Epoxy under plywood floor question

[afreegreek]

I have used 1/2" plywood for the floor on my trailer.
I, first, coated the underside with several coats of CPES.
I, then, coated the underside with several coats of Raka epoxy.

Since the underside of the trailer will not be in direct sunlight, I figured that I would not need to provide uv protection.

Anyone have comments? suggestions? experiences?


.

I would like input on whether I need to provide UV protection for the exterior underside of the trailer, which is epoxy coated plywood.

In general, is there reflection of the sun's UV rays to this area?


.

no you don't need UV protection for epoxy that is not directly exposed to UV light.. as far as I understand UV light is absorbed or diffused by most surfaces and not reflected.. try lying on a hammock at the beach and see if you get a tan on your back... UV is a very narrow band of frequency and is easily disrupted..

from Wiki..
Many polymers used in consumer products are degraded by UV light, and need addition of UV absorbers to inhibit attack, especially if the products are exposed to sunlight. The problem appears as discoloration or fading, cracking, and, sometimes, total product disintegration if cracking has proceeded sufficiently. The rate of attack increases with exposure time and sunlight intensity.
It is known as UV degradation, and is one form of polymer degradation. Sensitive polymers include thermoplastics, such as polypropylene, polyethylene, and poly(methyl methacrylate) as well as speciality fibers like aramids. UV absorption leads to chain degradation and loss of strength at sensitive points in the chain structure. They include tertiary carbon atoms, which in polypropylene occur in every repeat unit. Aramid rope must be shielded with a sheath of thermoplastic if it is to retain its strength. The impact of UV on polymers is used in nanotechnology, transplantology, X-ray lithography and other fields for modification of properties (roughness, hydrophobicity) of polymer surfaces. For example, a poly(methyl methacrylate) surface can be smoothed by vacuum ultraviolet (VUV).[30]


IR spectrum showing carbonyl absorption due to UV degradation of polyethylene
In addition, many pigments and dyes absorb UV and change colour, so paintings and textiles may need extra protection both from sunlight and fluorescent bulbs, two common sources of UV radiation. Old and antique paintings such as watercolour paintings, for example, usually must be placed away from direct sunlight. Common window glass provides some protection by absorbing some of the harmful UV, but valuable artifacts need extra shielding. Many museums place black curtains over watercolour paintings and ancient textiles, for example. Since watercolours can have very low pigment levels, they need extra protection from UV light. Tinted glasses, such as sunglasses also provide protection from UV rays.

[eamarquardt]

I just love it when a good "myth" is laid to rest!!!

I'd go swimming now but I just ate and have to wait a half hour.

Cheers,

Gus

What do you mean, 1/2 hour?? I was assured many years ago, it had to be at least 1 hour!

My mother was an RN. Who ya gonna believe?

Cheers,

Gus

[Larry C]

Here's some more interesting reading from the highly respected Wests System.

http://www.epoxyworks.com/14/ThinningEpoxy.html

3) Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous.

If you want to know the ingredients of the product you wish to use, check the MSDS, it lists all ingredients, I believe it's listed with the greatest concentration shown first, with lower concentrations in descending order.
IMO/ you should always read the MSDS before purchasing a product to be sure it won't cause you possible harm, and to to know if your actually getting what you think you are.

Here's the MSDS for couple of popular products used by members:

CPES:

http://www.rotdoctor.com/products/msdspdf/CPES_WARM_PART_A&B.pdf

Wests System 105 Resin W/ 207 Hardener:

http://www.westsystem.com/ss/assets/MSDS/MSDS105.pdf
http://www.westsystem.com/ss/assets/MSDS/MSDS207.pdf


Raka 127 Resin w/ 350 Hardener:


http://www.raka.com/raka%20127%20900%20tabletop%20superfast.html
[url]http://www.raka.com/epoxy%20hardener350.html[url][/url]

reading the manufacturer's MSDS is always a good idea but, it's not always 100% of the information.. usually they only list constituents that are toxic or flammable or deemed to be potentially hazardous or reactive in some way.. many times all of the constituents are not included on the MSDS.. it's about safe use and handling for the user and for helping medical personnel know what you've been exposed to.. in some industries MSDS are also given to the local fire department along with quantities stored and their location in the facility..

