I have painted walls and wood work before Having just had a wall re plastered that I intend to paint with emulsion, the plaster is drying out nicely but I wondered how Ask a tradesman. Like 4. Like 0. Generally after a week. Related Questions I need to build a 51' long by 5' high wall. As a general rule, the cheaper the mix, the greater the shrinkage. Also, since the rate of contraction slows as the concrete ages, the time between the placing of the concrete and the laying of the tiles is important in determining the stress upon the flooring system.
The shorter this period i. The stress from the contracting concrete substrate is compounded by the tendency for ceramic tiles to expand. The most common and largest cause is thermal expansion. As the room is heated by the sun or heaters, the ceramic tiles start to expand as they heat up. However, as ceramic tiles are not good conductors of heat the concrete substrate is much cooler and therefore expands at a much slower rate.
The SABS standard for locally manufactured ceramic tiles which meets the AIIa European specification will, according to international literature, have a thermal linear expansion rate of approximately 0.
Another source of expansion is irreversible moisture expansion. This type of expansion is often misunderstood and only occurs when certain types of crystalline structures of clay are present in the body of the ceramic tiles.
When these crystals come into contact with water, they react with it and swell which in turn increases the size of the tile. Tiles that are prone to irreversible moisture expansion also have massive problems with the stability of their glaze as they tend to craze i. As this is huge quality issue for ceramic tile manufacturers, irreversible moisture expansion is very closely monitored and therefore a very rare phenomenon.
Tiles that meet the AIIa European specification will have an irreversible moisture expansion of less than 0. Since each component moves at different rates and sometimes in opposite directions, the movement creates sheer within the thin adhesive bed.
When the sheer force exceeds the tensile strength bond strength of the adhesive de-lamination occurs. The maximum bond strength is determined by the mix design of the tile adhesive. The more cement and additives used i. Bond strength, however, is also proportional to amount of contact between the tile surface and the adhesive i.
Then the actual bond strength will only be 0. Thus poor application technique can dramatically reduce bond strength. Another important factor is the porosity of the tiles or the substrate. If the porosity is high, moisture is sucked out of the tile adhesive which results in partial hydration of the cement and a weaker strength development of the bond. This is an increasing problem in South Africa with people trying to contain building costs by reducing cement content in concrete floors and plasters.
Low cement content equals increased the porosity. It is important to note that a strong bond is only part of the solution. From a theoretical point of view, the sheer stress in a system with a rigid tile i. As discussed previously the greatest contributor to the sheer stress is the concrete and its rate of shrinkage.
The easiest way to counter this is by ensuring the concrete is given sufficient time to cure before tiling. The SABS standard calls for a minimum period of 28 days from the laying of the concrete and tiling. With fast track building this period can often not be adhered to. In this case, the bond strength and the flexibility of the system must be increased to handle the higher stress.
The most common methods would be to:. The ambient conditions and characteristics of the installation are important, especially the potential for large temperature fluctuations. Dark coloured tiles on a north facing external balcony will expand and contract significantly more than a light coloured tile in a south facing room. In winter, the difference between the maximum and minimum temperatures is at its highest and consequently tile expansion and contraction is also at its highest.
This effect is further compounded by people using heaters, fires and underfloor heating to warm rooms. The size of the tile is another parameter which affects sheer stress. As the tile size increases so does the sheer stress in the system. This is evidenced by the fact that as the size of tiles has increased in recent years, so has the incidence of tenting.
Once a tile is above mm x mm, the use of a flexible polymer modified adhesive is recommended. As mentioned earlier the quality of the application is vitally important. A good quality tiler can make a poor quality adhesive work while a poor quality tiler will make the highest quality adhesive fail.
Another important factor is the thickness of the tile adhesive bed under the tile. Once the bed thickness drops below 4 mm the sheer forces increase above the tensile strength of an entry level European C1 tile adhesive. In the South African context, this is often the result of incorrect trowel choice or excessive bedding by tilers trying to extend the adhesive and maximize the amount of m2 tiled per bag.
The European standard for the application of tile adhesives calls for a thin layer of adhesive to be applied first with the flat side of a notched trowel. Thereafter additional adhesive is applied and raked with the notch side of the trowel. This procedure ensures that the bed thickness is at least 4 — 5 mm. Another common error found locally is when the excess tile adhesive has not been removed from between tiles prior to grouting as per the SABS standard.
Tile adhesive is relatively hard and it tends to transfer sheer stress from one tile to another. This results in huge sheer in the middle of the tiled room and tenting. A properly designed grout is softer and more flexible to allow it to act as a cushion to help reduce the transfer of sheer.
This is, however, only half the story as sheer stress also increase as the joint width decreases. There is a trend towards smaller joints but clients must be informed that this will increase the risk of an adhesion failure in the project.
One of the more important application practices to reduce sheers forces is the installation of perimeter and intermediate expansion joints. Expansion joints break the transfer of sheer across the floor resulting in lower stresses at the centre of the panels. Since expansion joints localize failures to within the panels, repair work is quicker and more cost effective as the areas to repair are smaller.
In a tenting failure, the ceramic tile usually comes clean off the adhesive bed leaving an imprint of its backing. This is often misinterpreted to be a sign of a poor quality adhesive. Any tips for tiling direct to plaster? How long does it need to dry?
Tiling onto plaster is relatively straightforward, provided you have prepared properly and use the right tools and products. Make sure you plan ahead to prevent any mistakes — take care with your setting out and ensure the surface is clean, dry, sound and flat. Before you start tiling, ensure that the tiles you are using are suitable for the surface you are going on — and that includes plaster.
If the wall has recently been plastered, you should allow 4 weeks drying time, before brushing with a stiff bristle brush and priming with Dunlop Tilers Primer diluted with water when using ready-mixed or two neat coats when using cement-based adhesives.
It is vital that any areas of damage are repaired with a filler or even re-plastered if necessary!! Building-up of the background may also be necessary to achieve SR1 surface regularity so there is no lippage. SR1 is a maximum of 3mm of deviation over a 2m straight edge. When tiling in a wet area, water sensitive backgrounds including plaster, will need to be waterproofed or tanked. A perfect product to achieve this would be Dunlop Shower Waterproofing Kit. Simply use a brush or roller to apply the Waterproof Primer to the shower area walls and floor if required to the required height and leave to dry.
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