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Renovation & Design

Applying new subfloor over old tiles should be OK

Alex Schuldtz / Holmes Group

TV host and contractor Mike Holmes installs insulated subfloor panels in a basement.

Question: I have a quick question about the laundry room floor in the basement. There are many damaged areas of vinyl tile and it isn’t stuck to the concrete floor well. We’ve removed most of it. There has not been any actual water in the basement, but it had very high humidity in the summer until we put in a special exhaust fan. To make it usable we temporarily put rubberized interlocking flooring down, but I’d like to make a more permanent fix. Can I safely put a new subfloor product, like Dricore or Barricade, over top of the damaged vinyl, assuming it isn’t too uneven, or do I need to remove it? The websites seem to suggest I can just go over top. Should I put down some kind of barrier or spray it with a sealant or something? Thanks for the help, Marshall P.

 

Answer: Installation of most pre-manufactured subfloor products are normally designed to be installed over any surface, regardless of condition. Laying it over top of your older vinyl tile should not require any modifications, unless there are significantly uneven sections, which may require some floor levelling products before installation.

For the last decade or more building product manufacturers have realized the need for inexpensive, moisture resistant subfloor materials to be used over existing concrete floor slabs. These products provide a relatively stable and smooth surface, which provide a good substrate for flooring materials to be installed. Many of these modular systems are approximately two feet square with tongue and groove edges. Because concrete floors can be prone to condensation and moisture issues, especially in basements, the subfloor must incorporate a mechanism to prevent moisture damage. While this may vary between different brands, it typically will include dimpled plastic sheathing or some form of foam on the underside of the wood-based squares. The benefit of using a composite or extruded foam underlay is that it will protect the top surface from rotting, while providing a good thermal break, which makes the finished floor warmer.

Modular subfloors are designed to be placed directly over an unfinished floor, but most will accommodate installation over several types of older flooring. Since concrete floors can be uneven due to settlement and cracks, the underside layer will have some flexibility for small inconsistencies. If these deflections are more than minor, plastic shims or other levelling products may be available for use, often sold with the subfloors. Alternatively, common floor levelling compounds could be mixed and spread over the uneven surfaces, which have been used for this purpose for decades by flooring installers.

When dealing with older floor coverings which were adhered directly to the older concrete surface, like in your home, the need for removal will depend on two main factors. Firstly, how uneven is the surface between areas of missing or deteriorated flooring and those which are still intact? If the flooring is thin vinyl tile, like in your basement, there should be very small differences between the good and bad sections. Most vinyl tiles are only a few millimetres thick, which should be well within the tolerances of the modular subfloor. As long as the individual subfloor sections do not have significant areas where they join overlying a depressed portion of concrete, they should be good. Even in that situation, rot resistant shims could be used to line up adjacent sections, if necessary.

The second condition to evaluate is whether the existing flooring will be subject to moisture damage or mould growth after covering with the new subfloor. Some forms of vinyl flooring materials have a wood-fibre based backing, while others will be solid vinyl throughout. If you have vinyl sheathing with that type of underside, which looks like paper or cardboard, then removal may be necessary. Because the new subfloor will create a partial vapour barrier, due to the plastic or foam insulation backing, it may create an ideal environment for this to occur. While it will protect the surfaces above from moisture, the new subfloor may promote condensation and mould growth due to the prevention of heat and air circulation underneath. On a bare concrete floor this should pose little concern, but in flooring with a paper-like backing it could surely occur.

From your description it sounds like you have older floor tile, which is most often composed of solid vinyl. That material should be as moisture resistant as it comes, so worrying about mould growth should not be of much concern. Since many tiles are loose already, removing and disposing of them should be simple. Where they are still well adhered to the concrete, leaving them intact may be the best choice. Many older vinyl tile have embedded asbestos fibres, which are only released during physical damage, often during removal. So, leaving the older tile undisturbed, as long as they are stuck down, will be prudent. If there are several moderately uneven sections, mixing up some floor levelling compound and trowelling it to straighten out the area should improve the smoothness of the new subfloor.

Modular interlocking subfloor systems are normally quite adaptable and designed to be laid down over top of slightly uneven surfaces. Removing all of the older vinyl tiles should not be necessary unless the floor is substantially uneven, which may be fixable with the use of some shims or common floor levelling compound.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

 

 

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