Thread: The poll to divide a universe ... Decking timber ... grooves up or down?

Having had my go at what I have done and got away with, I have one question and one point to make.
A) If one wanted to get rid of the grooves, is it feasible to punch the nails further in and sand the grooves away with a big floor drum sander thingy?

B) About this 'theory' of grooves down for "airflow".
Provided that you have nailed the boards lake a lady, delicately enough for the grooves still to exist under the boards, I concede that some air may squeeze down there, but so will water. I rather have the joists with bitumen or other stuff to protect them from water, and no pockets for additional water to stay there forever. I find this idea that air will somehow find it's way between the boards nailed with a ton of force against the joist, a bit what to say ... aloof.

I didn't notice anyone mentioning another reason for "grooves down" that I read somewhere: water on the underside of decking has a greater tendency to drip off a grooved surface compared to a smooth one. This would reduce the time the timber is damp and hence extend its life.

Is this true?

Originally Posted by tony2096

I didn't notice anyone mentioning another reason for "grooves down" that I read somewhere: water on the underside of decking has a greater tendency to drip off a grooved surface compared to a smooth one. This would reduce the time the timber is damp and hence extend its life.

Is this true?

Theoretically. The grooves provide a series of narrow curved surfaces. This discourages water from clinging onto the timber through surface tension. In still air conditions, a smooth flat surface might provide sufficient area to retain some water in contact with the surface for an extended period. This would lead to greater penetration of moisture and extended drying time.

Originally Posted by tony2096

I read somewhere: water on the underside of decking has a greater tendency to drip off a grooved surface compared to a smooth one. This would reduce the time the timber is damp and hence extend its life.

Is this true?

"Drip Groove-. A semicircular grove on the underside of the drip cap or the lip of a window sill which prevents water from running back under the drip or sill. ... "

window and door sills in uk have grooves routed into them ... surely they wouldn't do it if it didn't work?

Originally Posted by jackiew

"Drip Groove-. A semicircular grove on the underside of the drip cap or the lip of a window sill which prevents water from running back under the drip or sill. ... "

This is standard practice in the building industry even on high rise buildings on precast and in-situ concrete on window sills, patios etc. usually done as a "V" groove.

Grooves down allows for better ventilation - who thought up the "its better grip" whn grooves up idea? Grooves up means EASIER TO DAMAGE!

Originally Posted by bitingmidge

Hmmm... but, on the other hand if it's not a problem having the groove side up, why isn't there decking timber grooved on both sides????

Ah, but there is! ... http://www.ajsmith.clara.net/deckinghardframes.htm

Originally Posted by hexbaz

Ah, but there is! ... http://www.ajsmith.clara.net/deckinghardframes.htm

Bit expensive to export to the land of Oz.

Originally Posted by Barry_White

Bit expensive to export to the land of Oz.

I was not suggesting that such a thing would be exported to Oz, just answering BM's question - "why isn't there decking timber grooved on both sides????"

The grooves are down on my decking, by the way.

Grooves down, although it's my belief the Rough head finish came first the reasoning second. An old timber merchant told me this a few years ago when PJK was prime minister in an attempt to help our fledgling "timber value adding" sector he imposed a tarriff on all finished timber products, but not unfinished. So the Yanks/Canadians etc came up with "rougher head dressing" on one face only to avoid the duties as it was not viewed as finished product but rawer resource. And the consumers were given some "interesting" (including reduced glare off batons for the roofing guys)reasons for the finish by enterprising sales staff, as popularity grew, our domestic manufacturers had to follow suit.
If what he told me is correct would this not be a classic case of "The Emperors New Clothes"? :eek:
Another reason I tend to think there is some truth in this besides PJK did do the tarriff thing, is that as Marc said, if airflow was the crucial point in using this finish, the grooves should be deeper and wider Ala decent T&G flooring. But then again its only Pinus species (AKA noxious weeds) and the quicker it rots the quicker you can replace it with real timber

G'day All.
We produced 110x30 reeded Spotted Gum decking for export to japan. They installed it reeded side down. this allows airflow, waterflow and adds to the life of the joists due to the limited likelyhood of fungus developing.
Hooroo.
Regards, Trevor
Grafton

Hey Trevor....is that your gun?

HH.

G'day HH.
Yep sure is. I shoot IPSC open division
Glock model 22 originally in 40 S&W.
Johnny Howard bought the 40 barrel from me in the buyback (stealback) I replaced it with a 357 Sig barrel, Cmore sight, and a KKM comp.
Goes like a dog shot in the ****.
Hooroo

thanks for the great thread i'm about to start a 12x4 metre deck i was going to build it reed up ,but now will do it the correct way thanks for helping me avoid a stuff up that will be one less in the project