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Screed and Plaster Hardener (SMA)

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Description

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A specially designed latex admixture for the use in cement compositions.The addition of SCREED AND PLASTER HARDENER confers numerous advantages over untreated mortars and concrete, such as:

  • Greatly improved adhesion to substrate
  • Mixes may be applied in thin layers
  • Excellent resistance to water and water vapour
  • Improves toughness and flexibility
  • Better resistance to frost
  • Improved resistance to chemicals
  • Diminishing dusting
  • Non Toxic

USES

  • Patching and repairing concrete areas
  • Industrial flooring, screed and topping
  • Nosing for stairs indoors/outdoors
  • Flooring for dairies, food factories, fertilizer stores where improved chemical resistance is required
  • Lining of effluent ducts, tunnels and canals
  • Corrosion protection of steel reinforcing rods in concrete and steel structures
  • Screed for bathrooms and showers
  • Waterproofing of water tanks, reservoirs and retaining walls

SURFACE PREPARATIONS: FLOOR SCREED

  • Where the existing floor is old or dirty, it is ESSENTIAL to remove all contaminants such as oil, grease, paint etc. to ensure adequate development of bond when topping is applied. Any unsound crumbly concrete must also be removed
  • An efficient way of preparing an old floor is to use a mechanical scrabbler to remove all unsound materials. If concrete is in reasonably good order light scrabbling will suffice, e.g. to a depth of about 2-4 mm
  • To new floors, to which for example a levelling screed needs to be laid, it may still be desirable to remove the upper surface to ensure no weak surfaces are present. Light scabbling to depth of up to 4mm will normally suffice. Alternatively good results can often be obtained by etching either new or old concrete floors with Hydrochloric acid (1 part of concentrated acid diluted with 2 parts clean tap water) followed by thorough washing to remove all traces of acid
  • If screed bars are used to define thickness of screed, these should be positioned after the above preparation

PRIMING

  • The application of a priming coat is essential to obtain maximum adhesion of the subsequently applied screed. The prepared floor should be thoroughly damped with water, hosing is suggested, followed by removal of excess standing water. A priming coat, consisting of 2 parts ordinary Portland cement and 1 part SCREED AND PLASTER HARDENER slurry, must then be thoroughly brushed into the floor using a stiff broom.

THE TOPPING IS APPLIED WHILST THE PRIMING COAT IS STILL WET.
SPREADING RATE ADDITIVE: 5lt = 30 sq/m

MIXING RATIOS: GENERAL PURPOSE TOPPING

SIFTED RIVER SAND: 83 KG
ORDINARY PORTLAND CEMENT: 28 KG
SCREED AND PLASTER HARDENER: 5 LT
SPREADING RATE = 5 sq/m & 10mm
IT IS ESSENTIAL THAT THERE ARE NO ULTRA FINE CLAY-LIKE MATERIAL PRESENT IN THE SAND.

MIXING

  • Although fine sand may be used, especially where very smooth surfaces are required, it is essential that there should be no ultra fine clay like particles present in the sand
  • Mixing should preferably be carried out in a concrete mixer, although hand mixing is permissible where the total weight of the dry batch does not exceed 50 kg. Premix sand and cement in a mixer, pour in SCREED AND PLASTER HARDENER, mix for 2 – 3 minutes and finally CAUTIOUSLY add water little by little until the required consistency is achieved
    CAUTION: OVER ADDITION OF WATER CAUSES RAPID THINNING OF MIXTURE

APPLICATION

  • Screed based on the above composition can be laid to any thickness, down to feather edge if necessary, providing that a sufficiently fine grade of sand is used
  • Pour mortar mix over the still wet priming coat and struck off. Trowel to the required finish. A clean steel trowel is recommended for this operation
  • Re-trowel is not recommended after stiffening of the mortar has commenced. This may cause surface cracking
  • The whole surface should be trowelled, not just sections of it, to avoid variations in shade, texture, etc.

SPREADING RATE

23 Kg of mixture = 1 sq/m @ 10 mm thickness

CLEANING OF EQUIPMENT

All tools must be cleaned immediately after use as hardened cement have excellent adhesion and are therefore difficult to remove once set.

WATER PROOF RENDERINGS

  • Where the main requirement of the rendering is improved water resistance and proofing, a modified application technique is recommended
  • After preparing the substrate as described for screed, two sealing coats consisting of 2 PARTS cement slurried with 1 PART SCREED AND PLASTER HARDENER must be thoroughly brushed on the surface. The second sealing coat must be applied as soon as the first coat is touch dry, i.e. after 20 to 30 minutes.
    The sealing coats should be applied at right angles across each other, thus ensuring complete coverage of the substrate. Small quantities of water may be added to obtain brushable consistency.
    IT IS VERY IMPORTANT THAT THE THICKNESS OF EACH SEALING COAT SHOULD NOT EXCEED 1.6mm OTHERWISE CRACKING MAY OCCUR.
    The double sealing coat MUST DRY OUT COMPLETELY for a period of AT LEAST 48 HOURS.
  • After the sealing coats have dried thoroughly, apply a tack coat consisting of 2 PARTS cement slurried with 1 PART SCREED AND PLASTER HARDENER. Apply final coat WHILE TACK COAT IS STILL WET.

SPREADING RATE TECHNICAL DATA

75 kg slurry = 163 sq/m (dependent on surface)
(50kg cement: 25lt liquid)
The composition of the final coat is as follows:
14 litres SCREED AND PLASTER HARDENER
50 Kg Cement.

SPREADING RATE

64 KG MIX = 150 sq/m (dependent on surface)

CLEANING OF EQUIPMENT

All tools must be cleaned immediately after use as hardened cement have excellent adhesion and are therefore difficult to remove once set.

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