Water pooling on deck

Forums › Home Workshop DIY › Water pooling on deck - solutions?

jonathan18

6998 posts

Uber Geek

ID Verified

Trusted

#306786 21-Aug-2023 13:46

Our deck has a couple of places where water pools in heavy or constant rain; the photo below shows the worst of these. It's always done this - I imagine the builder didn't get the slope correct. (I also think he should have thought about laying the timber 90 degrees to this; the deck runs between the main house and a sleepout, so it would have made sense to have it so water could run off the ends where the deck doesn't sit against a dwelling!)

Whatever the cause, I'm looking for advice on a relatively straight-forward solution that doesn't involve lifting the timber.

Easiest option would be drilling holes; I've read some suggesting using an 8mm drill bit. If I did do this, am I best to do one per board at the lowest point (ideally in a line to make it look not so bad!)? Or, if more than one per board, how many and how far apart? I've read warnings that such holes will expose the inside of the timber so will rot more quickly; I wondered if drilling a larger hole and inserting a grommet of some kind could offer some protection?

Another option would be shaving a few mm off the sides of the boards to provide better drainage (circular saw? router?); I do wonder, though, if this will fully clear the pooling? (This isn't something I'd be comfortable doing myself, but could look to get the builder who should be building a fence for us soon to do.)

Anyway, thanks any ideas.

1 | 2 | 3

3321 posts

Uber Geek

Trusted

#3118581 21-Aug-2023 14:10

You're right, it doesn't look like the falls are correct.

The first-best way of fixing it would be lifting the boards, shimming them up a little and putting them back down. If you were doing this, you might look to make the spacing a little wider too. At a guess from the shape of the puddle, your boards are expanding when wet so the water isn't going down the joins?

The problem you will have drilling any kind of even vaguely aesthetically-okay hole is that any hole that small will clog up pretty quickly and stop draining.

I've never done this, but one alternative might be to cut a big enough hole at a lowpoint for a drainage/sump pit (Bunnings example, there are lots of alternatives). Clearly the intention is that this is connected to a drain but YMMV with just letting it spill under the deck.

Alternatively, you could try painting with some kind of water repellant / hyrdophobic paint. I suspect your pool is big enough that it wouldn't solve it on its own though.

MyHeritage

Shop MyHeritage and uncover your origins and find new relatives with a simple DNA test. (affiliate link).

concordnz

420 posts

Ultimate Geek

Trusted

EMT (R)

#3118618 21-Aug-2023 14:42

Main problem appears to be joins between boards look to be expanding 'shut' because too close (combined with a footing which has 'sunk' I suspect.)

I be tempted to run a circular saw down the join between boards to open it up a little more to allow drainage between boards like it should have (keeping blade depth shallow so it only goes the depth of the top boards)

You do run the risk of this looking 'odd' when compared to the rest of the spacings.....but it should fix the issue.

(it depends on what kind of 'cost/fix' you are after...)

I agree that drilling holes in the low points won't fix it - they fast/easily fill with moss/gunk, no matter how big you make them. A grommet of any kind adds more problems than it solves - it gives a raised point at the hole, preventing water from going down it, until it gets high enough.
It also creates a surface against the sides of the hole, preventing the wood drying out and causing it to stay wet and rot out fast.

tweake

1057 posts

Uber Geek

#3118678 21-Aug-2023 16:23

as above the gaps have closed up. you can still see the gaps between the boards in the puddle so i suspect its simply filled with dirt and needs a good clean out. just check underneath to make sure someone has not put something under there for the dirt etc to sit on and fill up.

mattwnz

19389 posts

Uber Geek

#3118681 21-Aug-2023 16:30

I would remove a board in the centre and plane it down or run it through a saw bench to narrow it, and then reinstall, which will then provide a drainage slot. If the board can't be removed cleanly, you can buy another board and plane it down.

RunningMan

7972 posts

Uber Geek

#3118684 21-Aug-2023 16:31

jonathan18:. (I also think he should have thought about laying the timber 90 degrees to this; the deck runs between the main house and a sleepout, so it would have made sense to have it so water could run off the ends where the deck doesn't sit against a dwelling!)

This is because the grooves in the top surface should run in a different direction to the foot traffic - better grip when walking.

Have the gaps between boards just filled with moss or something? A water blaster may clean that out, but be careful with the pressure - just enough to get the job done, not damage the timber, which can happen if you get too close.

jonathan18

6998 posts

Uber Geek

ID Verified

Trusted

#3118691 21-Aug-2023 16:41

Thanks - the cause and probable solutions are noted in the posts above; we have a terribly productive copper beech tree near the deck that delights in raining down all matter of detritus over the seasons, and that seamingly breaks down and fills the gaps between the boards.

I've already managed to provide much better drainage by cleaning out the gaps with a craft knife blade (where I can), and I imagine it may improve over time as (if I can maintain the gap) the timber may dry out a bit and not swell so much. The problem is that this isn't easy as the gap is minimal, and it'll need to be repeated frequently. As such a permanent solution is desirable!

