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Banish that shrinking feeling

A damp start

Problems caused by moisture in subfloors can be avoided by taking steps to ensure that the subfloor is dry and free from defects. At Altro we always recommend installations are undertaken in accordance with BS 8203. The first thing is to carry out a moisture test using appropriate equipment. Sometimes a subfloor appears dry but has hidden problems such as leaky pipe work; usually a pressure test can confirm this. 

The growth of mould is common when a subfloor is damp, causing the adhesive to fail and the flooring to lift. Mould manifests itself as a blue, grey or black discolouration. The mould becomes trapped between the damp subfloor and newly installed covering and can also give off a musty, unpleasant odour.

As well as shrinkage, a damp subfloor can also lead to a pressure build up which causes bubbles or blisters to form. They can be very small or relatively large and often release considerable amounts of water onto the flooring when pierced. Releasing the water can be a temporary solution, but in reality more extensive action is needed to remedy the cause of the blistering.

When speed is of the essence

At Altro, we appreciate that when a floor is required quickly, there is not always time to wait for construction moisture to dry out. If the subfloor is damp due to new concrete but the floor is required quickly, Altro XpressLay safety flooring may be the best option. Adhesive-free, it can be laid without using a damp proof membrane and at up to 97% relative humidity. It has a unique underside emboss which creates air channels, enabling moisture to escape. Altro XpressLay can be walked on straight away and has a 10-year warranty and 15-year life expectancy.

Another option is to use a barrier such as Altro Everlay A or B, which can be laid over a variety of surfaces, including a damp subfloor or flooring that has been exposed to spillages. It reduces normal subfloor drying time, which reduces laying time, and tolerates construction moisture up to 92% relative humidity on floors with no damp-proof membrane.

Sticking together

We recommend adhesive that will do the best job for the type of Altro flooring you install. Using an inappropriate adhesive can mean that the flooring doesn’t take, causing lifting or shrinkage.  Water-based adhesives and damp subfloors, or floors prone to spillages, for example, do not mix well! AltroFix 19 Plus, which is solvent and water-free can be used with all Altro safety flooring, applied to a dry subfloor. Once it is cured, it is unaffected by spillages of water and most other liquids. If in doubt about the best adhesive to use, please contact our customer care centre who will offer guidance.

Bonding Issues

Using adhesive on a damp subfloor can cause bonding problems between the subfloor and the covering. Alkaline salts originating from the concrete can be carried by moisture from the subfloor and can chemically attack the adhesive, causing loss of adhesion between the subfloor and the covering. 

Where there is a water-based adhesive, it will become emulsified and fail. These alkaline salts can also attack the plasticisers in the flooring making it brittle and causing it to shrink. Sometimes moisture from the subfloor can cause the latex screed to delaminate. This can often be seen on the surface of the flooring as a rippling effect. 

Discolouration is mainly seen in heterogenous flooring, although this also occurs in some light-coloured homogenous products. The discolouration tends to appear as a pale yellow colour. This is believed to be the result of substances originating from under the floor migrating into the covering. This discolouration can fade over time as the subfloor dries out but a long term solution is required to prevent the discolouration from recurring.

In all the above cases, the permanent solution is the same. Moisture in the subfloor that is not due to construction should be identified and dealt with accordingly. The cause of any leak must be identified and fixed. Where problems have already occurred, the latex screed and the covering should be removed and replaced. 

With new and existing buildings a damp subfloor should be treated with a suitable damp proof membrane, such as Altroproof Solo Universal or Altroproof Solo Fast Track. Requiring a single coat, they are suitable for use on substrates of high moisture content with a relative humidity of more than 75%. They are ideal for fast-track installations over green concrete and for refurbishments.

If you have any queries about the issues raised in this article, please contact our customer care centre on 01462 489 516, via live chat or @AskAltro on Twitter.

Posted: 12/01/2015 10:29:29 by Lea Charnley | with 0 comments