Spotted Gum decking cupping

[problem child]

Got some good feedback cheers everyone - I like the idea of ripping them but the #loody screws are near the edges of the boards. A post suggested turning them over - that would work if the cupping was consistent across the boards but it ain't. I understand by pulling the whole lot up and then relaying them I might get close to putting the screws back in the same holes which presumably will just see them lift again because they ain't properly anchored. What I really would like to do is tell the builder to come and do it properly, which probably means ripping all the boards up, buying some new ones which are properly seasoned (kiln dried) and putting them down with a decent gap not a cigarette paper gap as someone rightly pointed out The problem for me is my "expertise" which I have garnered here will be overruled by the builder who isn't compelled to do anything. I will add some photos over the weekend - should have done that earlier - sorry folks. Again thanks for the advice so far.

[Lplates]

pulling the whole lot up and then relaying them ...

FYI, There is a big difference in the quality of screws out there. I tried this when i was laying my small deck at the front of the house and made a mistake. Some of the screws i got from the big green B store were made of A grade Chinese cheese steel. They went in ok...mostly, but when you tried to take some of them out again (from pine joinsts, the merbau boards were pre-drilled) the heads snapped clean off. I think the heat generated by the friction of driving them in was enough to soften the steel and weaken it.

Be warned if you decide to start removing them....It may cause more trouble.

Good luck.

[AngelaPetruzzi]

Have the boards cupped from day 1 or is it just now that you are noticing it? Melbourne has had a pretty wet and miserable winter...Maybe before you go to heavy with sanding, wait till Spring/summer and see if the boards dry and settle down.
If you sand the boards early, then they dry and settle, you may end up with an uneven surface.

If you have to sand, then a belt sander with 24 or 40 grit would be the way to go. To get an even flat surface you would need cross cut first.

Too early yet to sand or coat decks in Melbourne...timber needs to be completely dry.

[rustynail]

Got some good feedback cheers everyone - I like the idea of ripping them but the #loody screws are near the edges of the boards. A post suggested turning them over - that would work if the cupping was consistent across the boards but it ain't. I understand by pulling the whole lot up and then relaying them I might get close to putting the screws back in the same holes which presumably will just see them lift again because they ain't properly anchored. What I really would like to do is tell the builder to come and do it properly, which probably means ripping all the boards up, buying some new ones which are properly seasoned (kiln dried) and putting them down with a decent gap not a cigarette paper gap as someone rightly pointed out The problem for me is my "expertise" which I have garnered here will be overruled by the builder who isn't compelled to do anything. I will add some photos over the weekend - should have done that earlier - sorry folks. Again thanks for the advice so far.

If the screws are staggered along the joist turning the boards will mean the holes will be opposite to their original position. If the screws are in line then you have a problem.
Cupping is a common problem with wide decking. Particularly with backsawn material. The cupping will be opposite in direction to the annual rings. If this is the case then the timber is responding to its own tensions. If the cupping is following the direction of the annual rings, it would be fair to assume the problem is being caused by weather conditions and will probably settle back to flat as the timber seasons .

[FenceFurniture]

You have to love this forum and its members eh? Such a diverse bunch of answers which should give the OP a really broad picture.

However problem child, you need to answer the questions that Ray put up. Without those answers then he doesn't have the whole picture, and so it will follow on that you won't either....

G'day PC

A couple of questions first.

When the boards were originally laid, what gap was there between the boards?

Are the screws flush with the top or below the surface?

Were the boards still a bit green (some sign of sap/moister) when they were screwed down?

Has the deck been treated with a decking oil / paint / stain and if so, has it been redone since original installation?

Is there any plastic or rubber strip on top of the joists under the boards?

How far from each edge are the screws?

Are the floor joists hardwood or softwood (treated pine)

And pics please! Pics pics pics.

[FenceFurniture]

Cupping is a common problem with wide decking. Particularly with backsawn material.

It better not be with my new shed deck Ken. They're only 95mm wide, but they are 45mm thick. They're old floor joists and are mainly Tallow wood, much of it ¼sawn. Will be starting to lay the boards tomorrow.

[rwbuild]

Hi PC
Ok. so joists are softwood. Could you answer the rest of my questions please before I offer my assesment

[ian]

... What I really would like to do is tell the builder to come and do it properly, which probably means ripping all the boards up, buying some new ones which are properly seasoned (kiln dried) and putting them down with a decent gap not a cigarette paper gap as someone rightly pointed out.

you probably don't want to use kiln dried

Kiln dried boards will be at minimum moisture content which means minimum width -- as soon as they get wet they will expand

[FenceFurniture]

you probably don't want to use kiln dried

Kiln dried boards will be at minimum moisture content which means minimum width -- as soon as they get wet they will expand

I guess that's the case with hardwoods Ian, but some of the KD pine I've been using lately looks like it's just come out of the swimming pool. Mainly the rough sawn stuff - actually damp to touch, and has been undercover at the hardware store (and it's big turnover sizes). Hasn't rained appreciably here for two months either.

[ian]

my first thought is that it's in the wrong stack

[Kuffy]

I thought most decking boards were kiln dried to be somewhere between 15%-18%.

[ian]

They may be, but I got the impression that the OP -- Problem Child -- was thinking that if he replaced his existing boards with new KD ones, the cupping problem would go away

[rustynail]

It better not be with my new shed deck Ken. They're only 95mm wide, but they are 45mm thick. They're old floor joists and are mainly Tallow wood, much of it ¼sawn. Will be starting to lay the boards tomorrow.

95mm is a good width for decking. You do realise there are two boards in each one of those big mothers you are about to put down?

[FenceFurniture]

95mm is a good width for decking. You do realise there are two boards in each one of those big mothers you are about to put down?

Yeah I do, but there's a problem with splitting them in half - embedded nails. In any case because the deck is for working on I want it to be pretty hefty to accommodate hefty blows etc. Machinery will get rolled across it too.

[rustynail]

Yeah I do, but there's a problem with splitting them in half - embedded nails. In any case because the deck is for working on I want it to be pretty hefty to accommodate hefty blows etc. Machinery will get rolled across it too.

Rustynails - Always a worry.
Did I say that!?