The need for speed

Martin Yarker on fast-track preparation for fast-track screeds

THE ‘need for speed’ is a phrase not solely confined to our motorway systems – in the flooring industry the move towards ‘fast-track’ installations have certainly gathered pace in the past 10 years, evidenced by how quickly newly-built commercial and industrial buildings spring up in a seeming race against time.

First, let’s make sure we’re all clear as to what a screed is. When we refer to screeds, we’re talking about a levelling medium applied to a sub base, typically a concrete slab, that’s been laid to a fairly inaccurate tolerance but is ready to receive a floor finish that’s laid to an accurate tolerance.

A screed is therefore installed to largely remove these deviations.

The screed material itself normally consists of an aggregate, most likely sand, bound together by a binder. The most common binder is cement, a combination of cement and PFA or GGBS, or it may be another material, for instance calcium sulphate-based materials.

It could also be an epoxy or polyurethane resin. There are some more obscure binders but they’re rare so we won’t cover them here.

So, what makes a screed fast-track?

Like most construction materials, screeds rely on a specified water content to enable the mix to perform to expectations. However, what’s left of that water after placement and cement hydration has got to be got rid of before the screed can be put into service.

So, quite simply, if you reduce the water that goes into a building you can speed up the construction time.

When we look at the different screeding materials we can see how the drying times differ.

The general rule-of-thumb for drying times is one day per each millimetre of thickness up to 40mm, then two days per millimetre over 40mm. It’s worth noting this also presumes a dry, well-ventilated environment.

By using this formula and assuming a 50mm screed we can predict the drying times for the more common screed materials to be around 60 days.

The better the preparation…

It’s been an open secret in the flooring industry for years (yet it’s still the cause of more flooring failures than almost any other factor!) that ‘the better the preparation, the better the finish’.

So, how can we tell what is to be the best preparation method to achieve the best finish for the resin topping that has been chosen?

This depends on three factors:

  • The surface profile of the floor being refurbished
  • Any underlying issues within the slab
  • The environment the floor will be subject to

Let’s look why each factor is critical:

  • Surface profile

Probably the most obvious example of the need to have the correct profile for the correct environment happens when a company move to a new location. A typical scenario, for example, could have a warehousing and logistics operator moving to a unit where the previous occupiers didn’t need to have a laser-levelled floor surface.

Anything less for the logistics company would mean serious consequences for the forklift traffic moving across an uneven slab.

Underlying issues in the slab
What lurks underneath a slab can often affect the performance of any resin or polyurethane topping to a great extent: a clear example of this is the case of a company who relocate to a unit where heavy engineering has been the previous use.

Oils, grease and lubricants can significantly contaminate a slab, and if not treated correctly, become a barrier and not allow a resin topping to perform as designed.

Location considerations
The third, but in my opinion most crucial factor, is ensuring the correct resin system is installed in the correct environment. This is so much more than a simple ‘horses-for-courses’ correlation and the price to pay (literally) for getting it wrong at this stage is hard to quantify.

So, just how do you ensure you have the correct ‘fit’? Simple. Do your research – FeRFA (Federation of Resin Formulators and Applicators) would be my first port-of-call.

Here you find a cornucopia of information in the shape of ‘The FeRFA Guide to the Selection of Synthetic Resin Floors’ probably the most comprehensive tome in the resin flooring industry, a must-go-to resource.
And so to prep…

Just as there are many factors to take into consideration when it comes to ensuring you have selected a floor that’s fit-for-purpose, the question of how to prepare the floor is imperative, so let’s take a quick overview as to some popular choices available:

Captive shotblasting
To prepare concrete floors prior to installing resin flooring systems, the surface needs to be ‘profiled’. This can be achieved by using captive shotblasting which uses shot that is propelled at a high velocity towards the floor; on impact with the floor it loosens the surface laitance.

The shot is recycled via a series of magnets in the chamber, and the debris is vacuumed away into the collection box normally located at the rear of the shot-blaster.

The finished floor is left completely uniform in profile, ready for the resin finish to be installed, a popular preparation method and surprisingly quick.

Micro planing
If the slab needs to have a substantial amount of its surface removed (perhaps due to concrete corruption) then one option is to use micro planing. Skill and care is needed to remove only the thickness required to remove the deteriorated concrete surface.

The speed of removal is governed by the actual amount to be removed; however, these machines are built to enable large areas to be prepared at optimal speed.

Diamond grinding
Where space doesn’t permit other preparation methods, diamond grinding is an option. Again, this is a ‘captive’ system meaning it’s dust encapsulated. The finish obtained by this process is unlike both shotblasting and micro planing in that it leaves the surface smooth, still removing surface contamination.

Available in handheld units, large planetary grinders and sit-on machines, these aren’t necessarily the quickest pieces of kit, but they’re most certainly effective in how they perform.
So, there we have it, a mini-guide to fast-track preparation and fast-track screeds.

A final thought: if you think it is expensive to professionally prepare flooring, wait until you pay the cost of not.
0121 5086970
Martin Yarker is technical advisor – Industrial Flooring at Mapei UK