Large Scale Central

My yard and

Track and Trestles
#1

OK I decided to start a new thread on this so I can get some fresh eyes on the matter. My yard is being built on a cabinet that will be used for care storage and other stuff. The top of this cabinet is a flat surface 5 feet wide and 10 feet long. I need to make the top completely water tight and even be able to have a certain amount of standing water on it. But it can’t leak down into the cabinet. Several methods have been tossed about and I have reservations about all of them.

The idea I have been holding onto is PVC boards glued together on the edges to form a solid PVC surface. While this sounds great I have some reservations. #1 is cost. I just went to HD and the 1X8X12 (3/4 X 7 1/4 nominal) boards are 45 apiece. I would need 9 of them that’s $405 bucks just for the top. Also I am worried that I still have 8 joints. Am a I sure they won’t crack or separate over time? How much does PVC expand and contract with heat, will this cause issues especially at the joints? That’s a lot of money for an experiment. Plus its bright white and would need something to coat it and make it look nice.

What about pressure treated plywood. I could get away with two sheet at $35 a sheet and would have only two joints to contend with. So that only $75 for the wood. I would have to somehow seal the two joints and then would need to apply a coating on that becuase I doubt even PT ply would be great with standing water on it.

Another thought I had was something very thin say Masonite hard board and then pour a 1" slab of cement on it.

No matter what I do I would need to put some sort of coating on all of these surfaces to help protect them and make them look nice. How are flat roofs made. Could I use some sort of roll on asphalt or ??? and then spread some course sand or fine gravel and have sort of an asphalt roof. What about something like SnoSeal that is rolled onto mobile homes and campers to seal their roofs?

I am open to all suggestions. I need to balance cost, practicality and reliability all in one. I have joists placed 10" on center now for support. I just need a practical water proof flat top.

#2

Reading about flat asphalt roofing I am wondering if this wouldn’t work over PT plywood. Lay the plywood and then alternating layers of roofing felt and tar and then finally a tar layer and spread some nice basalt fines over it that will not only look good but be practical as well.

Thoughts?

#3

Devon Sinsley said:

Reading about flat asphalt roofing I am wondering if this wouldn’t work over PT plywood. Lay the plywood and then alternating layers of roofing felt and tar and then finally a tar layer and spread some nice basalt fines over it that will not only look good but be practical as well.

Thoughts?

That sounds like it will do the trick for you.

#4

Devon Sinsley said:

Thoughts?

Yea, just one. Don’t over-think it…(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

#5

No Masonite outdoors. End of discussion, even the tempered will swell.

Only problem with the tar is when it dries out and cracks, will you see them under the paper and rock?

Raise the floor just enough to peak your plywood sheets for drainage underneath. I’d paint the ply with marine grade paint. Tar the seam if you must…

Use the screen method to hold the rocks and scenery and use a ladder for your tracks.

Well that’s my suggestion.

Is it done yet?

John

#6

Ken, ya beat me to it…way overthinking, no concrete either, it’s porous.

#7

Asphalt shingles. Make a roof out of it.

#8

Basically, you need a roof…

#9

Flat roofs have a pitch, so water doesn’t pond on them. Many flat roofs now use a rubber membrane, like a rubber pond liner material. 5x10 membrane shouldn’t be too expensive, but I am not sure how to adhere it to the substrate.

Substrate should be a good quality plywood, outdoor grade would be best. Don’t get the thin stuff, it will warp. Trust me.

Concrete is porous, like Dan said. Water will leach through it. So no concrete.

Tar, will dry out and crack, like John said. I don’t know about roof coating products. I would suspect they are better for coating roofs then straight tar.

Rolled roofing could work, but not on a dead flat surface. The rolls need to be overlapped at the seams, and lapped so the water running off the “roof” doesn’t try and get into the seam.

Here I thought you had a plan. But in reality, you are winging it, just like I do.

