Epoxy under plywood floor question

[Larry C]

Rob,
Epoxy is quite different than varnish or paint. Unthined Epoxy will bond to the surface of wood very well without deep penetration. Just do an experiment comparing a piece wood sealed using your method with varnish, and another piece sealed with unthined epoxy. Let them both cure for several weeks. Now... try to remove the varnish and the epoxy by scraping & or sanding. IMO/ experience, the epoxy will be much more difficult to remove, even though the surface is not penetrated deeply.
I have always understood that never thinning epoxy on something intended to seal out water is a good practice. For repairing rotted wood in a non structural application, it may be fine, but as Andrew, and Wests info states, thinned epoxy leaves a soft, porous surface that is not water proof.
Straight epoxy bonds well to bare wood, and leaves a semi hard flexible to
very hard rigid surface depending on the epoxy. The epoxy coating will be mostly water proof (depending on how many layers) and, much harder than a varnish only coating. Deep penetration does not appear to be necessary.
The epoxy does need to be protected from UV, and if finishing bright, varnish is a popular choice.

My $.02

Larry C.

Thank you Larry.

From reading all the posts about epoxy, it does seem to be/behave much differently than traditional finishes.

Does the epoxy adhere to, but not penetrate the wood, even the softer areas?
With paint or varnish, the softer wood would soak up the material like a sponge.
If it does "bridge" those areas, it sure would be an easier finish to apply!

Rob

Rob,
Epoxy does penetrate the wood, but not as much as your thinned varnish. I read about a controlled test that was done to see how much actual penetration epoxy had in Western Red Cedar, a popular boat building wood that is very soft. Contrary to popular belief, the actual penetration with an epoxy that is considered thin was only a few 1/1000ths of an inch. However, this seems to be enough to hang onto the wood without failure.

Yes it does soak into softer areas more, and it's a good practice to continue applying more epoxy to those areas. The practice I follow when laminating with fiberglass is to precoat the bare wood, and let it set up till it's tack free, and then apply the glass, and wet it out.

The seal coat helps prevent starving the glass in areas that the epoxy soaks into more than others (softer areas). If you wet the glass directly over the wood, the epoxy will soak in the softer areas more than others, possibly leaving the glass starved for epoxy in some areas.

If you know what you are looking for (resin starved glass), you can just keep adding more epoxy to these areas. However, those that are not experienced with direct laminating over wood, should probably do the seal coat method. Falling temperatures during application also help draw the epoxy into the wood.

I personally use the seal coat method to make the lightest possible layup for racing kayaks, but I also do direct lamination to save time if weight is not an issue.
Of course vacuum bagging probably offers the greatest epoxy penetration of all methods.

Larry C

[48Rob]

Thank you for the explanation Larry.

Rob

[afreegreek]

I've never tried to measure the penetration, or the difference in penetration between thinned and straight epoxy but I've sanded plenty off.. what I've discovered is the epoxy will penetrate evenly for a distance (as in a continuous unbroken surface) then it penetrates further in tiny spots (like little threads).. what you end up with is something like this... TTTTTTTTTT .. a solid surface on the outside with little spikes going much deeper..

the other thing I've found is epoxy on solid wood that has been planed or sanded does not penetrate as far as plywood veneer.. plywood veneer is rotary cut and has many cracks and fissures in it that allow the epoxy to penetrate even further.. this probably doesn't mean much in the adhesion department but it sure makes a difference when you're trying to sand it off to get back to bare wood.. you may sand right through a layer trying to get past it all..

anyway, what matters is the solid surface of epoxy is thin and quite brittle.. this is why epoxy alone is not a great sealer.. the first time a rock or other object hits the underside of the trailer the seal is broken and moisture will soak like a sponge... after that water gets in it won't be long before you've got a blister.. blisters that are not repaired will simply grow.. one way to get past this is to use fibre reenforcement.. but now you're talking more money... the fibre will thicken the coating of epoxy and add some strength so the impact may not cause a fracture but limit it to a dent..

