How to prevent a garden deck sub-base from rotting

[owen]

Or just concrete blocks will do at a pinch

It sounds like the deck is rotting from the top or the joists down, probably from moisture trapped between the deck boards and the joists, I don't think staddle stones would help in this case.
Laying the decking with the grooves downwards actually helps a bit, letting air over the top of the joists.

 

[Wildman]

timber is no longer dried properly or really pressure treated only dipped, same has happened with fencing stakes etc, best answer is old engine oil it soaks in and dries fairly quick and more effective then creosote

 

[TheTiddles]

timber is no longer dried properly or really pressure treated only dipped, same has happened with fencing stakes etc, best answer is old engine oil it soaks in and dries fairly quick and more effective then creosote

Out of curiosity, when was the last time you were at a pressure treaters and saw the wood enter and exit the chamber but also the person pulling it out the secret hatch so the conspiracy is maintained? Asking for a friend...

 

[TheUnicorn]

hadn't heard about ridge down laying, I thought it was a choice for aesthetics, but air flow makes a lot of sense. I have to say when you walk across a wet (slimy) deck and your foot is going in the same direction as the grooves you can pretty much kiss goodbye to any chance of staying upright.

Also agree with others who've said you need a good gap between boards, my sister's decking was laid (before her time) with no gap at all and it was a soggy rotten mess.

I always think a wooden deck, whilst really nice at first, is just a big bill waiting to happen.

 

[Wildman]

Out of curiosity, when was the last time you were at a pressure treaters and saw the wood enter and exit the chamber but also the person pulling it out the secret hatch so the conspiracy is maintained? Asking for a friend...

often go to local sawmills and see how they "treat" the timber, obviously not all are the same. But I no longer have faith in the preservative properties of them.

 

[TheTiddles]

often go to local sawmills and see how they "treat" the timber, obviously not all are the same. But I no longer have faith in the preservative properties of them.

So you’ve not then, thought so.

 

[MARK.B.]

timber is no longer dried properly or really pressure treated only dipped, same has happened with fencing stakes etc, best answer is old engine oil it soaks in and dries fairly quick and more effective then creosote

The drying bit may true Wildman , When i worked at a Timber treatment Firm 95% of all the timber was pressure treated ,varying times and treatments for different grades of protection and the solutions used now are just as good or better than those used 30 years ago.

 

[TheUnicorn]

The drying bit may true Wildman , When i worked at a Timber treatment Firm 95% of all the timber was pressure treated ,varying times and treatments for different grades of protection and the solutions used now are just as good or better than those used 30 years ago.

suprised to hear that, I would have said (with no actual knowledge to back it up) that with more and more health and safety and environmental legislation modern chemicals would be less effective than older stuff, creosote being a case in point

 

[Spectric]

I know that in a protective metal finish I used to buy there is no longer any arsenic in the later stuff, not sure what it contributed but was warned never to sand without a respirator.

 

[TomGW]

Why not simply use a roll of dpc 100mm wider than the joists, giving 50mm each side to act as a drip rail? That should keep the joists dry.

 

[Stevekane]

Been thinking about these problems myself but in relation to a garden table Im about to make, Im using presure treated 75mm fence posts topped off with 45mm boards, and there will be a few half joints, my concern has been wetess sitting in these joints, I think that I will be able to position most of the joints underneath and sheltered by the wide boards above, and to give each joint a liberal coat of preservative, or any better ideas?

 

[pe2dave]

Suggest once the joints are glued, you inspect and 'fill' any gaps to resist penetration? Although the excellent ideas re some watertight insert between touching surfaces might apply equally to a table, since again, water will find a way in and sit, unless prevented from doing so.

 

[MARK.B.]

suprised to hear that, I would have said (with no actual knowledge to back it up) that with more and more health and safety and environmental legislation modern chemicals would be less effective than older stuff, creosote being a case in point

Will not dissagree about the original creosote/old oil being the best stuff for dunking your posts and timber in ( still have 25 litres of the good stuff stashed away ) I was refering to the chemical solutions used in the vacuum chamber ,a lot of changes have been made over the years to the contents of them so they are both safer to the enviroment and the user ,the makers say the new formulations will make the timber last longer .