it's correct that the list goes from most to least but does not always give an indication of true proportion... #1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

here's a link on understanding what information is included and how to understand it...

http://www.nmsu.edu/safety/programs/che ... S-info.htm

I agree you don't get complete information of the true ingredients with some MSDS lists. They are intended mostly for safe handling, and emergency response, they tend to hide proprietary info. However, I don't understand what you mean by:

#1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

It may only be parts per million, but it's still the second greatest ingredient in the mix, unless I am reading this wrong?
Are you saying the MSDS is ONLY listing the constituents that may be hazardous, and that may only be a small percentage of the total of all ingredients?? If that's the case, we have been reading the MSDS info incorrectly for years where I work?

Here's the MSDS from Raka's popular 127 resin:

1. INGREDIENTS:
Reaction products of Epichlorohydrin and Bisphenol A CAS # 025-085-99-8 >80%
Alkyl Glycidyl Ether CAS # 068609-97-2 <20%
Benzyl Alcohol CAS # 100-51 -6 <10%
The balance of materials are trade secrets CAS # Proprietary <5%

From what I read, which may be totally incorrect, ingredient #1 is over 80% of the total mix, and ingredient # 2 is less than 20%, but more than 10%. It doesn't state whether the percentages are by weight or volume. Do these numbers represent the total volume/weight, or just the hazardous portions?
I don't see this explained in the link you provided, but I may have not delved deep enough.

[Larry C]

I agree you don't get complete information of the true ingredients with some MSDS lists. They are intended mostly for safe handling, and emergency response, they tend to hide proprietary info. However, I don't understand what you mean by:

#1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

It may only be parts per million, but it's still the second greatest ingredient in the mix, unless I am reading this wrong?
Are you saying the MSDS is ONLY listing the constituents that may be hazardous, and that may only be a small percentage of the total of all ingredients?? If that's the case, we have been reading the MSDS info incorrectly for years where I work?

Here's the MSDS from Raka's popular 127 resin:

1. INGREDIENTS:
Reaction products of Epichlorohydrin and Bisphenol A CAS # 025-085-99-8 >80%
Alkyl Glycidyl Ether CAS # 068609-97-2 <20%
Benzyl Alcohol CAS # 100-51 -6 <10%
The balance of materials are trade secrets CAS # Proprietary <5%

From what I read, which may be totally incorrect, ingredient #1 is over 80% of the total mix, and ingredient # 2 is less than 20%, but more than 10%. It doesn't state whether the percentages are by weight or volume. Do these numbers represent the total volume/weight, or just the hazardous portions?
I don't see this explained in the link you provided, but I may have not delved deep enough.

I think I answered my own question.

A little Google research:

MSDS

SECTION 2 - HAZARDOUS INGREDIENTS

This section lists all the hazardous ingredients found in a product (unless an ingredient is a trade secret). The concentration of each ingredient is also listed. Concentration means the weight of the ingredient as a percentage of the weight of the product. The % Concentration may be expressed as a ratio of:

Weight to weight
Weight to volume, or
Volume to volume

of the total mixture.

[afreegreek]

Here's some more interesting reading from the highly respected Wests System.

http://www.epoxyworks.com/14/ThinningEpoxy.html

3) Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous.

If you want to know the ingredients of the product you wish to use, check the MSDS, it lists all ingredients, I believe it's listed with the greatest concentration shown first, with lower concentrations in descending order.
IMO/ you should always read the MSDS before purchasing a product to be sure it won't cause you possible harm, and to to know if your actually getting what you think you are.

