Dryvit One-Coat
®
®
DUK909
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Dryvit One-Coat
DUK909
A. Material
1. Application of mixed material shall not take place during inclement weather unless appropriate protection is provided.
2. Air and surface temperatures must be 5ºC (41ºF) or rising at the time of One-Coat application. Applications should not commence or should be stopped where there is a potential for rapid freezing.
3. As for all cement based products One-Coat should not be applied to frosted substrates or those that have recently been subject to prolonged rain and have become saturated as this can compromise the bond strength and promote surface efflorescence (white lime bloom), and variable colour due to uneven suction.
4. To avoid colour and shade variations ensure bags of material to be used on a given area are of the same batch number. If this isn’t possible, different batches must be mixed together thoroughly.
5. Due to their small size indicative samples do not always fully reflect the final appearance of the product when applied over large areas, both in terms of texture or colour. It is advised that a trial application is evaluated to confirm these requirements are satisfied prior to commencing any project.
6. Full masking protection should be provided to adjacent areas of work, windows, doors etc and to give clean straight edges and be removed immediately after finishing.
7. To avoid etching the surface and leaving a permanent mark, take care to remove splashes of material immediately, especially from glass or aluminium .
8. Maximum storage temperature shall not exceed 38°C (100°F). Minimum storage temperature shall not be less than 5°C (41°F). Store product in unopened bags, off the ground and under cover in dry cool conditions. The product has a shelf life of 12 months from the date of manufacture if kept in dry storage in the original unopened bags. If stored at high temperatures and/or high humidity, the shelf life may be reduced to less than 6 months.
B. Substrate i. Substrate Condition
1. The requirements for Dryvit One-Coat renders are the same as if applying ordinary sand and cement renders; BS EN 13914-1 Code of practice for “External renderings” and BS 8000 code of practice
“Workmanship on Buildings Sites” Part 10 should be followed at all times. Construction should conform to
BS 5628 code of practice for use of masonry.
2. Ensure all surfaces are dry, clean, sound and free from contamination that may interfere with the adhesion of the applied material.
3. Before commencing rendering it should be ensured that all brick and block work mortar joints are flush pointed and have had a minimum of 7 days curing. This should be increased during prolonged wet spells.
Note - there’s a possibility of the joint lines showing through the render finish if the One-Coat is applied onto wet mortar joints.
4. The majority of masonry substrates are suitable for Dryvit One-Coat render, but certain precautions or surface preparation may be required. This is particularly the case where different material types are found within the same façade. Although Dryvit One-Coat has certain weather proofing properties and is designed as a decorative finish it doesn’t possess structural capability and can crack if the substrate has not been designed or constructed to accommodate potential material movement, either through initial drying out or normal flexural movement. Due to seasonal and daily weather conditions, these types of movement are normal in most structures.
5. Buildings constantly move due to seasonal and daily weather conditions. Cracking of the substrate can occur, generally at the weak points in the building, such as openings or near corners if poor construction techniques have been used or insufficient movement/restraint has not been allowed for in the design. In such cases the One-Coat render will itself mirror this cracking although not being responsible for the cause.
6. When applying One-Coat in hot weather, do not apply in direct sunlight and always try to work in the shade. When hot weather persists it is recommended that an even mist spray of clean water is applied to the substrate before application to reduce surface suction. ii. Substrate Type
Key coat slurry mix – 2 volumes of Dryvit One coat to +/-1 volume of Dryvit Prymit as the gauge liquid.
1. Concrete block - Dryvit One-Coat can be applied as a single coat application with no key coat slurry required on concrete blocks. It is advised not to use different strength concrete coursing bricks. If this is impossible, make sure these areas are fully meshed with the Dryvit Ultramesh to compensate for differential substrate movement.
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Dryvit One-Coat DUK909
2. Lightweight block or AAC (aerated autoclaved concrete) - To reduce water suction in highly porous materials, or lightweight blocks (Aerated Autoclaved Concrete) the surface should be lightly spray with water prior to One-Coat application. Care should be taken to avoid excessive watering as saturating the block will increase subsequent drying shrinkage and could create cracking in the finished One-Coat. Spray or brush-apply a surface sealer coat of Prymit immediately after damping the wall. Then leave it to dry and apply the One-Coat render. If the mortar joint strength is greater than the block strength, please note there is a possibility of general block work cracking.
