View Full Version : Exposed aggregate concrete sidewalk
10-07-2002, 10:06 AM
I have a walk that is exposed aggregate. Peebles to about 5/8" to 3/4". Problem #1 it is disinegrating in spots. Is patch repair possible? Problem # 2 what is the technique for doing this type of conc. work
10-08-2002, 10:59 PM
Paul,I've done many exposed aggregate walks over the years.Most with good results-one disaster.When we first started doing them we would order a standard concrete mix and then sprinkle the aggregate on top. We eventually ended up with a ready mix supplier that would furnish river stonein place of standard crushed stone,eliminating the need to add to what came out of the chute.When we added the aggregate we would place the concrete in the forms,screed it flat and then seed the aggregate on top and float it in with a magnesium float until it was completely embedded.It's alot of work and of course critical that you get uniform coverage with the aggregate or you end up with a blotchy final product.If it's mixed at the plant it comes out consistently uniform. Either way,once you place it in the form,screed it off,edge & groove it as quickly as possible to move the stone before it sets. You'll have to do this a couple times.After we screeded we'd float it and then wait until it set enough to give it a light broom finish-which we did. After brooming it take a hose and spray it lightly,washing off only the very top layer of cream.This is a several step process alternating brooming and spraying.You must be careful not to use too much water pressure so as to loosen the aggregate or dilute the top wearing surface-that will lead to failure of the aggregate to be firmly embedded.When the concrete has become almost too hard to work you can give it a final spray to completely clean the top surface.Our one disaster was a long sidewalk for a good customer who wanted(along with his 30 year old son)to help(big mistake).We started pouring late in the morning(big mistake)on a day that would get to 95.It's tough to get someone to understand the urgency of getting concrete in place & screeded/floated/edged & grooved if they've never done it and spend all of their working life behind a desk.By the time we got it down it was already starting to set and we had a real tough getting the aggregate floated in. When we left for the day I was not optimistic about our effort. Over the next several months it gradually self destructed as pebbles loosened and came out.We ended up tearing the whole thing out and replacing it.It was an expensive lesson as many have been over the years.Tuition at Harvard,if I could have learned it there would have been reasonable.So, to answer your first question on how to repair? I'll wait to read that from someone else.
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