Here we did trial to show how the polymethylhydrosiloxane will influence the water repellent performance and softening coefficient of gypsum or plasterboard. We will show this silicone oil is a good hydrophobizator for building materials. This silicone oil is is equivalent to MH-1107(Dow Corning), TSF-484(Momentive),DF-1040(Momentive),Rhodorsil H68(Rhodia),SILRES BS 94(Wacker) and KF-99(Shin-Etsu)

1. Using Methyl Hydrogen Silicone Fluid 202 to
improve the water repellent performance of
building gypsum
Author: Cooperant LAB between Zhejiang Castchem Ltd and Xinan University
Translator: Wujong, Sales Manager at Castchem Inc
Abstract: The Castchem’s Methyl Hydrogen Silicone Fluid 202(hereinafter referred to as
CASTCHEM202) was added to the building gypsum to improve its waterproof property. The
absorbability, strength and softening coefficient of building gypsum in different water and
gypsum ratio, and different dosage of CASTCHEM202 was tested. The results indicate that
CASTCHEM202 can improve the softening coefficient by 70% and decrease the water
absorption capacity to a minimum of 7.6%.
Introduction
Gypsum building material has excellent fire resistance, air permeability and sound absorption
property, the good appearance of white color and smooth structure is good for decoration,
combined with light weight and relatively low prices, gypsum building materials were
developing very rapidly in recent years. Currently, the gypsum building material is mainly used
to produce plasterboard,ceiling,building blocks,plastering powder and gypsum-based
self-leveling materials etc. However, the application of gypsum building material was also
limited because it is not good at frost-resistance,water-resistance and hot-resistance. This
experiment mainly aimed at improving the water-resistance by adding methyl hydrogen
silicone fluid (CASTCHEM202) into gypsum, and improving its softening coefficient too.
1.The Experiment
1.1 Raw Material
Gypsum, produced by a company in Zhejiang Province, China. Details show in Table 1 and
Table 2.
Table 1: Chemical constituents of gypsum (%)
CaO SO3 SiO2 Fe2O3 K2O
33.52 48.32 0.59 0.04 0.03
MgO Al2O3 Na2O SrO H2O
0.06 0.18 0.02 0.06 16.50

2. Table 2: The basic physical properties of gypsum
Water demand
of normal
consistency
Condensation
beginning time
Condensation
ending time
Breaking
strength
Compressive
strength
pH value
45% 4 mins 6 mins 7.59 MPa 24.1 Mpa 6.7
Water-proofing agent: Methyl Hydrogen silicone fluid 202(Polymethylhydrosiloxane,CAS
63148-57-2), produced by Zhejiang Castchem New Material Co.,Ltd, purity=100%.
1.2 Test method.
1.2.1 Testing of Strength and Softening coefficient
According to GB/T 17669.3-1999(Building gypsum mechanical properties determination
method), the strength test was going to begin immediately after forming 40x40x160mm
gypsum block, ageing and drying to constant weight in 40℃ oven. Softening coefficient is
specific value between strength of the gypsum block in water saturation status and in drying
status. Normally, the gypsum block will get water saturation status in 2 hours after immersing
water.
1.2.2 Water absorption test.
Weigh out constant weight of the gypsum block and write it as G1. After that, put it into the
water with temperature between 17℃ and 23℃, immerse it 30mm under water, don’t cling
together with bottom and wall of the water tank or with test samples each other. Take out the
gypsum block after 2 hours immersing in water and towel off the moisture in surface. Weigh
out it as G2 and work out the water absorption rate, accurateness adjusting to 1%.
2. The results and analysis
2.1 The proportion of gypsum and water influences the water absorption rate.
Weigh out 300g of gypsum and stirs an amount of water make it into gypsum slurry, drying to
constant weight in 45℃ oven. After that, work out the water absorption rate according to the
test method mentioned in 1.2.2. Because of the 45% water demand of normal consistency and
quick condensation time, our tests chose 0.45,0.50,0.55,0.60 separately as water/gypsum
proportions(Chart 1).

3. From the Chart 1, the water absorption of gypsum block will go up according to the
increase of water/gypsum mix proportion. When the water/gypsum mix proportion is
0.45, the water absorption of gypsum block in 2 hours is 22.8%. In mix proportion of 0.50,
0.55, 0.60, the water absorption rates are 25.6%, 28.8% and 32.6%. This is because of
the water content in gypsum slurry increasing when water consumption increased. After
drying, the water content evaporated and the porosity of gypsum block enlarged. When
immerse the gypsum block into water, the blocks with bigger porosity will be more easy to
absorb the water.
2.2 The effect to water absorption of gypsum blocks after adding Methyl hydrogen
silicone fluid 202(CASTCHEM202).
We separately tested the addition of CASTCHEM202 in proportion of
0.2%,0.4%,0.6%,0.8% and 1.0%, to get the results of effect to water absorption of gypsum
blocks. At the same condition, we also analyzed the effect of adding CASTCHEM202 into
gypsum slurry with different water/gypsum mix proportion. Recorded as Chart 2.