I think the circular saw option to open up the gap is probably the easiest (and it looks like this will solve the pooling), but is something I'll ask the builder to do as I'd rather not #%#$ it up! Would he be able to use a particularly narrow blade so as to minimise the aesthetic impact?

Anyway, while on the question of decks - what would people recommend as the most effective deck cleaner? I don't want to stain it, but rather just clean it up as best as possible. I've used sodium percarbonate before, which was ok; but is there another product that is the bee's knees (along with scrubbing, of course...)? I was wondering about this oxalic acid-based cleaner: https://www.bunnings.co.nz/intergrain-4l-ultraprep-timber-cleaner_p1563243

Many thanks.

jonathan18

6998 posts

Uber Geek

ID Verified

Trusted

#3118693 21-Aug-2023 16:45

RunningMan:

Have the gaps between boards just filled with moss or something? A water blaster may clean that out, but be careful with the pressure - just enough to get the job done, not damage the timber, which can happen if you get too close.

I used the patio cleaner on the deck this year in early Autumn, before the leaves, catkins etc fell; and I normally do another clean before summer when we start using the deck. It looks like I may be best to do a clean (with the blaster if necessary) at the end of autumn so as to minimise the blockage before the heavy rain season arrives, but ideally an expanded gap on these boards will help (as it's exacerbated by this part of the deck being lower).

openmedia

3050 posts

Uber Geek

Trusted

#3118694 21-Aug-2023 16:47

We had the same issue as the deck was originally installed with very small gaps between the boards. We ended up lifting the deck and re-setting all the planks. End result is we needed one plank less and the deck now drains beautifully.

Generally known online as OpenMedia, now working for Red Hat APAC as a Technology Evangelist and Portfolio Architect. Still playing with MythTV and digital media on the side.

Wombat1

400 posts

Ultimate Geek

#3118696 21-Aug-2023 16:53

Timber will need to be lifted. Anything else will be a half job.

mdf

3321 posts

Uber Geek

Trusted

#3118704 21-Aug-2023 17:12

jonathan18:

<snip>

I think the circular saw option to open up the gap is probably the easiest (and it looks like this will solve the pooling), but is something I'll ask the builder to do as I'd rather not #%#$ it up! Would he be able to use a particularly narrow blade so as to minimise the aesthetic impact?

The thickness of the blade is the "kerf". Most circular saw blade kerfs are a bit over 2mm (converted from frankenstein north american measurements). You can get thinner, but they're a pretty unusual tool for a builder to have (more of a fine woodworking thing).

If ripping down the boards is the option you go with, ask about a track saw - essentially a circular saw on rails that will cut much straighter than a standard circular saw. I can imagine this being one of those simple in theory, hard in practice tasks and anything to make it easier will be a good thing!

I think any kind of cutting will have an aesthetic impact though. Your boards look to have silvered off, and chances are you will end up with much newer looking wood in the cuts, at least until they silver too. The cut edges will also likely have a sharper corner. The reeded deck boards usually have rounded over corners.

Handle9

9648 posts

Uber Geek

Trusted

Lifetime subscriber

#3118735 21-Aug-2023 18:16

The "correct" solution is to lift the timber and respace it. The easy solution is to brush the water off with a broom after rain.

mattwnz

19389 posts

Uber Geek

#3118745 21-Aug-2023 18:40

I have seen a brand new deck installed by a builder with almost no gaps between the boards but it is reasonably flat or maybe slightly angled to the edges, so it doesn't pool.But IMO the OP really needs to fix the dip that is causing the pooling with the structure underneath, and increasing the spacing between the boards would also help with prevent it pooling. .

concordnz

420 posts

Ultimate Geek

Trusted

EMT (R)

#3118748 21-Aug-2023 18:49

Another possible effective solution,
(if it does shrink in summer and open the gaps)

In summer get some hard Black plastic (or stainless) Wedges/slices you can hammer down in the gaps where the pooling occurs.

If you have 10-15mm gap between the wedges in the pooling area, this will stop the planks swelling closed completely - and give a 'drain' for the water.

It will also have the side benefit of stopping a lot of the tree fall getting trapped in thoes boards and be easier to sweep that off the decking.

concordnz

420 posts

Ultimate Geek

Trusted

EMT (R)

#3118749 21-Aug-2023 18:50

Hardwood decking can be fitted a lot closer as it doesn't expand in the wet, like Pine does.

mattwnz

19389 posts

Uber Geek

#3118752 21-Aug-2023 18:59

RunningMan:

jonathan18:. (I also think he should have thought about laying the timber 90 degrees to this; the deck runs between the main house and a sleepout, so it would have made sense to have it so water could run off the ends where the deck doesn't sit against a dwelling!)

This is because the grooves in the top surface should run in a different direction to the foot traffic - better grip when walking.

Have the gaps between boards just filled with moss or something? A water blaster may clean that out, but be careful with the pressure - just enough to get the job done, not damage the timber, which can happen if you get too close.

I thought most people put the grooves on the underside, as it allows water to drip off the underside? I personally am not a fan of grooves on the top surface, as it reduces the surface area your foot is in contact with and can be slippery in the longitudinal direction, especially when it gets algae growing on it.

1 | 2 | 3