Concrete Expansion Joint Material

[RichardinHuaHin]

The wife wants to add some concrete around the house and cut down on the yard work. Everyone I spoke to that does concrete has no idea what expansion joints are of course. Has anyone added concrete and had this problem? Wondering where on earth I can buy this stuff without dealing with international shipping costs or is there something else that will work?

Thanks,

Richard

[bankruatsteve]

Expansion joints are usually used in places where it freezes. Not an issue here.

[Wanderer555]

Hello,

Yes, I would agree that the use of expansion joints to limit the spread of cracks due to the base material settling or similar is not common here in many areas.

I am not sure if the asphalt impregnated fiberboard is available in Thailand, but do know that 'Sika' has a large line of good quality concrete joint products made with polyurethane or similar. Sika products are widely available here, and they should be able to point you in the correct direction...

Cheers!

Edited July 12, 2016 by Wanderer555

[moench]

Drill in the existing concrete some hole and put some rebar ( 12 mm ) ,the new or extended concrete must have reinforcement to.so now no settings at this point, if the new concrete areal larger than 3 m is better to make a sow cut (above your rebar )Your concrete will cracking at this point .so now filled this joint with silicon ( home pro,home mart)

[canopy]

What you may be after is called an isolation joint. When pours are done at different times in different shapes and sizes they will move, shrink, and expand a little differently. An isolation joint allows this movement to occur without cracks. Agree it would be nice to find the expansion joint material here.

[Reigntax]

I believe what you are after is just a bond breaker if placing the new concrete directly against existing.

The new concrete will be at its max length during placement and only shrink during curing and for the next year or so. Due to its thermal mass and unless you are considering a single slab dimension of approx 10m, the coefficient of expansion will be negligible.

The unsighly crack between the new and old could be filled with some type of flexible mastic or silicon mainly to stop debris from settling in the crack, causing expansion to always occur by increased seperation between the edge of both concrete sections.

Correct concrete mixture, especially minimising water and correct curing will result in less shrinkage, a stronger slab and minimise cracking.

Remember a plastic membrane underneath to reduce moisture loss and correct design and placement of steel to suit the intended use and ground bearing capacity.

[KMartinHandyman]

1/2" rigid styrofoam insulation board would be my choice.

Arts and Craft, office/school supplies and builder supply shops

Edited July 14, 2016 by KMartinHandyman

[canopy]

I believe what you are after is just a bond breaker if placing the new concrete directly against existing.

What you are describing is a type of construction joint.

Remember a plastic membrane underneath to reduce moisture loss

Membranes are a type of vapor retarder intended to minimize the transmission of moisture upward through the slab from sources below. I have never heard of this being used for an outdoor pour.

[eyecatcher]

1/2" rigid styrofoam insulation board would be my choice.

Arts and Craft, office/school supplies and builder supply shops

Yep thats the easiest and best solution.

They use it here on the roads.

Perfect as it acts as shuttering against the next pour.

Here they would afterwards cut off the excess with a knife and perhaps dribble some petrol on it to melt it lower then seal the top with hot bitmac.

For a domstic job an epoxy mastic is your best bet for finishing off.

Not the silicones or frame mastics as they dry shrink and fall out in a week in this heat.

[manfredtillmann]

#2 wrong

#3 no, sika does not come into this, that's something for later

#4 no, definitely not. 12mm mild steel reo bar doweling across a weather exposed concrete joint will destroy both sides of your paving in a very short time.

if you join onto an existing slab and the opposing side / end of your new slab is not confined, just pour it onto a well prepared base.

if you have a sharp corner included, use a dummy joint, thais drop a reo bar into the surface of the freshly poured concrete for that, other nations have specialised tools. it creates a defined weak spot where the concrete will crack in a straight line. the best method is a diagonal line from the external point of the existing corner to the corresponding point of the new section.

if the existing slab is on plastic or any other moisture membrane, do the same for the new slab. if not, don't do. concrete, acting as a wick, allows the underlying ground to 'breath', thereby limiting it's expansion due to water uptake. a moisture membrane will prevent that, allowing the ground to expand during periods of heavy rain etc.

having dis - similar base preparations will lead to cracking and height differences between different pours.