Advanced Structural Designs

ACN 097 789 87 92 Vasey Cres CAMPBELL ACT 2612

Telephone 61612171 Facsimile 61612170

Email mal@structuraldesigns.com.au

Should I be considering Ritek Walls on my next project?

If you do not know much about the product we suggest you visit their website to see their standard details but to cut a long storey short Ritek is two sheets of 9mm FC glued to castellated steel studs that can be stood and braced to act as permanent concrete formwork. The walls can be reinforced vertically and horizontally where necessary. Standard panel widths are 1200mm and heights are 2700, 3000 or 3600mm.

A couple of recent projects in Canberra using this product would be Ivan Bullum’s development at the old Starlight Drive-in in Watson and Barry Morris’s Forum in the city. They are generally used for load bearing party walls and are generally 150 thick. Whether they are reinforced or not will depend on whether they are transferring loads to columns or simply carry loads to a lower floor or footing.

It is useful to look at costs up front to keep alternatives in perspective.

Type of wall	Fire Rated Performance (Hrs)	Acoustic STC/Rw	Cost of lost Letable Area	Cost/ m^2	Total Cost
Ritek 150 core filled	90/90/90 (1)	50	$0	$140	$140
Ritek 150 reinforced	90/90/90	50	$0	$165	$165
Reinforced 150 blockwork	90/90/90	47?		$120	$120
230 Brick	240/240/240	52?(2)	$26	$120	$146
Special Performance Bricks (140 wide)	120/120/120	50	-$3	$81	$78

1 These values are very conservative and more testing is required

2 These values are extremely variable and dependent on brick density and face porosity as well as workmanship.

This is of course only a small part of the storey, as you may need to add on Gyprock if you are unhappy with the finish or need to have a large number of power points and switches in the wall. The variability of the Rw’s obtained on site is also a major issue for the brickwork options but there should be far less variability with Ritek. For more information on problems with the current BCA requirements and field performances click here.

Ritek has recessed edges and can be taped and filled like any other FC product so if you are happy with the finish it can be competitive against double brickwork depending on your choice of brick. If you are using the wall as a beam to transfer loads to columns below it will out perform the blockwork solution and give a superior final finish and acoustic performance. This is where Ritek is at its most competitive, reinforced to transfer loads and where the clean flat durable surface represents the final product.

On the other hand, if you are battening out for gyprock in any case you will find the reinforced blockwork option appreciable cheaper. Always remember to factor in increases in wall thickness at around $30/m^2 for every extra 100mm.

Our experience has been that many builder start out with the intention of using the FC face as the finished product only to find that they simply cannot achieve a suitable finish and end up slapping gyprock over it.

Construction issues

Having the right pump on site can be make pouring the concrete filling a safer and more manageable operation. If you can get a 50 mm hose with volume control this is generally recommended. We know Joe Spinelli has one but there are probably others in town. The pour should be done in maximum lifts of 600 to 1000 mm according to their literature with high slump concrete. It is important to carefully police the strength of the mix required as builders will tend to order blockwork mixes which are far too weak for many applications. The reason these mixes are suitable for block walls is that the blocks draw a large amount of moisture from the mix and thereby strengthen the concrete.

Pioneer supplied the mix for the Phoenix Development on Northbourne Avenue where they had a large number of blowouts at the base caused by the large lateral pressures from high slump concrete. Eventually they settled for a mix that arrived on site with an 80 mm slump and had a super-plastisizer added to bring it to 150 mm.

If you have over 30mm of rain between standing and pouring the walls we suggest drilling holes in the base to let the water out after the rain. Even if we could live with the weak concrete in the base of the walls (which we often can’t), water standing in the walls tends to weaken the FC bond to the studs and lead to blowouts at the base.

Voids in the concrete filling are rare but obvious as the FC darkens with the wet concrete against it and unless the weather is exceedingly wet you will see the problem the following day. Where repair to this type of defect are necessary they are time consuming and tricky if you are using the FC as your finished product so it is worth taking care in the filling operation.

An issue worth considering in design is the fact that it is difficult and time consuming to have wall reinforcement continue around the corner of these walls. Whilst it represents good engineering practice and can add considerable lateral strength to a building it also increases the cost/m^2 and should be avoided where possible.

Setting up and bracing the wall system is crucial to its success as is cleaning it after the pour before any mortar dries. If you need a dark coloured or gloss finish the Level 4 finish that is normally attained may not be sufficient for your requirements.

If you have any particular queries related to this or any other building product or need some preliminary framing advice from a structural engineer in Canberra ACT or the surrounding district call Mal Wilson on Ph (02) 61612171.

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