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View Full Version : Best finish for ply floorboards?



FlyingDuck
17th July 2005, 10:55 AM
Just finished making new marine ply floorboards for my boat, which is a 5.1m centre console Quintrex. I am just wondering what is the best finish to protect the ply against the expected years of abuse from salt, sun, sea, & fish guts.

Have been recommended stuff called "Tredgrip" by evelon. Any body used this before?

Was thinking, at least for underneath the boards, of a thick coat of bitumen paint. Any suggestions?

Daddles
17th July 2005, 12:03 PM
Are you looking for non-slip as well?
I don't know that you're going to find something that will last for ever, certainly no top coat. I don't know this Tredgrip stuff so I can't comment on that. The problem with wood is not the top coat itself, but when that topcoat gets penetrated allowing water in which leads to rot. Floorboards on a tinny are going to cop a hard life with things being dropped on them (anchors, gaffs, esky's, fishing buddies, etc) so this is the route I'd take.

Get one of the very thin, epoxy, timber 'preservatives'. These are very, very thin epoxies and soak right into the timber protecting the top layer of the ply. The fumes are pretty ghastly so it's an outside job with protection but the upside is that your ply is not sealed but not with a top layer that can be broken. Then apply whatever you want over the top of it, lots of it.

Drill all holes before you do this (screw holes, etc) and make sure they are soaked in the epoxy because if you drive a screw through the wood after sealing it, you are breaking that seal and letting in water. Personally, I bed all screws, bolts etc in sikafex but that's only practical if you are leaving the part in place for long periods.

The other thing you'll need to consider is the curing time of the top coat. Just because something is 'dry' doesn't mean it's ready for abuse. For example, the enamels I use on my hulls are dry within a couple of days but take a couple of months before they are hard enough to take the knocks of boating life.

How about a piccy of the boat? What other additions are you planning (rod holders, etc)?

Cheers
Richard

bitingmidge
17th July 2005, 01:35 PM
I would suggest giving it a couple of coats of epoxy first, but Richard would argue with me!

:D :D :D

P

Daddles
17th July 2005, 02:17 PM
If you want to go the epoxy route, either start with the timber preservative (CPES or Shipways or whatever the local product is) that I mentioned earlier, then give it a few coats of epoxy. The trouble with epoxy is that is it rigid. Floorboard will be flexed and so the epoxy will crack, letting in the moisture. A flexible coating would be best I would have thought.

Cheers
Richard
doncha love spending other peoples money :D

STEPHEN MILLER
18th July 2005, 10:39 PM
Start another fight, epoxy is quite suitable to use on the floor of a boat epoxy will flex to a certain extent other wise it would be useless as a boat building material. Our 10m yacht is epoxy and dynel sheet over gabbon ply thats hull deck floors etc.
One point make sure you do both sides of the floor drill all screw holes over size and epoxy.
Where my son has recently redone the floor in a boat at his work where it was fibreglassed on top but not the bottom and the floor rotted from the bottom up.
The floors in the boats they build are fibreglassed on top with a chopper gun and coated with resin on the bottom
So epoxy the lot than use and no slip top coat as that is the bit that gets the wear something like International interdeck etc :)

Daddles
18th July 2005, 10:46 PM
Hmm, so the dreaded poxy is flexible eh? I wouldn't have thought so.

Richard

journeyman Mick
18th July 2005, 11:40 PM
Flying Duck,
we used to use a product called "tredgrip" on commercial aluminium boats, It was a thick rubbery paint appled with a textured roller and seemed to work and last quite well. Don't know if it's the same as what you're looking at, but if it is it should last for a long time on a private boat.

Mick

FlyingDuck
19th July 2005, 09:25 PM
Yep, your tredgrip sounds like what I have got here. What sort of an undercoat primer did you use? On the can it just says to use a "primer" and the man in the shop just recommended some standard 3 in 1 water based primer, but looking at Daddles first post, maybe the way to go is the epoxy timber preservative.

I will post some pics soon.

FlyingDuck
19th July 2005, 09:26 PM
Journeyman Mick, another quick quesiton. Do you have to use a textured roller with this stuff to get the non slip surface, or would a paint brush also work?

journeyman Mick
19th July 2005, 11:31 PM
FD,
it was more than 10 years ago so the memory is a bit vague, As it was on Aluminium I'm assuming that we used an etch primer of some sort. The more textured the applicator is that you use, the grippier the paint will be.

Mick

delamaree
20th July 2005, 11:13 PM
spot on with the epoxy, only do both sides of the ply as tar will lift in the humidity of an underfloor environment. For non - slip, mix in aluminium powder to your final coat. Easy to clean, cheap, long lasting, even looks kinda pretty.

