External Floor Screed 🏗️ Should you lay screed outside?

[@christofferselvik9895]

Looking for a very hard wearing screed, around 8-10cm thick (4cm where it will meet a concrete ramp). Will have vehicles up to 3tons with snow chains. Exterior, in the French alps, so temperatures from -20 to +35 degrees Celsius. Will be laid over a rubber based phonic insulation on a concrete concrete slab.
If the screed can’t take the wear, I am also looking for something to cover it that can absorb the wear.

[@SpeedScreedLimited]

Thank you for the question Christoffer. Due to the nature of it I passed it onto my good friend Mike Rhodes at Ronacrete. This is his thoughts:
I am less concerned about wear resistance of the screed, although snow chains will caused greater wear than typical heavy duty traffic, than I am about a the effect on insulation boards of dynamic loads imposed by 3 tonne vehicles, particularly where loads are transmitted through a nominal thickness of 40mm (very close to the minimum Ronafix floating screed thickness of 35mm), considerably increasing load transmission to the insulation, just at the point where vehicles transition to and from the ramp. Ronafix Pre-packed Wearing Screed 15mm+, two component factory produced polymer modified granolithic wearing screed, bonded to the prepared substrate with Ronacrete Standard Primer, two component factory produced polymer modified slurry primer, is most suited for this application.
Minimum and nominal floating polymer modified screed thickness
Ronafix polymer modified screeds may be used thinner than is specified by BS 8204 Part 1 because of the superior essential characteristics conferred by the Ronafix polymer. The minimum thickness of a polymer modified floating screed is 35mm, when the insulation board is strong enough to accept transmitted loads without deformation. To ensure that a minimum 35mm thickness can be achieved, the nominal screed thickness may have to be ≥ 50mm, depending upon the specified surface regularity of the screed and substrate levels variation. SR2 surface regularity allows variation of 5mm under a 2m straight edge and allowable concrete slab levels variation may be ≥ 10mm.
The following is from BS EN 13813 Screed material and floor screeds - Screed material - Properties and requirements
Table 5 - Wear resistance BCA classes for cementitious and other screed materials
BCA Class AR6 AR4 AR2 AR1 AR0,5
Maximum wear depth in microns 600 400 200 100 50
Ronafix Pre-packed Wearing Screed 15mm+ wear resistance
Wear resistance of Ronafix Pre-packed Wearing Screed 15mm+ has been independently tested and achieved AR0.5 (the greatest resistance to wear) when subjected to the BCA test procedure in accordance with BS EN 13892-4.
Water Permeability. Test Authority: British Precast Concrete Federation.
Freeze/thaw cycling. Test Authority: British Precast Concrete Federation.
Ronafix 3:1 mortar, p/c = 1:10. 24 hours -18°C/+20°C
Cycles Flexural strength N/mm²
Sample 1 Sample 2 Control 1 Control 2
0 10.8 11.6 7.2 6.0
15 4.5 3.2
30 10.5 0 0
60 11.0
120 10.9 10.5
He may have meant phenolic insulation and the strongest Kingspan insulation made with phenolic foam is Kingspan Kooltherm® K103 with a compressive strength@ 10% compression of 120 kPa, likely strength @ 2% compression 50-60 kPa (60kPa = 0.06N/mm2, 1,000 times weaker in compression than Ronafix Pre-packed Wearing Screed 15mm+, two component factory produced polymer modified granolithic wearing screed
Compressive Loads - quotation from Kingspan brochure
“Un-reinforced floor screeds can be used in conjunction with Kingspan Kooltherm® K103 in most applications. The compressive strength of Kingspan Kooltherm® K103 offers considerable advantages over some other floor insulants. Providing a minimum compressive strength of 120 kPa at 10% compression allows greater floor loads to be considered and therefore additional scope in the use of Kingspan Kooltherm® K103. However, where floor loads are to be excessive, consideration should be given to the use of Kingspan GreenGuard® which has greater compressive strength. For further information please contact the Kingspan Insulation Technical Service Department (see rear cover).”
Deformation of Insulation
