Preparing for plastering and how to avoid plaster cracks

Plastering is the most important part of the finishing job in a building project, whatever error
made during plastering may be difficult to correct,because after it, is just to paint and fix
other accessories.
Plastering takes a lot of cement and is important the mix ratio quality is not reduced because
of the consequences.
Care should be taken right from the type of sand you ordered, bricklayers prefer the sticky ones
because they bond easily without applying too much power to splash the mortar on walls (though
this does not automatically means is the best to use.)
The sand must be clean, should not have dirts, and any sand with dirts should be sieved.
As said adequate numbers of cement with standard cement and sand ratio should be maintained.
Is also important you get good hands to do the jobs for you.
cracks
Plaster cracks leading to an opening a door.
To get a good plastering job, tell the masons to apply guage. Guage is just a term used by
masons/bricklayers which is using a thin material especially wood with rope to mark out how the
plastering will spread round the surface of wall of the building to achieve perfectly vertical
walls. Blockworks are usually not done to perfection especially when the bricklayers are not
very good, often time, the blocks will not stand perfectly vertical, therefore some areas will
require more mortar filling to others to compensate for the bad areas, so guaging is what you do
to achieve a perfect plain. In doing this some areas will require more mortars than the others.
Plastering is usually applied between 15mm to 25mm, but some areas may require more mortar, in
such cases, apply cement and sand, leave to dry till the next day before you apply the finished
coating for a smooth surface. Leave the area you filled till the next day and allow to dry
before you apply the final coat on it.
I prefer a mixture ratio of 1:5-1:6 for cement, sand mix.
Causes of plaster cracks

Cracks in building
Plaster cracks as a result of electrical works


(1) Deep filling not allowed to dry properly-Don’t give plastering project to your
masons/bricklayers on per day payment because when you pay for the job done per day, a mason
must finish up the portion giving to him before the day runs out, so he will fill and won’t wait
for it to get dried before applying the final coat. The plaster filling requires minimum of 6
hours to get dried, but a mason that is expected to be paid on daily basis will not have the
luxury to leave such portion till the next day so that he can take home his pay, hence the
plaster will be applied before the filling get dried, this will inevitably cause cracks. The
plaster filling will shrink and contract in the process of drying, this will cause it to leave
strips of cracks inside which will allow air to fill the space and inevitably will also affect the plaster
finish on top.
(2)Bad plaster sand-The sand is supposed to be fine with no impurities and should be able to bond
well with the cement.
(3)Shortage of cement-When the cement is not adequate, the plaster will not bond well and will
results in cracks.
(4)Pipe holes left by plumbers and electrician-The pipe holes where pipes are placed in should
not be covered immediatelywith plaster, because of the space, the holes are better not left to
the plumbers and electrician but there should be a mason/bricklayer on site that will be
responsible for filling back the holes. First fill the gaping holes with broken blocks, then
apply plaster, leave to dry till next day or more before final coating to finish.
(5)Poor workmanship-Get a good bricklayer/mason for this project.
(6)Dirts and impurities in plaster sand will also affect the outcome of your plastering.
When you notice a minor crack, apply cement slurry by that I mean mix pure cement with water,
then use brush to run the cement along the lines of the plaster.
An architect with decades of experience

38 Comments

  1. Good man! I enjoy your tips. Will require your inputs towards my building plan in a few weeks time.
    God bless you.

  2. hallo, thanks for all this info here. However, how do i calculate volumes from an excavation say 5m x 8m x 2m. and how many trucks of 15tonne do i expect for this. imagine loam soil. Thanks

    1. You’ve already done the calculation yourself 5m x 8m x 2m=80m3.
      Depends on type of truck assuming 5 tons truck which is taken as 3.8m3 .
      Then (80/3.8)m3=21 trips of 5 tons truck or 4 1/2 tons of 20 tonnes truck.

  3. Nice informations. Carry on these type of useful informations. This will be great helpful for future reference. Thanks wonderful

  4. excellent lecture. Very easy to understand. You have done Nigerians proud . Thanks. With your support my house has been roofed. I have found your advise on plastering again very useful as I know now what to look for.
    I need advise on electrical work, and Plumming before plastering, in rest of material and costing. Thank you.

  5. I just stumble on your website and i found it educative. However, i have little observation with regards to the thickness of plastering. What is appropriate is this: any plaster that exceed 12.5mm should be reinforced. Thanks

  6. U tried 4 dt info. Keep it up. Texture of plaster sand varies frm places to places and it may also affect your mix ratio. Then wot is important is check ur mix after the first mix whether plastic &bonded well &easily hold 2 d wal when throw wt force.

