Customers, who do not want to lose out on their rooftop space, are requesting for elevated structures on their terrace. Most of the elevated structures need grouting (which involves drilling holes into the terrace for fixing the bolts) to ensure stability of the structure. However, the customers are concerned about water leakages and in case of apartments, the resident living on the topmost floor is sometimes unwilling to give permission to drill onto the roof.
To alleviate all of these concerns, we have waterproofing solutions to seal the grouted area and non-penetrating solutions using adhesive & foundations for our discerning customers. EcoSoch has installed numerous elevated structures using our fabricators with grouting and has installed a non-penetrating elevated structure on top of our office roof, which you are welcome to have a look. We have elaborated these solutions below
Elevated structures with grouting
First, the roof surface needs to be cleaned and using the base plate as reference, drill 4 holes onto the terrace as shown below. You can use a separate wooden template for marking the holes as well.
The diameter of the drill bit should be the same or slightly larger than the diameter of the anchor bolts that are going to be used. Since the anchor bolt will be M10x100, use a drill bit of 10mm or 12mm dia. The depth of the hole should not exceed 75mm as can be seen from the image below. Use an insulation tape or a drill with depth stop to mark the depth of 75mm from tip of the drill before starting the drill work. This will prevent excessive drilling and damaging the roof.
Once the drilling is done, clean the holes to make it dust free and also the surrounding area. Next, the process of filling the holes with waterproofing cement or chemical mortar commences.
First option: Application of Hilti Injectable Mortar
Once the hole is drilled, a chemical anchor dispenser (from Hilti) is used to inject & fill the entire hole with a chemical mortar to provide the 1st level of protection. The advantages of Hilti mortars are spelt out below:
- High performance and technical superiority as per international approvals
- Reliable solution providing high performance in diamond-cored holes using the new roughening tool
- Mortar suitable for all-year use: cures at temperatures down to -5°C / 23°F
- Long working time allows greater flexibility during installation
- Also suitable for water-filled holes and underwater applications
Refer to the below instructional video to understand how to drill holes and use the Hilti product:
Once the hole is filled with Hilti’s chemical mortar and the anchor bolt is fixed, its surrounding needs to be waterproofed to provide the 2nd level of protection with the help of Plain Cement Concrete (PCC) and Dr. Fixit LW+ which is a unique cement additive for concrete for integral waterproofing. Its features and benefits are provided below:
- Waterproofs by filling pores and cutting capillaries
- Good workability
- Increases cohesive strength of the mix
- Delays corrosion
- Prevents cracking in plaster
Details of LW+ and its application is provided below.
Second option: Use PCC with waterproofing compound (Dr. Fixit LW+)
Dr. Fixit LW+ is an integral waterproofing compound which can be mixed with PCC to ensure waterproofing of the terrace floor wherever the holes have been drilled.
The grouting of the structure shall be done by PCC 1:2:3. A 1:2:3 mix has 1 volume of cement, 2 volumes of sand and 3 volumes of coarse aggregate. That could be, for instance 6 buckets. 1 of Cement, 2 of sand and 3 of gravel.
Method of Application
- Mix cement & aggregates as per the mix design (1:2:3), mix in dry state for 1–2 minutes.
- Start addition of 75–80% mixing water & mix for 2-3 minutes.
- Fixit Pidiproof LW+ is added as per the recommended dosage (200 ml per 50 kg bag of cement) into the remaining mixing water, then add to the mix & mix for another 2 minutes.
- Fill the drilled holes with the PCC and drop the anchor bolts into the filled hole. Ensure that the anchor bolts stay upright till the PCC in the filled holes set.
- Once set, place the base plate with the column onto the anchor bolts and tighten.
- Apply the PCC onto the base plate and fully cover it. Height should be minimum of 50mm or 2 inches.
- Moist curing of PCC must be done for 2 days using gunny cloth for increasing the strength and decreasing the permeability.
Third option: Foundation for Columns
After the drilled portions are filled with PCC and Dr. Fixit LW+, apply a coating of PCC on the base plate area as shown below:
Then you can make the square foundation of 300x300x400mm and M20 grade concrete (mix proportion will be 1:1.5:3 for cement:sand:coarse aggregates) as shown in the diagram below:
Elevated structures with No roof penetration
If the customer insists that there should be no drilling onto the roof, then we can use an Adhesive+Foundation based solution for installing elevated structures. The foundation would have to be RCC and not a PCC.
RCC Foundation Preparation
- The dimension of the square foundation should be 450x450x250mm. So, prepare a mold to this dimension.
- Make the rebar cage of 400x400x200mm and place it inside the foundation mold. Then place the L bolts (M10x100) inside the mold using the template as shown below
- Next, pour the concrete into the mold, let it set, remove the mold and start the 2-day curing process using gunny cloth. After 2 days, the RCC foundation would be ready.
Method of Application
- Roughen the roof surface with a metal brush so that there is good adhesion of the foundation block to the surface using the adhesive.
- Clean the roughened surface to make it dust free
- Use Fosroc Nitobond EP which is an Epoxy resin concrete bonding agent for bonding the foundations to the roof surface. It is supplied as a two-part material (a green hardener and a white base) for ready onsite mixing and use. The coverage provided by Nitobond EP is approximately 2.6 m2/litre. We have a square foundation of 450mm x 450mm which gives us an area of 0.45 x 0.45 = 0.2025m2. One litre can cover 2.6m2 which is 2.6/0.2025 = 12 foundations. Check out the mixing and application video:
- Once the adhesive is prepared, pour it uniformly onto the roof surface where the foundations are going to be placed as shown below:
- Next, place the foundations on top of the adhesive and let it set as shown below. Once it is set, you can do finishing work using PCC to seal the bottom of the foundations if required.
- Finally, place the columns on top of the foundations and secure it using nuts/washers.
The elevated structure that has been placed on top of our office uses non-penetrating solution and looks as below: