First Grade Quality Cement ?

[Krub]

Hi,

Can you tell me if these are first grade cement bags ?

Thanks

[Gary A]

There are several grades of cement. I think general construction grade comes in a green bag. The blue bag is a higher grade and the red bag is high tensile and pretty expensive. I know they wanted to use the red bag cement for my roof support columns. Everything else was green bags.

[penzman]

It all comes down to the "recipe" when they mix it. Your best grade cement will become crap if not mixed properly as many try and cut down on cost by cutting corners, as when painting, they'll add water to the paint bucket.

[roiet]

It all comes down to the "recipe" when they mix it. Your best grade cement will become crap if not mixed properly as many try and cut down on cost by cutting corners, as when painting, they'll add water to the paint bucket.

<{POST_SNAPBACK}>

Mixing a bit longer makes your house stronger and it lasts longer.

[tango]

Hi...sorry no data on color of bag vs grade of cement, but I'm working on it.

However, recently been following the construction of a new "French' Restaurant near Lotus CMai and the foreman told me the best trucked mix is CPAC #210.

Important as Patan Road, on which the restaurant is situated, was recently completed and looks 20 years old not 20 months old. The city did not use CPAC and the grade was obviously inferior...even city hall officials were out in force on foot checking the cracks etal.

[thai_norman]

From CPAC you order the strength you need for the specific job, ie footings for a swimming pool you may use 240, but the walls of the swimming pool maybe 320.

For general building you would use Chang cement for footings and beam work, and Sua cement for brickwork and rendering off.

[Digger]

It all comes down to the "recipe" when they mix it. Your best grade cement will become crap if not mixed properly as many try and cut down on cost by cutting corners, as when painting, they'll add water to the paint bucket.

<{POST_SNAPBACK}>

The adding water to paint is not always to cut costs - if you read the tin, it suggests adding water at ratio of 10% to the paint and that goes for the better Thai brands as well as the very cheap ones. I have no knowledge of this other than reading a tin in Home Pro when I was waiting for a member of staff, but seems to confirm it to me (and I had exactly the same assumption as you which is why I looked at a tin that had English instructions).

[thai_norman]

Digger is quite right, 20 to 30 years ago we always had to dilute paint, that was before dulux etc, in Thailand and other third world countries you still have to dilute paint, then again 20 years ago, painting and decorating was a trade, now lots of skills have been lost, woodgraing and marbling to name two.

[roiet]

From CPAC you order the strength you need for the specific job, ie footings for a swimming pool you may use 240, but the walls of the swimming pool maybe 320.

For general building you would use Chang cement for footings and beam work, and Sua cement for brickwork and rendering off.

<{POST_SNAPBACK}>

Sorry to ask about the cement for the swimming pool. The strength 320 for the pool walls is also a matter of thickness of the wall, isnt it. What is 320 ?

Is it 320 pound per square foot or what ?

Thanks your advice.

[miminem]

Just a little input.

Concrete is an empirical ( had to use my dictionary for this one) science

The cement is important but quality (no salt except with special CPJ cement) and quality of water is important too.

Too much water, you get cracks and your concrete gets weaker.

Sand must be clean too, with enough fillers. Size and shape of gravels is important too.

May be I am asking too much here.

The figure 320 or 240 or whatever is the expect resistance of concrete to compression. The higher it is , the better.

With special cemnts, you cn get up to 800 but it is quite expensive and not relevant for a simple house construction.

Important: do not forget to put some still in your concrete, whatever you want to do with it ( compression or tension), it helps to prevent the cracks.

[cdnvic]

You can use a densifier to harden the exterior of the concrete. This makes it much less vulnerable to water penetration and protects it from dropped objects on the surface. Most densifiers are acrylic or polymer fillers which fill in the microscopic pores in the concrete that allow moisture to move around within the structure, causing problems later on.

Penz was right about the mixing procedure. Better to have so-so concrete mixed properly than top grade stuff made sloppily. Thin section self leveling mixes who normally have alot of additives in them are very fussy about mixing ratios.

Aggregate (gravel/sand) consitancy is one thing that makes me cringe at Thai construction sites. Too much large aggregate and you won't achive a proper bond and will tumble when it gets lateral pressure, too much sand, and the structural strength fails when compressed. Get the two uneven, and it completely messes up the engineering on the structure, with non load bearing walls full of rock, and pillars full of sand. You rarely get this with a truck mix, but watch the guys doing it bucket by bucket.