 

[TheUnicorn]

the makers say the new formulations will make the timber last longer

well, I'd not exactly take any manufacturers claims as gospel

 

[TheTiddles]

well, I'd not exactly take any manufacturers claims as gospel

Has the thought ever occurred that just because something is old, it may not be the best? I’ve rarely seen Airbus going round museums nicking biplane engines for their new aircraft, nor a formula one team making a chassis from wood because that’s how all the best carriages were made.

It may be hard to believe that the collective endeavours of humanity epitomised by the phenomenal acceleration of scientific achievement over the last couple of centuries might actually have done things better than before, but if you truly don’t believe that’s possible... maybe stay off the internet and get back to your local squire’s personal library for your sources of information?

Aidan

 

[Jacob]

Has the thought ever occurred that just because something is old, it may not be the best? .......

Has the thought ever occurred that just because something claims to be "new, improved" it may not be the best?
Particularly true of longevity and preservation - if you want to know how to make new stuff last look at old stuff which has survived.

 

[Stevekane]

Suggest once the joints are glued, you inspect and 'fill' any gaps to resist penetration? Although the excellent ideas re some watertight insert between touching surfaces might apply equally to a table, since again, water will find a way in and sit, unless prevented from doing so.

Hello Dave, intresting idea, I did have thoughts about glueing the joints, ordinarily for indoor projects I would use PVA but because this is going to live outside with a polytarp over it in the winter I wondered if trying to glue the joints might cause me problems? the joints will be screwed together anyway. Im intrigued by the use of deck tape,,is this neoprene tape I wonder?as Ive used this before on my boat, the fittings were bedded down on this and when I first encountered it I thought it was a bedding compound, but in fact its a grey roll of soft thin sponge, self adhesive on one side and when squashed it compresses into a fairly dense and waterproof joint,,I have a roll of this too,,,
My plan was to keep the joints tight and as sheltered as possible, but I had also thought about using something like sanitary sealant in the joints too,,esp given that it dries to a rubber like jointing,,,I know its not your usual go to for a wooden joint but could it work?
Steve.

 

[TheUnicorn]

Has the thought ever occurred that just because something is old, it may not be the best? I’ve rarely seen Airbus going round museums nicking biplane engines for their new aircraft, nor a formula one team making a chassis from wood because that’s how all the best carriages were made.

It may be hard to believe that the collective endeavours of humanity epitomised by the phenomenal acceleration of scientific achievement over the last couple of centuries might actually have done things better than before, but if you truly don’t believe that’s possible... maybe stay off the internet and get back to your local squire’s personal library for your sources of information?

Aidan

I seem to have offended, sorry, but my point was simply that just because a manufacturer says something does not make it true. I am happy enough to take someone's experience into account and give it value, as they don't have a vested interest, the same cannot be said of manufacturers, and that was my entire point.

 

[TheUnicorn]

My plan was to keep the joints tight and as sheltered as possible, but I had also thought about using something like sanitary sealant in the joints too,,esp given that it dries to a rubber like jointing,,,I know its not your usual go to for a wooden joint but could it work?

I would make sure that anything you use is rated for exterior use or you may end up scraping it all out in a years time and starting again

 

[TheTiddles]

I seem to have offended, sorry, but my point was simply that just because a manufacturer says something does not make it true. I am happy enough to take someone's experience into account and give it value, as they don't have a vested interest, the same cannot be said of manufacturers, and that was my entire point.

Nobody’s offended, just plain bored of the endless moaning about how anything new can’t be any good because of health and safety, cheap manufacture, young people not being properly educated etc... if people are so fond of the past, stay in it.

Your point was that modern chemicals can’t be as good as old ones, for which you have offered nothing to support that. Many chemicals have been removed from use for some serious reasons, to keep people like you alive.