Deformation of insulation under point loads is likely to damage a screed. 120-150kPa (0.15N/mm2) boards are popular for floating screed application and are adequate for residential use at traditional floating screed thickness but may not be strong enough for vehicle loads, even when loads are transmitted through an 80-100mm thickness of screed. Floor insulation boards are designed for use with ≥ 75mm thickness of screed and thinner screeds will transmit higher loads to the insulation. It is likely that only a higher strength polystyrene void former or foamed glass insulation will be suitable for the loads transmitted. A structural engineer must be consulted to determine insulation strength required for avoidance of screed cracking.
The following are benefits of Ronafix polymer modified screeds
 Improved strength gain and 28 day strengths in new screeds
 Suitable for wet areas
 Suitable for exterior application
 Greater durability, tensile and flexural strengths are maintained for decades longer than in traditional screeds, see the durability paragraph below
 Reduced minimum thickness for bonded, unbonded and floating screeds
 Reduced shrinkage
 Low water absorbency, making screeds resistant to frost attack. Polymer rich mixes will not allow passage of water under hydrostatic pressure
 Some mix designs suitable for use as medium to heavy duty wearing surfaces
 Suitable to be laid to falls
 Faster drying than traditional screeds and calcium sulphate screeds
 Compatibility with resin floorings, unlike traditional screeds and calcium sulphate screeds
 Superior corrosion protection of embedded steel; calcium sulphate screeds are not compatible with embedded steel
Comparison of key strength data in 3:1 sand/ cement and polymer screeds and % improvement in strengths of polymer screeds compared to 3:1 sand/ cement
Screed type Tensile strength % improvement in tensile strength Flexural strength % improvement in flexural strength
Sand/ cement 3:1 3 N/A 7 N/A
Ronafix Pre-packed Wearing Screed 15mm+ 6.5 > 115% 11.5 > 60%
Strengths quoted in N/mm2
Ronafix Durability
Ronafix has been used to improve the performance of high strength mortar for more than 50 years. Five decades of use and accelerated ageing test both show that Ronafix admixture considerably increases mortar durability. The following is a table showing results of testing of mortar 3:1 sand: cement with 9 litres of Ronafix polymer admixture and additional water to produce workability. Samples were heat aged at 700C for up to 365 days to simulate ageing to BS 4551:1970, BS 12: 1972. 365 days testing is approximately equivalent to 260 years UK service life. Flexural strength of unmodified control samples remained at approximately one third of Ronafix mortar strength and tensile strength of unmodified sample fell to 0.7N/mm2 by 20 years equivalent ageing and became unmeasurably low by 40 years equivalent ageing.
Ronafix Samples Unmodified Samples
Accelerated age of sample Flexural strength Tensile strength Flexural strength Tensile strength
20 years equivalent age 10.5 3.5 7 0.7
40 years equivalent age 15.5 3.0 4.9 Unmeasurably low
80 years equivalent age 14.7 2.0 5.5 Unmeasurably low
260 years equivalent age 14.1 2.3 5.4 Unmeasurably low
All strengths expressed in N/mm2
Slip resistance of Ronafix wearing screeds
Slip resistance of Ronafix Pre-packed Screed 6-50mm was determined using “SlipAlert” equipment (ramp/trolley method, please see BS 8204-3, page 25 Annex A1 - Determination of slip resistance of pedestrian surfaces by the ramp/trolley method, alternatively known as the roller coaster method), results below 130 are deemed to have achieved low slip risk. The table below shows values achieved and equivalent Pendulum Test Values (PTV). PTV ≥ 40 is regarded as low slip risk.
Slip Resistance Ronafix Pre-packed Screed 6-50mm Steel Float Finish
Test Conditions Test Method Specimen 1 Specimen 2 Specimen 3 Specimen 4
Dry SlipAlert 115 115 115 117
µ 0.64 0.64 0.64 0.6
PTV 58 58 58 55
Wet SlipAlert 121 124 125 126
µ 0.52 0.48 0.47 0.46
PTV 49 46 45 44
Slip resistance of Ronafix Pre-packed Wearing Screed 15mm+ is similar.

[@itstime6495]

could you lay an external screed over a plastic coating (decothane) or does it need to come up first? Cheers

[@SpeedScreedLimited]

Nice to hear from you. What are you wanting the screed to do? Bond with the decothane or just sit on top? How thick is the screed going to be? Just trying to get a feel for what you are wanting to achieve.