Sorry, I don't know of Thai brands for densifier but if you need to know I'll look it up at the office.

cv

[roiet]

Just a little input.

Concrete is  an empirical ( had to use my dictionary for this one) science

The cement is important but quality (no salt except with special CPJ cement) and quality of water is important too.

Too much water, you get cracks and your concrete gets weaker.

Sand must be clean too, with enough fillers. Size and shape of gravels is important too.

May be I am asking too much here.

The figure 320 or 240 or whatever is the expect resistance of concrete to compression. The higher it is , the better.

With special cemnts, you cn get up to 800 but it is quite expensive and not relevant for a simple house construction.

Important: do not forget to put some still in your concrete, whatever you want to do with it ( compression or tension), it helps to prevent the cracks.

<{POST_SNAPBACK}>

From your explanation I am learning. The walls of my house are polished with concrete of 1cm thickness. This polish was applied 2 days after the brick wall was finished. I tried to stop the builder from applying the polish because the wall was still wet. The polish dried quickly and paint was applied 1 week later and the first cracks appeared 5 days later. The whole house was painted again to cover the cracks . 1 year later the house has 120 hair thin cracks, most of them 3-4 meters long.

Some experts told me the builder should have added 4 % instead of 2 % cement, the brick wall needs 2 weeks to dry, the polish needs 1 month to dry before painting. The acrylic exterior paint should only have 15 % water added and not 30 %. So I learned my lesson .

I am lucky with my swimming pool, rock solid CPAC truck mix.

miminem thanks a lot for your advice , if I ever build a house again I will hire you as an expert, o.k. ?

[miminem]

With pleasure.

However, it is not concrete that you put on your wall, it is mortar. Concrete has gravel, Mortar has not and is mainly used for surfacing and getting a good finish.

about cracks, if you have too much water in your mortar, it will crack because, when dry , the water would have gone (obvious) and will leave spaces that will allow for cracks at the weak points . But if not enough water, the mortar is not workable and you get a bad finish.

Having your wall wet is not a bad thing as dry walls will suck quickly the water out of the mortar and then wht do you get: cracks. So before applying mortar on dry walls, better to splash some water on them.

Also, avoid direct sun as again, it will dry to quickly.

So good experience, materials and test is required.

[Gary A]

I have learned a little more about cement. The red bag is universal and makes good mortar as well as high tensile construction. The dark blue bag is a high tensile construction grade. Siam cement makes about nine grades.

As far as the mixing you won't have problems with them skimping on the cement if you buy the material. Why would they? I also bought the paint myself. The painter added water to it and the whole thing got two coats. I would have thought if he had not added so much water one coat would have done the job. My girfriend already had the job price from him so he wasn't milking the job.

[stevehaigh]

the 3 most important factors in concrete construction are

1) water/cement ratio

2) vibrating to remove air pockets

3) slow curing

here's an excerpt from a book i'm writing about building techniques in thailand

############

The strength of concrete depends on 3 factors:

1) The proportions of cement, sand, rock and water in the mixture

2) How well the air pockets are removed from the poured concrete

3) How long it has to cure and the curing conditions

In all of the above factors, I feel that Thai builders generally do a bad job.

Cement/water proportion

The ratio of water to cement will control how strong your final concrete is. The more water that is in the concrete mix, the weaker your concrete will be.

This graph shows the relationship between the amount of water in the concrete as a ratio of water to cement, and its effect on the concrete strength (after 28 days).

The graph above shows that by doubling the amount of water in the concrete mix, you will approximately half its strength!

Concrete should be firm enough that if you form a tower about 1 foot (30cm) high and about 4 inches (10cm) diameter, it should droop no more than about 3 or 4 inches (7-10cm). If it drops instantly into a pile of rock swimming in cement, you have a problem!

I find that Thai builders love to make concrete too wet, because it’s easier to work with. Keep a close eye on the consistency of the mix and tell them if you are not satisfied.

The water in concrete should be clean and not salty. Concrete books say it should be good enough to drink. I wouldn’t drink the water coming out of my pipes, but it is good enough for concrete.

