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Kahoa 02-08-2014 04:46 PM

Waterproofing retaining wall

Building a greenhouse on a sloped hill. A 16 ft x 32 ft retaining 40 inches high consisting of 8x8x16 cmu has been built. The entire interior section will be backfilled with dirt/gravel to make for a level surface inside the greenhouse. The upslope exterior side of the retaining wall and 1/2 of each edge wall will be below grade. A French drain is being installed on the upslope side. Our current plan is to use masonry waterproofing on the exterior below grade sections of the retaining wall only. My question is whether or not the interior below grade portions of the retaining wall need to be waterproofed. Advice is greatly appreciated.


stadry 02-08-2014 04:58 PM

your retaining wall's on the downside, right ? i'd be waterproofing the upside AND installing a drainage system,,, on the downside, leave drain openings in the wall & backfill w/clean 57 stone,,, you don't want to be trapping any water behind the wall,,, not sure what 'masonry waterproofing' material you're using but, if its from the apron/vest stores, it wouldn't be suitable/acceptable for our work,,, we do this for a living !

1 can only waterproof from the exterior side :yes:

Kahoa 02-08-2014 06:07 PM

Thanks for the response. The architect actually specified a drainage pipe on the interior of the wall (inside the greenhouse) on what would be the downslope side just in case there is water buildup within the greenhouse. I'm also putting in a drainpipe below footing level on the upslope exterior of the wall because that is where most of the rain water accumulates. So I'll only waterproof the exterior. I was considering Drylok Masonry Waterproofing as it is locally available. We live in Hilo, Hawaii, and there is not much to choose from. I there another product that you would recommend?

stadry 02-08-2014 06:26 PM

thought that might be what you had in mind :furious: its good IF you don't have to rely on it serving the purpose for long AND you'll have time to redo it fairly often :censored: we use hlm5000 - call these guys - - they'll have it or an equal,,, basf's the manufacturer & they're ALL over the world :thumbsup:

good luck !

ps - wear long sleev'd gloves & put it on w/long handled brush - find them in the cleaning section @ apron/vest stores

joed 02-08-2014 06:54 PM

Not sure I totally understand what you are doing, But I think you are filling the inside of a retaining wall to make a flat surface. Why would you care about water proofing the inside. Let the water leak out to the outside. It will releave any pressure the water build up will create.

Kahoa 02-08-2014 08:22 PM

Thank you itsreallyconc and joed. I'm squared away now. Fortunately there is a vendor across island that should have the hlm5000.


Daniel Holzman 02-09-2014 08:53 AM

Not quite clear on your objective. A retaining wall is usually designed to retain soil, NOT water. Interlocking block type retaining walls (Versalok etc.) are not intended to retain water on the uphill side, hence the need for a drainage pipe along the bottom of the wall, which carries water safely around the wall, and eliminates static water pressure.

If your drainage pipe works correctly, there will be no water pressure on the uphill side, hence no need to waterproof the uphill (or downhill) side of the wall. If the pipe does not work correctly, and you successfully waterproof the uphill (or downhill) side of the wall, you need to make sure the block is rated for the extra pressure. Very few are.

The only exception I can think of is the design of a retaining wall to hold effluent in a septic system. The wall needs to be waterproof, but for this reason it is rarely made of block, rather made of concrete with a waterproof membrane on it. I have only seen a few walls like this, they need to be designed to handle the additional static water pressure.

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