How to Use Acrow Props

Acrow props were invented and first brought to market back in 1935 and were enthusiastically embraced to begin with by main contractor McAlpine as an alternative to timber props. Since then, Acrow props have become a popular supporting act found on many construction sites across the UK and beyond.

Acrow props are strong, resilient, safe, and easy to use while being lightweight enough for a single operative to install on their own. Perfect for small renovation projects, or concrete formwork, acrow props have proven to be a versatile addition to every builder’s tool kit.

Whether you are installing a steel beam for an extension or opening up a wall to install a new window, acrow props are the safe and affordable answer.

Are Acrow Props Easy to Use?

Acro props are very easy to use and can be installed by a person on their own. They weigh between 10kg for a size zero and 17kg for a size three, so are not difficult to handle.

Acrow props are telescopic, which makes them ideal for a wide variety of applications, and easy to transport and store when not in use.

Their threaded outer tube makes them infinitely adjustable to site conditions. The collar supports a pin that can be raised and lowered with a handle.

What Are Acrow Props Used For?

Acrow props are a tool used for propping loads, most usually masonry walls, when creating a new opening, replacing a failed lintel, removing a wall, or supporting a trench.

Whatever propping activity you are planning the first thing to do is to measure the area to be propped. How wide is the opening? How much material is required to be made safe overhead?

At Wade, our steel acrow props are made to BS4074 with a single piece outer tube, which makes them more resilient than other welded two-part props.

Acrow props are used to support a temporary reinforced concrete former on a UK construction site.

How to Use Acrow Props

Check that the acro prop that you are using is the correct size and height for the propping job required. If it is too short, don’t be tempted to make up the difference with timber offcuts or concrete blockwork.

Make sure the surface on which they stand is sound. You may need to use a sole board or scaffold board to ensure a secure foundation. Propping off a clean, dry, stable, surface is best.

Use a level to determine that the acrow prop is properly vertical. The forces acting upon an acrow prop may be strong enough to make a prop fail if it is not as plumb as possible.

Using Prop Mates and Scaffold Boards:

If propping against a flat surface, such as a ceiling, use a scaffold board to spread the weight, and improve contact between the top of the acro prop and the area requiring support.

There are screw holes in the spreader plates at the top and bottom of an acro prop. Use these to fix the props to the header and footer boards that you use.

Make sure you have enough prop-mates (sometimes called strong boys) to hold up both leaves of a cavity wall. Using prop-mates can mean that you only need to prop from one side of a cavity wall, leaving the other side free for access.

Installing Prop-Mates and Strong Boys:

Using strong boys on acrow props is convenient and easy. The strong boy transfers the weight of the inner and outer leaf of a cavity wall directly to the acrow prop. This leaves one side of the wall free for working access.

How to Install Strong Boys:

1. Drill out the mortar bed all the way through the wall. Make the slot at least 180mm wide to take the 150mm wide zinc-coated prop-mate plate. It’s always good to have a little bit of room to play with.

2. Slot the strong boys on top of the acrow props and adjust until the base of the plate is in good solid contact with the bottom of the brickwork. Do not overtighten as you may dislodge the masonry you are trying to support.

3. Measure the centre of the cavity to the centre of the acrow prop. It should be no more than 215mm (9 inches).

4. On older walls, where the mortar has degraded and the masonry is clearly less stable, the minimum spacing of 900mm should be reduced.

5. The maximum recommended safe working height for prop-mates is three metres, and the individual SWL (Safe Working Load) is 340 kg.

Installing Your Acrow Props:

When putting your acro prop in position always put the pin in the lower pinhole visible in the slot. This will give you more adjustment when tightening up the prop into position.

Always make sure the pin goes all the way through and out the other side!

Wind the handle by hand until it won’t go any further, then tap it with a hammer to secure it. Make sure the winding handle is left hanging vertically for safety, and so it cannot be accidentally loosened.

Bracing Your Acrow Props:

Acrow props can be braced using scaffold tubes and fittings. This may be an essential consideration when:

• The propping is required to be in place for a long period of time.

• The propping is required to bear the loading of a wide opening of more than three metres.

• The propping is adjacent to a ‘live’ area such as a public space, or highway.

How Many Acrow Props Do I Need?

The rule of thumb is to allow for a prop every 900mm (3 feet). If an opening is 1m wide then use a minimum of two acrow props. It’s never a good idea to use fewer than is necessary.

Acrow props have weight limitations that relate to the height of the opening and the amount of loading that they can take. This can complicate matters, especially in high-stress areas such as walls below gable ends, or walls that support joists.

Some propping projects may require input from a structural engineer to ensure the job can be carried out safely.

What Size Acrow Prop Do I Need?

Acrow props come in five sizes, 0 to 4, with five height and safe working load ranges, for any number of situations.

Size zero are most often used in bracing and support for concrete formwork, as they have the highest Safe Working Load and can take up to 42 Kilo Newtons (KN).

As a general rule, the longer the prop is extended the lower the load they will be able to support.

Size two is probably the most versatile of props. It can be used to support structures above a new ground-floor door or window opening. It can also be used to support an upper floor when a new support beam is introduced to replace a supporting internal wall.

The key choice to make is regarding how much weight an acrow prop can take. Install too many, and access to the work area can become difficult. Install too few, and you risk failure.

If in doubt, always seek the professional advice of a structural engineer. Getting propping right can save time and money. Getting it wrong can be costly.