View Full Version : Prairie boy looking for some good advice
06-20-2008, 12:24 PM
I don’t own a boat (live in the Southern Canadian prairies) but while I was researching wood coating information came across this site and thought it may be a good source for knowledgeable unbiased information.
I recently purchased a large timber peg structure to use as a Pergola over top of a concrete slab on the South side of my house.
It is a pine product composed of 10” by 10” beams and 3” by 10” beams held together by Oak pins.
It has already started to chink just sitting in my garage waiting to be erected. Once erected it will be exposed to heavy sun, large temperature and large humidity extremes (-40 to 70 F winter to summer; and heavy rains in summer and close to 0% humidity in winter).
I am looking for advice on how to protect the wood from rotting from the rain and sun. I would rather be able to see the grain of the wood and would not like to see too glossy of a finish on the thing but I would go that way if it was the best way to protect it over the long run. Also I would prefer not to have the finish flake off with age, so when I’m refinishing some time down the road it doesn’t have that repainted over old paint look.
I’m thinking that If something works on boats it should do the trick here. Any suggestions, pros/cons, etc.
06-20-2008, 01:56 PM
If this is pine it's probably a western pine like Sugar or Lodgepole. That means it is prone to rot under the right conditions, so keeping the pine dry and with plenty of airflow is important. Eaves become important as well as coatings that inhibit rot, the transmission of water vapor and UV damage.
I'd pay special attention to where side-blown wind can get into a joint where it won't dry easily, and on those faying surfaces treat the wood with copper napthanate before the final finish. Be careful, as this stuff takes weeks to dry before it can be painted over. Trade names are Cuprinol and others, it looks like green kerosene. Unlike Red Lead and other marine solutions, it's cheap and locally available.
Top coats that slow water vapor transmission and protect from UV are numerous and eradily available, as they are all house paints and stains. You'll gain absolutely nothing spending more for marine products. I would use a soft caulk like common window and door seal to close any checking and open joinery before topcoating.
If it's from Timberpeg it's probably Eastern White pine. If it's green timber it will be easier to assemble and erect sooner than later.
You might try some Flecto Varathane #66 oil finish. It doesn't get light spots or streaks like most other linseed based oils do when they get wet. I'd recommend finishing the timbers before you assemble them. If you are really concerned about rot look into the borate products like Tim-Bore, Bora-Care, and Impell rods. The borate treatments would be done prior to any finish application.
Couple more thoughts.
This being a pergola, I’m assuming that the design is some sort of open trellis in a ‘stacked’ arrangement, say, with 3x10 trellis joists over 10x10 beams, and without a covering roof and eaves. Are you planning on flashing the tops of the horizontal members? Depending on the design and joinery involved I’ve gone about this several different ways; 1) flash the tops of all horizontals if there isn’t a lot of complicated notching, 2) flash just the trellis joists if flashing the main beams is awkward, 3) flash just the main beams and consider the trellis members as replaceable, 4) no flashing and just caulk and maintain as needed ... or just let her go.
An outside pergola is an open structure exposed to the elements, not a house or a boat that needs to keep water out. Unless the beams are well seasoned, and you want to paint them, I wouldn’t get too carried away with caulking all the checks and joinery. Caulking can trap moisture in and cause more problems than just letting things dry cycle. The 10x10’s are likely sawn ‘boxed heart’ and are going to get some large checks, and if they are green they will take years to dry down and will still continue to move seasonally. For posts, where the checks are vertical, I’d not caulk them at all. If they are horizontal beams I’d only caulk checks that looked like they would catch and hold water, i.e. facing up. Same with joinery, I wouldn’t caulk verticals or bottoms. Personally I don’t care for the look of caulked timbers and prefer to keep it to a minimum and out of sight as much as possible. Some folks don’t like, and never get used to, large checks. I think checks can be a part of what is appealing about large solid timbers. They express the nature of the material. Otherwise, why not just build box beams and use plywood or boards?
The choice of finish, if any, really depends on the look you want and how much maintenance you want to take on. If you like the gray weathered look there are bleaching oils or a product called LifeTime wood treatment that might work for you.
06-21-2008, 02:40 PM
Pay close attention to what Bob S says. He's the resident wood wizard.
If it were me though, with temp extremes running to -40F, I'd use the wood to build a Prairie Schooner and head south.
06-21-2008, 04:54 PM
Thanks for the good advice gentlemen. As for the prairie schooner idea; just 8 more years ‘till this prairie boy heads to the warm west coast.
06-21-2008, 06:27 PM
Doug...that's a small replica prairie schooner....the real ones had wheels about 6-7 feet tall and were big , heavy monstrosities.....room for a family of four and household goods and the family piano. I donated the wheels and chassis to one of those that made the land rum of '89 into Oklahoma for a local museum, the bed had been removed to build part of granddad's house...he bought it from a Mr. Carlisle that had actually been in the land run as a small boy, when his family moved west....and they would literally crush a man if he were run over......
06-21-2008, 06:45 PM
Don't forget good old-fashioned borax. Very effective fungicide, water soluble, dissolve all a gallon of water will take and spray it liberally into endgrain, cracks and checks. Keep the children and pets away, though, until it's dried and you can seal over it.
06-21-2008, 06:46 PM
Chuck, Well until you went and blabbed the new guy prolly didn't know that:p:D
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