  7. @ Blder Muhammed, i concur with you. Any plaster more than 12.5mm should be reinforced with a mesh. Sometimes if more than 50mm should reinforced 2ce.

    Another technique is to reinforce soft sand with some sharp sand to prevent shrinkage cracks. Do not use a soft sand with clay content due to the clayey properties to water.

    The Block wall must be wet prior to plastering so that the intial setting time would take the required time be established properly while after plastering, the plaster must be cured for about 4 days. It is a pity that Curing is not a culture in this part of the world, that is why our walls and concrete are always cracking. Just designate a labour for curing works.

    Great blog, i salute you emma.

  8. what a great info u hve here i am a builder n am enjoying ur blog….keep it up sir.as regards plastering can i use a tile as a means of guage for plastering.thanks

  9. Hell o,
    I love your tips, very beautiful and helpful. However, I have a ten bedroom (face me) apartment left to me by my late father and I’m interested in developing this structure. I think I’ll need your insight.
    Thanks.

  10. I acidentaly ran in2 ur website yl searchn 4 some tips.,i must u r doin a gud job.mix ratio 1:6 wch u stated, i dnt tnk it z dt gud 4 plastering bt it can be use as a mortar ratio 4 block layin

    1. Thanks Nnamani, most times the aggregates affects what to use. I agree is not okay in some cases so we may say 1:3,4,5,6 as case may be.

  11. How do I calculate the number of cement bags for plastering and mortar joints. You guys are always ahead, thank you all.

  12. Technically your wrong in saying that if u pay a mason per day the job will crack due to the concrete not having enough time to dry(^6 hrs..lol)…all concrete cracks first of all; even if there not visible. Secound the Egyptians discovered hydrous calcium sulfate thousands of years ago when building their pyrmaids, and now in days we have rapid set, luminite and other concrete drying acceleration additives…paying time and material or by the day would for most jobs decrease the masons pay and save money…the most important thing in finding a mason or plasterer is expirence the more they have the better job u will have.

  13. And alot of masons will look at u funny if u say gauge…just tell them u want it straight so they need to put corner beads, expansion joints, and screet or jay metal for bottoms…and u don’t leave cement that’s drying alone let it dry and wet it down after dry at least once before the finish coat to cure it…u prob won’t post my comment but I have a family pplastering and lathe license and hate to see people misinformed…friends plastering

  14. Dante Friends, i prefer you comment like a pro instead of like a rival. All the masons i have worked with use and understand the term GAUGE when it comes to plaster just like Emma mentioned.Besides, this is a blog not meant to teach you everything on building but tips,hot tips and secrets indeed.

    Earlier, when i started supervising site works i used professional terms and all the people on site saw me like mumu,oluku,sabi-sabi, but later i had to learn their language and flow smoothly with them. I had to start talking feet,inches instead of meters and mm,and sometimes i even teach them.When you go to Rome, do like the Romans, but when you are at home, say what we understand .If your workers or masons are educated and fluent in these jargons,then ride on, otherwise speak what they understand.I am a practicing architect too. Sorry if i was offensive.

    Emma is doing a wonderful job that many builders would hate to divulge…hence, hateful comments are not a surprise to me.
    Emma God bless you.I just saw this site.

  15. Thanks for the great job you are doing to educate us.May God bless you. I’ve spent the last 3 hours reading your articles but i did not read any one on kitchen. I love spacious kitchen and toilet

  16. my building walls have tiny cracks running for about 1 – 2 meters long. pls what can I do to solve this problem bcos it is an eye sore?

  17. Hi,

    I need a bit of advise. My new house elevation involves quite a bit of mesh work on which cement plastering will be done. I heard that mesh work with cement plaster leads to cracks in future. Is there a way to avoid this, by a different mix ratio or adding some other chemical or material to avoid cracks in future?

    Thanks in advance,
    Shankar

  18. Emma u r a grt guy n sincerely av always make lots of refeence to ur site on construction perhaps am a young grad of civil-engr basicly building which I av been able to expose to 4 the time being ,I will encourage u to pls give a hint on road construction……n hw properly can one set out slab form work to b cast of a 450mm including the beam,note d beam is 300…fnks

  19. @Bldr Kunlefads, what should be the mix ratio of sharp sand and the soft one in plastering.@Mr Emma,keep it up.your blog is educative

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