I can't see spending the time and money doing this to try and protect a $40 sheet of plywood when for less money you could just buy marine grade ply and wipe on a few coats of boiled linseed oil and be done..

boiled linseed oil has been around for hundreds of years and has a proven track record.. it's the base for many paints and varnishes, it's cheap and effective.. it penetrates very deeply, it will not crack, it won't peel off, you can re apply as many times as needed.. and best of all, it will keep liquid water out and let water vapour escape.. the latter being the key to preventing rot..

sometimes in this modern world of high tech gadgets we forget that an axe is still a very effective tool...

[jmedclay]

Wish I'd known that a year ago, along with a few other things. But then again, few wouldn't do it differently the second time around I think.

A lot of old technology is excellent technology.

[48Rob]

I've never tried to measure the penetration, or the difference in penetration between thinned and straight epoxy but I've sanded plenty off.. what I've discovered is the epoxy will penetrate evenly for a distance (as in a continuous unbroken surface) then it penetrates further in tiny spots (like little threads).. what you end up with is something like this... TTTTTTTTTT .. a solid surface on the outside with little spikes going much deeper..

the other thing I've found is epoxy on solid wood that has been planed or sanded does not penetrate as far as plywood veneer.. plywood veneer is rotary cut and has many cracks and fissures in it that allow the epoxy to penetrate even further.. this probably doesn't mean much in the adhesion department but it sure makes a difference when you're trying to sand it off to get back to bare wood.. you may sand right through a layer trying to get past it all..

anyway, what matters is the solid surface of epoxy is thin and quite brittle.. this is why epoxy alone is not a great sealer.. the first time a rock or other object hits the underside of the trailer the seal is broken and moisture will soak like a sponge... after that water gets in it won't be long before you've got a blister.. blisters that are not repaired will simply grow.. one way to get past this is to use fibre reenforcement.. but now you're talking more money... the fibre will thicken the coating of epoxy and add some strength so the impact may not cause a fracture but limit it to a dent..

I can't see spending the time and money doing this to try and protect a $40 sheet of plywood when for less money you could just buy marine grade ply and wipe on a few coats of boiled linseed oil and be done..

boiled linseed oil has been around for hundreds of years and has a proven track record.. it's the base for many paints and varnishes, it's cheap and effective.. it penetrates very deeply, it will not crack, it won't peel off, you can re apply as many times as needed.. and best of all, it will keep liquid water out and let water vapour escape.. the latter being the key to preventing rot..

Thank you for further explaining.

anyway, what matters is the solid surface of epoxy is thin and quite brittle.. this is why epoxy alone is not a great sealer.. the first time a rock or other object hits the underside of the trailer the seal is broken and moisture will soak like a sponge... after that water gets in it won't be long before you've got a blister.. blisters that are not repaired will simply grow.. one way to get past this is to use fibre reenforcement.. but now you're talking more money... the fibre will thicken the coating of epoxy and add some strength so the impact may not cause a fracture but limit it to a dent..

I can't see spending the time and money doing this to try and protect a $40 sheet of plywood when for less money you could just buy marine grade ply and wipe on a few coats of boiled linseed oil and be done..

When presented this way, it does seem like a lot of effort for a finish that doesn't hold much promise of success...

So the marine plywood is better because; it has better? Exterior glue, and no voids?

Applying boiled linseed oil will prevent some of the water from getting in, and allow some/most of the vapor back out?
How would it work in an area where another piece of wood is in constant contact, like a floor joist, or where it contacts the steel frame?
In this scenario, water/moisture could become trapped between them.
Would the oil coated plywood around the contact area be able to breathe enough to keep the area from staying damp/moist?
Would a person have to apply another coat(s) every year?

When I'm trying to protect a trailer floor that will be exposed to road hazards and water spray, I use oil based paint, thinned for the first coat or two, and apply until I feel the wood is encapsulated, then apply a thick rubberized undercoating to protect the finish from rocks, etc.
I also use a self sealing sheet flashing product to isolate the wood from the metal frame, to prevent chafing and breaking the finish.
All bolt holes and screw holes are well sealed so that no channels are left for water to get under the waterproof finish.

If marine plywood and a couple coats of oil will perform as well, or better, then that is good news.

