Bricks, Masonry, Asphalt and Concrete - Exposed aggregate patio
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03-11-01, 07:17 PM
I am attempting an exposed aggregate patio on my own. I don't want to end up with a lot of extra rock lying around and I don't want to run out either, so how do I approximate the amount of aggregate needed (tonnage) per square foot? Will the aggregate size make a difference? What is the best size of aggregate to use?
2000
03-12-01, 01:09 AM
Estimate by cubic volume, not by pounds. Size and shape of the aggregate makes a difference. Best size? Aggregate selection is a matter of personal preference and the slab thickness. Typically for a 3 1/2" to 4" slab 3/4" would be the maximum screened size.
Estimating by cubic volume plus understanding aggregate shapes: For example, 1/4" aggregate. One cubic foot will cover 48 square feet at a depth of 1/4" inch. Depending on the shape of the aggregate, (sharp diamond, rounded marble, or flat oval, etc.), one cubic foot will cover from 1.5 to 2.5 or more times 48 square feet. 1/4" is the screen size. A rock may fall though the screen but be longer than it is
wide. That same rock seeded will cover more surface area. 72 square feet per cubic foot for most 1/4" rock is a safe bet.
Estimating by cubic volume plus understanding aggregate shapes: For example, 1/4" aggregate. One cubic foot will cover 48 square feet at a depth of 1/4" inch. Depending on the shape of the aggregate, (sharp diamond, rounded marble, or flat oval, etc.), one cubic foot will cover from 1.5 to 2.5 or more times 48 square feet. 1/4" is the screen size. A rock may fall though the screen but be longer than it is
wide. That same rock seeded will cover more surface area. 72 square feet per cubic foot for most 1/4" rock is a safe bet.
03-12-01, 09:31 AM
Thanks for the helpful info. Got any suggestions or tips on properly exposing the aggregate, sealing the suface or anything else I might run into on this project? It is approximately a 800 sq. ft. patio, I will be using railroad ties for dividers and edging placed probably in 6'x6' squares. It is in a historically wet area, so I plan on a 4" gravel base and a 4" slab with wire reinforcement. Thanks again.
2000
03-12-01, 08:46 PM
To mix, pour, consolidate, float, seed, and expose, 1/2 yard sections alone requires speed and proficiency. Contemplating handling 40,000 pounds of materials at least twice I would simplify matters. In a flat second I would arrange for delivery, a concrete pump, and hire help.
If you will be mixing and hand seeding, instead of ordering exposed aggregate mix, pour, cure, then break small test sections after 3 days. Breaking reviles defects like bug holes, lack of consolidation, how well the aggregate is seated, and how strong the concrete is. Esthetics do not make durable concrete. Knowledge and experience do.
With the forms at the final elevation and for 1/4" rock there is no strike off allowance. For 3/8" to 5/8" rock the mix is screeded 1/8" below the forms. The distance increases with the aggregate size. Seed time varies with the aggregate size and method. With a 4" slump mix small aggregate is embedded near the time normal finishing would occur. Otherwise a 3" slump mix is used and the mix is seeded after bullfloating and before free water appears. Your mix should not exceed 4" slump, unless super plasticizer is used.
After embedding the aggregate should be fully covered by a 1/16" slip coat. Exposing starts in 1 to 3 hours when no free water is present and the concrete will bear some weight. Start with the finest mist and least amount of water pressure possible. When the timing is right the slip coat flows like milky water and the sand and rock will stay in place. As exposing progresses a soft broom is used (a special broom is made for the purpose). The effluent will kill plant life. Sand at the edge of the forms will act as a filter (allow to harden then discard).
Invest research time into the sealer used. Ensure that it's rated for exposed aggregate. Many types are
available. A high solids UV stabilized acrylic would be a good choice. Once chosen, reuse the same sealer as necessary.
Concerning the base: after compacting the rock I would add landscape fabric then a 3-4" layer of compacted sand. Concerning cracking: in addition to the wire adding 4-6 ounces of fiber per cubic yard will help to control cracking.
If you will be mixing and hand seeding, instead of ordering exposed aggregate mix, pour, cure, then break small test sections after 3 days. Breaking reviles defects like bug holes, lack of consolidation, how well the aggregate is seated, and how strong the concrete is. Esthetics do not make durable concrete. Knowledge and experience do.
