Tuesday, May 17, 2011

Concrete Grill Countertop Pour

Last weekend I placed the grill countertop using a fiber reinforced Type S mortar mixture. The mold had a knockout for a cutting board on the right. It is sloped to the front for drainage with some channels made from clay. The opening for the grill was split in half and wrapped with foam for easy removal.

The mix design was pretty simple, 1 bag of Type S mortar, 1 gallon of water, 1/2 gallon of latex modifier, and 5 pcy polypropylene fibers. The latex and fibers went into a bucket and then were broken apart using the mixing paddle on the drill. The water and mortar were mixed together by hand and then the latex and fibers were added.
All of those fibers gave it the consistency of wet manure. This was by far the cheapest countertop mixture I have ever tried.

The mortar was pressed into place by hand. It was very workable but needed pressing because of the fibers in the mix. I sprinkled some green dye here and there on the mold surface, just to see how it would turn out.

Finished, troweled, and resting. Since mortar isn't as strong as concrete I let everything sit 3 days before stripping the mold. Beforehand I rough ground the bottom and torched the loose fibers.

I have been impressed. The surface texture was as good as any countertop I have produced. It is curing a few more days under wet towels before a rough grind and sealer coat.

Saturday, May 14, 2011

Concrete Tiki Torch Holder

Placing the grill countertop with the new mortar mix went well. A full post is coming. In the meantime here is a little something cool. I had some extra mortar after placing the countertop and quickly threw together the pieces of the polyurethane tiki man mold. I really didn't do much to consolidate it and then used a piece of an old tiki torch to make a hole in the top.

The results turned out way better than I expected. It stripped from the mold easily and I am ready to start casting these in earnest. I may experiment with some acid stain and sealer.

The mortar weighs more than enough to make a steady base. The patio is going to need a bunch for the upcoming annual tiki pary. Time to get to work.

Tuesday, May 10, 2011

Concrete Grill Construction

Last weekend we got a new grill and the old built-in needed some work. I deconstructed the existing grill and rebuilt it back for the new top. The old grill was an nonfunctional grill flat top from the 50's that got replaced with a big green egg. The bright mortar in the top three courses was what it took to get back to solid material.

Fiberboard template.
The top will have a knockout for a cutting board which is on the right side here. The cutting board area is sloped to the front to minimize ponding water. I split the knockout hole for the grill to make it easy to pull everything out. The pattern on the bottom of the cutting board area is modeling clay for some drainage. The hole for the egg is surrounded with ribbed foam to allow for the concrete to shrink without cracking.

Project S - Phase 1

So the point of Project S is to investigate using a prebagged Type S masonry mortar for a concrete countertop base. This project is moving pretty quickly because I am using the selected mixture for the new grill top. Yesterday I put together a few mixtures and am using 1-day compressive strength asfor iteration.
I am going to be conservative and say 1-day values are 40% of 28-day compressive strength. Mixture variables were water-to-cement ratio and latex addition rate, things easily purchased or modified for the home do it yourselfer.
Mixture S1.0 - Standard mortar mixed per manufacturer's recommendations. That is 1/5 gallons of water per 80lb bag, resulting in a water-to-cement ratio of 0.79. This was a very workable mixture.
Mixture S1.1 - Same as above but with 1:1 water to latex. Latex bonding agent, this was Sika Latex R from Home Depot, adds tensile strength, reduces permeability, and reduces efflorescence in high lime mixtures such as mortar and block mixes. Slightly less workability but much less efflorescence.
Mixture S1.2- Same as above but only using latex. Low cost latex bonding agent sold at home improvement stores is about 7% solids/93% water. Although I didn't adjust for this, with equal parts latex replacement the water to cement ratio will drop a little.
Mixture S2.0 - Standard mortar mixture but with water dosed for a 0.60 water-to-cement ratio. This is equivalent to 1 gallon and 20 oz per bag of mortar. This was probably too stiff for a good countertop mixture.
Mixture S2.1 - Same as above with1:1 latex to water. This was even stiffer.
Mixture S3.0 - Standard mortar mixture but with water dosed for a 0.42 water-to-cement ratio. There was no way to achieve this naturally, so I used a high range water reducer. I know it isn't available, but it was a let's just see situation. This was a very workable mixture.
Mixture S3.1 - Same as above with 1:1 latex to water. This was a very workable mixture.
S1.0 - 1082 psi 1 day, 2705 psi estimate at 28-days.
S1.1 - 775 psi, 1937 psi
S1.2 - 818 psi, 2045 psi
S2.0 - 1824 psi, 4559 psi
S2.1 - 1565 psi, 3913 psi
S3.0 - 2378 psi, 5944 psi
S3.1 - 1445 psi, 3613 psi

Latex tends to entrain more air so compressive strength tends to go down. I didn't expect it to go down this much. However, the latex did smell a bit funky and may have gone bad. It previous experience 1:1 latex works well in countertops.
Looking at this data I selected S1.1 as a candidate for full-scale testing. The mix I will be using for the grill top will be hand-mixed in the garage and will take three batches of
1-80lb bag of Type S Mortar ($5.00 each)
1/2 gallon water (freeish)
1/2 gallon latex bonding agent ($12 per gallon= $6.00)
0.13 lb polypropylene fibers ($6.00 per 1.5 lb bag = $0.50, These can be purchased at local specialty concrete supply stores. One bag will go a long way)

So total cost for melamine, caulk, screws, and concrete is around $75.

Monday, May 9, 2011

Project S-Crete

Lately I have not been very happy with my countertop concrete produced using prebagged 5000psi dry concrete mixtures. I have used a number of different brands and they are highly variable on aggregate gradation, coarse aggregate size, and fine aggregate angularity. For someone used to batching concrete in a laboratory, the variable is driving me crazy. I end up usually adding more water than I would like because the aggregate is dirty and one of the last pours had really large aggregate that had to be pulled out by hand. More water results in lower strength, more shrinkage, and inconsistent color. Luckily all of the last countertops have been black which is a little more forgiving. The big size aggregate (I'm talking one bag with a 3/8" top size and the next from the same brand with 1 1/2") and variable workability makes it difficult to get a really nice surface texture. I have spent too much time doing slurry fills and grinding recently.
Last weekend I got a new grill and had to modify our built-in brick grill to fit it. In the process I ended up relaying a bunch of deteriorating brick. That gave me an idea. My best concrete countertops have been placed using mortar. Buying sand and cement and weighing it out in the garage is a pain. Brick mortar comes prebagged, why not develop a countertop mix using as simple as possible products from Lowes, Home Depot, etc. Here goes Project S-Crete.
The rules are simple, create a forgiving countertop mix using Type S masonry mortar mix. Type S mortar mix contains Portland Cement, Hydrated Lime, and Fine Sand. It is designed to produce 1800 psi at 28-days using a water-to-cement ratio of around 0.80. I figure lowering that should up the strength and might make an acceptable mixture. I will be developing a series of iterative mixtures to determine one with acceptable properties. The selected mixture will be used as the top for the grill. The primary concern with using mortar for countertops is shrinkage. Hopefully lowering the w/c and possibly latex will help control any problems with cracking.
Stay tuned for updates and results.