Air pockets in poured concrete

Freshly poured concrete is full of air pockets. Air does not support any weight (surprise, surprise!). It is vitally important that the air is shaken out of the concrete before it hardens. This is usually done by stabbing or poking it repeatedly with a piece of steel rod.

These 2 pictures show the effect of vibrating more or less air out of the same concrete in 2 different places.

The left side shows the area under the post bases where the concrete was poked for about 2 minutes. As you can see, the air bubbles are very small.

The right side shows where the concrete was not vibrated for long enough. This air pocket is about 2cm long and 1cm high.

You can buy a concrete vibrator for bigger jobs, but that is expensive (about 10,000 baht). I suggest you tell your builder you want 2 extra people on concrete days that do NOTHING but vibrate the concrete. And check that it is what they actually do. If your builder looks reluctant, give him 500 baht to pay for the workers.

Curing concrete

Concrete gains most of its strength in the first 28 days after it is poured. Think of those first 28 days like it’s a new baby. You need to take extra care not to over stress it (by loading too much weight on it) and it has to cure properly.

Concrete gains strength by curing NOT BY DRYING!! It must be protected from drying too quickly, which in Thailand, in the dry season is admittedly a big challenge.

If concrete dries too quickly, it will not have chance to cure and the concrete will be weak.

You should leave wood forms on as long as possible, both to provide support and to stop it drying too quickly. This is especially important on structural components like floor joists and posts.

Also cover new concrete with something to protect it from the sun and try to keep it moist. The Thais will think you are crazy, kon bâa!, watering concrete, especially after you have spend all morning complaining the mix is too wet, but it is very important you look after your new baby for the first 28 days. You cannot fix it later (although the builder will try by patching it up with cement mortar!)

The graph above shows the effect of exposure of concrete to the air after pouring. Concrete that is exposed to the air immediately after pouring will only reach 50% of its ideal strength and will stop curing after 28 days. Concrete that is protected from drying for a full 28 days will gain up to 125% of its ideal strength in 28 days and will keep getting stronger. (The Hover dam in America is still curing, 60 years after it was built!).

############

if anyone is interested in the whole book, i need proof readers with building experience in thailand, pls let me know via PM.

thanks, steve

Edited April 16, 2005 by stevehaigh

[roiet]

the 3 most important factors in concrete construction are

1) water/cement ratio

2) vibrating to remove air pockets

3) slow curing

here's an excerpt from a book i'm writing about building techniques in thailand

############

The strength of concrete depends on 3 factors:

1) The proportions of cement, sand, rock and water in the mixture

2) How well the air pockets are removed from the poured concrete

3) How long it has to cure and the curing conditions

In all of the above factors, I feel that Thai builders generally do a bad job.

Cement/water proportion

The ratio of water to cement will control how strong your final concrete is. The more water that is in the concrete mix, the weaker your concrete will be.

This graph shows the relationship between the amount of water in the concrete as a ratio of water to cement, and its effect on the concrete strength (after 28 days).

The graph above shows that by doubling the amount of water in the concrete mix, you will approximately half its strength!

Concrete should be firm enough that if you form a tower about 1 foot (30cm) high and about 4 inches (10cm) diameter, it should droop no more than about 3 or 4 inches (7-10cm). If it drops instantly into a pile of rock swimming in cement, you have a problem!

I find that Thai builders love to make concrete too wet, because it’s easier to work with. Keep a close eye on the consistency of the mix and tell them if you are not satisfied.

The water in concrete should be clean and not salty. Concrete books say it should be good enough to drink. I wouldn’t drink the water coming out of my pipes, but it is good enough for concrete.

Air pockets in poured concrete

Freshly poured concrete is full of air pockets. Air does not support any weight (surprise, surprise!). It is vitally important that the air is shaken out of the concrete before it hardens. This is usually done by stabbing or poking it repeatedly with a piece of steel rod.

   

These 2 pictures show the effect of vibrating more or less air out of the same concrete in 2 different places.

The left side shows the area under the post bases where the concrete was poked for about 2 minutes. As you can see, the air bubbles are very small.

The right side shows where the concrete was not vibrated for long enough. This air pocket is about 2cm long and 1cm high.

