GENERAL PROBLEMS AND LAYING TECHNIQUES
The general techniques that must be taken into consideration for indoor flooring projects are less demanding than the ones for outdoor flooring and they only involve the problems related to technical joints in special cases in which – depending on the considerable size of the surface to be floored and/or the particular working conditions of the floor itself – it is advisable to use expansion joints that can absorb variations in the flooring caused by temperature swings. The joints that are left open between the terracotta elements (in correspondence with the technical expansion joints made in the sub-floor) should not be grouted with mortar or synthetic grout, but closed using specially designed rubber strips or, better yet, with special sealing materials that can handle any deformation. For average-sized indoor flooring, it will be sufficient to prepare an open joint around the edge of the floor field near the vertical walls, which can be absorbed visually by the thickness of the skirting that is used. When particularly large floors are being laid, it is advisable to have technical joints every 6 to 8 meters, both lengthwise and crosswise. In general, it is important to note that the overall process involved in completing an indoor terracotta floor that can be utilized and enjoyed fully is based on a series of work phases that can be summarized as follows:
- laying the terracotta elements
- sealing the joints
- washing the floor field
- treating the flooring.
LAYING THE TERRACOTTA ELEMENTS.
The phase involved in laying the terracotta elements generally begins once the masonry work and painting have been completed (with the exception of completing the finishing coat if necessary). With all types of laying, the elements must be laid in the direction of the groove. In modern execution procedures, there are basically three alternative criteria related to the laying techniques used for terracotta elements: 1. contemporary (using synthetic adhesives); 2.modern (semi-wet mortar laid as a screed; 3. classic (promptly-laid wet mortar).
CONTEMPORARY (using synthetic adhesives)
The first laying system is the one involving a gluing technique (using industrial products that have recently been introduced in building practices). This technique can be used on existent floors as well as on screeds that have been prepared especially for this purpose and have dried completely. This system, which is particularly suited for restructuring and restoration work, offers the advantage of working with adhesives that have a low moisture content, thus making it possible to carry out final floor treatment after a much shorter amount of time than the other laying techniques described above. There are various types of adhesives available, but it is essential to follow all the detailed instructions given by the manufacturer. The main execution phases involve: 1. Preparing a sub-floor (screed) that is perfectly flat to make it easy to keep the terracotta elements level with each ther, since only a thin (3-5 mm) layer of adhesive is used (thus offering very little laying adaptability and tolerance). 2. Cleaning the laying surface (thoroughly removing debris, dust, oil or other types of residue) once the screed is completely dry, before starting the actual gluing of the terracotta elements. 3. Preparing a uniform layer of adhesive, using a special notche trowel to spread it in a layer that is 3-5 mm thick. 4. Laying the terracotta elements so the timing corresponds to the quick-setting of the adhesives being used, without letting the glue create a “film” due to prolonged exposure to air. The terracotta elements must be ”thwacked” evenly on the adhesive – either individually with a rubber hammer or using a roller-vibrator machine over larger flooring areas – so that the gather surfaces of all the terracotta elements are in contact and set with the glue 5. Preparing the “open” joints between the various terracotta elements according to design specifications (generally 4-5 mm), using special spacers if necessary.
MODERN (semi-wet mortar laid as a screed)
The second laying system involves spreading bedding mortar over the entire surface to be floored (or, to facilitate optimum building-site management, over larger areas) in the form of a well-compacted and leveled semi-wet screed. More specifically, the main execution phases are as follows: 1. making the bedding screed for large areas of the flooring surface (thwacked and leveled with a “straightedge” so it is perfectly flat) that will have a tacky consistency and a thickness of at least 3-4 cm for the subsequent laying phases of the terracotta elements. 2. Dusting an adequate amount of dry. cement (cement powder) over the screed. 3. Laying the terracotta elements after wetting them with water to facilitate consolidation with the screed, taking advantage of the setting action of the cement powder. 4. Preparing the “open” joints between the various elements in terracotta according to design specifications (generally 3-5 mm), using special spacers if necessary. 5. Compacting using a roller vibrator (in order to ensure complete setting and consolidation of the terracotta elements with respect to the bedding support) and wetting the laid floor. CLASSIC (with wet mortar laid immediately when the individual terracotta elements are put in place) The third system involves forming the screed and setting surface for the terracotta elements. This is done in a single operation. In essence, the leveling screed and the support surface used for setting the elements are completed at the same time. This is done immediately rather than working over a large area, so that the bedding operation of the rather wet mortar coincides with the process of laying the individual terracotta elements. In effect, the process is similar to the masonry technique used for fair-faced brickwork: the mortar is “loaded”, the terracotta element is laid and then the excess mortar is scraped away with a trowel. Obviously, this criterion is suitable when laying large terracotta elements (over 30×30 cm) and above all when using handmade terracotta where, due to the greater and more evident shape/size tolerance of the different pieces produced using hand workmanship methods, it is advisable to use more flexible laying criteria that can adapt to the specific geometric aspects of each individual element. The fact that the screed has not been spread completely flat over an extended surface area allows the layer to prepare a bedding thickness (together with alignments and joint spacing) that can adapt to the needs of each terracotta element. The use of cement lime mortar (instead of cement mortar) makes it possible to copy the laying methods and thus the appearance of the terracotta flooring that has been part of the glorious historical Italian tradition. This type of laying involves preparing “open” joints, according to design specifications, that must generally be at least 5-6 mm in width, using spacers if necessary.