Rob

[afreegreek]

rotary veneer is made using a long knife held against a turning log.. a sheet of veneer comes off like a roll of paper.. because of cutting stress from the knife and the fact you're making something that was round lay flat you produce cracks in one side of the veneer.. thin veneer from large diameter logs has cracks that are so fine and so narrow there's little visible difference between the tight side and the loose side... as the log gets smaller and the slice gets thicker, these cracks get deeper, open wider, and are easily seen..

what you end up with is like corduroy cloth.. smooth on one side, and ribbed on the other.. one is fine, it's from the thin slice off the large log.. the other is the thick slice off the small log..

when ply is laid up, it's veneers are run through steel rollers that apply a controlled thickness of adhesive... this thickness is adjusted to suit the spec of the sheet.. exterior ply spec is much less than marine.. a thinner glue line is applied, and it's applied to (in general) a much coarser veneer surface..

what this means in the end product is glue line contact (face to face) that may be as little 25% of the total surface area.. this is not only weaker bond but also leaves voids for moisture to collect in.. this is one of the major factors in de-lamination.. moisture in the voids going through freeze thaw cycles can quickly blow a sheet apart..

marine ply spec is a much thicker glue line and is (in general) applied to a much smoother veneer surface.. what this means is a glue line that is near 100% (face the face) contact.. no voids..

[Moho]

I'm glad to see the CPES myths being dealt with in a factual manner. I've started typing out quite a few times opposing the product but just ended up not completing it due to the numerous people who avidly support the product here.

Sometimes in this modern world of high tech gadgets we forget that an axe is still a very effective tool...

I couldn't agree more.....

[Larry C]

.



anyway, what matters is the solid surface of epoxy is thin and quite brittle.. this is why epoxy alone is not a great sealer.. the first time a rock or other object hits the underside of the trailer the seal is broken and moisture will soak like a sponge... after that water gets in it won't be long before you've got a blister.. blisters that are not repaired will simply grow.. one way to get past this is to use fibre reenforcement.. but now you're talking more money... the fibre will thicken the coating of epoxy and add some strength so the impact may not cause a fracture but limit it to a dent..

I think epoxy is a great sealer of wood. Each brand has it's own hardness, and I have never found one that was actually brittle. Wests system is a very hard epoxy, but not brittle (hammer test). System 3 is a little softer, and Raka is softer yet. I have used epoxy as sealer for years, and never had water intrusion failure, even when the surface was scraped to the wood by a rock. Water did not migrate from the gouged area even though I didn't fix it till the end of the season. Seams are the area that epoxy alone has possible problems cracking from movement, but the addition of fiberglass at the seams solves that problem.

I helped a friend that didn't have much money, build 2 kayaks using cheap door skin ply ($6 sheet) This type plywood is full of voids (flashlight test) and isn't recommended for exterior use. The boats were simple 4 panel hard chine hulls, and only the seams had fiberglass tape. The rest of the plywood, inside and out was 3 coats of epoxy. He uses and abuses these boats by leaving them outside, not really taking good care of them. As of yet, I see no sign of water intrusion on either one.

I do agree using marine ply is a good idea, and I an doing so on the sides of my build. However, finding marine plywood is sometimes difficult.
I had to drive 150 miles round trip to get mine.

Also, I use linseed oil on lots of projects, but linseed oil on bare wood that is left bare will only last awhile, and has to be redone periodically. This would be difficult on a teardrop floor.

"afreegreek"

I am not disputing your opinion, which I value, and have learned from on several occasions. It is just my own personal observation using epoxy.

Larry C

[jstrubberg]

I wouldn't use linseed oil for an exterior finish. It's very good at protecting wood, but it's not a sealer. It actually sinks down into the wood fiber itself. The top layer will end up exposed to both UV and water unless you are dilligent about wiping on coat after coat on a regular basis.

Linseed oil is a great finish for furniture, and I've used it to restore a side table and a handful of wooden longbows. You can mix linseed oil with shellac to create what used to be called french polish. It will build a layered finish, but it's a pain to maintain as it's very soft.

I would stick with an epoxy or varnish for somethign like a camper that you expect to sit out in the weather. I've used a mixture of two part epoxy and acentone wiped on bows as a tough, flexible finish. Wonder how it would work on a trailer?

