a question about milling and retreating pressure treated lumber

[LMHmedchem]

This question could fall under many categories including carpentry, garden & lawncare, and painting. My guess was to put it here, so my apologies if that was the wrong guess.

I need to replace an old wooden trellis in my yard. I have looked at options available from local stores and find them to be pretty pathetic and ridiculously costly for what they are. Most are something like untreated 1/2" square stock that has been stapled together ("together" being a reasonable close description of the joints). I'm not going to pay $40-$50 per panel for something like that when I need 2 panels.

I decided to make a trellis instead. I am a good carpenter with the necessary tools so that part is not a problem, through I am always grateful for advice given an any area.

My question is about the materials I am going to use. I thought I would use ground contact pressure treated lumber, but that only seems to come in framing dimensions (2"x8", 2"x10", etc), which is understandable. I can get a couple of 2"x8" planks and mill them down to what I need and that would be cost effective. The issue is that I believe that after milling, most of the exposed surface will no longer be pressure treated. That more of less defeats the purpose of using pressure treated. I could paint the exposed surfaces with an copper naphthenate end cut treatment, but maybe I should just use regular #2 pine, treat it with copper naphthenate, and skip the pressure treated altogether. Allot of this depends on how well the pressure treatment penetrates the wood, which I don't know off hand.

I suspect that I am not the only person with a question like this so I thought I would post and ask for advice.

Thanks for taking the time to read,

LMHmedchem

 

[Eddie_T]

I think pressure treated ground contact lumber is saturated. That's the reason for pressure.

 

[Flyover]

This makes me curious to know:

If you merely paint non-treated lumber with some sort of water seal, what happens when little tiny cracks and scratches form in that seal later (either from things nicking it or from expansion/contraction -- or from penetration by fasteners used to build the trellis)? Won't water get in and rot the wood behind it?

 

[Snoonyb]

The penetration is "generally" 1/4", for both methods, with heart wood classed as difficult, in both methods.

Were it I, I would compose or purchase the least costly, and were it to be covered in foliage, forget it, because were it to deteriorate, the foliage would likely support it. And were it to be finished. just repeat every couple of yrs.

 

[LMHmedchem]

If you merely paint non-treated lumber with some sort of water seal, what happens when little tiny cracks and scratches form in that seal later (either from things nicking it or from expansion/contraction -- or from penetration by fasteners used to build the trellis)? Won't water get in and rot the wood behind it?

Most treatments need to be re-applied on some schedule. Since preservatives have been re-formulated to meet environmental regulations, many of them indicate that they need to be reapplied every year. This is particularly true of the least expensive options. Some people use a pump hand sprayer to re-treat their fences and decks every year.

This is one of the reasons for using pressure treated wood where the treatment has been forced into the wood fairly deeply. My belief is that ground contact pressure treated wood has been more or less fully saturated, which is one reason it's so heavy. I am not completely sure about that. I have seen a variety of opinions expressed on that point and my guess is that it depends on the specific product. Most pressure treated wood is labeled "not for ground contact" any may not have treatment that penetrates much further than painting.

Were it I, I would compose or purchase the least costly, and were it to be covered in foliage, forget it, because were it to deteriorate, the foliage would likely support it. And were it to be finished. just repeat every couple of yrs.

I think I am leaning in this direction. I will probably get pine and mill it to what I want. That way I won't have to deal with all the toxic sawdust. I have also been told that ground contact pressure treated has a tendency to misbehave when it is cut up into strips by cracking and twisting and such.

If I use pine I will coat it with copper naphthenate. Using several coats with dry time in between will allow the copper to buildup in the wood and provide better protection. I may also thin it some for the first coat to allow for deeper penetration. I will probably use a water proofing treatment on it after that, in part because I already have some. It's almost impossible to re-treat something like this once there is significant plant growth all over it so you are more or less stuck with what you start with.

I am also looking at ripping some cedar fence pickets which might be cost effective. I would need some larger cedar stock for the frame and I'm not sure about that. I also don't know if cedar would still benefit from a treatment of some kind after it is constructed. I seem to remember using cedar oil as a finish on something once but that was long ago.

LMHmedchem

 

[Snoonyb]

You mite also contact a fence co. to see if they are demo-ing any old cedar, as a resource.