7 Bathroom Renovation Mistakes on the Costa del Sol

Bathroom Renovation Mistakes on the Costa del Sol: How to Avoid Cost Overruns

Renovating a bathroom on the Costa del Sol is an investment that can range between €4,500 and €9,500 for a mid-range option, but bathroom renovation mistakes on the Costa del Sol can push the budget up by 30% or more. In this article, based on the experience of industry professionals, we break down the 7 most common mistakes that make a bathroom renovation more expensive and give you the keys to avoiding them. If you are thinking of renovating your bathroom in Marbella, Estepona or any town on the Costa del Sol, this guide will help you plan your project better and keep control of your budget.

1. Not Checking for Hidden Damp Before Starting

One of the most costly mistakes is starting the work without carrying out a prior damp survey. Damp can be present in walls, floors or ceilings, and if it is not detected in time, it may require additional repairs that increase the final cost. On the Costa del Sol, the proximity to the sea and ambient humidity make this issue especially relevant. A prior survey, which can cost between €200 and €500, can save you thousands of euros in unforeseen repairs. Furthermore, if you detect damp, you must address it before installing the new finishes.

Professional Detection: Thermography and Hygrometers

Visual inspection is not enough to locate rising damp or leaks in embedded pipes. A professional technical survey uses thermal imaging cameras that detect temperature differences on surfaces, revealing areas with active damp that are not visible to the naked eye. Penetration hygrometers measure the moisture content in porous materials such as brick or plaster, making it possible to quantify the level of saturation. In a typical bathroom renovation on the ground floor or basement of the Costa del Sol, it is common to find rising damp that requires a chemical barrier using silicone resin injections into the wall, at an additional cost of €40 to €60 per linear metre. This treatment must be carried out before applying any waterproof coating, otherwise the water will migrate laterally and saltpeter stains will appear on adjoining walls.

Waterproofing in accordance with CTE DB-HS Regulations

The Technical Building Code, in its basic health document (DB-HS), establishes that wet areas must be waterproofed with continuous systems covering floors and walls up to a minimum height of 20 cm in bathtubs and 2 metres in showers. In professional practice, it is recommended to apply a two-component acrylic membrane of 2 mm thickness over the entire bathroom perimeter, with geotextile reinforcement at corners and expansion joints. The cost of this professional waterproofing ranges between €25 and €40 per square metre, depending on the brand (Mapei, Weber, Sika) and the number of coats applied. A frequent mistake is relying solely on tiling as a waterproof barrier; the joints between tiles are not watertight and water can seep into the substrate, causing efflorescence and delamination in less than two years.

2. Keeping the old plumbing

Plumbing is the nervous system of your bathroom. If the pipes are more than 20 years old, they are likely to be damaged or fail to meet current regulations. Replacing all the plumbing can add between €8,000 and €20,000 to the budget, but it is a necessary investment to avoid leaks and future problems. Rather than risking having to break up the newly laid floor, it is better to renew the pipes during the renovation. This is especially important in older properties on the Costa del Sol, where installations are often outdated.

Polypropylene pipes versus copper: technical advantages

Copper pipes installed in buildings from the 1970s and 1980s present internal corrosion problems, especially in areas with slightly acidic water such as that distributed in some coastal municipalities. The copper oxide that detaches can stain sanitary porcelain and reduce the internal diameter of the pipe, decreasing flow rate. Replacement with random copolymer polypropylene (PP-R) pipes offers significant advantages: they are inert to corrosion, have a smoother internal surface that reduces pressure losses, and their thermal fusion joint creates a monolithic piece without mechanical joints that could fail. The material cost for a standard bathroom is €120 to €180 in PP-R versus €250 to €400 in copper, although labour is similar. Multilayer pipes (PEX-Al-PEX) are an intermediate alternative combining the flexibility of cross-linked polyethylene with an aluminium barrier that prevents oxygen diffusion, protecting the metal components of the boiler or water heater.

Watertightness tests before closing off pipework

The regulations require a watertightness test at 1.5 times the working pressure for a minimum of 30 minutes before closing the chases and tiling. In practice, professionals apply a pressure of 6 to 8 bars and verify that there is no pressure drop with a calibrated pressure gauge. This test must be carried out in two phases: the first with the installation exposed to detect visible leaks, and the second after the mortar in the chases has set, to confirm that no pipe has been damaged during the process. The cost of this check is included in the plumbing item, but if it is omitted and a leak is discovered after tiling, the repair involves lifting tiles, locating the exact point and re-waterproofing, with an average cost of €800 to €1,200 per intervention.

3. Changing the layout once work has begun

Changing the bathroom layout (moving the toilet, shower or washbasin) after work has started can increase the total cost by up to 30%. This is because it involves modifying drains, plumbing and electrics, which requires more labour and materials. To avoid this, it is essential to plan the exact layout before starting and not to make changes on the go. If you have any doubts, consult a professional before making final decisions.

Drain planning: slopes and maximum distances

Moving a toilet involves modifying the soil stack or horizontal collector, and minimum slopes are critical: 1.5% for 110 mm pipes and 2.5% for 90 mm pipes. If the distance from the toilet to the soil stack exceeds 3 metres, it may be necessary to install a macerator pump, costing between €350 and €600, plus the associated electricity consumption. In ground-floor buildings on the Costa del Sol, it is common for the soil stack to run through the ceiling of the garage or commercial premises below, which makes access easier. However, on intermediate floors, modifying the route may require chases in the floor slabs, with the consequent structural reinforcement if the reinforcement bars are affected. A prior technical feasibility study, including the exact location of soil stacks and inspection chambers, costs between €150 and €300 and avoids irreversible decisions during the work.

Coordination of trades: the order of intervention matters

The correct sequence of works is: demolition, plumbing and electrical work, masonry for chases and levelling, waterproofing, tiling, installation of sanitaryware and taps, and finally carpentry and painting. If this order is altered, for example by installing sanitaryware before the waterproofing is completed, there is a risk of damaging the membrane during assembly. A detailed schedule with weekly milestones, specifying which trade is on site each day, reduces downtime and prevents workers from getting in each other's way. For bathroom renovations of 4 to 6 m², the optimal execution time is 12 to 15 working days, with a crew of 2 to 3 skilled tradesmen. Extending this timeframe implies costs for renting alternative accommodation or loss of income if the property is intended for holiday rentals, which on the Costa del Sol can generate €80 to €150 per night in high season.

4. Electrical installation not up to code

In many older homes on the Costa del Sol, the electrical installation does not comply with the Low Voltage Electrotechnical Regulations (REBT). If, during the renovation, it is discovered that the electrical panel or wiring is not up to date, it will need to be adapted, which entails an additional cost. It is advisable to include a review of the electrical installation in the budget and, if necessary, its upgrade. This not only guarantees safety, but also avoids unpleasant surprises.

Protection volumes in wet areas according to REBT

The REBT establishes four protection volumes (0, 1, 2 and 3) depending on the distance from the bathtub or shower tray.

References

• Technical Building Code
• Ministry of Transport and Housing