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Is 'dot and dab' OK?

dot and dab.jpgTo dot’n dab or not to dot’n dab,
that is the question!                    

 

Believe it or not, there is a British Standard (BS) relating to wall and floor tiling. BS5385 says that the tile adhesive should be spread fully over the wall or floor in small sections so that tiles are fixed before the adhesive forms a skin. The tiles should then be pressed and twisted into position ensuring full contact with the adhesive and breaking any skin that may have formed.

But not a lot of people know this, including some tilers! Essentially, this standard means that, ideally, there should be 100% adhesive coverage. Dotting and dabbing the adhesive in lumps, however, means that coverage could be as little as 50% or even less. So, here are the main reasons why tile adhesive should NEVER be dotted and dabbed.

Adhesion

Tiles are heavy things and large format tiles that are increasingly popular are sometimes too heavy for one person to lift or, at least, put into position easily and properly. So, tiles need all the help they can get to stick firmly. The operative word here is ‘all’ meaning 100%. The tiles need, ideally, 100% adhesive fixing to stay firmly in place. With the ‘dot and dab’ method of using adhesive, however, the adhesive coverage could be as little as 50%, sometimes even less, the potential consequences of which are fairly obvious – the tiles can easily drop off or crack!

Voids

The dot and dab method of using tile adhesive leaves gaps or voids under the tiles that can cause significant problems.

Dampness: Condensation can occur in these voids which are also easy routes for moisture. Dampness will break down and weaken the adhesive (which is NOT waterproof) and possibly also the substrate (plaster or plasterboard, for example) thus greatly increasing the chances of the tiles dropping off or coming loose.

Fixings: The tiles will need drilling where bath or shower fittings are required. However, the tiles will have no support underneath where voids occur and, therefore, the tiles will almost certainly crack under the pressure and vibration of drilling.

Vibration/Expansion: Areas of unbonded tile with voids underneath will be prone to vibration, expansion and contraction which can easily result in cracked tiles.

Adhesive thickness: When tile adhesive is dotted and dabbed, the thickness of adhesive is usually much more than it should be. Ready mixed adhesives, for example, should have a maximum bed depth of adhesive of 3mm. This excessive thickness will result in excessive shrinkage of the adhesive as it sets, stress on the tile and, ultimately, failure. It will also increase the drying time of the adhesive.

Support: Wherever there are voids under floor tiling, then, clearly, there is no support for the tiles which will very easily crack or break under the weight of people or fittings.

Reasons for dotting and dabbing

There are probably three main reasons why some tilers use the dot and dab method of using tile adhesive.

Ignorance: Some tilers are not fully aware of the regulations covering tiling or don’t fully understand the function or mechanics of tile adhesive, all the different types of tile adhesive, depending on its purpose and location, or the potential consequences when the method is used.

Cost: Dotting and dabbing cuts down on the amount of tile adhesive used and also the time it takes to apply, thus cutting costs.

Laziness: Some tilers just can’t be bothered to spend the extra time to do the job properly.

Conclusion?

The message is clear – the dot and dab method of using tile adhesive should NEVER be used and any tiler who tells you it’s OK is, well, apart from an unmentionable, just plain wrong!