Sealing the spacing of Pine Decking Boards

[JoshuaMars]

Hi there Fellow wood workers.

Im in the middle of errecting a kids cubby house, double story.

The top story is a large deck and the floor of it will be the roof of the bottom level which I want to be water sealed.

Is there anything I can seal between the boards to seal the deck to make it like a roof.

Thanks in advance.

MARSY

[silentC]

Assuming that it's level, if you seal up the gaps, the water will have nowhere to go and you'll end up with a pond up there and, eventually, rotten boards. If you want it water tight, you probably should build in a slight fall so the water runs off. Have you installed this decking yet? If so, what gap do you have between boards?

[JoshuaMars]

Nope, the decking is not nailed yet, Dont think the level issue will be a problem either. Its not fully level. After all, its only a kids cubby and was my first attempt at a construction type work.

The gap I was thinking was the old 3mm idea. its only 2.6m by 2.6m

Any idea.

MARSY

[Bleedin Thumb]

Nope, the decking is not nailed yet, Dont think the level issue will be a problem either. Its not fully level. After all, its only a kids cubby and was my first attempt at a construction type work.

The gap I was thinking was the old 3mm idea. its only 2.6m by 2.6m

Any idea.

MARSY

Marsy,
The 3mm rule is for hardwood that tends to shrink with age, softwood on the other hand tends to swell. I usually leave 6mm (or greater) on kids play decks as the dirt and stuff falls through easier and doesn't block the gaps.
As far as making the top waterproof.. I did one at my place by placing FRC sheeting over the decking and sealing the joints with mastic compound.
It works very well but looks very ordinary. but for kids stuff...
As Silent stated make sure the water can run some were that it wont cause problems.

[silentC]

OK, well in no order of preference, here are some ideas in addition to Bleedin's:

1. Use ply instead of decking and seal it with bondcrete or marine enamel.
2. Use 10mm cement sheet (expensive) instead of decking and seal joints with mastic.
3. Mill tongue and groove on the edges of the decking
4. Make the roof from fibro or something and erect the deck over the top with a gap between. Put plenty of fall on the roof.

I made an exposed platform on a cubby for my kids with cheap pine ply. I sealed it with some marine gloss enamel that is recommended for traffic areas on boats. It has lasted 3 years so far. Looks a bit shabby now but still intact.

[JoshuaMars]

Ive seen Tonge and Grove pine decking at Bunnings. Might be the way to go.

Should I still seal between the decks though?

It is a shame there is no elasta seal that could do the job if there was 6mm spacing.

MARSY

[silentC]

How waterproof do you need it to be? Do you want it to be absolutely watertight?

Another way you could do it is to use a plastic membrane under the deck. Make the slope run with the boards, so the water runs into the gaps between the boards and then out the end. Or leave a gap under the deck and hang a tarp in there.

[Bleedin Thumb]

Ive seen Tonge and Grove pine decking at Bunnings. Might be the way to go.

Should I still seal between the decks though?

It is a shame there is no elasta seal that could do the job if there was 6mm spacing.

MARSY

Marsy,
What you describe sounds like a caulking exercise as you would do with a boats deck. However pine isnt really suited to this use as it expands and contracts too much, you also still need ply underneath which makes it uneconomic.
I would go either #1 or #2 of Silences' suggestion or put thin fibro over the deck boards as I described.

Edit More I think of it I would go #1 option using sealed marine ply.

[JoshuaMars]

Ply does sound like it could be a good choice.

How thick do you think?

Plus with the watertight question.

Would like the kids to be able to play in it and even leave toys, paper, stereo in it without worrying about water damage.

Is bondcrete or marine enamel expensive? I need to cover 2.6m by 2.6m

Ive read previous posts with people who have used sealed marine ply, most have only had for under 5yrs and said that its stood up to time, but is looking a bit untidy. Im looking to keep mine for next 15 yrs min.

Cubby house WIP pics to come.

[silentC]

Depends what you are putting under it in the way of joists. I used 16mm but it was only spanning about a metre.

It's a shame it's not 2.4 x 2.4 because you could have done it with two sheets. You will need three and you'll have to be clever about how you lay it out so that you don't have a pissy little 200mm strip.

Bondcrete is dirt cheap. It's basically watered down PVA. You give it a few coats to seal it. The marine enamel is quite a bit more expensive. I can't remeber how much mine was. I bought Norglass Marine Clear Gloss. You would need to check the tin to make sure it's OK for high traffic areas. They also make a deck paint that has non-slip particles in it. It's not suitable for sealing but I sealed with the gloss then painted the non-slip on so the kiddies wouldn't go asre-up.

I didn't use marine ply - I just used cheap stuff (about $80 a sheet). My plan was to seal it well so that water couldn't get in. I painted the floor with clear gloss and the walls and ceiling with coloured enamel, in all different colours.

If you pay attention to waterproofing the rest: walls, doors, windows etc. there's no reason that it wont be as water tight as your house. If you seal the ply and the joins and put a good fall on it so water runs off it should be OK.

Maybe some of the boaty people on the forum might have something to contribute?

[JoshuaMars]

My spacing is 45cm so Im quessing 16mm ply would be amble.

I think I will go the Ply with the bondcrete. The top deck will hardly been seen unless you up there so Im happy with that.

Below is a link of my work in progress of the cubby.

http://www.woodworkforums.ubeaut.com...793#post385793

Any hints and indeas?

MARSY