Mold Making Tutorial: Old-Growth Cypress Concrete TableTop

We recently visited SureCrete Design Products, a decorative and specialty concrete manufacturer, at their headquarters in Dade City, FL. While there, we did some rubber mold making demos to showcase how flexible molds can be used to create a variety of unique, decorative concrete products. Typical applications include, but are not limited to:

  • full countertops & tabletops
  • individual countertop or tabletops elements such as sink inserts, decorative edging/trim strips and drain boards
  • decorative panels and tiles
  • outdoor and indoor furniture
  • planters
  • textured pool decks, walkways, patios, driveways, stairs, countertops with the use of rubber stamping and texture mats

 
For one demo, SureCrete provided us with a slab of old-growth cypress (pictured below). It was approximately 48″ x 20″ x 3″ and a “mold box” was already built around it using melamine-laminated particle board.
 

Old-GrowthCypress


 

 

UndercutsonCypressSlab

 
 
Here are the basic steps that we took to make a mold of this model during the 90-minute demo:

Seal the Model

Porous models must be sealed prior to the mold making process. There are many sealing options available, but we chose Poly PVA Solution for this model. PVA is a water-soluble solution that can be washed off after the mold making process and is available in clear and green options.
 
We applied it by brush and then allowed it to dry.
 

PVASealer


 

 

PVASolution

 

 

 

 

 

 

Create Block-Outs

Because of the protrusions on one side of the slab, there are large empty spaces within the mold box.
 

UndercutsonCypressSlab


 
To cut down on the amount of rubber needed, we cut foam to block out those spaces.
 

 

ReducingWalls

 

 

 

 

 

 

CuttingFoam


 
We coated the foam in EasyFlo 60 liquid plastic (thickened with PolyFiber II) to give it a smoother, non-porous surface.

 

 

 

 

 

 

PlasticCoatedFoam

 

 

 

 

 

 

FoamCutoutsinPlace

 

 

 

 

 

 

Apply Release Agent

We applied Pol-Ease® 2300 Release Agent to the cypress, baseboard, mold box walls and foam, and then brushed it out with a dry brush to promote even coverage.
 

MoldMakingReleaseAgent


 

 

PolEase2300

 

 

 

 

 

 

Calculate Amount of Rubber Needed

We used Poly 74-45 Liquid Rubber to make this mold. It is a mid-range hardness, polyurethane mold rubber with a mix ratio of 1A:1B.
 
To following calculation was used to determine how much rubber was needed for the mold:

  • calculate the volume of the mold box (23″ x 50.25″ x 3.5″ = ~4,045 in³) and the approximate volume of the cypress (20″ x 48″ x 3″ = ~2,800 in³)
  • subtract the volume of the cypress from the volume of the mold box (4,045 in³ – 2,800 in³ = 1,245 in³)
  • take that result and divide by the specific volume of Poly 74-45 liquid rubber (1,245 in³ ÷ 27.5 in³/lb = ~45 lb of Poly 74-45 Liquid Rubber)

 

calculate rubber needed-01


 

 

Measure, Mix & Pour Liquid Rubber

We measured Part A & Part B separately by volume, then combined and mixed them thoroughly in a clean mixing container. We used a Poly Paddle mixing tool to mix by hand.
 

PartBPoly74-45


 

 

PartAPoly74-45

 

 

 

 

MixRubberThoroughly


 
We poured the rubber into the mold box and allowed it to rise over to the model. It is best to pour rubber into rubber and avoid pouring it directly onto the model.

 

 

 

 

 

 

Poly 74-45 Liquid Rubber

 

 

 

 

 

 

PourLiquidRubberOverModel

 

 

 

 

 

 

PolytekLiquidRubber

 

 

 

 

 

 

AllowRubbertoFlow

 

 

 

 

 

 

AllowRubbertoCure


 
We allowed the rubber to cure overnight (~16 hours) at room temperature before demolding.

 

 

 

 

 

 

Demold

To demold, we began by removing the mold box walls and foam.
 

DeconstructBox


 

 

PryMoldBox

 

 

 

 

 

 

RemoveMoldBoxWalls

 

 

 

 

 

 

SidesofMold


 
We carefully loosened all edges of the mold with putty knives and crowbars.

 

 

 

 

 

 

LoosenEdgeofMold

 

 

 

 

 

 

LoosenEdgesandCorners


 
We peeled back the mold from the model, paying attention to areas where the rubber may have caught (i.e., in knots in the wood).

 

 

 

 

 

 

DemoldRubberMold

 

 

 

 

 

 

KnotsonWood

 

 

 

 

 

 

UrethaneRubberMold


 
We carefully freed the rubber from the knots using a utility knife.

 

 

 

 

 

 

Cut

 

 

 

 

 

 

FinishedMold

 

 

 

 

 

 

KnotDetail

 

 

 

 

 

 

Cast Concrete

SureCrete’s Xtreme Series precast mix was poured into the mold (a particle board block-out was used).
 

Concrete in Mold


 
Later in the day, we demolded.
 

 

TurnOverMold

 

 

 

 

 

 

DemoldConcrete

 

 

 

 

 

 

SureCreteConcrete

 

 

 

 

 

 

ConcreteCasting

 

 

 

 

 

 

ConcreteKnotDetail
 
The concrete was then stained with SureCrete’s EcoStain. 
 
MoldMakingProject

 

 

 

 

 

 

FinishedConcreteTabletop


 
Do you need assistance in selecting an appropriate mold material for your next project? Ask our technical support team:

 

 

Call us at 800.858.5990.
Email us at sales@polytek.com.
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