First Project- Should I have used PT? I used Douglas Fir.

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Forum topic by kenbass4 posted 04-04-2012 05:24 PM 1692 views 0 times favorited 16 replies Add to Favorites Watch
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5 posts in 2265 days

04-04-2012 05:24 PM

Ok, I built this using Douglas Fir. I keep going back and forth…should I have built it with PT? I need some piece of mind because Im driving myself crazy. How long will this last if I keep it treated? What should I use to treat it? I was thinkin about wrapping the bottoms with tyvek or tar paper to protect from moisture. Thoughts?

there are 2 swings on this now. I want to add a deck and slide to this at the end of the summer or next year.

16 replies so far

View thebicyclecafe's profile


23 posts in 2271 days

#1 posted 04-04-2012 07:04 PM

Douglas fir can stand up to mouisture quite well- so for the most part the studs should hold up quite well. However it’s not rot resistant, so where the studs touch the ground are of concern. At this point, maybe you can just try your best to encase the bottoms with latex paint, or seal it with a thick layer of polyurethane?

View brtech's profile


1029 posts in 2944 days

#2 posted 04-04-2012 07:05 PM

There is no black and white answer.

PT will last longer

Some of us worry about kids and chemical contact with the PT treatment. The newer stuff is better than the old stuff.

Dunno if tyvek or tar paper will do anything for you. I’d probably just build up a good exterior finish poly with some UV inhibitor in it and renew it every year. One idea that I saw in another thread for this is to get clear base paint (no tint). It has loads of good stuff and dries clear. Weird to get, but very cost effective.

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5 posts in 2265 days

#3 posted 04-04-2012 07:14 PM

Thanks for the tips. How long would you expect DF to last if I maintain a good Poly with UC inhibitor? Roughly?

View Jeff's profile


438 posts in 3216 days

#4 posted 04-04-2012 07:21 PM

In my experience your kids will grow out of it before the studs rot.

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5 posts in 2265 days

#5 posted 04-04-2012 07:24 PM

phew…that makes me feel better. Everyone keeps saying i should have used PT.

View BlankMan's profile


1490 posts in 3375 days

#6 posted 04-04-2012 07:58 PM

No matter how safe they say PT is I don’t know that I’d use it for something kids may be climbing on. I don’t even use it for my raised gardens that I grow vegetables in, I use cedar for those.

Depending where you are located you may not want to use polyurethane. Large temperature and humidity swings could cause it to crack, it’s not flexible enough. I built a bird feeder probably 10 years ago now, been outside ever since, the pine is still yellow, shows no signs of weathering. I sealed it with Spar Urethane, it’s more flexible then polyurethane and seems to have done a good job. Haven’t put another coat on since it’s been out there in our Wisconsin winters.

-- -Curt, Milwaukee, WI

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Mainiac Matt

8082 posts in 2350 days

#7 posted 04-04-2012 08:14 PM

As mentioned, the new ACQ PT (which is all you’ll find for retail sale) is much safer than the older CCA PT(copper, chrome, ARSENIC)... Of course the CCA preserves much better, as evidenced by it’s continued use for marina pilings, and other industrial projects.

None the less, I wouldn’t use either one on something that little kids play on, as they often can’t keep their hands out of their mouths.

If you’re really worried about it, dig a 12” diameter hole about 6” – 12” deep at the location of each post and fill them up with 3/4” washed stone (the kind they use in septic tank leach fields). That will keep the feet from being in contact with wet soil all the time and go a long ways to extend the life of the timbers.

-- It’s the knowledge in your head, skill in your hands and motivation to create in you heart that makes you a woodworker. - Mainiac Matt

View bondogaposis's profile


4754 posts in 2373 days

#8 posted 04-04-2012 08:15 PM

Your kid will outgrow that little toddler seat much faster than DF will rot. Also PT lumber isn’t the best structurally due to knots etc. You did good.

-- Bondo Gaposis

View Mainiac Matt 's profile

Mainiac Matt

8082 posts in 2350 days

#9 posted 04-04-2012 08:16 PM

if you feel that you must treat it with something…. let it whether for a few months b4 doing so.

-- It’s the knowledge in your head, skill in your hands and motivation to create in you heart that makes you a woodworker. - Mainiac Matt

View WDHLT15's profile


1747 posts in 2498 days

#10 posted 04-05-2012 12:26 AM

Get the feet out of the dirt. The washed stone like ssnvet says is good or set them on some concrete pavers.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln.

View oluf's profile


260 posts in 3061 days

#11 posted 04-05-2012 03:04 AM

Cut the tops off of four gallon milk bottles. Set the legs in the bottles and fill them with quickrete. They won’t rot off.

-- Nils, So. Central MI. Wood is honest.Take the effort to understand what it has to tell you before you try to change it.

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18283 posts in 3697 days

#12 posted 04-05-2012 04:32 AM

Get the feet out of the dirt and keep them up where moisture will drain away from them. Either paint or use high quality 99% UV protection like Log On and it will last long enough for the kids to out grow it ;-)

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View felkadelic's profile


218 posts in 2562 days

#13 posted 04-05-2012 04:47 AM

There was an article in one of my magazines (I think it was WOOD) that discussed using an epoxy to seal the areas where the wood would contact moisture from the ground. Might be worth looking into—let me know if you’d like me to try to find the issue number.

View tomd's profile


2155 posts in 3792 days

#14 posted 04-05-2012 04:58 AM

Cut four small squares out of PT wood and screw to bottom of legs this will keep it off the gound and will not rot, also I would just paint the rest.

-- Tom D

View doughan's profile


96 posts in 2613 days

#15 posted 04-05-2012 05:00 AM

what ssnvet said …..sealing the ends won’t do much to the rate of rot but speed it up… will still get wet and the sealer will hold the moisture in as well.

ask restoration carpenter what happens to fir beams that are painted.the paint wearout on top before the side and bottom allowing moisture in and then it won’t dry because of the paint.wet wood rots faster.
set it on rock and seal the whole piece of wood or don’t seal at all.sealing just the bottom and a little up the sides would be like wrapping it in a plastic bag.once the water is in it will stay

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