Some simple decking questions

[dylanswall]

Hi, just about to start decking my small patio garden (about 25m2) and have some very simple decking questions that I can't seem to find the answers for/ just need some reassurance on. For reference I am using 4"x2" treated joists over a concrete patio (raised onto evenly spaced patio slabs) and 120 mm x 30 mm soft wood decking (all purchased from e decks so please don't tell me they are on a par with B&Q, quality wise). Here goes:

1) Staining appears to be a no no, decking oil a definite. Is that so?

2) When applying decking oil (or stain depending on your answer to question one), should I apply it before laying the decking so I can get it on both sides or do I just need to apply it to the top side once the decking is laid? My query being that won't stain/ oil prolong the decking life and therefore I should be coating both sides?

3) Probably a stupid question, but why aren't the joists laid flat as I would have though that would be easier to lay the decking on (I am assuming because this would mean it would bow under weight?)

4) The decking is currently sitting in my garden in the rain (delivered today). I am assuming shrinking is going to be a big problem and should therefore leave only a small gap between decking/ lay the joists and wait for the weather to clear up. If so, how long does it take decking to dry out and should I worry about shrinkage in respect of the joists?

5) My garden is enclosed by walls so the joist frame is going to be up against that, therefore I can't screw from the outside in (I will try where I can). I have read I can squew (is that the word) fasten the joists from the inside of the frame, I will be using 100mm spax wirox joist screws, how many should I use for each joint? Where I can screw the joists together from the outside, will two of these do per attachment?

6) And lastly, as it is fully enclosed by walls, I was going to lay the joists so they virtually but up against the walls for added security (as am not going to be attaching the frame to the walls), does anyone forsee any problems in doing this and, if so, should I be leaving a gap (if so, how much) between the frame and the walls?

Thanks for all your help and sorry it is a bit long winded.

 

[dylanswall]

One other question about shrinkage, surely this effects the length more than the width? But in the forums people only mention how it effects the gap inbetween decking planks?

 

[big-all]

wood is just a load off fibres
wood may expand by around 0.5 to 2mm every 20 m
it will however expand 10% easily accross the grain

you need to find the finnished size quoted for your boards lets assume 143mm
you then need to decide a gap you need say 7mm
you then lay your first board then at every 3 or 4 point your going to put a screw in [minimum 3] you measure the width off the board say 148 and add a 2mm spacer check at all spacer points accross

 

[WabbitPoo]

1) Oil.

2) Wouldnt do any harm to do both, but I never do.

3) You answered that quetion!

4) Build the frame, lay the boards, all in dry weather if poss as you'll do a better job then.

5) 4

6) If the wall is dead flat then yes, leave a 5mm gap. Of a knobbly brick wall then I wouldnt worry unless it'll breach the damp course, which makes ome people uneasy.