How to fix wood rot in deck supporting structure?

dbarmettler

Hi,

I am looking for advice on how to address wood root in deck supporting structure.

Having read some of the posts in this forum I was going to take the steps below to address it.

1.remove anything soft or spongy with chisel (already done, see photos)

2.apply wood hardener to remaining timber and let it dry

3. source timber to replace empty slot, cut to size, apply waterproof primer undercoat and paint to match.

4. screw or glue the timber of same size into gap

5.fill any remaining gaps with builders bog

6. Seal edges with wet area silicone

Keen for some feedback on whether or not those steps are appropriate?

What type of timber do I need to source for outdoor frame?

At what point do I need to be concerned about impacting structural of remaining timber ?

I attached some photos where I have completed step 1 above and just put a supporting piece of timber as interim measure and covered up the area with a tarp to prevent further rain exposure until I hear back from this forum.

Thanks

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Comments

EricL

Hello @dbarmettler

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your deck.

It will be necessary to remove all the rot in the joist. All soft, black, rotted affected spots must be removed until you are back to unaffected timber. If the rot has travelled too far into the timber, I recommend replacing entire joist.

Wood hardener can't be used on structural timber pieces as it is only a cosmetic fix. It's possible to use H3 framing timber to patch the damaged areas. However, if the rot has compromised the structural integrity of the timber joist, it's best to replace it with a new one.

Let me call on our experienced members @Nailbag and @Dave-1 for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

Dave-1

Good evening @dbarmettler

Finding rot in your timber is a tad scary I must admit. Tho it dosnt scare me as much as I use to be.

To answer your questions...

1.remove anything soft or spongy with chisel (already done, see photos)

A - Did you remove the floor boards from above the rot? That is a large area and id be chckeing either side of it by half a foot or so.

2.apply wood hardener to remaining timber and let it dry

A - I am actually impressed with the wood hardener products, Ive been looking for a spot to test and see how good they are.

3. source timber to replace empty slot, cut to size, apply waterproof primer undercoat and paint to match.

A - I dont know if I would "fill" the spot, I would use the wood hardener and seal the timber yes. I would also attach two pieces of timber horizontaly either side of the beam under the floorboards about a meter long. (Will retain its strength that way)

4. screw or glue the timber of same size into gap

A - Id skip this one 🙂

5.fill any remaining gaps with builders bog

A - My main concern is keeping out moisture that cause dit in the first place, if its sealed then Id be happy.

6. Seal edges with wet area silicone

A - Would give the silocone a miss and use a waterproof seal that you can see throught so as to be able to keep an eye on it.

Things to Note

Thin tipped Screwdriver poked hard into wood around the area that you have chiseled out to check for rot.

Fix the spot on the roof that has leaked that caused the dampness in the timber first.

Because the chised slot is in the middle of the beam id err on the side of caution and fix the horizontal struts to the side to keep the strength.

The wood harderners seem to be more advanced then years ago tho as @EricL says "structual" timber is something I dont think I would use it on.

Just looked at the pics before signing off, the floorboards look damp and the timber above them also looks a little damp. Have you pushed a screwdriver intro the support?

Dave

Nailbag

Hi @dbarmettler I would be following @Dave-1 steps through to #4. However personally my experience with Oregon is that once you have sections of rot it will continue to spread like a cancer and needs to be cut out as placing support timbers either side is an excellent suggestion that will assist structurally but won't stop the rot from spreading.

As Dave suggested check around the affected areas for softness. Where that stops and mark out say 100mm either side and 90mm down and cut that section out. A recip saw makes this job easy if you have access to one. See attached photos.
To do this you will need to remove the boards above. Apply the wood hardener, then apply an exterior undercoat.
Glue and screw the new insert piece which could be 90mm x 45mm treated pine.
There should now only be small gaps which you u could use a multipurpose filler such as this one which cures quickly and very hard. Easy to sand and no mixing. If you end up with larger/deeper ones then as Dave suggested use Builders bog. Before it fully cures scrape away the excess to make sanding easier.
Apply the undercoat then the colour coat.
To help prevent moisture build up on there top of the joist, you could consider this product, just bear in mind it will change the height of the effected boards to the existing ones. I use this type of product when laying all new boards when the deck is weather exposed.

If you ever discover rot where it’s a structural issue, then as painful as it will be, the entire piece of timber should be replaced. I had a deck where the posts were so rotted I could push my fingers straight through. I had to support the entire end of a deck 3m above the ground and replace 4 of 6 posts. (pic attached). I also had sections of rot in the facia and like you in a few joists. But as I was re-decking I replaced those.

Nailbag

Screenshot 2024-04-18 at 9.28.40 PM.png Screenshot 2024-04-18 at 9.51.32 PM.png

dbarmettler

https://www.workshop.bunnings.com.au/discussion/comment/36782#Comment_36782

Hi @EricL and @Dave-1 ,

Thanks for the welcome and prompt response.

Based on your responses I am going to address the leak on the roof to stop the source of the issue, do an interim repair (following steps outlined by @Dave-1 to stop the floor boards being a trip hazard and because structural, err on the side of caution and seek to replace the entire timber joist.

A1 - Did you remove the floor boards from above the rot? That is a large area and id be checking either side of it by half a foot or so.

AA1: I only lifted the floor boards that sunk into the joist. It became a trip hazard so I pushed the rot out and placed something rigid for temporary support. So far I had only been looking for soft spots (by touch but also sound) from the side, so I will take your advice and lift up the floor boards on either side to check condition.

A2 - I am actually impressed with the wood hardener products, Ive been looking for a spot to test and see how good they are.

AA2: Noted, I was going to purchase this product https://www.bunnings.com.au/earl-s-250ml-wood-hardener_p1585306.

A3 - I dont know if I would "fill" the spot, I would use the wood hardener and seal the timber yes. I would also attach two pieces of timber horizontaly either side of the beam under the floorboards about a meter long. (Will retain its strength that way)

AA3: Noted, what product is recommended for the waterproof sealing?

A4: Just looked at the pics before signing off, the floorboards look damp and the timber above them also looks a little damp. Have you pushed a screwdriver intro the support?

AA4: I will do some investigation of extent of rot.

Thanks again

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/80612#Comment_80612

Hi @dbarmettler,

Paint is an effective sealer of timber.

Even though you've only cut out a small portion of the beam's overall size, it's now structurally compromised with a reduced load capacity. The rot likely spreads further into the timber, past the super spongey section you've removed. Given it's quite difficult to assess the spread of rot, which could be isolated to the centre of the beam and not penetrating the faces, I'd recommend either having the beam assessed by a professional carpenter to ensure it's not compromised or replacing it entirely just to be safe.

Mitchell

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