4. Chart 2: The effect to water absorption of adding CASTCHEM202 into gypsum slurry with
different water/gypsum mix proportion.
From the Chart 2, when the CASTCHEM202 added proportion was increased, the water
absorption of gypsum block will be generally decreased. In water/gypsum of 0.60, the
water absorption was continuous decreasing along with the CASTCHEM202 in added
proportion of 0.2%,0.4%,0.6% and 0.8%, and reached the minimum in 0.8%. But when the
CASTCHEM202 additive proportion went up to 1.0%, the gypsum block’s water
absorption was going up too and more than in proportion of 0.8%. In water/gypsum of 0.50,
the changing of water absorption is almost the same with in water/gypsum proportion of
0.60, the difference is that the minimum water absorption value is reached when adding
0.6% CASTCHEM202. In water/gypsum of 0.45, the minimum water-absorption is 7.6%.
The reason: As the water repellent agent Methyl hydrogen silicone fluid CASTCHEM202
added into the gypsum, the polysiloxane with -Si-O-Si main molecular chain and organic
molecular side chain will combine with -OH molecular chain in gypsum raw material, to
form a low tension hydrophobic membrane in the surface of gypsum inner porosity. This
hydrophobic membrane will prevent the gypsum block from water or moisture penetrating.
When the CASTCHEM202 added proportion is increasing, there are more hydrophobic
membranes formed and water absorption will be decreasing. Because of the tiny air
permeability of polysiloxanes, the water absorption will be still going up if continue to
increase the CASTCHEM202 adding after critical value has been reached.
2.3 The effect to strength and softening coefficient of gypsum block after adding
Methyl hydrogen silicone fluid 202(CASTCHEM202)

5. Under normal consistency water demand(45%), we tested on CASTCHEM202 adding
proportion of 0.2%,0.4%,0.6%,0.8% and 1.0% to see the effect of strength and
softening coefficient, recorded as Chart 3 and Chart 4.
Chart 3: The effect to strength by adding proportion of CASTCHEM202
From the Chart 3, the strength of gypsum block was improved after adding
CASTCHEM202. Compressive strength when in CASTCHEM202 proportion of 0.2%
and 0.4% was almost the same with the original gypsum block. As the proportion of
CASTCHEM202 was continuous increasing, the compressive strength starts to go
down. When in CASTCHEM202 adding proportion of 0.8%, the compressive strength
reached a minimum of 10.3% lower than in the original gypsum block. The strength of
original gypsum block with water saturated in 2 hours is only 12.2MPa, but it will go up
along with the increasing of CASTCHEM202. When the proportion of CASTCHEM202
reaches 0.6%, the strength will float in a small scope.

6. Chart 4: The effect to softening coefficient by adding proportion of CASTCHEM202
From the Chart 4, adding CASTCHEM22 is efficient to improve the softening
coefficient of gypsum block. In adding proportion of 0.8%, the softening coefficient will
reach above 70%. This is the assurance for the application of gypsum board/plasterboard
in water resistant required places.
3.The water repellent mechanism of Methyl hydrogen
silicone fluid
The Methyl hydrogen Silicone Fluid has three ways to crosslink and curing in the particles:
(A) Use the hydroxyl on the silicon atoms to polymerize mesh structure, this is the main
way. (B) Use the vinyl on the silicon atoms, organic peroxide as catalyst, like the way of
vulcanization. (C) Use the vinyl and silicon hydrogen bonds on silicon atoms for addition
reaction. The Chart 5 is the mechanism of forming the mesh structure. After the siloxane
crosslinked the mesh structure, the organic groups will orientational place outside and
form an organic silicon resin membrane with insoluble polymer network and few
molecules thickness in the material surface. The water or moisture can not infiltrate into
this membrane, so the material will get perfect water resistant performance. This
membrane structure won’t clog the pores, so it will also get a good breathability.

7. Besides, the silicone resin structure is similar to the quartz, the Si-O bond energy is strong
enough to prevent it from alkaline substance, acid rain and ultraviolet light, in that case the
silicone resin has a good weather resistance performance.
The CASTCHEM202 is a kind of polysiloxane with -Si-O-Si- main molecular chains and
organic side molecular chains, it can bond with the -OH in the gypsum material and form a
mesh structure in the surface of pores. This water repellent membrane won’t destroy the
configuration of the hydration products and crystalloid.
We fetched two piece of gypsum mixed with water in same quantity, added
CASTCHEM202 in one of them, another didn’t add anything. Form them to blocks and
store in the lab for 7 days, then dry them to test the water repellent performance. See
Chart 6, we added 5 drops of ink on each block, we took the below picture after 2 minutes.
From the Chart 6, we can see the ink has already infiltrated into the blank sample, but ink
can not infiltrate into the sample added CASTCHEM202. This is the same with the
previous test result.
4.Conclusion
(1).The water absorption of the gypsum block will increase as the water proportion in
gypsum slurry increased. In that case, lowing down the water/gypsum rate will improve
the water repellent performance of gypsum block.
(2). As the dosage of CASTCHEM202 increased, the water absorption of gypsum block

8. has a significant decrease. But the dosage of CASTCHEM202 has a critical value, when
the dosage is too much, the water absorption will increase because of the tiny
breath-ability performance of CASTCHEM202.
(3). The addition of CASTCHEM202 won’t influence the brecking strength and
compressive strength too much, but it will greatly improve the softening coefficient of
gypsum block. When the CASTCHEM202 dosage gets to 0.8%, the softening coefficient
can reach at 70% or more.
For more technique data of CASTCHEM202, please contact with:
Email: info@zj-castchem.com
WhatsApp:+86 15068719527
Website: www.zj-castchem.com