Here's the MSDS for couple of popular products used by members:

CPES:

http://www.rotdoctor.com/products/msdspdf/CPES_WARM_PART_A&B.pdf

Wests System 105 Resin W/ 207 Hardener:

http://www.westsystem.com/ss/assets/MSDS/MSDS105.pdf
http://www.westsystem.com/ss/assets/MSDS/MSDS207.pdf


Raka 127 Resin w/ 350 Hardener:


http://www.raka.com/raka%20127%20900%20tabletop%20superfast.html
[url]http://www.raka.com/epoxy%20hardener350.html[url][/url]

reading the manufacturer's MSDS is always a good idea but, it's not always 100% of the information.. usually they only list constituents that are toxic or flammable or deemed to be potentially hazardous or reactive in some way.. many times all of the constituents are not included on the MSDS.. it's about safe use and handling for the user and for helping medical personnel know what you've been exposed to.. in some industries MSDS are also given to the local fire department along with quantities stored and their location in the facility..

it's correct that the list goes from most to least but does not always give an indication of true proportion... #1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

here's a link on understanding what information is included and how to understand it...

http://www.nmsu.edu/safety/programs/che ... S-info.htm

I agree you don't get complete information of the true ingredients with some MSDS lists. They are intended mostly for safe handling, and emergency response, they tend to hide proprietary info. However, I don't understand what you mean by:

#1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

It may only be parts per million, but it's still the second greatest ingredient in the mix, unless I am reading this wrong?
Are you saying the MSDS is ONLY listing the constituents that may be hazardous, and that may only be a small percentage of the total of all ingredients?? If that's the case, we have been reading the MSDS info incorrectly for years where I work?

Here's the MSDS from Raka's popular 127 resin:

1. INGREDIENTS:
Reaction products of Epichlorohydrin and Bisphenol A CAS # 025-085-99-8 >80%
Alkyl Glycidyl Ether CAS # 068609-97-2 <20%
Benzyl Alcohol CAS # 100-51 -6 <10%
The balance of materials are trade secrets CAS # Proprietary <5%

From what I read, which may be totally incorrect, ingredient #1 is over 80% of the total mix, and ingredient # 2 is less than 20%, but more than 10%. It doesn't state whether the percentages are by weight or volume. Do these numbers represent the total volume/weight, or just the hazardous portions?
I don't see this explained in the link you provided, but I may have not delved deep enough.

I'm just saying that in general terms as there's no prescribed or mandated way of listing constituents or their proportions.. a lot is left up to the discretion of the manufacturers of the product.. some will give exact proportions and some give none.. for example the MSDS for CPES which has a lot of constituents may say < or > 50% for isopropyl alcohol or may just list it as a constituent in a descending order with other constituents and give no percentage at all.. I've seen MSDS that do both.. I think a lot of manufacturers want to give you as little of that information as possible so as to not give you a recipe for their product, others will give you the most they have knowing it's the process of manufacturing that is more important than the constituents.. a list of ingredients alone will not get you an apple pie.

usually the percentages are by weight but some are given as volume, some are a percentage of allowable exposure rates.. these are listed as TVL, PEL, STEL, LD50 etc..

also there's a number associated with each constituent, that number is a reference number to the MSDS of the constituent itself.. isopropyl alcohol for example.. this will give you access to the latest MSDS on that constituent so as to make sure there's no confusion with the name.. 2-propanol, isopropanol, isopropyl alcohol, rubbing alcohol, iPrOH which are all the same thing..

[Larry C]

Here's some more interesting reading from the highly respected Wests System.

http://www.epoxyworks.com/14/ThinningEpoxy.html

3) Water resistance of a piece of wood is not enhanced by deep penetration. Wrapping wood in plastic makes a pretty good waterproof seal without any penetration at all. Likewise, an epoxy coating on the surface is more water-resistant than a thinned epoxy coating that has penetrated deeply into the wood because, in most instances, the epoxy thinned with solvent is porous.

If you want to know the ingredients of the product you wish to use, check the MSDS, it lists all ingredients, I believe it's listed with the greatest concentration shown first, with lower concentrations in descending order.
IMO/ you should always read the MSDS before purchasing a product to be sure it won't cause you possible harm, and to to know if your actually getting what you think you are.

