Liquid Rubber on raised SubFloor in a damp basement?

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Posted by: from Lasalle
9/18/2013 at 7:20:32 AM

My basement is damp and we just had a 4" water flood from a leaking shower drain that we only noticed 5 months later (the water collected without us knowing). Now that the damage is done with the wooden footings rotting below the raised plywood. We need to replace everything including the warping hardwood floors. We've already decided to go with either engineered wood or most likely some sort of basement approved laminate. The problem is that the concrete floor is lower at the center of the 24X24 basement. The current floor is raised 2 inches at the walls, and 6 inches at the center. We want to replace the floors to the same height since the walls and doors are not coming down and we simply need new floors. We also want to make sure that ...

A - No wood touches the concrete floor (which it currently does)

B - All wood under, including the footings/joists and even the plywood, is protected from moisture and humidity coming from the concrete

C - If there is ever a leak, we don't want the subfloor wood to absorb it

D - We need water to evacuate on it's own

For the last part, we were told simply to open up the central drain. At the moment it is sealed shut to prevent water coming in from the city. I was told to put in a valve and then a proper grate. Sounds simple enough.

Now for the wood...

I was told to use this product called BLUE WOOD but apparently my contractor was laughed at and told to stop watching TV when he went to buy some. He was advised to instead use regular wood, not even to use pretreated wood. Also, blue wood is apparently not available in Quebec.

So his backup idea is to pre-treat all the wood with a product called Liquid Rubber. The idea sounds good, even if it's more time consuming and costly. Anyone ever done this? Any opinions?

We tossed around the idea of using those dimpled plastic membranes directly on the concrete floor, but since there is such a steep incline, it would not work as well, plus the fact that if there were to be a leak, then all the water would collect in the center of these dimples. The dimples allow for airflow underneath it but does nothing on top to prevent water collecting.

Any thoughts?

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Date/Time9/18/2013 at 11:25:57 AM


Sorry to hear of the problem. Two thoughts come to mind.

First is the drainage issue. Any moisture/water has to have someplace to go. Whether it be the result of a flood or over-flow or simply moisture from the air and ground, there needs to be a natural process to allow for evaperation and dispersment.

The second is that it might be worthy for you to consider re-surfacing the cement floor with a levelling compound.

I would suggest that you talk with a structural engineer about this issue and get his/her recommendation. The drain thing ... a check valve may handle your concerns about back flow. Regardless, you should get professional advice (plumbers cement workers, flooring experts) and be a little suspicious of the big box store advice. Problems like yours are not the norm and may require unique consideration.

Nice place ... Lasalle, I use to live in Westmount and had a good friend in Lasalle.

Good luck.


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Renato in Lasalle
Date/Time9/18/2013 at 2:28:53 PM

Thanks for your reply.

Resurfacing the concrete would be great except it would mean having to TOTALLY gut the basement which is not an option. The walls, stairs, fireplace, etc..., must stay as is. Resurfacing would mean to take it all out and start from scratch. The raised subfloor is the only option I can afford and is basically a replacement to the existing floor.

Thanks again for your advise.

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Date/Time9/19/2013 at 7:45:22 PM

One suggestion would be to build the sub-structure with SPF lumber, but sit it on dense foam board. The foam board could be shaved to act as shims. You would want to make sure you have plenty of ventilation under the sub-floor, as you don't want moisture to accumulate. I have heard of installing mechanical ventilation to suck the air out from below the floor. This is assuming your basement is relatively dry to begin with and you don't have leaks through the foundation.

You may be violating building codes with respect to clearances to combustibles for the furnace, water heater, etc. Also, you are not supposed to cover the floor drain. You may want to check with the municipality.

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Date/Time9/22/2013 at 10:00:07 AM

First I would open up the center floor drain and install a backflow preventer. Without a drain your basement is basically an aquarium that will hold any water that gets in. You also have to find and fix the source of the moisture.

The dimple products work by allowing any water that gets in underneath it a clear path the drain and out of the basement. It also allows airflow so you don't have moisture and mold problems, and it keeps the wood from direct contact with the concrete and water.

You can use regular wood but I would strongly recomend pressure treated for the floor joists. The liquid rubber I would avoid, it sounds expensive and time consuming. Also there is the chance of not getting even coverage and the rubber will not allow the wood to breath and might cause rot problems latter on. With such a steep slope (4" over 12'), you don't have that many options for a level floor. I would lay down 2x6 pressure treated lumber cut to the slope of the floor on 16" centers and lay down some kind of ridgid insulation in between.

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Jeff from Newson Interiors in Dunrobin
Date/Time9/24/2013 at 6:53:01 PM


Sounds like there was an awful lot of amateur engineering going on in your basement.

The floor drain should never be blocked. If it were open the shower leak wouldn't have collected and damaged anything. It shouldn't be covered at all as you cant access for possible service as well the trap can go dry and with no water sewer gases are entering the house.

The minimum slope for the basement slab is 1/4" per foot toward the drain. Assuming the drain is in the center there is twice the required slope. There is no easy fix for this really. I'm guessing from your description that the partition walls are placed on top of the built up floor. They would need to be removed to restructure the sub-floor so walls and door heights become insignificant.

If the basement was damp even before the shower leak you need to address the cause of that before spending anything on reconstruction.(foundation leak, lot grade, hydraulic pressure etc).

I would definitely use some type of dimpled underlay system (DMX) and put your floor structure on top of it. ( no wood touches concrete) The membrane must be open at the floor drain so any water on top can find the drain.(water can only get on top from an inside plumbing leak) foundation moisture will remain under the membrane, and run to the drain. Don't use any other waterproof membranes as moisture will get trapped between the 2 layers.

The back-flow preventer is a good idea as well if your area has a history of sewer back up.

There is no easy answer, but I hope that helped.


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