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Competencies covered

MSFFL2017: Install carpet cushion underlays and gripper accessories

MSFFL2018: Install unpatterned tufted and bonded carpet floor coverings

Dealing with problem subfloors

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Some concrete subfloors can present particular problems when you are trying to fix the carpet grippers and mouldings to the surface with nails.

Below are some of the most common problems and suggested solutions.

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Drummy surfaces

Drummy surfaces have a hollow or drum-like sound when you tap the surface with your finger.

Because of the lack of support under this top layer, a concrete nail is likely to break up the surface concrete and not hold properly.

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If the problem is not too extensive, you may be able to use hardboard nails on the soft sections.

Alternatively, you can fix the carpet gripper into place with adhesive.

If the whole surface is drummy, you may have to remove it completely and apply a levelling compound to replace the surface layer.

In this case, the gripper should be stuck down with adhesive.

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Aggregate surfaces

Poorly finished concrete sometimes shows the aggregate (or 'screenings') protruding above the surface.

This makes it hard to achieve a firm base for the gripper to sit on.

One solution is to grind the surface flat with a grinder.

Another is to chip out the exposed aggregate and apply a filler or levelling compound.

If you do need to use a levelling compound, the gripper should fixed be with an adhesive.

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Sandy surfaces

Sandy surfaces are often found in renovated houses, especially where a fireplace has been removed and the surface is filled with a mortar mix rather than concrete.

Hardboard nails are better than concrete nails in this type of surface material, although you may need to use a longer length nail, such as 50 mm.

Alternatively, you can prime the surface and then apply an adhesive.

A similar problem with crumbling subfloor material can occur in aerated concrete floors.

One example of an aerated concrete product is Hebel Powerfloor, which is installed in 75 mm thick panels and generally laid over floor joists.

To ensure that the gripper is soundly fixed, prime the subfloor surface first, apply adhesive, and then fasten the gripper strip with 50 mm spiral shank nails.

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Uneven surfaces

Ridges and hollows cause problems when the carpet gripper is unable to sit flat, which often shows up in the completed installation.

In these instances, you will need to grind down the high spots and you may also have to fill in the holes and low spots with a suitable filler.

Again, this will affect the fasteners you use to fix the gripper into place.

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Magnesite is a levelling compound that was once commonly used in commercial buildings.

Hardboard nails hold better in this material, but make sure the nail length does not exceed the thickness of the magnesite.

Adhesive can also be used, although the surface should be primed first.

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Learning activity

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You will have covered the topic of patching and levelling in the unit Subfloor coatings and toppings.

Give a brand name product that you would use to patch and fill any hollows in a concrete subfloor after chipping out aggregate screenings with a cold chisel.

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