Archive for February, 2019

maclennan team working

Winter Deck Waterproofing

We are in the middle of a season where main contractors and clients are insisting on deck waterproofing. You should not be waterproofing a deck in the Winter unless you are able to give a contractor 14 days notice of dry weather with a moderate temperature of 5c and rising.

Clearly, this is not possible.

If you do not follow the manufacturer guidelines the waterproofing will fail and the cost of remediation will make the cost of a delayed programme pale into insignificance.

MacLennan also has hand applied systems that we install under our 10-year guarantee, we offer more than other waterproofing and roofing contractors.

before and after adequate surface preparation

Image 1 - This shows a before and after of adequate surface preparation, ground down and free of dust and laitance. 

lumpy concrete surface

Image 2 - This shows bad preparation. A lumpy, laitance filled concrete surface will be at risk of poor adhesion. Proper preparation is essential.

removing existing waterproofing

Image 3 - Waterproofing being removed from a surface that was ground, jet washed and vacuumed. The point being that good preparation is difficult to achieve. In cold wet conditions it is impossible.

damage to cold decks

Image 4 - This shows a failure of work carried out in Winter months. Wet, cold decks make a poor surface substrate.

water damage to decks
deck conditions maclennan have dealt with

Images 5 & 6 -  Deck conditions MacLennan have been called in to waterproof in winter months.

We always advise our clients that Deck waterproofing work with any material or system must happen in the spring and summer.

They often disregard that and try and make the weather the waterproofing contractors problem.. The following rules apply winter or summer but will be even more critical in the Winter.

All surfaces must be correctly prepared. Preparation has to be grinding or scabbling and then either jet washing or vacuuming away of the ingrained dust. Removing the dust is one of the most critical elements of preparation and may require jet washing to remove ingrained dust.

It is critical that all laitance is removed and the resulting surface is sound and dust free.

Primed & Ready

Surfaces are primed in summer to prevent outgassing and aid bond. Surfaces are primed in Winter to provide a sound dry surface and aid bond.

Most Primers do not work in cold conditions or on damp surfaces. There are primers available that are less temperature sensitive and can go on a touch dry surface but they are far more expensive and still limited by site conditions..

You cannot prime a wet surface. You cannot prime a freezing surface even with special primers. This will lead to an expensive failure.

Covering up?

Covering a deck with a tarpaulin is doomed to fail. In all likelihood when you remove the tarpaulin you will spill the water onto the deck. You must use tenting and heating so as work can be carried out under it.

Contractors are always pressurizing waterproofing sub contractors to attend site when the site is clearly not ready. This serves no purpose. You cannot apply waterproof membranes to damp substrates or in cold conditions. Waterproofing contractors who know what they are doing cannot and will not attend.

The clients team is always well aware of the required environmental conditions. 5 and rising, 3 above dew point, dry ( Blue paper test) Do not use Epoxy primer at below 10c.

On-site pressure

It is site managers who when put under pressure of a time critical programme will try and pressurise the waterproofing company to carry out the work. The ones who know their job know it is wrong but want to be seen to be getting the job done.

This attitude is what leads to the millions of pounds worth of waterproofing failures every year. The job should be done properly in the right conditions.

maclennan team working
maclennan team and van

Large New Build Basement

Basement Design & Build tips – External Waterproofing


External Waterproofing

Some basement build & external waterproofing tips we think you should know.

External waterproofing is a barrier installed under and around a basement to prevent the ingress of water, it is normally either a bitumen, bentonite clay or plastic type material.

Most of the materials are completely waterproof, however, they all have to be joined and lapped. It is the detailing of joins and laps which is impossible to complete defect free.

This is largely due to building site conditions as they are by nature dirty , muddy and in the UK frequently wet.

All waterproofing systems have to be installed in the dry and most rely to some degree or another on clean walls or over site, reasonable temperatures and dry surfaces.

failed bentonite basement waterproofing
failed bentonite basement waterproofing

“It is only by poor design and cost-cutting procurement that the risk of a leak is built into basement construction. All basements can be and should be dry”.

The facts.

1 External waterproofing on its own does not comply with British Standards BS8102.

2 Most water ingress is above the water table. Water ingress is just as likely to occur from surface water draining through the soil.

3 External waterproofing cannot be installed defect free. A precedence set in law.

4 Liability for failure will always be with the designer, architect, engineer. Manufacturers do not accept design liability.

5 Manufacturers do not accept design liability, Manufacturers guarantees do not cover workmanship and materials and are rarely honoured. Also; Manufacturers always rely on the argument that all failures are workmanship issues.

