Frequently Asked Questions

Function and

How many Hydrorock infiltration blocks do I need?

The number of Hydrorock® blocks needed depends on the surface area and the soil type.

Use our calculator to calculate how many blocks you require. Our calculator can be found here.

Why is the use of Hydrorock dependent on the soil type?

The rate at which Hydrorock absorbs water depends on the manner in which the water can reach the blocks.

For rainwater to penetrate the soil, the soil must be sufficiently penetrable. Also the groundwater level has an impact on the infiltrating capacity. The closer the density of the soil type, the slower the infiltrating process and the more infiltration blocks you will need.

When water comes into direct contact with the blocks, the speed at which water is absorbed is approximately 400 litres per m2 per minute. When water reaches the blocks through a porous type of soil, it has a retardant effect, which is also then regarded as normative. Use our calculator to calculate how many blocks you need for your soil. Our calculator can be found here.

Can Hydrorock be used with high groundwater levels?

The infiltration blocks should always remain above groundwater. The blocks would otherwise be filled with groundwater as opposed to surface water. Therefore always check the water table prior to constructing. With a high groundwater level, work with blocks that are shorter, such as the D34 or D112.

How are the infiltration blocks placed?

Hydrorock blocks have an intricate fibrous structure facing in one direction. A horizontal direction of the fibres stimulates drainage. A vertical direction of the fibres, however, stimulates infiltration.

In relation to the carrying capacity of the blocks, they are to be positioned vertically for buffering and infiltration (the ‘this side up‘ sticker will be at the top). If the carrying capacity is of minor importance, the blocks can also be placed horizontally for drainage purposes of surface and rain water. We recommend placing the blocks one after the other in a horizontal position (lying down) for optimum drainage. You can find the positioning instructions here.

How are the Hydrorock blocks connected to each other?

One strong characteristic of Hydrorock is that each block has its own separate buffer, drainage and infiltration functionality. Depending on the size of the required buffer function and soil type, several blocks can be place next to or behind each other. The blocks then transfer the water from one to the other. Use type BD when connecting to rainwater discharge.

How are Hydrorock blocks connected to rainwater discharge?

The connection to rainwater discharge is done by connecting the drainpipe to Hydrorock type BD blocks. This version has a ø 100mm perforated tube which runs through the block, through which water can enter. The tube can be connected to rainwater discharge, drains, pipes, drainage hoses, gutters, etc. The blocks are in connected to each other in a longitudinal direction by means of a small piece of perforated tubing. The buffering capacity can be increased by placing type BD and type D blocks to the side(s) without a tube. The blocks then transfer the water from one to the other by themselves.

What is the water absorption capacity of the infiltration blocks in terms of time?

The speed at which Hydrorock absorbs water depends on the manner in which the water can reach the blocks. When water comes into direct contact with the blocks, the speed at which water is absorbed is approximately 400 litres per m2 per minute. When water reaches the blocks through a porous layer such as sand, it has a retardant effect, which is also then regarded as normative. The water absorption capacity / permeability rate of porous sand is approximately 50 to 60 litres per hour. This means that 50 litres of water on a surface of 1 m2 takes about an hour to sink through. Uptake of water via the perforated tube in type BD blocks occurs at a rate of 100 litres per linear metre of pipe per minute.

What is the permissible load / carrying capacity?

The permissible load of standard Hydrorock infiltration blocks is 2,500 kg/m2 (4,500 kg/m2; for High Density (HD) models). Class A15/B125/C250/D400 in accordance with DIN -AND 1433 applies to all vertically arranged blocks, constructed according to positioning instructions and according to the type of block indicated construction depth and ground cover on top of the block.  You can find the positioning instructions here.

Can the Hydrorock blocks be cut to size without losing their functionality?

The Hydrorock blocks are delivered in standard dimensions, but cutting the blocks to size is relatively easy. You only need to make sure that it is properly sealed using the filter cloth. You can proceed as follows:

  1. Use a utility knife to cut the filter cloth a few centimetres from the side all the way through, starting on the side where the sticker is placed. Cut the cloth through at the top, then on the side and finally through the bottom (the folding seam is located at the bottom).
  2. You now have something that resembles a hood. Remove the hood from the block.
  3. Using a wood saw, saw the block to the required size.
  4. Then slide the hood of the filter cloth over it, making sure it overlaps.

The infiltration block is now cut to the desired size and the filter cloth is in its proper binding position.

How many brackets are needed for the linear gutter?

The brackets are placed between the transition from block to block. 2 brackets are necessary when using 3 blocks.

Should the brackets be screwed to the linear gutter?

No, the linear gutter and brackets operate using a handy click system, making screws unnecessary.

Do I need fall for correct drainage?

As opposed to drainage hoses, Hydrorock® blocks do not need fall for proper drainage. The unique material sees to it that it makes no difference how the infiltration blocks are positioned. By positioning the infiltration blocks behind each other (if so required in different directions) the optimal draining function is achieved. In this way they always function as rainwater buffer and return the absorbed water to the surrounding soil.

Is Hydrorock resistant against erosion by plant- and tree roots?

Hydrorock® is manufactured from stone wool, a 100% natural material. Underground the Hydrorock® infiltration blocks maintain an excellent condition for decades. Standard synthetic buffers suffer from surface damages and need replacement. Hydrorock® is resistant against erosion by plant and tree roots. The cotton-base membrane of the filter cloth does not mould or rot. It has a large breaking strength and is resistant against the natural materials in the soil. Flora and fauna thrive excellently on Hydrorock®.


How much maintenance does the Hydrorock system require?

The system does not require any maintenance in the event the blocks are correctly positioned. In contrast to other solutions, it is not possible for soil to enter the system. The blocks therefore do not have to be cleaned or inspected.

When disconnecting the rainwater discharge, blockage in the pipes due to dirt should be prevented. This is easily done by placing a leaf and sand trap. These systems are simple and quick to clean. Should you however still wish to clean the system, we advise tying the separation system in a loop. This way the system can easily be hosed down and effectively cleaned in the event of blockages.

Hydrorock buffer lus schoonmaken

Hydrorock buffer with loop for easy cleaning.

Prices and

Where can I find the Hydrorock price overview?

For the latest prices, we recommend you to contact your nearest retailer. The retailer will be able to provide you with an exact quotation.

What is the warranty on Hydrorock products?

The warranty on Hydrorock products applies for a period of 10 years whereby the manufacturer guarantees performance, shape retention and functionality. Warranty is applicable if these requirements and methods are adhered to:


  • The water absorption, the absorption capacity of the blocks remain between 88% and 94% of the block volume;
  • The water delivery to the soil, if the conditions have remained unchanged;
  • The carrying capacity;
  • The shape retention;
  • The composition of the product.


Where are Hydrorock products available?

Hydrorock products for the business market are available through various professional retailers. Find our points of sale right here.

Are Hydrorock products also available for private individuals?

Hydrorock has a product range specially catered to private individuals: Hydroblob. Hydroblob has an extensive retailer network. There is most likely a retailer in or close to your area. Please refer to our special Hydroblob website for more information.

Is Hydroblob also available in other countries?

Certainly, Hydrorock works with professional retailers in many European countries. We are more than happy to refer you to one of these retailers. Marlux, for example, is our specialised retailer in Belgium, France and Germany. Hydrorock also works together with authorised retailers outside Europe. In China, Hydrorock is used to collect rainwater from highways, for example. Our official retailer in Australia sells Hydrorock mainly to prevent desiccation.

Still have questions? Then send us a message!

Email us at info@hydrorock.com
or call us +31(0)10 30 20 000