How to prevent a garden deck sub-base from rotting

[RichD1]

I found some rot in my decking which I laid about 15 years ago but when I took a couple of the lengths up the frame underneath was in quite a poor state. Rotten in places and heavily black stained and damp in others.

I've decide to completely renew but wonder how to protect the subframe from the same fate.

I'm using pretreated timber but the surfaces that trap water like under the joint between deck board and joists is a problem also cut ends on the timber frame.

My initial thoughts turned to painting the top surface of the frame with Blackjack to seal the interface between the deck and the joist and also paint over the cut ends of any joist which need cutting.

Is this a good way forward or are there better solutions bearing in mind that once down the base cannot get any further protection like the decking boards.

Richard

 

[Awac]

https://www.harrodhorticultural.com...html?Aff=GPL&gclid=CLfQg7qNi9ICFYoaGwodWlkLzg
https://ecowoodtreatment.com/
I keep banging on about this stuff, and no I don't have shares! It's very, very good.

 

[adidat]

Use the recycled plastic stuff. Just laid a load of dino decking gear, but it comes with a high price tag...

Adidat

 

[TheUnicorn]

Use the recycled plastic stuff. Just laid a load of dino decking gear, but it comes with a high price tag...

But even the composite decking still seems to get laid on a wooden frame (which always seems a bit odd). In theory you can get a metal subframe but in reality most seem to use a wood frame still.

are there better solutions bearing in mind that once down the base cannot get any further protection like the decking boards.

With decent fixings (torx maybe best) I see no reason why you couldn't raise the deck to treat the frame. Just mark a giant 'v' across the whole deck in chalk so you know the order it goes back.

 

[RichD1]

https://www.harrodhorticultural.com...html?Aff=GPL&gclid=CLfQg7qNi9ICFYoaGwodWlkLzg
https://ecowoodtreatment.com/
I keep banging on about this stuff, and no I don't have shares! It's very, very good.

Sounds good stuff. Shame it adds the silvery patina as I like the new wood look but I guess underneath out of sight is not a problem.

Richard

 

[owen]

Deck tape. You put it on top of all the joists and noggins before you lay the decking

 

[Jacob]

Basically very easy - you keep it off the ground and well ventilated on staddle stones or some variation thereof. Where wood meets stone the stone needs to be "weathered" i.e have a slope so that there is nowhere for water to ledge, hence the mushroom shape. Ditto where wood meets wood - any crossings need to be weathered too.
It also needs to be high enough above splash-back from heavy rain. Wood lasts for years if it can dry out well in between soakings.

 

[harryc]

https://southgatetimber.co.uk/products/details/deckwise-wrap-joist-and-post-tape
Like Owen above suggested I have used the above after I found rot in my pressure treated joists after just 10 years.
Will have to wait and see how effective it actually is over time.

 

[RichD1]

I like the idea of deck tape but I've just worked out that I would need at least 4 rolls at £20 a roll. Think I will stick with Black Jacking.

Richard

 

[johnnyb]

make sure somehow that the wood is properly treated by whoever does it. raise it off the ground it will last.

 

[Blackswanwood]

Basically very easy - you keep it off the ground and well ventilated on staddle stones or some variation thereof. Where wood meets stone the stone needs to be "weathered" i.e have a slope so that there is nowhere for water to ledge, hence the mushroom shape. Ditto where wood meets wood - any crossings need to be weathered too.
It also needs to be high enough above splash-back from heavy rain. Wood lasts for years if it can dry out well in between soakings.

View attachment 108188

This is ultimately the best way imho. One of the modern equivalents of staddle stones deformed decking are Dekposts made by Supreme Concrete (part of Ibstock).

 

[Jacob]

This is ultimately the best way imho. One of the modern equivalents of staddle stones deformed decking are Dekposts made by Supreme Concrete (part of Ibstock).

Or just concrete blocks will do at a pinch

 

[Awac]

Sounds good stuff. Shame it adds the silvery patina as I like the new wood look but I guess underneath out of sight is not a problem.

Richard

New wood changes over time, what this does is gives it an even colour.

 

[Awac]

Basically very easy - you keep it off the ground and well ventilated on staddle stones or some variation thereof. Where wood meets stone the stone needs to be "weathered" i.e have a slope so that there is nowhere for water to ledge, hence the mushroom shape. Ditto where wood meets wood - any crossings need to be weathered too.
It also needs to be high enough above splash-back from heavy rain. Wood lasts for years if it can dry out well in between soakings.

View attachment 108188

Great photo, where is this building?

 

[Jasper42]

Not really related to the sub base but decking related

https://apple.news/Apg5qtT3lRQKZA21irNF4uw

 

[Glitch]

Sounds like the joists are rotting from the top down. Is that right?

Need to make sure the boards have a big enough gap to make sure water runs off the joist and that crud can be regularly brushed out.

I had to repair some joists on my decking. We thought a sunken flowerbed was a great idea but the presence of soil/compost just accelerates the rotting process. Flowerbed has now gone. I did use decking joist tape on the renewed areas and also added Jouplast adjustable decking risers to replace some of the dodgy supports the 'builder' had cobbled together.

Wonder if Bedec Barn paint would be better than a bitumen based paint on the tops of the joists?

 

[Jacob]

Great photo, where is this building?

Don't know - I googled "staddle stones" and lots of similar things came up and I screen shot that one.
That sort of barn/granary construction was common (world wide) and also kept out vermin, if high enough

 

[Rorschach]

15 years, I would consider that as doing very well for something sat out in all weathers very close to the ground.

Any treatment you do is only as good as the way you can implement it. You will never do a perfect job and if one area starts to rot, was it worth the effort?

If you want a deck to last forever, build a plastic one, but it will cost you, otherwise I would consider 15 years to be a reasonable period for replacement.

 

[eribaMotters]

I laid Iroko boards on 3x3" tanalised timbers treated to order. These sat on a concrete base that had a slight fall. Joists packed out with slate to sit level and the boards fixed with 2 1/2" stainless x-head screws. In the 25 years it was down before we moved the surface received a light jet wash each year. I replaced a couple of the boards where they had twisted and couple of short lengths where they had shrunk on the length. Removal was easy and I found no signs of any rot.

Colin

 

[pe2dave]

Some modern ideas here, decking used and tape.