Mixing Concrete

[rhino533]

I'm not a Pro when it comes to concrete. Could anyone tell me the proper mix ratio for Concrete and Sand? Should I add any gravel? I'm using the concrete to fill holes and support concrete posts that are 1.5m tall. Thanks!!

[jayenram]

The mix of concrete these days is different to when I was a lad but as a rule of thumb, I still use:

1:2:4 mix (smooth finish) - 1 part cement, 2 parts sand, 4 parts aggregate (by weight)

1:3:6 mix (rough finish, foundation concrete) - 1 part cement, 3 parts sand, 6 parts aggregate.

For mortar (brickwork), 1 part cement, 3 parts sand.

For screed I would use the same formula as mortar perhaps with slightly less sand.

The volume of water added is a little trial and error but basically the slump should be no more than 50 mm for bog standard construction.

J

Simple slump test: fill a small bucket with concrete and vibrate well. Tip the bucket upside down on a level surface and gently remove the bucket leaving a concrete cone. The top of the cone should not slump more than 50 mm from the height of the bucket.

[BEENTHEREDONETHAT]

Typically, a batch of concrete can be made by using 1 part Portland cement, 2 parts dry sand, 3 parts dry stone, 1/2 part water. The parts are in terms of weight – not volume. For example, 1 cubic foot of concrete would be made using 22 lbs cement, 10 lbs water, 41 lbs dry sand, 70 lbs dry stone (1/2" to 3/4" stone). This would make 1 cubic foot of concrete and would weigh about 143 lbs. The sand should be mortar or brick sand (washed and filtered if possible) and the stone should be washed if possible. Organic materials (leaves, twigs, etc) should be removed from the sand and stone to ensure the highest strength.

For a more comprehensive explaination try Wikipedia

[RY12]

Are there problems with finding quality cement or sand in thailand or does it not much matter? The reason I ask is becasue I hear people talking about thai houses falling apart quickly, is it ever the actual concrete that decays? What about fiber mesh to add to the mix, is that available and advisable?

[jayenram]

Are there problems with finding quality cement or sand in thailand or does it not much matter? The reason I ask is becasue I hear people talking about thai houses falling apart quickly, is it ever the actual concrete that decays? What about fiber mesh to add to the mix, is that available and advisable?

I my (very inexperienced) opinion, the 'falling apart' of Thai houses has more to do with the inadequacy of the foundations or the cost 'savings' on steel reinforcement than the quality of the concrete.

As far as 'fibre mesh' additives, I'm lost on this one.

[RY12]

As far as 'fibre mesh' additives, I'm lost on this one.

Ooo! fancy commonwealth fellow reverses his r's, "fiber=fibre" lah-dah-da! just kidding, i love playing the part of the obnoxious american. fiber mesh is an additive they put into the conrete mixture here in the US at least, it looks and I think is, the same as fiber glass strands. after it's dried you see little hairs sticking up everywhere. supposedly it makes it stronger and prevents cracking.

Edited May 2, 2008 by RY12

[Naam]

As far as 'fibre mesh' additives, I'm lost on this one.

Ooo! fancy commonwealth fellow reverses his r's, "fiber=fibre" lah-dah-da! just kidding, i love playing the part of the obnoxious american. fiber mesh is an additive they put into the conrete mixture here in the US at least, it looks and I think is, the same as fiber glass strands. after it's dried you see little hairs sticking up everywhere. supposedly it makes it stronger and prevents cracking.

it helps as much as a prayer to the deity in which you believe.

[soundman]

Concrete mixing ratios are usually printed in pictographs on the side of the cement bag.

Slump test for correct water amount - but as a general rule of thumb the guide on the side of the bag is OK. If in doubt err on the conservative side with the water.

Different brands of cement are more suited to different applications. Buying the cheapest bag of cement may not be in your best interests for structural work.

Steel fiber added to the mix is gaining polularity for some building tasks, however, I have not once seen it utilsed in Thailand.

Soundman.

[naka]

An easy to use formula is 8 bags (25kG) to 1 cubic meter of premix aggregate ... for a basic 20mpa mix.

But hey, why not ask google particularly if you must have high strengh concrete.

Naka.

[tatom]

I worked for a concrete company for 25 years. When fiber mesh came out it became an instant hit. No more wresteling with rolls of steel mesh. Out of curiosity, I tested several batches of concrete with fiber. My boss saw me in the test room and asked what I was doing. I explained and told him I wasnt sold on it. It failed miserable. I asked what the boss thought. he said he didnt think much about it either, smiled and said, "but Im selling a sh!tload of it!

[stoneman]

I'm not a Pro when it comes to concrete. Could anyone tell me the proper mix ratio for Concrete and Sand? Should I add any gravel? I'm using the concrete to fill holes and support concrete posts that are 1.5m tall. Thanks!!

It would sure be nice if Sakrete was available here...I have looked and never found it..

Stoneman

[distortedlink]

It`s simple.

One part cement, three parts sand, whether you use gravel or not.

[Khun Jean]

In Thailand it is the amount of water you should monitor very carefully. Many builders like a 'fluid' concrete and with trucks use more water to make a little bit more money.

Do a slump test, and if it is not good, send it back.

It is easy to put in forms but structural it is very bad.

Vibrating is often not used either. Probably because the watery mix.

[DocTom]

Here is a related query for the experts please. It concerns additives for concrete and mortar.

A friend and excellent buider in the UK recommends the use of Unibond PVA as a mix additive, and also as a painted-on bond agent when repairing cracks, etc. The PVA acts as a plasticiser, and as a glue. PVA (polyvinyl acetate) is the key ingredient.

The trouble is that I cannot find Unibond here in Thailand, and nor can I see PVA as an ingredient in any of the on-shelf products in the DIY stores.

So please can anyone advise me if such a product containing PVA (similar ro Unibond) is available here, and if so supply its name and details?

[soundman]

Here is a related query for the experts please. It concerns additives for concrete and mortar.

A friend and excellent buider in the UK recommends the use of Unibond PVA as a mix additive, and also as a painted-on bond agent when repairing cracks, etc. The PVA acts as a plasticiser, and as a glue. PVA (polyvinyl acetate) is the key ingredient.

The trouble is that I cannot find Unibond here in Thailand, and nor can I see PVA as an ingredient in any of the on-shelf products in the DIY stores.

So please can anyone advise me if such a product containing PVA (similar ro Unibond) is available here, and if so supply its name and details?

TOA company have a range of concrete additives. Ask for a catalog at a paint store, or look on their website, has English version. also Lanko products are found in most hardware stores.

[dotcom]

One additive you will really like is sodium silicate.

It will act as an accellerator & increase resistance to moisture.

Should be able to find this at home pro.

About a coffe cup (8 oz) per bag or less is enough.

[ukfool]

As far as 'fibre mesh' additives, I'm lost on this one.

Ooo! fancy commonwealth fellow reverses his r's, "fiber=fibre" lah-dah-da! just kidding, i love playing the part of the obnoxious american. fiber mesh is an additive they put into the conrete mixture here in the US at least, it looks and I think is, the same as fiber glass strands. after it's dried you see little hairs sticking up everywhere. supposedly it makes it stronger and prevents cracking.

Not fancy, just correct English.

Edited May 3, 2009 by ukfool