THE SCREED SCIENTIST
Type of cracking
Reason for cracking
Reflective cracks Laying screed on damp concrete.
Thermal Cracking Laying screeds below 0°C.
Preventative Measures Allow concrete slab to dry for at least six weeks.
Keep the floor temperature at or above 5°C for 4-5 days.
Use polythene sheets to control the curing and drying process.
Surface Cracks Uncontrolled drying/curing.
Consult your screeding specialists for advice. Different products and solutions are available to mitigate this issue.
Cracks from excessive loads
Allowing traffic to proceed on screed before it has reached full strength; lack of appropriate protection.
Stress cracks
Cracking due to incorrect mix proportions and / or mixing
Lack of expansion or crack inducement joints.
Incorrect water-to-cement ratios; incorrect/insufficient mixing.
Consult a structural engineer before placing loads on a screeded surface.
Carry out screed testing.
Install expansion or crack inducement joints at 50% of screed depth.
Use the amount of water, cement, and aggregates recommended; mix screeds with forced-action mixers; opt for ready-mixed screeds.
almost always appear is at corners. Since screeds cannot shrink around corners, the stress builds up, causing cracks. To relieve stress, expansion or crack inducement joints should be installed at relevant points, at half way in the screed thickness. Joints should be installed as recommended by the architect or engineer.
Early or excessive loading If weights are loaded too soon, or loads are heavier than anticipated, the screed will crack. To reduce the risk of cracking, the structural engineer should be consulted before placing any loads on a screeded surface. Additionally, temporary screed protection (e.g. corrugated plastic and heavy-duty polypropylene mesh sheeting) should be provided based on the level of traffic and loads expected, and maintained until the final floor finish is installed.
twitter.com/TomoFlooring
Ground and air temperature Laying screed in cold, wet weather usually leads to cracking. Temperatures below the freezing point will make the water in the screed freeze. As frozen water expands by about 9%, it may cause a disruptive reaction, potentially damaging the integrity of the screed and leading to cracks. Keeping the floor temperature above 5°C for 4 or 5 days, by using layers of hessian, cardboard, or polythene, will help prevent cracking and ensure that the screed has enough time to dry and cure to achieve full strength.
Visit the Screed Scientist website for more information on screeding and underfloor heating.
Do you have a flooring conundrum to put to the screed scientist? Email
sarah@opus.bm.co.uk to have your questions answered by the experts!
15
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64