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Hi this is Carl the landscape guy. In this video I will show you how we complete cement-bonded grouting of natural stone slabs. This chapel forecourt is being redesigned. The natural stone slabs laid in sand have sagged over the years, forming trip hazard joints. The plates will be re-installed later, so they will be picked up, cleaned and stored off to the side. The dirt is excavated out to the planned size and a base layer of mineral crushed stone is prepared and compacted. Then we set the frame stones. On the gravel surface, the sandstone slabs are now placed in a layer of permeable concrete. An adhesion compound is applied to the underside of the sandstone slabs. The entire chapel forecourt is laid this way. Meanwhile, the work for the sandstone wall has started. The wall will frame the little forecourt at one side as a retaining wall. You will find a detailed video about natural stone masonry on my channel, I’ll also link it at the end of this video. Okay that was it for the preparatory work, because this video is specifically about how to grout natural stone slabs. Before grouting the slabs are watered well. Moisturizing is very important, even more when it is hot out, so that the natural stone does not draw moisture from the fresh grout filling later on. For mixing, we fill a bucket with water. The mixing ratio is 5 L of water per 25 kg of cement. If the mixing ratio is wrong, color differences may occur after hardening. Therefore, always try to use the same mixing ratio for the entire area. For very narrow joints, the mixture can be a little thinner, so add more water. These are joint widths of about 1-3 inches. With these wider joints, the material can be mixed with a little less water, making it a little thicker. Mixing is best done with an electric mixer. Some mortars have coarser proportions of material, so make sure you have the right mixing tip. I would recommend one that is open at the bottom for easier and quicker whisking. We slowly add more water until the mixture is right. As soon as the dark filler material begins to deposit black streaks on the surface, it has enough water. Here we use the Marbos PFM – ZE melan in 25kg bags. The mixed batch should then be applied promptly onto the slabs. Since the mortar starts to thicken immediately, we start to work it into the joints right away. The joints are to be well-filled and the excess material is to be pulled off. The quicker the excess material is removed, the less it needs to be washed off later. The outer edge of the slabs joints should be sealed up before grouting, so that no grout can seep out the sides. If the mortar becomes too thick, it can be slightly rewetted with some water. While one employee distributes the grout, a second guy should mix the material so that there are as few breaks as possible during grouting. The mortar must now be washed from the surface of the natural stone slabs before it sets too much. But wait until the new grout is slightly hardened. There are two methods for cleaning the slabs that we would suggest. For the first one, it is smart to lay out a wooden board to protect the new grouts. For washing, a professional wash box should be used and filled with clean water. Then the natural stone surface is washed with a sponge board. First, a surface section is washed with circular movements. This loosens the mortar from the surface and smaller groves. Then wash out the sponge board before wiping the surface clean. It is important to always pull in one direction and put the sponge board down on its entire surface. As soon as mortar streaks are visible, the sponge board should be washed out again. Also, depending on the size of the area, the water in your box should be changed every now and then. With this method you can work your way out of the corner. For surfaces with a higher proportion of joints, it’s possible to easily pull out the joint with the sponge. Try to pull across or diagonally and not along the joint. For deeper spots a regular cleaning sponge can be used, but this is not suitable for washing larger surfaces. The second option is to wash the surface by spraying it with a fan spray nozzle. This method speeds up the process, but requires more attention and practice. With the nozzle, the excess material is sprayed off the surface. The intensity of the beam can be varied by the distance. The jet of this Gardena nozzle is very appropriate for this.
#grouting #flagstone #diybuild