Deck Board Theory

[The Medway Handyman]

Sorry, I've been thinking again.

Deck boards supplied by the sheds are flat one side & grooved on the other, the grooves being about half the surface area of the board.

I have 3 decking books, all published in the USA which show predominately flat decking boards - rare to see a photo of grooved boards.

The idea of the groove I suppose is to make the board less slippery. It would achieve that in part by keeping water off the surface & in the grooves. However when the grooves fill with dirt, that advantage is lost.

On the other hand, the grooved surface means that only 50% of the surface area of the board would be in contact with your foot at any one time, whereas a plain board would have 100% contact.

So which has the higher slip resistance? And in what conditions?

P.S. My deck has been down since July 2000 and no one has ever slipped on it - despite many drunken parties.

[mark]

Your foot would to some extent mould itself to the grooves and therefore provide a mechanical grip as well as a friction grip.

mark

[Harry Bloomfield]

It happens that mark formulated :

..and the grooves would provide somewhere for the water to be pushed out of the way into - just like a normal road tyre versus a slick.

[Bazza]

Sod all the slipping theory, now what about your drunken parties!! sounds much more interesting.

[The Medway Handyman]

I can see that with bare feet, but shoes? Would a rubber sole be pliable/soft enough? And what about if you are facing in the same direction as the grooves?

Hmmm.

[George]

Perhaps its because you don't hold the parties when snow or ice is on the ground.

[Frank Erskine]

Your weight is applied to 50% less area, so the pressure on the contacted surface is doubled...

Also the ridges in the planks break up the surface tension of any water lying there.

[The Medway Handyman]

Yes, I can see that. So 50% higher pressure but 50% less contact area - which is better for slip resistance?

Indeed. Good point.

[The Medway Handyman]

Thats what the deck was designed for - entertaining. I have two very attractive daughters who invite their mates to our BBQ parties, so it often sees 30+ people. Decking can cause hangovers :-)

[Andy Champ]

Sod the parties, what about the daughters? :P

Andy

(It gets sad when you find your friend's daughters attractive. Perhaps they'd like to meet my sons...)

[The Medway Handyman]

Stunners the pair of them, both blue eyed blonds. Both with plenty of attitude however :-)

[Andy Dingley]

Friction increases with pressure, so it's somewhat inversely proportional to the area. Grooves are thus good.

Although we all learn at school that "friction is _independent_ of area", this is about as much use in practical methods as the "light rods" and "inextensible string" used in all the other physics experiments that fail to work in practice.

[somebody]

yeah me too :-)

When, where? Should I bring my own beer?

[somebody]

Forget my other post, it should have read...

yeah me, me, me, me, me.... too too too too too too too

[The Natural Philosopher]

Why do cars not have slick tyres except on dry rcaing tracks?

[matthew.larkin]

The only deck I ever made was done with rough sawn tanalised timber. No grooves etc. And not a slip to be had.

The comments later in the thread about surface area are right in a sense, but when my (shoe-wearing) foot is down on rough sawn timber I would imagine that there is a similar contact area as there is with nicely planed grooved decking boards. My shoes have gaps in them, and as the surface of the rough timber is, well, rough I don't imagine more than 50% of the soles of my shoes are actually in contact with the surface of the timber anyway.

Perhaps the grooves do have some benefit, certainly cross ways, but I've found on several occassions (in public places too) that the grooves which run length ways can be just as slippy as any flat, smooth surface would have been in the same circumstances.

I think its more of a design thing; people like the grooved timber as its "smarter" and timber companies like it because they can charge a premium for it.

I'll be doing another deck in the next few months, and plain rough sawn timber will be going down there too.

Matt

[Franko]

I laid my deck was laid last year using grooved boards, when we had frosty weather the decking was like a skating rink when walking with the grooves but much firmer underfoot when walking across the grooves. I get the impression that the grooves can give a false sense of security and I will probably give it a coat of non slip paint this year.

Franko.

[Donwill]

It would be safer to have the grooves going across the boards as well as longitudinally making a checkerboard pattern. Are there any manufacturers that make boards like that? I don't think I've seen any. Maybe there are some clever people out there that can design some kind of grooving machine to retrospectively groove the boards in situ. Don

[Frank Erskine]

That would seriously weaken the planks.

[Bob Mannix]

Don't think it would as the depth is a small percentage of the total. Got me thinking however - wouldn't it be better all round if the grooves were cut at 45deg to the plank dimensions? That would give better grip if they were laid herring-bone style, and they might look nicer too.