You can buy a concrete vibrator for bigger jobs, but that is expensive (about 10,000 baht). I suggest you tell your builder you want 2 extra people on concrete days that do NOTHING but vibrate the concrete. And check that it is what they actually do. If your builder looks reluctant, give him 500 baht to pay for the workers.

Curing concrete

Concrete gains most of its strength in the first 28 days after it is poured. Think of those first 28 days like it’s a new baby. You need to take extra care not to over stress it (by loading too much weight on it) and it has to cure properly.

Concrete gains strength by curing NOT BY DRYING!! It must be protected from drying too quickly, which in Thailand, in the dry season is admittedly a big challenge.

If concrete dries too quickly, it will not have chance to cure and the concrete will be weak.

You should leave wood forms on as long as possible, both to provide support and to stop it drying too quickly. This is especially important on structural components like floor joists and posts.

Also cover new concrete with something to protect it from the sun and try to keep it moist. The Thais will think you are crazy, kon bâa!, watering concrete, especially after you have spend all morning complaining the mix is too wet, but it is very important you look after your new baby for the first 28 days. You cannot fix it later (although the builder will try by patching it up with cement mortar!)

The graph above shows the effect of exposure of concrete to the air after pouring. Concrete that is exposed to the air immediately after pouring will only reach 50% of its ideal strength and will stop curing after 28 days. Concrete that is protected from drying for a full 28 days will gain up to 125% of its ideal strength in 28 days and will keep getting stronger. (The Hover dam in America is still curing, 60 years after it was built!).

############

if anyone is interested in the whole book, i need proof readers with building experience in thailand, pls let me know via PM.

thanks, steve

<{POST_SNAPBACK}>

Great Steve, thanks a lot for professional advice

Watering concrete is very important. After my house was finished I built a 300 meter long wall around it. The builder left after the job was done. I sprinkled water for 3 weeks twice per day. I heard remarks that this falang must be really crazy . I ignored the remarks and do not regret. The wall is strong and has only a few small cracks.

[tango]

As promised further to Thai Cement Classification:

http://www.aecasia.com/CSM/cement.htm

View Other Cementhai Sales & Marketing Products

Cement

Elephant brand: Ordinary Portland Cement (TYPE I), suitable for civil engineering works, building structure and all concrete products.

Tiger brand: admixed cement, suitable for plastering and brick laying.

Erawan brand: Portland Cement (TYPE III), suitable for high early strength concrete works such as concrete piles, poles, and girders.

Blue Elephant brand: Portland Cement (TYPE V), suitable for structures that require protection from sulphate, such as ship docks and buildings in or near the sea.

3 Tigers brand: especially for concrete products that require fast-setting and high early strength, such as concrete blocks and culverts.

White Elephant brand: white Portland Cement for decorative works particularly terrazzo and washed sand.

White Tiger brand: white admixed cement for fixing and grouting ceramic tiles and mosaics.

Twin Tigers brand Tile Grout: privides better bonding for ceramic tiles, marble, granite, and large tiles.

Twin Tigers Dry Mortar: available for masonry works of brick and concrete wall block construction, plastering, finishing, floor leveling, and repairs.

CPAC Ready-Mixed Concrete for fast and convenient applications that provide the same standard for small jobs such as flooring, building extension, and housing, to large constructions such as buildings, roads, and bridges. Available as standard products and special products that include: CPAC High Strength Concrete, CPAC Fast Setting Concrete, CPAC Waterproof Concrete, CPAC Flow Concrete, CPAC High Early Strength Concrete, and CPAC Low Heat Concrete.

Also: keeping cement damp is crucial as expertly pointed out by others :

Curing is the hardening of concrete over a period of time.

To cure properly, concrete must be kept damp.

Concrete strength reaches:

70 % strength in 7 days

90 % strength in28 days

My advice, 'speaking from the safe distance of imperfect knowledge' as my old political science professor once said, is to await the rainy season, otherwise your concrete walls will look like the majority of buidings in Thailand_spider-webbed with cracks.

Check out the articles on concrete and on building in general at:

http://www.concretenetwork.com/ [a favourite]

http://www.jlconline.com

http://www.cement.org/masonry/

http://ciks.cbt.nist.gov/~bentz/mixhs0001.html [mixture proportioning]

and http://www.quikrete.com/calculator/calculator.html#concrete