Thread: Spotted Gum decking cupping

Originally Posted by problem child

I know what he will say if I get him back - wood is prone to expand and contract and that is natural - it is not his fault. Aside from pulling the whole lot up and relaying them with perhaps 90 mm boards is there any way out of this? It looks awful and also is a trip hazard.

Hi Pc, and welcome to the forum. He should probably have made 5mm gaps between the boards when laid, but of course it depends on the weather conditions then, and how much moisture was in the wood or not. I'd get him back and if he says "wood is prone to yadda yadda" then your response should be "well why didn't you allow for that with the gap width?"

One way or another the width of the boards has to be reduced to allow for expansion......or they have to be placed further apart. There is no real way out of taking the boards up and narrowing them (number them so you can put them back on the same screw holes). How they are narrowed depends on your equipment, and whether they are tongue & groove boards or rectangular profile. If they are T&G then they have to be re-profiled with the same T&G pattern (they can vary). If they are square edge then they can either go through a table saw or a thicknesser (which is easier, safer and more accurate).

You may be able to get some material assistance from a member near to you, who knows? Or perhaps take them to a joinery or similar.

Doesn't sound like much fun does it? Sorry about that. Maybe someone more experienced than I can think of an easier solution....(rwbuild or DaveTTC are both builders)

The only other way i can think of again means taking the boards up, but re-laying them in different (new) screw holes with the right gap between the boards. This can be fraught with difficulties of "near-misses" (aka "just-hits") on the old holes though. This comes about because (say for instance) you increase the gap by 3mm: if the boards are 90mm then every 30th board will end up exactly (in a perfect world) where the previous 31st board was. That means the last few boards are going to have very close holes to the old holes, which can screw things up very nicely.

some good honest advice - thanks. Is there a tool that can get rid of the cupping as well or do I need the professionals - I feel like I'm dealing with something as hard as diamonds

Yeah, Spotty is hard alright. That's why it's used for tool handles and the like (Cyclone shovels, axes etc). It's actually a fantastic timber - one of my faves.

As for removing the cupping - this may be problematic - not in terms of doing it so much, even though that could be quite tricky thicknessing - but by the required reduction in thickness. If the boards are cupped by say 5mm on one face then 5mm has to be taken off BOTH faces to get them flat again. That would make for rather thin boards. Again in a perfect world all the boards would be cupped the same and the T&G (if it's there) would still be in register, but there'll be Buckley's chance of that being the case (take 4mm off one face of one board, and 6mm off another board and the T&G won't register any more).

You may need to investigate the insurance thing......

Are they T&G?

EDIT: BTW, you may find that the cupping relaxes a little once the boards are pulled up and are "free" to do their thing. Will depend on the weather too. The damn of it is that they really need to sit for a while once free to do the relaxing - and that means no deck for a while......

If the gap needs to be bigger (thx for the heads up ff) There could be an alternative to pulling them all up. But if you want to pull them all up byball means go ahead

You could set a saw to the depth of your decking and using a straight edge as a guide simple rip a bigger gap down each board.

As for sanding. Get a walk behind floor sander and you may need to start with 24 grit.

The planer ... well that could work but you would still need to sand. Again I would hire a walk behind floor sander. If you did not want to hire a sander then I would go 24 grit on a 5" plus grinder with the appropriate backing plate



Dave TTC
Turning Wood Into Art

Heck ! What did he use to gap the boards ? Cigarette papers ?

I have often used 4 inch nails to gap decking boards, and have not ever had them completely close up.

As we are about to enter the dryer months, maybe they will relax in place .. at which point pull up and redo.

PITA ... [emoji16]

As for your poor planer

https://www.woodworkforums.com/f13/review-spiral-cutter-head-makita-planer-1900b-series-18v-198465

Oh and did I mention - welcome to the forum



Dave TTC
Turning Wood Into Art

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)

Just a little curious as we don't have a pix.

A while back, I saw a deck at a motel which only had 1 screw per joist in the middle of the boards and 2 at the joins. The deck looked fairly new and still appeared ok. Not having built one with screws but have used nails in the late 70's, 2 per joist, I'm wondering if this is the new way of doing it. My thought at the time was that it was going to be a future problem.

Dodgy brothers? Or is it ok?

Dodgy brothers

My thoughts as well at the time but I'm no tradie just an enthusiastic amateur who tends to build to the double brick outhouse standard.

PC, are you quite sure he was a licensed builder?

If the boards aren't reeded turn them over.

Originally Posted by rwbuild

G'day PC

A couple of questions first.

When the boards were originally laid, what gap was there between the boards? Yes, but probably not enough.

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

Were the boards still a bit green (some sign of sap/moister) when they were screwed down? No sign of sap but I reckon when they have got wet they have expanded such that now they touch each other and the water cant drain and the sides have cupped.

Has the deck been treated with a decking oil / paint / stain and if so, has it been redone since original installation? No treatment at all - I like au natural.

Is there any plastic or rubber strip on top of the joists under the boards? I think so, not 100% sure

How far from each edge are the screws? The screws are really close to the edge of the boards.

Are the floor joists hardwood or softwood (treated pine)

Definitely softwood.

Originally Posted by FenceFurniture

PC, are you quite sure he was a licensed builder?

Yes definitely.