Here's the MSDS for couple of popular products used by members:

CPES:

http://www.rotdoctor.com/products/msdspdf/CPES_WARM_PART_A&B.pdf

Wests System 105 Resin W/ 207 Hardener:

http://www.westsystem.com/ss/assets/MSDS/MSDS105.pdf
http://www.westsystem.com/ss/assets/MSDS/MSDS207.pdf


Raka 127 Resin w/ 350 Hardener:


http://www.raka.com/raka%20127%20900%20tabletop%20superfast.html
[url]http://www.raka.com/epoxy%20hardener350.html[url][/url]

reading the manufacturer's MSDS is always a good idea but, it's not always 100% of the information.. usually they only list constituents that are toxic or flammable or deemed to be potentially hazardous or reactive in some way.. many times all of the constituents are not included on the MSDS.. it's about safe use and handling for the user and for helping medical personnel know what you've been exposed to.. in some industries MSDS are also given to the local fire department along with quantities stored and their location in the facility..

it's correct that the list goes from most to least but does not always give an indication of true proportion... #1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

here's a link on understanding what information is included and how to understand it...

http://www.nmsu.edu/safety/programs/che ... S-info.htm

I agree you don't get complete information of the true ingredients with some MSDS lists. They are intended mostly for safe handling, and emergency response, they tend to hide proprietary info. However, I don't understand what you mean by:

#1 may be say 75% and #2 may be parts per million.. most MSDS that I've seen give you no clue..

It may only be parts per million, but it's still the second greatest ingredient in the mix, unless I am reading this wrong?
Are you saying the MSDS is ONLY listing the constituents that may be hazardous, and that may only be a small percentage of the total of all ingredients?? If that's the case, we have been reading the MSDS info incorrectly for years where I work?

Here's the MSDS from Raka's popular 127 resin:

1. INGREDIENTS:
Reaction products of Epichlorohydrin and Bisphenol A CAS # 025-085-99-8 >80%
Alkyl Glycidyl Ether CAS # 068609-97-2 <20%
Benzyl Alcohol CAS # 100-51 -6 <10%
The balance of materials are trade secrets CAS # Proprietary <5%

From what I read, which may be totally incorrect, ingredient #1 is over 80% of the total mix, and ingredient # 2 is less than 20%, but more than 10%. It doesn't state whether the percentages are by weight or volume. Do these numbers represent the total volume/weight, or just the hazardous portions?
I don't see this explained in the link you provided, but I may have not delved deep enough.

I'm just saying that in general terms as there's no prescribed or mandated way of listing constituents or their proportions.. a lot is left up to the discretion of the manufacturers of the product.. some will give exact proportions and some give none.. for example the MSDS for CPES which has a lot of constituents may say < or > 50% for isopropyl alcohol or may just list it as a constituent in a descending order with other constituents and give no percentage at all.. I've seen MSDS that do both.. I think a lot of manufacturers want to give you as little of that information as possible so as to not give you a recipe for their product, others will give you the most they have knowing it's the process of manufacturing that is more important than the constituents.. a list of ingredients alone will not get you an apple pie.

usually the percentages are by weight but some are given as volume, some are a percentage of allowable exposure rates.. these are listed as TVL, PEL, STEL, LD50 etc..

also there's a number associated with each constituent, that number is a reference number to the MSDS of the constituent itself.. isopropyl alcohol for example.. this will give you access to the latest MSDS on that constituent so as to make sure there's no confusion with the name.. 2-propanol, isopropanol, isopropyl alcohol, rubbing alcohol, iPrOH which are all the same thing..

Anyway.. The bottom line, IMO, is the MAIN ingredient of a popular product here, is the same ingredient found in Coleman Fuel. Maybe that's why it's so popular, we all love our Coleman's! Nothing beats the smell of N.... in the morning!

[angib]

You should not go swimming within 24 hours of applying epoxy - before that, you won't drown, but you will splash water on the epoxy and destroy the cure.

And, on a slightly more serious note, I'm pleased to see some support for not (as in, not ever) thinning epoxy being used as a water barrier. My teaching was that the solvent will evaporate leaving voids which then allow the passage of moisture/water. So 100% un-thinned epoxy always.