3. In-situ concrete and low porosity materials - For dense concrete, a single coat of ready prepared key-coat slurry should be applied by scrubbing onto the wall before the Dryvit One-Coat is applied.
4. Brickwork/Medium Density Blockwork - For these substrates a single coat of ready prepared key-coat slurry should be applied by scrubbing onto the wall before the Dryvit One-Coat is applied. Ensure all joints are finished flush with the surface.
C. Access
1. Scaffolding should be independently tied with provision for sufficient space (minimum of 150 mm) between the inner board and the wall to be rendered. This allows uninterrupted application as patch repairs and other breaks in the work can be visible.
1. Before work commences it is recommended a trial panel application is made to allow inspection by the client, customer, and architect etc, to confirm acceptability of the One-Coat finish, texture, colour and appearance.
E. General
1. Good building practice suggests constructing the sections of building to receive render using the same type and density of material throughout.
This minimises the potential for differential thermal movement and different suction each type of material may produce.
Man-made materials such as concrete or lightweight blocks tend to shrink, particularly soon after production whereas bricks made from natural materials such as clay can expand. Mixing materials in a wall will therefore potentially cause not only cracking but also shading issues, as the materials will have different absorption rates.
A. General
1. No additives such as sand, aggregates, rapid set binders, anti freeze, accelerators etc shall be added to
Dryvit One-Coat under any circumstances.
Such additives will adversely affect the performance of the material and void all warranties.
B. Mixing
1. Care should be taken to ensure One-Coat render is thoroughly mixed. Mixing in a suitable size bucket using a Dryvit recommended paddle attached to a slow speed (400/500 rpm) heavy duty drill is acceptable.
When larger quantities require mixing a forced action mixer is recommended. Mixing by hand or free fall concrete mixers must not be used. Mixing part bags should never be attempted. Note: One-Coat render may stiffen on standing. Re-mix the product to regain a workable consistency, but do not add any more water. Powder must always be added to the water.
1. Place 5.0 - 5.5 litres of potable water into the mixing vessel and whilst mixing add one full 25 kg bag of
One-Coat and mix for a full 5 minutes until fully homogeneous. The initial mix will appear dry, but gradually wet out under mixing action. Allow to stand for 5 minutes and then briefly remix. Note: In common with traditional renders slumping of the material may occur if the mix is too wet, increasing the risk of settlement cracks developing.
1.
Dryvit One-Coat render can be applied by stainless steel trowel, but must in all cases be thoroughly mixed as described in Section II. The material should be applied to a minimum thickness of 18 mm in 2 passes, the first pass 6-8 mm and the second pass 12-10 mm. Ensure that the second pass is applied when the surface of the first pass has stiffened, but not fully hardened. Compact it to the substrate surface and level it off with a straight edge, spatula or trowel until flat. When ruling level, hollows should be filled out immediately before a skin has formed. Take care to avoid small hollows, which may make it difficult to achieve a good finish.
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Dryvit One-Coat DUK909
B. By Spray machine
1. It is recommended that a render spray machine is used which allows quicker application and greater efficiency when applying Dryvit One-Coat. The spray gun must be held at 90° and at a distance of between
75 and 100 mm from the work surface so that the ribbons of material are flat enough to facilitate levelling.
1. Scraping should take place when the One Coat is set, but not fully hardened. The exact timing is dependent on substrate type, prevailing temperature, wind and humidity conditions and can be anything from 5-36 hrs after application. The render is ready when a thumb impression cannot be made in the surface, but it can be marked with a thumb nail. At this point scrape the surface in a tight circular action using a Dryvit One-Coat scrape float , taking care to remove no more than 2-3 mm from the surface. This is the best time and process to remove any slight imperfections and bring the application to the specified finished thickness. Early scraping will result in a slightly darker shade and later scraping in a lighter shade.
Therefore each elevation must be scraped at the same stage. Note: The minimum finished thickness after scraping is 15 mm.