[afreegreek]

.



anyway, what matters is the solid surface of epoxy is thin and quite brittle.. this is why epoxy alone is not a great sealer.. the first time a rock or other object hits the underside of the trailer the seal is broken and moisture will soak like a sponge... after that water gets in it won't be long before you've got a blister.. blisters that are not repaired will simply grow.. one way to get past this is to use fibre reenforcement.. but now you're talking more money... the fibre will thicken the coating of epoxy and add some strength so the impact may not cause a fracture but limit it to a dent..

I think epoxy is a great sealer of wood. Each brand has it's own hardness, and I have never found one that was actually brittle. Wests system is a very hard epoxy, but not brittle (hammer test). System 3 is a little softer, and Raka is softer yet. I have used epoxy as sealer for years, and never had water intrusion failure, even when the surface was scraped to the wood by a rock. Water did not migrate from the gouged area even though I didn't fix it till the end of the season. Seams are the area that epoxy alone has possible problems cracking from movement, but the addition of fiberglass at the seams solves that problem.

I helped a friend that didn't have much money, build 2 kayaks using cheap door skin ply ($6 sheet) This type plywood is full of voids (flashlight test) and isn't recommended for exterior use. The boats were simple 4 panel hard chine hulls, and only the seams had fiberglass tape. The rest of the plywood, inside and out was 3 coats of epoxy. He uses and abuses these boats by leaving them outside, not really taking good care of them. As of yet, I see no sign of water intrusion on either one.

I do agree using marine ply is a good idea, and I an doing so on the sides of my build. However, finding marine plywood is sometimes difficult.
I had to drive 150 miles round trip to get mine.

Also, I use linseed oil on lots of projects, but linseed oil on bare wood that is left bare will only last awhile, and has to be redone periodically. This would be difficult on a teardrop floor.

"afreegreek"

I am not disputing your opinion, which I value, and have learned from on several occasions. It is just my own personal observation using epoxy.

Larry C

I'm not trying to convince anyone that my way is better than the rest.. what I'm trying to do is make people aware that there are other ways of skinning the cat..

I too have made kayaks and small boats using epoxy and epoxy over glass and had good results.. I've also had a few failures too.. in addition, I've had a couple of decades worth of experience repairing failures that others have had with their boats.. everything from superficial scratches and dents to recovered vessels that have been soaking in water for weeks after they've sunk..

if money was no object and skill level was high it would be a different story, but lots people on this site have little of either.. someone who is in their garage armed with a jig saw, a dremel and a stack of Lowes lumber probably cringes at the price of epoxy systems and gets a knot in their gut when they start mixing a few hundred dollars of resin they have no experience with.. all I'm trying to do is make them aware that it's not the only way..

I used to teach woodwork and the one thing I learned doing that was not to throw people in the deep end of the pool.. nothing turns people off faster than a failure, especially one that cost them a lot of time and money.. epoxy is great stuff but it's expensive and leaves no room for error.. it's a one shot deal.. boiled linseed oil is cheap, practically fool proof, easy to maintain and very effective ..

[afreegreek]

I wouldn't use linseed oil for an exterior finish. It's very good at protecting wood, but it's not a sealer. It actually sinks down into the wood fiber itself. The top layer will end up exposed to both UV and water unless you are dilligent about wiping on coat after coat on a regular basis.

Linseed oil is a great finish for furniture, and I've used it to restore a side table and a handful of wooden longbows. You can mix linseed oil with shellac to create what used to be called french polish. It will build a layered finish, but it's a pain to maintain as it's very soft.

I would stick with an epoxy or varnish for somethign like a camper that you expect to sit out in the weather. I've used a mixture of two part epoxy and acentone wiped on bows as a tough, flexible finish. Wonder how it would work on a trailer?

raw linseed oil and boiled (polymerized) linseed oil are two different things.. they will both soak into the wood but raw linseed oil will not harden or build a coating on the surface of the wood.. boiled linseed oil will.. it is also a great sealant for wood.. any oils that saturate wood cells will keep out liquid water.. it will allow water vapour in and it just as easily lets it escape too and there's nothing wrong with that.. in fact moisture in wood is what keeps it supple.. it's when moisture content reaches high levels that it becomes a problem....... sure boiled linseed oil has to be maintained but so does everything else..

btw, true varnish is primarily boiled linseed oil with some resin and solvent..

http://en.wikipedia.org/wiki/Varnish