Boatmik
6th August 2005, 11:53 PM
If you want to go the epoxy route, either start with the timber preservative (CPES or Shipways or whatever the local product is) that I mentioned earlier, then give it a few coats of epoxy. The trouble with epoxy is that is it rigid. Floorboard will be flexed and so the epoxy will crack, letting in the moisture. A flexible coating would be best I would have thought.
Howdy Richard,

Nice to run into you at the working with wood show.

I was wondering what did the "dreaded (e)pox(y)" do?

How did it crack - where did it crack - what brand - what substrate?

I haven't had any such problems, but would like to know about yours!

Generally the boatbuilding epoxies are supposed to have a similar elongation to timber - ie they will break about the same time the timber will break. Some have a better elongation than others (Uni of Queensland did some testing on a stress/strain machine which was quite interesting about a decade ago).

So please tell me about your experience!

MIK
http://www.ozemail.com.au/~storerm
Wooden boat designs.

delamaree
10th August 2005, 06:04 PM
Ok, dispelling the myth, epoxy flexes. Not actually the epoxy - the substrate beneath it be it timber, steel or alloy. So epoxy "gives" as the substrate flexes. This depends on the amount of flex in the substrate and the thickness of epoxy. One inch thick epoxy will flex up to 2mm in a long substrate without cracking but over a shorter length will shear at the join lines of the substrate - particularly timber.

Ply boards flex about up to 5mm when correctly fixed (span / thickness) as a floor material and this amount is usually localised flexing from concentrated weights - big heavy things that usually take more beer out of the esky than they brought with them and rarely catch fish, often heard complaining about the freshness or suitability of the bait.

Each mm thickness of epoxy will "give" to about the same degree as if it were dry enamel paint - ie plenty of flex (11%) provided it is over some length. Epoxy will always crack at joints, seams and the like where the stresses are very large as a proportion of the area that absorbs that stress or flex. Epoxy is a short chain polymer thingy so will always suffer from localised stresses. This 11% remains the same provided the length is proportional - ie thicker requires longer lengths. So the real problem is how thick for any given length.

My honest answer is as thin as you can conceivably manage given your structural requirements. If laying glass, then 1mm thicker or 1.5 allowing for fairing, if clear coating then as thin as can give you the finish you require. Remember though, epoxy WILL add stiffness of about 10% per application eg for a 9mm ply this will equate roughly to the same stiffness as a 10mm ply for each application of the same thickness.

I have read many threads where people want to turn a thin shell into a sea-going vessel. If you want to double the serviceability of a thin ply then you crapped out and should have built the vessel differently in the first place, or purchased a more heavily built vessel. Everything has limits and epoxy coating timber is no substitute for a well built timber vessel suited to its environment.

For anyone still here on my wild ramble I am fantastically intruiged by the recyled plastic sheets available in 2400X1200 as an invincible ply substitute. Anyone who knows anything please contact me at [email protected]

Tony

Daddles
10th August 2005, 10:16 PM
So epoxy flexes, so it does work as a protector (ie, it doesn't crack), but you have to be careful about thickness - more isn't better.

Is that the right message to get out of this?

Richard

delamaree
11th August 2005, 12:40 AM
With epoxy, more is not necessarily better but more correctly, un-needed. Take for example a 50 foot vessel with lapstrake plank. This vessel under sea-going conditions is designed to be wracked or twisted up to 1 inch or 25mm over its length and retain its watertight integrity. Applying epoxy and glass over such a hull greater than the structural bonding depth of the epoxy and glass ie where it becomes filler, is asking for trouble. I have needed to apply epoxy and microballon mixtures of up to 10 inches thick on some parts of hulls but have made the owners vigilantly aware of the possibility of damage to the area and with their agreement.

As epoxy is a short chain bond it will develop stress cracks below its surface if applied too thickly with the result that a touch on the wharf knocks off a chunk. This is where most of the epoxy "bad" info comes from. On the good side, if applied over glass on a 50 footer to about 2.5 times the glass weight in mm depth it becomes an impenatrable shield and no amount of abuse will injure it. If the plan is to heavily epoxy then a composite of layers of finer glass impregnated into epoxy is the only way as you build layers to the final thickness. Bloody time consuming process though.

In the case of small vessels - say 20ft and under, without structural glassing a maximum of 2mm movement will not damage the epoxy coating - that is 1mm inward to 1mm outward or combinations of. If the plan is for rougher work than this then I suggest a fine glass mat (or substitutes thereof) over the hull impregnated with epoxy to 1.5mm over the glass before fairing.

In all, epoxy will flex, will crack depending on thickness, application and suitability for the task at hand. But the likelyhood of problems occuring can be planned for and overcome in the beginning.

Tony
[email protected]