How to repair timber deck frame?

[johnk]

hi everyone,

Looking for advice on the quickest and most efficient way to repair a small section of the frame on my deck without having to take the 3m+ merbu beams off.

It's a small section 30cm that I noticed was moving under the deck when I was about to start lightly sanding to recoat.

I was thinking that I would:

1. Remove as much of the rotten section as I can

2. Use a wood hardner on the rest of the section and then use an undercoat.

3. Cut a small filling wood section of outdoor pine and top this with a small section of marine ply. Squeeze this in and fill with liquid nails solution. Use an undercoat on this as well then dry.

4. Consider also using a poly filler 2 pack to fill in any remaining gaps and also undercoat this.

It's all under the deck and I dont want to cut the entire section and replace as I would have to pull all the beams out.

Thoughts?

[JacobZ]

Hi @johnk,

The extent you should go to repairing this rotted section of timber will depend on what function it serves in the deck. It looks likely that this rotten timber is acting as a bearer, which means the joists are directly supported by it.

From the photo you have provided, you can see that the perpendicular timber has been nailed into it. This indicates more of the deck is directly supported by this timber.

Unfortunately, if this section of the frame is rotten, there is a good chance more of this timber running along the wall is rotten, meaning more sections of your deck are being supported by rotten timber that has the potential to fail.

There's a good chance that anywhere this timber is touching the concrete wall, there will be further rot. Before deciding on a plan, I think it is important to check for rot along the full length of this wall.

I'd suggest you lift the ends of the decking boards and inspect the full length of this timber. There's a good chance you will need to remove and replace this rotten bearer.

Unfortunately, I think it is likely there is more to this job than just replacing a small section of rotted timber.

Let me know what you find. I will happily assist further once you've done some further investigation.

Jacob

[johnk]

Thanks Jacob,

Unfortunately my deck is 11m long and more than 3.3 wide. So at this stage as this issue is not structural, I intend to do this on a section by section basis only, and only if I get some small movement in the wall part of boards as the boards are very well held by 8 horizontal beams (across 3.3m). Otherwise I would have to remove all the boards and in fact as I have already found this may damage the existing boards due to the very tightly held wood screws that I have used. See pics.

Alterntaively, I am also thinking of just running a top board jammed against the wall to simply better support any future movement. When the whole deck is replaced in 10, 15 or 20 years then the under frame and this whole rotten beam against the wall can be replaced. 

On other thing - after applyinh 3 coats of an oil based stain, I am thinking of finishing off with some Linseed Oil (50% mineral turps) to further protect the stain from fading in the future. Any ideas or alterntiaves with this?   

[JacobZ]

Hi @johnk,

If you are confident it is not structural, then you should be fine to simply cut out and replace the rotted section, however, if the joists are relying on it for support, then it could be structural without your realising. I trust your instincts to make the right decision as I can't see everything that is happening.

As decking stains are essentially tinted decking oil, there is not much benefit in applying a different oil over the top. I would simply apply your 3 coats of stain, then do a touch-up coat every year or so.

Let me know if you have any further questions.

Jacob