Gaps between boards and joists when laying new deck

[heapey]

I've just finished building the frame for my 3mx3m deck, layed on top of old patio. All the joists are in, and noggins in the 2 outer sections, remaining ones to be done tomorrow.

Anyway, while checking the level, i have noticed that there are quite a few places were the underside of the deck board doesn't touch the joist. In some places this is by as much as 5mm. This is despite all of the joists being flush with the outer frame.

I've searched old posts for this as I wanted to find out if this is normal, and just the result of having bowed wood (I did check the wood as I went along and it didn't seem too bad), however I am unable to find any mention of this - maybe because its such a basic question ?

Now, onto a solution, does the following make sense:
1) anywhere there is a gap insert some shims to fill it, from old offcuts. Also give the shims a quick coat of preserver.
2) lay 4 boards and shims at a time - before fixing check that the level looks ok in both directions.
3) if all looks ok fix boards, then do next 4

Any advice on this would be much appreciated.
Cheers

 

[Woodster66]

Best thing to do is check the joists with a spirit level first to see if it is the deck board or the joists that are causing the gap, if the joists seem ok then I shouldn't worry to much about packing them out with shims, if on the other hand it is the joists try turning one the other way to see if this helps on that section before using any shims as over time the shims could break up and fall out leaving you with a board that will move up and down when walking over it, thus no point in shimming them in the first place.

If by turning the joist resolves the problem it maybe a good idea to spend an hour or two at construction stage now turning the rest so you get a level frame work to either screw or nail to plus the fact if it is a joist that is bowing then it could continue to bow a little further over time, again the shimming would be pointless as further bowing would also cause the gap to increase over time.

 

[Thermo]

sounds like youve not checked the crowns o the joists. All timber will have a crown to it, ie a slight bow on one side. You can see it looking down the length of the timber. The joists should be laid crown up, and as the weight goes n them over time they will settle. If its not to late then turn the joists now.

 

[big-all]

can also be caused by the screw pushing up the boards untill the screw "bites"

if the heads are not "lipped" on the screws you can unscrew untill the screw is clear /dropped and tighten again making shure you are kneeling on the board to hold it down

lipped means the wood has started to close around the screw head and if your unlucky you will push up a splinter causing more dammage

this only usualy happens when the screwhead is more than around 5mm below the surface

 

[heapey]

Thanks to the 3 replies to my message. I think i'd missed the obvious yesterday as i'd spent too long in the garden.
What i'd done earlier was fix 3 joist hangers to the frame, but used the same offcut to measure each one. Unfortunately the offcut i was using came from a
joist that was 9.6mm, but the actual joists i then fixed were 10mm. I'd already spotted this and chiseled away some of the end to get it fitting flush, but had then put 1 of the joists in with the chiseled bit at the top, which meant that it was now level at the fame, but not elsewhere.
So 2 schoolboy errors there for not using the same piece of wood to fix the hanger, and then putting the wood in the wrong way up!
Anyway, tuned it round and that immediately improved things. Also as suggested, i got someone to stand on the wood while i put the noggins in which helped a lot.

Some of the joists are also quite badly mishapen in all directions, though i did try to look for bowing as i had read previous posts about this.

Looking back I should have tried to get the shop to take some of the dodgy wood back and redeliver me some more but I tried to plough on regardless hence getting in a bit of a pickle now. (i've not got a big enough vehicle to pick the wood up myself.)

This i think is another lesson to be learnt if i was to do it again - i.e.check each piece of wood for straightness as soon as it is delivered, rather than later when the shop is closed for the bank holiday weekend.

Once again thanks for the advice, hopefully I won't have to ask any more questions. I've just got about 10 more noggins to put in and should then be ready for boarding, now with maybe just 2 or 3 bits of packing required, rather than one for every other joist per board!!

 

[Thermo]

always fix the timber flush first and then fix the joist hangers afterwards.