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.

Results:

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.