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.
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.
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?
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?
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.
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.
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.
I took a photo and am trying to upload it from my ipad, hope it works.
The 2.5 inch screw is a 9 guage i think. The 3 inch screw would then be a 8 guage. Today i found a place that sells 3.5 inch 10 guage SS screws. Overkill?
Yep, That would do it!
I might try to shift the hole over a touch so the new screw is getting a better bite on firm wood.
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