers of lighter weight fabric, such as two 6 ounce layers or two 10 ounce, etc.

Two 10 ounce layers will make a fairly tough deck. If you drop the 15 pound whatever, it'll still dent, but it's unlikely the sheathing will be breached, unless it has a sharp point or is dropped with a lot of force and this is the whole point of the sheathing.

To recap, always sheath Douglas fir or it'll check and split. This species also needs a fairly heavy sheath just to prevent the checking. Dynel (fabric) would be the better option for abrasion resistance or multiple layers of light regular cloth. Top coat with a tough durable paint or truck bed liner (recommended).

Did not know you allow conifer wood on marine ply surfaces in the US. Okume, Sapeli, Meranti are the surfaces common on EU marine ply. And that stuff is fine with some EP and a paint cover. The paint will show obvious when its worn and time has come for some effort.

So, sorry for insufficient advice.
Richard