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drtbk4ever 06-11-2012 02:48 PM

Loose stainless steel deck screws
 
Hey Gang,

I am wondering if stainless steel deck screws are more prone to loosening over time than other deck screws.

I used stainless steel to secure my brazilian hardwood decking (Pedra) to new pressure treated joist about 3 summers ago. I believe I used 3 inch screws. I've had to retighten most of the deck screws at least once and a few areas, more than once.

Is this common or are my stainless deck screws inferior?

Someone suggested my deck screws may actually be stretching as the Pedra expands and contracts.

I'd like some input as I am getting ready to finish the lower level deck with the same hardwood and don't want to have to retighten all those screws every year or two.

tony.g 06-11-2012 02:58 PM

Is it the timber which is shrinking rather than the screws working loose?

jcarlilesiu 06-11-2012 03:07 PM

Quote:

Originally Posted by tony.g (Post 941051)
Is it the timber which is shrinking rather than the screws working loose?

Exactly what I was thinking.

Those synthetic wood decking materials have large thermal expansion and contraction characteristics, to the point that many joists spacing is condensed to accommodate flexing during high summer heat.

My bet is that the screws haven't moved, and rather the "bite" from the decking has been loosened around the threads of the screw.

drtbk4ever 06-11-2012 03:55 PM

Quote:

Originally Posted by jcarlilesiu (Post 941058)
Those synthetic wood decking materials have large thermal expansion and contraction characteristics, to the point that many joists spacing is condensed to accommodate flexing during high summer heat.

The wood is actually a brazilian hardwood called Pedra not a synthetic. Pedra isn't as hard as Ipe, but hard enough that I had to predrill all screw holes. Maybe that is contributing to the problem.

Quote:

Originally Posted by jcarlilesiu (Post 941058)
My bet is that the screws haven't moved, and rather the "bite" from the decking has been loosened around the threads of the screw.

This is distinct possibility. Our climate is dry so the Pedra decking shrank a bit in the last 3 years. I initially thought I had installed with too small a gap between boards, but through shrinkage, the spacing is now perfect. Perhaps that gives you some perspective on the overall contraction.

I can tell when screws are loose because there is a clicking sound when I step in the area. I imagine it could be the noise of the deck board sliding over the thread of the deck screw.

Does that information help?

I'm hoping tightening my deck screws isn't going to be an annual maintenance item.

jcarlilesiu 06-11-2012 03:57 PM

Should have researched it. I assume that Pedra was a brand name for a synthetic decking material.

So are the boards twisting or lifting on you, or are the heads popping up? How do you know the screws are loose other than they will tighten down more when torqued?

drtbk4ever 06-11-2012 04:00 PM

Quote:

Originally Posted by jcarlilesiu (Post 941090)
Should have researched it. I assume that Pedra was a brand name for a synthetic decking material.

So are the boards twisting or lifting on you, or are the heads popping up? How do you know the screws are loose other than they will tighten down more when torqued?

No worries about the Pedra. It is an uncommon species of wood.

And it doesn't appear that the wood is twisting.

It is the clicking noise that alerts me to a loose deck board or loose screw.

jcarlilesiu 06-11-2012 04:02 PM

Quote:

Originally Posted by drtbk4ever (Post 941092)
No worries about the Pedra. It is an uncommon species of wood.

It is the clicking noise that alerts me to a loose deck board or loose screw.

Ahh.. if its clicking, that sounds like the threading on the screws aren't biting into the wood enough and you are actually pressing the board from compression down onto the next thread causing a click.

At that time, the board has additional space at the top allowing the screws to be screwed in more.

I assume the deck boards were laid directly on-top of the framing members before securing with the stainless steel screws? No cork or other material in between?

drtbk4ever 06-11-2012 04:13 PM

Correct.

kwikfishron 06-11-2012 04:16 PM

When you drilled the decking did you also drill the joist?

drtbk4ever 06-11-2012 04:28 PM

Quote:

Originally Posted by kwikfishron (Post 941107)
When you drilled the decking did you also drill the joist?

Even though I stopped drilling when I got through the Pedra, I'm sure I penetrated the joist to a certain extent. But it wouldn't be very deep and definitely not as deep as the screw length.

kwikfishron 06-11-2012 04:40 PM

I’ve been using SS screws in decking forever and never had that issue although all of these decks are in a much wetter climate than your’s.

All I could suggest is instead of re-tightening them, start replacing them as needed with a larger gauge screw.

Daniel Holzman 06-11-2012 05:43 PM

I built an ipe deck, similar wood to Pedra I assume, although harder. The correct way to predrill for ipe is to drill a hole sufficiently large that the threads of the screw do not contact the ipe (or Pedra) at all. The screw threads bite into the underlying pressure treated lumber, and the head of the screw holds down the ipe or Pedra.

I drilled all my holes using a tapered drill bit, specifically sized for the stainless screws. The ipe was 3/4 inch thick, and the drill bit is about 1-1/4 inch long, and the screws are 2-1/2 inches long. The screws can be pushed clean through the ipe with no pressure, and if you do the math you see that only the top 1/2 inch is actually drilled into the PT lumber. The tapered bit includes a countersink, so that is done at the same time as the drilling. I have had my deck for two years now, no problem with loosening of the screws. Possibly this is because ipe does not exhibit significant shrinkage or swelling transverse to the deck, it certainly does exhibit movement across the grain, leading to exactly the same effect you noted, i.e. the gaps are larger in the winter than the summer. I think a lot of wood exhibits much greater movement across the grain (horizontal) than transverse to the grain, so I am a bit surprised at your condition. Perhaps the effect is due to movement in the underlying PT lumber, although I would think that any PT movement would simply pull the entire deck board up or down depending on the direction of movement of the PT joist.

drtbk4ever 06-12-2012 10:00 AM

Thanks for all your input everyone.

We have had a couple days of fairly steady rain, so the humidity is up. I walked onto the deck last night and there were no clicks!! So it is clearly the expansion and contraction of the Pedra and/or the pressure treated joist that is causing my problem.

I guess I can approach the fix a couple of ways:
1) I can use Daniel's suggestion and redrill the holes such that the screws can slide cleanly through the Pedra decking. At the same time making sure I use screws that are long enough so there aren't any threads in contact with the decking which is a full inch thick. I will have to double check, but I don't think that is possible with the 2.5 inch screws.
2) Or I get the longest thickest guage screws I can find and cinch that decking down as tight as I can get it to try to reduce the contraction/expansion of the wood.

Thoughts?

kwikfishron 06-12-2012 11:30 AM

Can you post a link or picture of the screws you're using now?

spinfisher 06-12-2012 11:54 AM

If your having problems with loose boards you might want to pull them up and use an exterior sub-floor glue, then re-attach them to your joist.


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