I don't know where this obsession with getting penetration of liquids into wood came from. Since everyone's dad and grand-dad believed it, they seem to believe it too, but I've never seen any evidence that it actually does any good at all. I suspect it's an 'old husband's tale' (a tale told by the husbands of old wives).

[48Rob]

And, on a slightly more serious note, I'm pleased to see some support for not (as in, not ever) thinning epoxy being used as a water barrier. My teaching was that the solvent will evaporate leaving voids which then allow the passage of moisture/water. So 100% un-thinned epoxy always.

I don't know where this obsession with getting penetration of liquids into wood came from. Since everyone's dad and grand-dad believed it, they seem to believe it too, but I've never seen any evidence that it actually does any good at all. I suspect it's an 'old husband's tale' (a tale told by the husbands of old wives).

Andrew,

I've never used epoxy, and thus have zero experience with it, but I do have some experience with varnish and oil based paint.

When I am trying to protect a wood surface, plywood or dimensional lumber from moisture, the ultimate goal is to encapsulate the piece of wood.

This encapsulation can be easily done with straight "unthinned" material, "if" you use enough layers.
However, as wood has areas of the grain that are hard, and soft, or in other terms, very porous, and less porous, I find it easier to apply the first coat or two of material thinned for better/faster penetration of the soft wood areas.
Sanding after each coating is dry levels the surface and once the soft areas have absorbed enough material to be similar to the hard areas, the final coats of full strength finish are applied, to achieve a consistent encapsulation layer.

If I try to encapsulate the wood with only straight unthinned material, the finish is thick in the hard areas and thin in the soft areas.
The theory is pretty much the same as using a sanding sealer to control the amount of penetration of a stain or finish into the wood, so the appearance will be unaffected by the different absorption rates of the soft and hard areas of the wood.

If I'm going to all the trouble to encapsulate/seal the wood, applying the first coat or two thinned to give deeper penetration seems a good idea to me as invariably the finish will be scratched or marred in some way, breaking through the outer encapsulation layer.
Granted, if the damage is very deep, the layer of protection is compromised, but for the scratches that are shallow, having the deeper penetration would in my mind, offer me more insurance against the protective layer being compromised.

I'm not arguing against, or for thinning epoxy, as again I've no experience with it, but for protective finishes in general that are intended to "seal" the wood, old wives/husbands tale or not, thinning first makes sense to me.

I've seen many a do it yourselfer project ruined quickly by moisture intrusion because the person applied one or two or even three coats of a protective finish, but did not achieve "encapsulation" because the soft areas absorbed much more material than the hard areas, leaving them "unsealed".

Rob

[terryjones1]

I would like input on whether I need to provide UV protection for the exterior underside of the trailer, which is epoxy coated plywood.

In general, is there reflection of the sun's UV rays to this area?


.

no you don't need UV protection for epoxy that is not directly exposed to UV light.. as far as I understand UV light is absorbed or diffused by most surfaces and not reflected.. try lying on a hammock at the beach and see if you get a tan on your back... .

Sounds good! Thanks!


.

[Larry C]

And, on a slightly more serious note, I'm pleased to see some support for not (as in, not ever) thinning epoxy being used as a water barrier. My teaching was that the solvent will evaporate leaving voids which then allow the passage of moisture/water. So 100% un-thinned epoxy always.

I don't know where this obsession with getting penetration of liquids into wood came from. Since everyone's dad and grand-dad believed it, they seem to believe it too, but I've never seen any evidence that it actually does any good at all. I suspect it's an 'old husband's tale' (a tale told by the husbands of old wives).

Andrew,

I've never used epoxy, and thus have zero experience with it, but I do have some experience with varnish and oil based paint.

When I am trying to protect a wood surface, plywood or dimensional lumber from moisture, the ultimate goal is to encapsulate the piece of wood.

This encapsulation can be easily done with straight "unthinned" material, "if" you use enough layers.
However, as wood has areas of the grain that are hard, and soft, or in other terms, very porous, and less porous, I find it easier to apply the first coat or two of material thinned for better/faster penetration of the soft wood areas.
Sanding after each coating is dry levels the surface and once the soft areas have absorbed enough material to be similar to the hard areas, the final coats of full strength finish are applied, to achieve a consistent encapsulation layer.