With the forms at the final elevation and for 1/4" rock there is no strike off allowance. For 3/8" to 5/8" rock the mix is screeded 1/8" below the forms. The distance increases with the aggregate size. Seed time varies with the aggregate size and method. With a 4" slump mix small aggregate is embedded near the time normal finishing would occur. Otherwise a 3" slump mix is used and the mix is seeded after bullfloating and before free water appears. Your mix should not exceed 4" slump, unless super plasticizer is used.
After embedding the aggregate should be fully covered by a 1/16" slip coat. Exposing starts in 1 to 3 hours when no free water is present and the concrete will bear some weight. Start with the finest mist and least amount of water pressure possible. When the timing is right the slip coat flows like milky water and the sand and rock will stay in place. As exposing progresses a soft broom is used (a special broom is made for the purpose). The effluent will kill plant life. Sand at the edge of the forms will act as a filter (allow to harden then discard).
Invest research time into the sealer used. Ensure that it's rated for exposed aggregate. Many types are
available. A high solids UV stabilized acrylic would be a good choice. Once chosen, reuse the same sealer as necessary.
Concerning the base: after compacting the rock I would add landscape fabric then a 3-4" layer of compacted sand. Concerning cracking: in addition to the wire adding 4-6 ounces of fiber per cubic yard will help to control cracking.
03-14-01, 11:46 AM
Hi 2000,
In your response to dyi_in_KY, you state:
>>After embedding the aggregate should be fully covered by a 1/16" slip coat.
What is the slip coat made of? Is there a typical recipe for it? Is this just a slurry of cement and water? Does it have sand in in it? Last, how do you put it in place, do you trowel it on?
Next you talk about sealer:
>>Invest research time into the sealer used. Ensure that it's rated for exposed aggregate. Many types are
available. A high solids UV stabilized acrylic would be a good choice.
Is there a brand name of this sealer? I'm down in Texas, so the UV stabilzed really caught my eye!
Next, cracking:
>>Concerning cracking: in addition to the wire adding 4-6 ounces of fiber per cubic yard will help to control cracking.
What type of fiber is used in the concrete mix to control cracking? Is this available from Lowe's/Home Depot etc?
Thanks for putting yourself in the 20 question hotseat,
In your response to dyi_in_KY, you state:
>>After embedding the aggregate should be fully covered by a 1/16" slip coat.
What is the slip coat made of? Is there a typical recipe for it? Is this just a slurry of cement and water? Does it have sand in in it? Last, how do you put it in place, do you trowel it on?
Next you talk about sealer:
>>Invest research time into the sealer used. Ensure that it's rated for exposed aggregate. Many types are
available. A high solids UV stabilized acrylic would be a good choice.
Is there a brand name of this sealer? I'm down in Texas, so the UV stabilzed really caught my eye!
Next, cracking:
>>Concerning cracking: in addition to the wire adding 4-6 ounces of fiber per cubic yard will help to control cracking.
What type of fiber is used in the concrete mix to control cracking? Is this available from Lowe's/Home Depot etc?
Thanks for putting yourself in the 20 question hotseat,
2000
03-21-01, 12:00 AM
Slip Coat?
The "slip coat" is sand fines and cement at the surface layer. Ignoring exposed aggregate for a moment, the slip is what seals the surface during "normal" finishing operations.
Sealer?
Our resident construction supplier purchases from L&M Construction Chemicals http://www.lmcc.com/ The sealer is LUMISEAL. I should point out that this firm does not supply in small quantities. But there is no harm in asking.
For smaller quantities read the specs, then search for "exposed aggregate" "acrylic sealer". Try using http://www.c4.com and remember to use both terms enclosed within double quotes.
Fibers?
Typically the fibers are polypropylene or a related plastic. A concrete supply yard will have them.
The "slip coat" is sand fines and cement at the surface layer. Ignoring exposed aggregate for a moment, the slip is what seals the surface during "normal" finishing operations.
Sealer?
Our resident construction supplier purchases from L&M Construction Chemicals http://www.lmcc.com/ The sealer is LUMISEAL. I should point out that this firm does not supply in small quantities. But there is no harm in asking.
For smaller quantities read the specs, then search for "exposed aggregate" "acrylic sealer". Try using http://www.c4.com and remember to use both terms enclosed within double quotes.
Fibers?
Typically the fibers are polypropylene or a related plastic. A concrete supply yard will have them.