#10

With your top framing at 10" on center, you could consider using hardbacker board (probably 3/8’s or ½") and then surface the top after using a good exterior primer/paint. Hardibacker board is very weather resistant. I’ve had some down over ten years with no deterioration. You’ll need to frame the edges for appearance. It is heavy however. It comes in large enough sheets, that you may need only two or three. Sealing the seams shouldn’t be difficult.

#11

Devon.

Rubber membrane is the way to go. at my local hardware store I can buy membrane ten ’ wide in 1’ increments. the glue is available in quart cans and is basically contact cement. depending on local law you can get the good stuff with nasty organic vapors or the water based variety. they each have different application methods but work equally as well if directions are followed. the brand name I used is Rubbberall

http://www.watertighttech.com/products/roofing/

Al P.

#12

I understand not over thinking but this is one place where I think its best to think it through. Keeping flat surface water proof is difficult and I don’t want to be tearing up my yard every few years to fix it. So I would rather think this one to death.

Now for some of the ideas. This in essence needs to be a flat roof. After getting sticker shock at HD I realized that I do not need to reinvent the wheel. People have been making flat waterproof surfaces for years in the flat roof. Here are some of my thoughts. Shingles or rolled roofing worries me unless I can get a decent enough slope so that water cant seep up under the layers. A slope of some sort is desirable anyway and I am not sure how I will accomplish that at this point not that it is built.

Now this cracking business with the tar. If this is an issue then how is a roof done and not leak? I am assuming that the layers of felt are what is holding continuity. Now small superficial cracks may appear but spreading some of the crushed basalt fines over the top should make the appearance look fine and give it a natural look anyway. It just can’t leak. I am thinking this is the route to go for many reasons. Price will be manageable, it should be water proof with several layers of tar and felt (this is called the build up method for flat roofs) and then with the crushed basalt fines it will look natural.

I am thinking if I run some thin strips perpendicular to the joists with a thicker one in the middle and getting thinner as move out I can create a crown in the surface like a road. It wouldn’t have to be much just enough to add slop. I am thinking half inch in the center would enough.

Edited to say that I also very much like David and Al’s idea of using a rubber membrane instead of tar. This could be a good idea.

#13

The rubber membrane is glued with an EPDM adhesive, basically “rubber cement”. You roll it on the membrane and the substrate, let it tack up (dry) then place it and roll it with roller. Might be your best solution.

#14

Looking at the Rubberall site I think this is a great idea. PT ply with a slight crown and then a rubber membrane over it. Even a simple pond liner and whatever adhesive it takes. I like this idea.

#15

I shy away from Hardibacker. I think there must be 2 versions, and the version I bough fell apart during its first spring thaw.

#16

Devon, read my post above…EPDM adhesive. EPDM is the same as pond liner.

#17

When the tar cracked, we’d know after a rain. The bucket had a black mastic and we’d fill all the cracks and feathered the cover out and away. Hoping for a good seal.(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

One hoped for several good years before you added another layer …(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-surprised.gif) beside it was way better than thatched!(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)

John

#18

I think the rubber is the way to go. I know the rubber for a 5 X10 sheet wont cost much. On flat roofs they do ballast it. I am wondering how I can do this and not wash all my ballast away. They put up a gutter and then just lay the ballast in. If I make the gutter out of 1X2 PVC I can make some drain holes in it that can be screened over to keep ballast in.

#19

Rubber roofing is probably one of the better choices. You’ll need to make sure that you have enough overhang on all four sides of the cabinet so water won’t run down the sides of the cabinet. So whatever base you use should extend a couple inches on all four sides past the cabinet face.

Home Depot sells a 4’ x 8’ x 1/2" sheet of PVC. I believe the price is in the $80.00 range. While not quite large enough you would only have three joints to worry about. These would be glued with the Alek glue, usually found near the Alek display. The sheets of PVC are white so you would have to deal with that in some fashion if you don’t want a white surface.

#20

Overhang, or a drip edge Dan?