MDO Plywood and CPES?

[absolutsnwbrdr]

When first planning my new build, I was going to use Oak ply for the walls. Seal both sides with CPES, prime and paint the outside, and stain the inside. So in preparation for that, I ordered up some CPES. My plan has since changed, and I will be using MDO plywood, priming and painting both sides.

By definition, MDO is "a paintable surface made of plywood with a weather-resistant resin overlay bonded to the wood by heat and pressure.The overlay, which has 28% resin content, resists water, weather, wear and degradation."

So I'm thinking that the CPES isn't needed on these pieces. What do the pro's have to say?

[doug hodder]

I've sold tons of it in the sign industry. It will hold up just fine on a sign face...for a project like this that may be required to last quite a few years longer than a ply sign face...I did epoxy coat them, especially edges as always.

The epoxy will allow you to build it up in thickness and really flatten out the sides, but to many MDO is just fine as it is. They are pretty decent, but once you really look at it...you can see divots etc...in the material. It's intent is to provide a flat surface to apply graphics to that will be viewed at a distance. Not so great up close and personal. That's what I used on the Voyager. CPES is a waste of time on it however...no build thickness.

You might want to check...I believe that MDO can come primed both sides. Doug

[absolutsnwbrdr]

Thanks Doug. I don't believe the stuff that I'm getting is primed on either side, but I was planning on using Kilz Primer and a roller to give it a texture similar to FRP anyway.

Sounds like I will still at least use the CPES on the endgrain.

[Kharn]

When epoxying MDO, do you include a fiberglass layer?

[afreegreek]

CPES...

not sure why anyone is using this stuff.. it is made to "repair" dry rot in wood.. are you guys building trailers with punky, half rotten plywood? well if you aren't you are wasting your money.. what you are buying is $50 worth of epoxy resin and $10 worth of thinner added to it for $200.. in other words, you're parting ways with about $140 for no good reason.. just use epoxy and thin it out yourself..

am I saying CPES is a rip-off? no, I'm not saying that at all.. if you are using it for it's intended purpose it's well worth the money but none of you are doing that.. you are using for one of it's "also can be used for" purposes which is a WASTE of money and you are ripping yourself off.. just use thinned epoxy.. save some time and spend the money you would have wasted on CPES on something of value... like your wife

[absolutsnwbrdr]

Spend the money you would have wasted on CPES on something of value... like your wife

Already spent the money on the CPES a while ago, and no wife here

Plenty of threads around here over the years discouraging the purchase of CPES, but it worked well for me last time, so ....

Thanks for your concern

[afreegreek]

Spend the money you would have wasted on CPES on something of value... like your wife

Already spent the money on the CPES a while ago, and no wife here

Plenty of threads around here over the years discouraging the purchase of CPES, but it worked well for me last time, so ....

Thanks for your concern

job + no wife = money to burn BABY!!...

ya CPES will work as it is basic ingredient is regular epoxy.. they add a blend of thinners to it to thin it out and also to retard curing for a longer period of time so it can penetrate and wick it's way deeply into areas of compromised wood cells before it cures.. the idea is to rehydrate wood cells with epoxy and have the thinners evaporate leaving the cell walls reenforced without filling the entire cell with epoxy.. the formulation of thinners is pretty complex and probably took a ton of R&D to develop hence the steep price but for sealing good wood it's over kill..

since you've already spent the money you might as well use it.. just remember for your next build that regular epoxy thinned with acetone, lacquer thinner, or rubbing alcohol will do the same thing at 1/3 the price..

there are other thinners you can use too but these three will give you fast, medium and slow evaporation rates depending on how much surface you're trying to cover.. a large surface like a sheet of ply is best done with the alcohol..

[doug hodder]

When epoxying MDO, do you include a fiberglass layer?

I didn't...just resin over plywood, but there are a lot of layers of resin. I also used epoxy for the construction adhesive as well. I haven't used cloth over any of my builds exteriors.

The advantage to using MDO is that it takes epoxy on uniformly as opposed to regular ply. Much less work to get it all flattened out and looking good. How flat you want it depends on what you want your paint job to look like and how much effort you are willing to put into it. Doug

[Deryk the Pirate]

I used mdo plywood on my last build, and used regular epoxy on the edges and anywhere I cut it. Then a few layers of paint on top of it to make sure its sealed. There's been many discussions on cpes and if you do a few coats its fine.

[urbanfixie]

Afreegeek,

What ratio do you use to thin the epoxies usually? Do you have a brand you recommend? I was planning on ordering CPES this week for my build.

Thanks

[afreegreek]

Afreegeek,

What ratio do you use to thin the epoxies usually? Do you have a brand you recommend? I was planning on ordering CPES this week for my build.

Thanks

each brand has certain characteristics that are suited to different work.. for example Raka and Industrial Formulators have resin and hardener that are water white so it's good for wood you don't want to add a tint to.. maple with West Systems look ugly yellow so... it all depends on what you are doing with it.. the cured resin doesn't really have any noticeable difference, it's in the wet stage where differences are for the most part..

if I'm sealing wood I mix enough thinner so the epoxy will soak in and leave the pores open when cured and little to no coating thickness on the surface.. the exact ratio is done with sample of the wood keeping in mind the result you want.. it's probably around 20 - 30% .. just make a one pump sample and keep adding thinner as you brush a little on the wood... too thick? add a little more and try again.. you'll see as it soaks in.. you want it to soak all the way in but not look dry after sitting a few minutes.. too much will leave the wood looking half wet..

[Kharn]

Does pre-treating edges with CPES (or epoxy or a suitable paint) affect the ability to glue pieces together? For example, the Weekender has several plywood butt joints at angles other than 90 degrees that I would like to pre-seal prior to assembly to prevent delamination.

[doug hodder]

If you use epoxy as the adhesive, it kills 2 birds with one stone. Once you seal it with CPES...you need to plan on an epoxy for glue up, and you probably will need to rough it prior to gluing. I'd just use the epoxy for the adhesive/ sealer from the get go. You can thicken it to suit your needs. Much more versatile than CPES.

I've laminated up sheets of ply using epoxy as the adhesive with an 1/8" spline in them. See the stickies above on how to make large sheets of ply.

I don't believe that the white/yellow aliphatic glues will work once it's sealed, if that's what you're using, as they are relying on some porosity in the materials for their strength. Don't paint prior to glue-up...the bond will only be as strong as the paint to wood bond. Just my opinions, others may vary. Doug

[Kharn]

What if I cut the biscuits/splines after painting? At that point, wouldn't the biscuits be the structural strength and the surface adhesive just for waterproofing the seam (under and secondary to the post-assembly coatings)?

[doug hodder]

I wouldn't...just makes more work for yourself and potentially a higher risk of joint failure down the road. I'd just do it all in 1 shot, glue up the spline and the vertical joint. That type of joint with the correct adhesive is a complete package. Google butt joints with splines and see what they say. Doug