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Safe sealer or liner for concrete raised beds

I appreciate any help I can get on this: We recently built an energy-efficient greenhouse and the mason just finished building the concrete block raised beds. We need to seal or install a liner inside the raised beds to keep water (from the soil) from leaching through the seams of the concrete and we also need this sealer/liner to be safe for growing edible plants and trees (i.e. not leaching contaminates into our soil). We will mostly be growing fruit trees but plan on growing vegetables as well. Can anyone give us advice one what products would be appropriate?

Thanks so much! We look forward to your ideas.

Asked by Leah Marshquist
Posted Thu, 04/10/2014 - 07:45

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6 Answers

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1.
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Leah,
The two most likely products are epoxy paint (the type used for aquariums -- "fish-safe") and pond lining material.

Several web forums included references to Sweetwater epoxy paint; but it seems that Sweetwater no longer exists. It may have been purchased by Pentair: http://pentairaes.com/plumbing-electrical-paint/electrical-paint-safety/...

Here are some links that you might find relevant:
Grow Bed Liners

Alternatives to using liners in cement grow beds?

And while I was doing some web searching on this issue, I came across a web page that really won't help you, but is still very interesting:
Good Earth Aquaponics.

Answered by Martin Holladay, GBA Advisor
Posted Thu, 04/10/2014 - 09:08
Edited Thu, 04/10/2014 - 09:09.

2.
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I'm confused. Why is water passing through the concrete a problem? Are you worried about contaminates in the masonry?

You may be better off not lining the beds. Growers use clay pots for planting because they let water pass through. We put a hole in the bottom of our pots to let excess water flow out. These reduce the chance of mold or rot or waterlogged soil. You need to get rid of excess water in the soil by some method or your trees will die. Evaporation from the surface will not be sufficient, IMHO.

Answered by stephen sheehy
Posted Thu, 04/10/2014 - 11:06

3.
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Thanks, Martin, for the links! The "fish-safe"/ aquaponics angle is really helping my search. I found this liner that looks good: http://www.theaquaponicstore.com/DuraSkrim-Liner-s/134.htm Any thoughts?

Stephen: The raised beds should not have water passing through them for a few reasons. One is that concrete is known to make soils more alkaline over time and since we are growing a lot fruit trees that prefer acid soils, this was a concern. Originally, we planned on using Thoroseal which is what we used on our foundation but it is cement-based so are off to find a new solution. Another reason why we don't want water passing through is because eventually it will discolor the stucco finish and undermine the construction of the beds themselves. There is drainage at the bottom of the raised beds and we will be creating a soil mix that maximizes drainage. We were struggling to find a good sealer or liner that was good for maintaining the integrity of the masonry work while also not contaminating our soil. We also plan on incorporating worms in the raised beds to increase drainage.

Answered by Leah Marshquist
Posted Thu, 04/10/2014 - 12:11

4.
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Leah- I'm intrigued. We're designing a new house and a greenhouse is on our long-term wish list. What state are you in? What size is the greenhouse? How big are the beds? What fruit trees do you plan to grow?

Figs would be at the top of my list. Here in Maine, figs are impossible outdoors, even with the usual tricks. On the other hand, peaches do pretty well.
Is this a commercial operation or just for your own use?

Answered by stephen sheehy
Posted Thu, 04/10/2014 - 15:35

5.
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Stephen- Thanks for asking! Our greenhouse is near completion. We have a flight of stairs that needs to be built, a mis-ordered door to be replaced and a cistern to be connected to the gutters. After that we are sealing the raised beds and then filling them with 18 cubic yards of soil. Big job!

Here are some photos of the project. It does not photograph very well so it is hard to understand but we designed the greenhouse to be passive solar while also putting in a Subterranean Heating and Cooling System which uses a phase change to capture and store heat to be used later. We have not gotten to try the system out yet because we built the heat sink and greenhouse in the fall when there was no heat to capture. Because of this, we got to see how well the passive solar design of it worked on its own without any heat and we are really pleased! It never got below high 40s in the greenhouse when outside it was windy and only 1 degree out! We used Intus triple pane windows with spray foam insulation and are really happy with the results. The tiering of the raised beds will make it so that the fruit trees do not shade each other and also exposes more thermal mass surface to the sun to store more heat passively.

The greenhouse is 600 square feet and we hope to grow sub tropical fruit trees and see if we can get away with growing tropicals as well. In one of the pictures is a little room that is formed by raised beds. We eventually plan on welding an arbor over this space to encompass the room, with Dragon Fruit vines growing on the arbor. We'll build benches lining the inside of the room and because it is exactly the size of a queen size bed, we can roll slats across the benches to provide a support for an air mattress. So, this gives us a place for guests to spend the night -sleeping with the smell of dragon fruit flowers!

The main aisle of the greenhouse is wider than usual -typically you want to minimize the aisles and maximize growing space. We chose to make this a "flex space" where we can have our pomegranate trees in pots on wheels and I have designed table tops to go on top of the pots to transform them into tables. Lining the sides of the raised beds in the aisle will be fold away benches that I designed. This allows us to primarily use the greenhouse as growing space but for the rare times we want to have a large dinner party (like on special holidays) we can transform the greenhouse into a large dining room that seats 22 people. This makes our relatively small house, that much more useable. We don't have a dining room, we have a small living room and small bedrooms (all features we like) but it is nice to have auxiliary space to draw upon. -Especially space that is not heated with fossil fuels!

I would love to hear more about your greenhouse plans! Figs sound great to me! I know Logee's in Connecticut sells a hardy one but it might be Maine-hardy!

Leah

GreenhouseOutside.jpg TieredRaisedBeds.jpg TieredRaisedBedsStucco.jpg ArborRoom.jpg Interior.jpg Drain.jpg
Answered by Leah Marshquist
Posted Thu, 04/10/2014 - 17:42

6.
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Stephen- I realized I never answered your question about what state I am in. I am in Massachusetts in the Metrowest Boston area.

Also, that last photo is of the drain we put in our slab. We just boxed it out, let the slab guys work over it and now we are taking the boxes out and filling the space with gravel. After we install a liner or sealer and fill it with gravel we'll put landscapers cloth over it to complete the drain. It drains into our heat sink (you can see the gravel of the heat sink in the photo).

Leah

Answered by Leah Marshquist
Posted Thu, 04/10/2014 - 17:49

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