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Accepted Mix Proportions for Perlite Tile Mortars


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Perlite Plaster Aggregates Lightweight and Insulating Tile Mortars

A old (1972) product guide issued by: The Perlite Institute with an update by Rick Drewes of Stonehenge Tile and Bathworks

The widespread use of lightweight perlite aggregate to replace sand in tile mortars is easily understood when one studies the advantages that perlite has to offer. In addition to cost savings made possible by the reduction of labor and fatigue, tile contractors are able to give their customers better installations.


  1. lighter in weight.
  2. easier to handle and mix.
  3. easier to transport.
  4. less tiring to work with.
  5. clean, and convenient to measure as perlite is supplied in bags.
  6. eliminates messy piles and waste of aggregate; unused portions are easily removed and can be used elsewhere.
  7. lightweight perlite aggregated tile mortars impose less dead load on structural members.
  8. since the perlite aggregate is bagged dry, thawing out is not necessary in winter as is the case with sand.
  9. tile mortars containing lightweight perlite aggregate are:
    • light in weight
    • provide thermal insulation
    • crack resistant
    • vermin proof
    • resilient
    • uniform in quality
    • fire-proof
    • provide sound insulation
    • moisture proof
    • easy to use
    • bondable


Several different mix proportions are used by tile setters but the mix most commonly used is presented in the following table. All materials should be thoroughly mixed dry and then sufficient water should be added to obtain the desired consistancy. The use of excessive water should be avoided.

This mix can be used for both the scratch coat, leveling coats and tile setting bed. 48 hours should be allowed for the scratch coat to set up. On a scratched and plumbed wall, a softer consistency mortar is required than if tile is to be floated directly on a wire mesh or hardness cloth.


It is recommended that a thin coat of Portland cement paste be troweled or brushed over each previously soaked and drained tile before it is installed on a lightweight perlite mortar bed. This skim coat assures a satisfactory bond.

It is suggested that the tile setting bed be trowel cut both vertically and horizontally every three or four courses of tile to prevent cracking which may occur. Kitchen and lavatory ceilings may be easily tiled using lightweight perlite tile setting mortars. The lightweight of this mortar makes it much less tiring to trowel onto ceiling areas.


Kitchen and lavatory ceilings may be easily tiled using lightweight perlite tile setting mortars. the lightweight of this mortar makes it much les tire to trowel into ceilings areas.


Lightweight perlite tile mortars are especially suited for remodeling. The reduced weight of finished installations places a minimum of loading on old walls and the building structure.

An Update by Rick Drewes of Stonehenge Tile and Bathworks

The information on your web page is enough to show perlite is a viable aggregate (although the information is dated. Nowadays modified thinsets are used more than the old mudset procedures. We often use 25%-50% perlite per volume in Florida because most work is over slabs. With the newer technology of stronger and more flexible thinsets, however, I have had great success with the same percentages over wood floors as long as they have total ply-thickness of 1 1/4" and a minimun 2x10 on 16" centers.

I also have found it advantageous to "flat coat" plywood floors with straight modified thinset before applying a perlite mix coat for a good mechanical bond.

I am truly surprised more peole do not use perlite. It stretches thinset considerably.

Also, one of the main reasons I use perlite is because thinset is aptly named --- you cannot go deeper than 3/8". Thinset shrinks as it dries and perlite is the only thing I have found to use with larger tiles on floors to keep them where you left them. (Without the perlite, the thinset can shrink a little---and 1/16" to 1/8" is a heck of a lot of shrinkage when installing a large marble or tile floor.)

Please remember: Because this guide is rather old, the technical information has been given from sources considered reliable, but no guarantees of accuracy can be made or liability assumed. Your supplier may be able to provide you with more precise data.

Information given herein is from sources considered reliable, but no guarantee of accuracy can be made or liability assumed.  Your supplier may be able to provide you with more precise data.  Certain compositions or processes involving perlite may be the subject of patents.
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