SEALING THE JOINTS
Regardless of the type of laying technique being used, before proceeding you must wait at least 24 hours after the last phases involved in bedding the terracotta elements have been completed. The “grouting” operation completes the “rough” laying of the flooring that will remain visible. As we mentioned above, this is carried out by filling and compacting the joints that were left open when the terracotta tiles were laid. The joints can be sealed using two different kinds of specific preparations • cement-based mixtures; • industrially-prepared synthetic grout. Cement-based grouting The use of cement-based mixes makes it possible to grout joints with a repetitive thickness (3-6 mm) that can also be larger based on design indications. In general, we can subdivide these joints into three size ranges: up to 5 mm, from 6 to 10 mm, and over 10 mm. Joints up to 5 mm. For this type of joint, you must prepare a rather fluid cement grouting (composed solely of “325” gray cement and water) that is then poured over the flooring surface and spread particularly along the grouting lines using rubber-ended trowels until all the joints have been filled. During subsequent phases, the excess cement is cleared from the floor using a damp sponge and before the grouting has a chance to harden, river sand (fine, dry, clean sand) is rubbed carefully over the floor field using a medium-hard broom (broomcorn types are ideal). This operation using sand serves two purposes: the first one is to clean off any cement residue through abrasive action, while the second one is to create a sort of “frame” for the joints (once the sand has adhered to the surface layer of the joints), thus mitigating any shrinkage in the initial mixture composed solely of water and cement. Joints from 6 to 10 mm. With this type of joint (which we can consider average in size), you can proceed directly to mixing clean silica sand (100 lt), “325” gray cement (80 kg) and water. The mixture is then spread over the floor and at this point, again using a rubberended trowel, it is carefully allowed to flow into the joints and is tamped down. Before the grouting material has hardened, a dry mixture of cement and sand is spread over the top and is rubbed vigorously over the floor field to consolidate the surface structure of the mortar joints and carry out an initial basic cleaning of the field. This operation is completed by removing the excess mortar, cleaning the surface with a damp sponge and completing each individual joint. Joints of over 10 mm. The same procedure described above is used for this type of joint (not generally used in laying indoor floors). The only change is in the percentage of “325” cement (which is decreased to 50- 60 kg for every 100 kg of sand) in order to minimize shrinkage of the cement inside thicker grouting. Synthetic grouting To complete the joints with pre-packaged mixtures, first of all it is essential to check the type of use that applies to the products available on the market. More specifically: • the use of sealants free of synthetic resins or polymers that, once the work is completed, could create unsightly rings around the visible edge of the terracotta elements, ruining the evenness and beauty of the terracotta material used for the floor field; • the use of sealants that are not characterized by an excessive contrast in the final color arrangement with respect to the terracotta, both in terms of the maintaining a consistent shade of color between the joints and the tiling as well as to make cleaning the residue from the surface of the terracotta simpler and more effective.
CLEANING THE FLOOR FIELD
Before proceeding with final cleaning of the terracotta floor, you must wait for the entire flooring “package” to dry completely and release all the relative humidity created by the laying phase. We recommend: • waiting about 10-15 days if the floor was laid with industrially-prepared synthetic sealants; • waiting about 20-30 days if the floor was laid with cement mortar (in general, one week for every centimeter of thickness of the screed). During this waiting period, any surface protection on the floor (used to proceed with other building-yard activities) must allow the material to breathe in order to get rid of any moisture it has taken in. Therefore, we recommend using paper, cardboard or other types of material that allow transpiration. The goal of the washing phase is to intervene effectively (and permanently) on the floor field in order to remove all foreign matter that could compromise full enjoyment of the flooring as far as appearance is concerned. This includes: • traces of cement and residue left on the terracotta elements after the joints have been grouted; • calcium and saltpeter deposits caused by efflorescence of calcium salts contained in the bedding mortar or the grouting used for the joints; • enamel and synthetic paint stains. Acid cleaning solutions must be used to remove cement residue. Ordinary hydrochloric acid (mixed with water to make a 6% acid solution) or similar products are effective solutions to use. Simultaneous removal of cement, calcium and saltpeter residues is generally done using: • buffered acid prepared for more or less concentrated washing at the building site; • hydrochloric acid diluted with water (as described above). Enamel and synthetic paint stains can be removed using specific solvents. The cleaning operation is the most important one in order to ensure optimum results during the subsequent (and final) phase involved in treating the terracotta. Cleaning can be done either with ordinary scrub brushes or with professional cleaning machines, such as single scrubbers or wet-vacs that can exert more penetrating action on the laid floor and above all, can quickly remove waste liquids, thereby making the entire operation faster and more efficient. The operating sequence can be summarized as follows: • washing the floor with an acid solution and waiting for a maximum of 3-4 minutes (leaving the acid solution on the surface any longer than this could weaken the cement grouting mortar in the joints) in order to dissolve grout residue effectively (if the outcome after the first washing is not satisfactory, this operation can be repeated, slightly increasing the percentage of acid in the solution); • simultaneous scrubbing using brushes to enhance the cleaning action of the acid solution; • collecting (vacuuming) and removing the acid solution that has been used; • repeated rinsing with plenty of clean water once the floor is completely dry.