If I try to encapsulate the wood with only straight unthinned material, the finish is thick in the hard areas and thin in the soft areas.
The theory is pretty much the same as using a sanding sealer to control the amount of penetration of a stain or finish into the wood, so the appearance will be unaffected by the different absorption rates of the soft and hard areas of the wood.

If I'm going to all the trouble to encapsulate/seal the wood, applying the first coat or two thinned to give deeper penetration seems a good idea to me as invariably the finish will be scratched or marred in some way, breaking through the outer encapsulation layer.
Granted, if the damage is very deep, the layer of protection is compromised, but for the scratches that are shallow, having the deeper penetration would in my mind, offer me more insurance against the protective layer being compromised.

I'm not arguing against, or for thinning epoxy, as again I've no experience with it, but for protective finishes in general that are intended to "seal" the wood, old wives/husbands tale or not, thinning first makes sense to me.

I've seen many a do it yourselfer project ruined quickly by moisture intrusion because the person applied one or two or even three coats of a protective finish, but did not achieve "encapsulation" because the soft areas absorbed much more material than the hard areas, leaving them "unsealed".

Rob

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.

[Corwin C]

And, on a slightly more serious note, I'm pleased to see some support for not (as in, not ever) thinning epoxy being used as a water barrier. My teaching was that the solvent will evaporate leaving voids which then allow the passage of moisture/water. So 100% un-thinned epoxy always.

I don't know where this obsession with getting penetration of liquids into wood came from. Since everyone's dad and grand-dad believed it, they seem to believe it too, but I've never seen any evidence that it actually does any good at all. I suspect it's an 'old husband's tale' (a tale told by the husbands of old wives).

As a frequent user of RAKA epoxy I have to agree with angib. RAKA does actually recommend slight thinning for "prime coats" however they accomplish this by moderately heating the epoxy components (before mixing) and the surface to be bonded. From their manual: "The best way to thin epoxy without losing strength is to moderately heat the unmixed resin and hardener. Warm epoxy generally gives better results and if its possible try to heat the area to which you are applying the epoxy." Be aware here again that changing curing conditions will affect other aspects of the epoxy (pot life, bond, flexibility, toughness, hardness, etc.) Warm epoxy will go off quickly if you don't get it spread out immediately after mixing.

I have thinned RAKA epoxy with solvent, but it was in a situation where no other method available to me could be employed AND it was going to be later covered by another layer of glass/epoxy (had to get it to the bottom of a deep narrow void using a syringe.) It worked well for the situation, but was against manufacturers recommendations.

Perhaps a little saying a favorite college professor used to proclaim... "Always read the directions ... even if you don't follow them. Then when $#it hits the fan you'll know why."

[48Rob]

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

[Larry C]

BTW/ While we are discussing epoxy. Raka, one of the more popular epoxies, and my current favorite is on sale at 10% off your order if you spend a total of $200 or more. It's not a hugh discount, but it helps pay for shipping.
The only caveat is you only have till Tues by 8AM to purchase. I am going to take advantage of this by purchasing the 3 gal. 127/350 kit along with some fillers. I usually try to find someone to share a 6 gal. kit for even further savings, anyone in CNY interested, if so PM me.
http://www.raka.com/

Larry C

[doug hodder]

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, it's been my experience that it will cure differently in the harder and softer areas especially on a sheet of something like just sanded fir ply. They aren't true flat to begin with and the grain runs from very soft to pretty hard. Baltic birch isn't such an issue as it has a more consistent grain. On the fir ply, I have had to do many coats, 1 to get it all sealed and 2 because I sand a lot of it off between coats to "flatten" the sheet, important if it's going to be sprayed with auto paint.

That's why I like the MDO for a painted trailer. It cuts out a lot of the work that a fir ply requires. Marine grade mahoganies aren't such an issue, more evenly grained. Just my experience with it. I'm in the never thin crowd! Doug

[48Rob]

Thank you Doug!

Rob