Thread: Pressure Treated Plywood

Howdy,

Read the page carefully and you will find ...

Some pressure-treated plywood may contain arsenic and other toxic chemicals. Most pressure-treated lumber is not suitable for indoor use. Pets, children and adults may be exposed to toxic levels of these chemical. Pressure-treated plywood should not be used in or on the ground, as these chemicals can leech into the soil, contaminating ground water. Sawdust from cutting pressure-treated plywood should be collected and disposed of properly. Some newer pressure-treated plywood does not contain these toxic chemicals, and this type should be selected whenever possible.

The materials used to poison biological activity sound like they leach out in water.

For this it is not a good idea. Additionally the grade of plywood tends to be very poor (at least the ones I have seen) with loose knots and poor surfaces. Both of which would normally reduce the life of the material. Most of the material I have seen also seems prone to surface checking (fine cracks along the woodgrain.

In general there are two main ways of reducing deterioration of the timber.

The traditional method is to protect the surfaces with paint and varnish and allow for very good circulation of air so that any residual water can dry and leave the structure.

The more modern method is to encapsulate the surfaces with three coats of a boatbuilding epoxy. This costs more, but is a proven way of making wooden boats very durable, so you save on maintenance costs down the line.

Both are fine.

I think the pressure treated (nice bit of marketing - better than "insecticide/fungicide impregnated ply") is risky for the builder and risky for the longer term of the project in that it might contaminate water in the boat. Also the drop in quality of the ply.

Much better off buying better quality ply and painting or epoxying it properly.

Best wishes
Michael

Pressure treated chemicals have changed in recent years here in the USA. Chromated copper arsenate was the chemical of choice and still is used in commercial applications. Alkaline copper quat and copper azole are the new water born choices for retail and consumer purchases. These are less toxic and though 15 years of world wide use and some testing, suggests they preform about the same as CCA treated products, the jury is still out. In fact pressure treated products pricing has risen a fair bit since the implementation of the new treatment guidelines. You see, the copper cost a bunch and adds to the lumber prices significantly.

The new CA treated products in the USA do not epoxy well, so make your choices wisely. The water born treatments seal the pores quite well, preventing epoxy penetration. You can achieve a mechanical bond with very rough toothing, but it's not as good as the same bond on untreated wood.

I mention this in light of the likelihood of the same changes in your countries. The new chemicals are not epoxy bond reliable.

G'day to Michael & PAR,

The leaching chemicals into the environment, the risk to health and the reduced penetration for epoxy bonding are good reasons to explain why it is not used for marine purposes. I regret to admit that I'd not considered any of those points. Thanks for enlightening me.

Cheers,
redx

having worked in the treated pine industry(treatment plant)We use copper chrome arsenic.Will last 20yrs in the ground.Mushroom companies use it all the time as it does not rot out like normal timber.would i use it?
No!It is kiln dried,very unstable and expensive..Leaching is not a real problem though.Just don't burn it.

A mate uses treated tannalised pine all the time on his boat repairs and cabin top replacements . Bigger boats above 40 feet.

Im looking at meranti for durability and stiffness to replace what evers rotted in my trailer sailer cockpit . but im using tannalised pine on cockpit floor as its on frames and it was originally screwed down so not structural but i will glue back

Plywood sellers say its not suitable for marine as the glue isnt marine glue but its designed to withstand getting wet.