6 NHBC insurance have dealt with or are dealing with 20 million in water ingress claims since 2005. NHBC claims are running at £13,000 per day and this is just the NHBC. Claims for water ingress in 2012 were 4.8 million.

two storey basement being erected under a 112 year old church
A two storey basement being erected under a 112 year old church

Basement Build & Design tips

If you are building a basement for accommodation or recreation you will need to achieve a Grade 3 habitable basement to comply with BS8102 - the British standard for earth retaining structures.

The standard says you should involve a waterproofing expert from the start of the design process and seek their advice throughout. The expert should accept design liability, Not a manufacturer.

Mortgage companies will ask for guarantees when you sell the property. The only meaningful guarantees are Products Insurance backed guarantees and GPI insurance to give some cover in the event that the installers cease trading.

2 Forms of Waterproofing
In order to comply with British Standard’s, you should have 2 forms of waterproofing. if the risk of a leak is high, such as in a high water table or if building from block work or ICF rather than poured concrete.

Or if the consequences of a leak are unacceptable, which they will be in a habitable basement.

Look at your proposed basement as a box in the ground. Our recommended waterproofing (supported by BS8102) is that you waterproof the outside with either a membrane under the box and up the sides to stop water entering or build it with well compacted reinforced concrete with professionally installed hydrophilic joints and external joint protection.

In piled construction the internal concrete wall should be waterproofed with Crystalline slurries after construction as this will repair any minor defects unlike additives added before construction.

Basement Build & Design - Check list

1. Two forms of waterproofing for habitable basements.

2. Concrete should be waterproofed after construction not with additives prior to construction.

3. Post applied Crystalline slurries. This is because concrete additives often fail due to workmanship and site condition defects.

4. Waterproof the whole box down from DPC down to below the concrete slab.

The external waterproofing is referred to as Type A waterproofing.
Type A is an external sheet membrane or coating system which forms a barrier, on a habitable basement Type A should never be installed on its own.

You cannot expect Type A to be installed completely defect free - this is a precedence set in law

You cannot test the effectiveness of the system until the structure is buried in the ground. In the event of a leak, it is too late to repair and it is not possible to maintain.


Large New Build Basement
A gigantic new build basement Waterproofing system designed, supplied and installed by MacLennan

Type B Waterproof Concrete

Type B is an integrally waterproof structure. This means a structure built of well-designed concrete that is in itself waterproof. It is often said that this requires additives to the concrete but this is not true as concrete is waterproof. It is the joins and minor faults in workmanship which allow water ingress.

Type B is notorious for leaking. Waterproof additive companies are always repairing failures with our injection systems and cavity membranes. All of the waterproofed additive companies have to employ injection specialists to put right their frequent failures.

Additives do not stop leaks through cracks, honeycombing and join. The additional reinforcement and joins required by most additive companies add unnecessary cost to the construction.

Concrete waterproofing Should be carried out after the concrete is installed.
To repair and waterproof the faults. If you have a leak after the construction phase the additive companies will not return until fixtures and fittings and even internal walls are removed at the clients’ expense. They will not accept consequential damages.

Type A and waterproof additives should not be used together as type A protection will prevent autogenous healing if type A is installed soon after construction.

Type C waterproofing

Type C waterproofing is often in the form of a plastic membrane with a cavity drain, all built into the structure behind walls.

It is essential that drainage is reliable or that the system is pumped. The pump design is critical.

It is the most effective form of waterproofing for common-sense reasons, If the waterproofing leaks for any reason you have to be able to resolve the problem with the minimum of disruption to the occupier, You cannot do this with A or B systems.

All of this has to be considered during design and liability does fall on the designer if it is not.

A concrete structure without waterproof additives but with well-compacted concrete and no honeycombing and well prepared (scabbled) joins with water bars will provide a Type B structure.

A concrete structure with additives and reinforcement to BS8007 but with less than adequate workmanship in any small area will leak. Honeycombing occurs due to a lack of accessibility to poker due to the amount of steel. Water bars are difficult to detail and install and surface prep of joins is difficult due to steel.

No company can properly guarantee an external system on its own. Guarantees for external systems are not worth anything to the client ( why? because they can’t be remedied when they fail). Contractors and suppliers will always easily find reasons for not honoring guarantees.

Product insurance and insurance backed guarantees are not available for external Type A systems.

A type C system can be guaranteed by qualified waterproofing companies for 20 years as a stand-alone system on a well designed reinforced concrete structure.


Get in touch!

Ready to start a project or require more information about us?
Call us about your project or problem and we will be happy to help.

Call us today on:

0330 3200 240
Or email us here