FLOOR TREATMENT
Once the floor has been cleaned thoroughly and is completely dry (we recommend letting air circulate in the room even during the winter in order to allow the moisture to evaporate), you can carry out the final treatment phase (i.e. surface finish), which can be done using two different types of procedures and substances: 1. waxing (with creamy paste wax) that acts as a waterproofing agent; 2.waterproofing and waxing (with liquid wax). Treatment with creamy paste wax uses traditional types of products that, in addition to giving the floor a custom look, also waterproof the terracotta in depth. Before spreading the paste wax, it is advisable eventually to treat the floor with only one basic product that can level the floor and prevent moisture from rising through the tiles. Various types of wax are available on the market (clear, light, dark) and they can permanently affect the color tones of the floor. As a result, before actually treating the floor permanently, it is important to test the wax separately on a terracotta tile from the same lot as the one used to lay the floor. This will allow you to assess the different potential results ahead of time. In general, depending on the type of wax that is used, the results can range from: • shades that are close to the original color of the terracotta tiles that have been laid (clear wax);
- soft and natural color tones (light wax)
- marked shades tending towards deep brown (dark wax).
The waxing operation, which must be done on dry floors, involves spreading the creamy product evenly over the entire floor field, including the network of joints, using sponges or brushes. If you need to stop the waxing process, be sure to end along the grouting lines and avoid leaving any of the terracotta elements only partially treated. In order to achieve even greater protection, 24 hours after the first treatment spread a second layer of wax to finish. After an additional two-day period, proceed with the finishing coat by spreading a layer of liquid maintenance wax. The look created by using creamy paste wax – especially as compared to the results that can be achieved using synthetic water-based emulsions, as we will discuss further ahead – seems to be connected with a more natural, softer and somewhat shiny surface structure of the floor field. The second type of treatment that can be used as an alternative to the one described above is carried out in two phases:
1. actual waterproofing of the floor (using liquid solutions);
2. surface waxing (done likewise using liquid wax).
Waterproofing is done by applying solutions – generally monomers dissolved in water – that are spread over the terracotta flooring using a cloth, sponge or flat brush. When these solutions dry, this generates polymerization of the monomers, sealing the holes in the characteristic porous structure of terracotta and creating a surface layer that is protected against penetration by substances that could stain the floor once it is in use. At the same time, this waterproofing acts as a barrier against the efflorescence of salts that can cause unsightly surface phenomena. Lastly, it also helps level the visible surface of the terracotta elements. Instructions on exact application are usually furnished by the manufacturer, who will generally specify the correct way to use the product. In any case, when doing this second type of treatment, you are advised to:
1. evenly cover the surface to be treated in order to avoid differentiated absorption of polish after the treatment phase and thus an uneven appearance over the floor field;
2. start waterproofing from the point farthest away from the exit in order to avoid walking on the floor field before it is perfectly dry.
Spreading the liquid wax using a flat brush or cloth is the last operation that needs to be carried out. Forty-eight hours after the polishing emulsion has been spread, the floor is finally ready to be used. The floor field does not need to be polished since these water based emulsions polymerize as they dry, thus giving the floor a shine that is also water- and oil-resistant. The final result will be even and neutral in tone, with a wet/polished effect that is brighter than wax treatment. The overall color tone of the floor field will be more uniform. In ending this brief illustration on the laying and treatment procedures required for all terracotta products without any kind of finish process, it is important to point out to those of you who prefer to speed up the total completion time that both partially pre-treated terracotta (“pre-waxed terracotta” or “rough protected terracotta”) as well as finished protected terracotta are now available on the market. The latter category includes CottoFlash produced by Manetti, which represents the highest and most complete level of preventive treatment. In fact, together with in-depth protection, CottoFlash also features surface protection and a matt finish so that no expensive or special treatment is needed to finish the floor after it has been laid. Because of these features, CottoFlash naturally needs a certain amount of care during execution, i.e. the kind of care that would be used with any finished product and that mainly involves the laying phase (which can be done with either mortar or adhesives). Special care must be taken continuously to remove traces of mortar or adhesive with a damp sponge before they can dry and irremediably dirty the already finished and pre-treated terracotta elements.