Immediately brush down the surface to remove any dust or loose material from the surface after scraping using a clean soft bristle brush. Stand back and examine the work for blemishes and unevenness. It’s at this stage that any errors must be corrected, as rectification later is not practical.
B. Spray Textured & Smooth Textured Finish
1. Apply a level, compact 15 mm minimum thick first coat. Then allow it to dry and spray the textured coat to the desired finish. A smooth textured appearance can be achieved by pressing a plastic or stainless steel float onto the stiffened, but not fully dry textured coat.
C. Sponge or Trowel Finish
1. Use a sponge or trowel to finish achieving the desired effect as per normal render applications.
D. Detailing
1. Arrises and feature stops - Arrises can be formed at head, base and corner details using PVC type beads.
However, scraped finish renders may spall away from the nose of some angle beads during the scraping process. PVC beads provide the most successful result, but bead edges will be visible and must be accepted as part of the finish.
2. Lintels - Unless specifically advised otherwise, the head return to lintels should be formed using a corner bead set a minimum 10 mm lower than the underside of the steel lintel. The underside render should be sloped up to the steel lintel plate to leave a smooth trowelled finish. Do not attempt a scraped application as this may result in a poor finish due to the thinness of the lintel plate. If a Bellcast detail to the head of openings is required, the bead should be set at least 5 mm below the line of the block to ensure the rear face of the bead is flush pointed. It is advisable to check at an early stage with the main contractor or specifier the type of finish required to the exposed block underside.
3. Ashlar detailing - Additional render thickness should be applied to accommodate the depth of the ashlar cuts, typically 20 - 25 mm. As soon as the proposed finish is completed, usually the scraped finish, mark out the ashlar cuts using a chalk line and timber batten or similar while the render is still “green”. Run the cutter along the batten to the required depth, ensuring the cutting process removes the chalk line. Take care with the detailing to avoid highlighting inaccuracies; these can occur in alignment and levels particularly around windows and doors. It is recommended to keep the cut about 50 mm down from the head and 50 mm up from the cill base. This will help to hide inaccuracies along these points and keep ashlar lines away from any defined features such as transoms. Wherever ashlar cuts are required, it should be noted the finished render must maintain a minimum thickness of 12 - 15 mm at the base of the cut.
E. Protection and Curing
1. Care must be taken to protect One-Coat from heavy rainfall and rapid freezing immediately after application. Protect applied product from inclement weather until it is completely dry. If hot weather is prolonged or the render is exposed to sunlight or drying winds, it should be kept evenly damp for about 3 -
4 days by lightly spraying periodically with clean water. This is vital to ensure complete hydration of the cementitious product.
F. Cleaning
1.
One-Coat, Primers and Key-Coat Slurry should be removed from tools, equipment and mixers with clean water immediately after use. Cured materials can only be removed mechanically.
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Dryvit One-Coat DUK909
A. Crack
1. Windows and doors
The risk of cracking at high stress locations can be reduced, particularly on new buildings, with the following precautions; introduce a minimum 500 mm width of Dryvit Ultramesh to potential stress fracture locations, such as around windows and doors and crack-prone points such as weep vents. The application of mesh is an additional precaution to crack prevention in well constructed and reinforced substrate materials.
If existing masonry has cracked, or where abutment of two types of masonry meet, it is recommended that this is first repaired or reinforced by retrofitting a bed joint reinforcement solution alternatively repairs may be made by creating a movement joint. Once completed, Dryvit Ultramesh should be applied a minimum of 500 mm past the line of the cracking in all directions.
Movement joints should be introduced into the structure as recommended by the designer/brick/block manufacturer. The guidelines offered under BS 5628 – Code of Practice for use of masonry and BS 6093 –
Code of Practice for design of joints and jointing in building construction should be followed at all times. In general it is recommended that joints are placed at 6 m centres and within 3 m of a corner. Locations often correspond with down pipe locations. On certain applications the number of movement joints can be reduced and in some cases avoided with the introduction of Dryvit Ultramesh .
Care should be taken to apply stop beads/specialist movement joint beads to correspond with the building movement joints as cracking will not be prevented with movement joints created solely within the Dryvit One-Coat .
Note: All reinforcing mesh is fully bonded and embedded within the Dryvit One-Coat render during the first pass 6-8 mm application stage and not mechanically fixed.
B. General
1. DPC
The DPC should not be bridged by the render and a suitable stop bead should be created at the DPC level.
Do not apply render below the DPC level as it will be prone to staining, lime bloom and may also delaminate from the substrate.
Designs should be constructed with enough overhangs and drips to avoid water collecting in a single location by capillary action. To prevent staining to the render, overhangs should be designed to prevent water washing or splashing on to the surface.
3. Gutters and down-pipes
Make sure all guttering and temporary down-pipes are in position well before rendering work commences.
These must be constructed to ensure water is kept away from the render façades. This will avoid the formation of wet patches where water has collected from an open down-pipe hopper.
4. Discolouration
The natural processes of lime blooming and efflorescence are initiated by soluble salts rising to the surface of cementitious materials and can cause discoloration of the Dryvit One-Coat, but are not harmful to the product strength. Poor site control of rainwater, particularly from roof areas can cause lime blooming if water is allowed to soak into the masonry for any length of time and can take several weeks, sometimes months to evaporate from the substrate. If Dryvit One-Coat is applied before the substrate has fully dried and lime blooming occurs it can affect the overall quality of the render colour consistency, particularly dark colours, and even cause it to scale. Other factors that can increase the potential for lime blooming include wet weather and damp conditions during application.
5. Substrate
Cracks can appear where long expanses of concrete blockwork masonry exist without sufficient or no movement joints. In particular they can occur around openings, as these are areas where stress from concrete block work shrinkage is most likely to occur. Countering this can be achieved with movement joints which should be included within the design. In localised areas, bed joint reinforcement may assist in counteracting cracking. It should be noted that even if Ultra Mesh is used with the Dryvit One-Coat, long expanses of masonry still have the potential to crack and it would be recommended to retro-reinforce the blockwork and include movement joints cut into the masonry before the Dryvit One-Coat is applied.
6. Different
Movement can occur in the substrate due to the use of different density materials and is caused by using much stronger concrete bricks or clay bricks as coursing materials below windows, closures near corners and at floor levels etc. Cracking often occurs as the materials expand and contract at different rates and
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Dryvit One-Coat DUK909 can be reflected through the Dryvit One-Coat finish if not corrected. It is therefore recommended that the use of different substrate materials should be avoided at all times.
Note: This list of design considerations is not exhaustive and in the case of particular design queries, please contact the Dryvit Office .
1. Regular maintenance checks should be carried out to ensure that architectural details for shedding water clear of the building are present and functioning. External plumbing, fittings, gutters and downpipes should be in good condition to reduce the extent of penetration of water into the render. Any defects observed should be repaired by a trained contractor as soon as possible in accordance with Dryvit recommendations.
A. Health and Safety
1. Dryvit One-Coat contains cement powders that when mixed with water or become damp release alkalis that can be harmful to the skin. During use avoid inhalation of dust and contact with skin and eyes. Wear suitable protective clothing, eye protection and a dust mask. The use of barrier creams provides additional skin protection. In case of contact with eyes, rinse immediately with plenty of clean water and seek medical advice. In case of contact with skin, rinse with plenty of clean water, then cleanse with soap and water.
B. Fire
1. Dryvit One-Coat is non-flammable.
1. Refer to the product Safety Data Sheet.
DISCLAIMER
Information contained in this document conforms to standard detail and product recommendations for the installation of the Dryvit One Coat products as of the date of publication of this document and is presented in good faith. Dryvit UK Ltd. assumes no liability, expressed or implied, as to the architecture, engineering or workmanship of any project. To insure that you are using the latest, most complete information, contact Dryvit UK.
Dryvit UK Ltd,
Unit 4 Wren Park,
Hitchin Road,
Shefford, Bedfordshire, SG17 5JD
Tel 01462 819555
Fax 01462 819556 www.dryvit.co.uk
Printed in UK R0:06-28-12
©Dryvit Systems, Inc. 2012
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